# data[].attributes.attachment_link.title
Από το άτομο στα κουάρκ ...

# data[].attributes.headline
Έξι στοιχεία για το Καθιερωμένο Πρότυπο

# data[].attributes.subject
Έξι στοιχεία για το Καθιερωμένο Πρότυπο

# data[].attributes.attachment_link.readable_text
In ancient times, Greeks interested in forecasting the future would voyage on the seventh day of the month to the Temple of Apollo in Delphi to seek insight from the oracle. Today, we don't need to decipher the riddles of a high priestess; scientists build mathematical models that predict everything from the economy to the weather.

One particularly powerful mathematical prophet is the Standard Model of particle physics. It produces sharp predictions about the subatomic world.

"The Standard Model is a collection of ideas that tells us about nature and how all the particles in the universe interact with each other," says Tulika Bose, a physics professor at the University of Wisconsin.

The Standard Model describes the behavior of the smallest building blocks we know: six types of quarks, six types of leptons, three fundamental forces (and their four associated particles), plus the Higgs boson.

Like the soothsayers of antiquity, the Standard Model speaks in riddles that only trained practitioners can interpret. But unlike Pythia of Apollo, the Standard Model is an amalgamation based on the work of thousands of independent scientists, and its predictions have weathered decades of experimental testing.

Today in Symmetry, learn six fabulous facts about one of the most robust scientific models in the world.

1: The name "Standard Model" was a placeholder that never got replaced

By the 1960s, physicists had built up quite a collection of what they considered to be fundamental particles-discrete pieces of matter that could not be broken down any further into constituent parts. There were so many different particles, they referred to them as the "particle zoo."

But in 1964, physicists Murray Gell-Mann and George Zweig theorized that many members of the particle zoo were actually composite particles made up of even smaller pieces, which we now call quarks. The list of true fundamental particles was significantly smaller, and scientists began to see new patterns. This was the beginning of the development of the Standard Model of particle physics.

The first references to a "standard model" appear in papers published in the 1970s. At this stage, physicists were still using "standard" as an adjective, not as part of a proper noun.

"If you start digging through the papers, you see in lowercase, 'the standard model of gauge interactions' and 'the standard description of electroweak interactions,'" says Richard Ruiz, a theorist at the Institute of Nuclear Physics in Krakow, Poland.

"This was the era of model-building. The ideas that worked the best were considered standard-but in the traditional sense of the word. Over time, in the '80s and '90s, slowly the 'S' and the 'M' got capitalized."

2: The Standard Model makes some assumptions

The Standard Model makes some basic assumptions about the universe. And it would function very differently if any of them turned out to be untrue. Here are a few of those assumptions:

The laws of physics are the same throughout the entire universe. (An electron on the moon has the same mass as an electron on Earth.)

Probability is conserved. (So all those coaches saying, "Give it 110%" are suggesting the players breach an inherent axiom of physics.)

Cause-and-effect relationships are unbreakable. (You cannot be born before your grandfather.)

Processes happening at the same time that don't intersect spatially are independent of each other. (Someone cooking an omelet in Brazil will not impact the performance of the Large Hadron Collider.)

There is a finite number of particles and fields. (That's why a major goal of particle physics can be summed up by the slogan from anime franchise Pokémon: Gotta catch 'em all!)

Special relativity and quantum mechanics are canon. (The Standard Model and all its assumptions are derived from these roots!)

3: The Standard Model is built from experimental measurements

The Standard Model's equations currently suggest that our universe could be metastable: With an unlucky quantum occurrence, it could collapse.

But scientists think it's unlikely the universe is actually in existential danger. They attribute this anxiety-provoking prediction to the data the Standard Model is working with-our inexact measurements of the masses of the two heaviest known fundamental particles, the top quark and the Higgs boson.

These particle masses matter so much because the Standard Model is derived from experimental measurements.

Just as you can't use the Pythagorean theorem to figure out the length of the hypotenuse of a right triangle without knowing the length of the triangle's other two sides, you can't use the Standard Model to make predictions without other inputs. By itself, the Standard Model cannot predict the mass of the various fundamental particles, nor can it predict how strongly they will interact with each other.

Because the Standard Model's predictions depend on data from experiments, the predictions are not static, but constantly evolving as detectors and analytical methods improve.

And as predictions become more precise, there are hints that some of them might no longer be consistent with each other. "It's a bit like a scavenger hunt where each measured value is a clue that helps lead us to the next," Ruiz says.

4: The Standard Model needs at least 18 independent inputs

The Standard Model is quite a bit more complicated than the Pythagorean theorem. Whereas Pythagoras needed only two inputs to determine the length of the third side of a right triangle, the Standard Model needs values for at least 18 independent variables to predict the behaviors of subatomic particles. These inputs include factors such as the particle masses, the strength of the Higgs field, and how the various forces intersect with each other.

"It's like 18 independent knobs that each have a fixed value," Bose says. "They are free parameters that are not tied to each other."

The Standard Model funnels these independent values into equations that can predict how particles form, decay and bond to create all matter in the visible universe.

5: The Standard Model has evolved

The Standard Model needs inputs such as the masses of particles to make predictions. But some particles, such as photons and gluons, have no mass.

An early version of the Standard Model assumed that another type of particle, the neutrino, was massless as well. But when scientists discovered that was not true, theorists needed to fit this discovery into the Standard Model's equations. (And they are still working on it!)

According to Bose, the Standard Model has developed through decades of trial and error. "The initial description of the Standard Model was far from complete or correct," Bose says. "Our understanding has changed significantly over the years."

Physicists are hopeful that future discoveries will provide further insight into the big questions in physics that the Standard Model fails to address.

6. The Standard Model cannot explain all of physics

The Standard Model is a trustworthy guide when it comes to its 17 fundamental particles and three fundamental forces. But observations from astronomy and cosmology let us know that there's more to the subatomic world.

"A big open question is gravity," Bose says. "We don't have any way to account for gravity on subatomic scales."

Gravity, dark matter and many other phenomena are omitted from the Standard Model, and experimental results so far have only served to discredit promising ideas for ways to include them.

But Bose isn't worried. As the history of the Standard Model shows, just knowing where the questions lie is an important step. Interesting questions lead to intriguing answers, and intriguing answers lead to even more interesting questions.

"It's one of the greatest theories of all time-and almost a theory of everything," Bose says. "We're excited to see how new experimental results might shake things up and enable the Standard Model to keep growing and evolving."

In ancient times, Greeks interested in forecasting the future would voyage on the seventh day of the month to the Temple of Apollo in Delphi to seek insight from the oracle. Today, we don't need to decipher the riddles of a high priestess; scientists build mathematical models that predict everything from the economy to the weather.

One particularly powerful mathematical prophet is the Standard Model of particle physics. It produces sharp predictions about the subatomic world.

"The Standard Model is a collection of ideas that tells us about nature and how all the particles in the universe interact with each other," says Tulika Bose, a physics professor at the University of Wisconsin.

The Standard Model describes the behavior of the smallest building blocks we know: six types of quarks, six types of leptons, three fundamental forces (and their four associated particles), plus the Higgs boson.

Like the soothsayers of antiquity, the Standard Model speaks in riddles that only trained practitioners can interpret. But unlike Pythia of Apollo, the Standard Model is an amalgamation based on the work of thousands of independent scientists, and its predictions have weathered decades of experimental testing.

Today in Symmetry, learn six fabulous facts about one of the most robust scientific models in the world.

1: The name "Standard Model" was a placeholder that never got replaced

By the 1960s, physicists had built up quite a collection of what they considered to be fundamental particles-discrete pieces of matter that could not be broken down any further into constituent parts. There were so many different particles, they referred to them as the "particle zoo."

But in 1964, physicists Murray Gell-Mann and George Zweig theorized that many members of the particle zoo were actually composite particles made up of even smaller pieces, which we now call quarks. The list of true fundamental particles was significantly smaller, and scientists began to see new patterns. This was the beginning of the development of the Standard Model of particle physics.

The first references to a "standard model" appear in papers published in the 1970s. At this stage, physicists were still using "standard" as an adjective, not as part of a proper noun.

"If you start digging through the papers, you see in lowercase, 'the standard model of gauge interactions' and 'the standard description of electroweak interactions,'" says Richard Ruiz, a theorist at the Institute of Nuclear Physics in Krakow, Poland.

"This was the era of model-building. The ideas that worked the best were considered standard-but in the traditional sense of the word. Over time, in the '80s and '90s, slowly the 'S' and the 'M' got capitalized."

2: The Standard Model makes some assumptions

The Standard Model makes some basic assumptions about the universe. And it would function very differently if any of them turned out to be untrue. Here are a few of those assumptions:

The laws of physics are the same throughout the entire universe. (An electron on the moon has the same mass as an electron on Earth.)

Probability is conserved. (So all those coaches saying, "Give it 110%" are suggesting the players breach an inherent axiom of physics.)

Cause-and-effect relationships are unbreakable. (You cannot be born before your grandfather.)

Processes happening at the same time that don't intersect spatially are independent of each other. (Someone cooking an omelet in Brazil will not impact the performance of the Large Hadron Collider.)

There is a finite number of particles and fields. (That's why a major goal of particle physics can be summed up by the slogan from anime franchise Pokémon: Gotta catch 'em all!)

Special relativity and quantum mechanics are canon. (The Standard Model and all its assumptions are derived from these roots!)

3: The Standard Model is built from experimental measurements

The Standard Model's equations currently suggest that our universe could be metastable: With an unlucky quantum occurrence, it could collapse.

But scientists think it's unlikely the universe is actually in existential danger. They attribute this anxiety-provoking prediction to the data the Standard Model is working with-our inexact measurements of the masses of the two heaviest known fundamental particles, the top quark and the Higgs boson.

These particle masses matter so much because the Standard Model is derived from experimental measurements.

Just as you can't use the Pythagorean theorem to figure out the length of the hypotenuse of a right triangle without knowing the length of the triangle's other two sides, you can't use the Standard Model to make predictions without other inputs. By itself, the Standard Model cannot predict the mass of the various fundamental particles, nor can it predict how strongly they will interact with each other.

Because the Standard Model's predictions depend on data from experiments, the predictions are not static, but constantly evolving as detectors and analytical methods improve.

And as predictions become more precise, there are hints that some of them might no longer be consistent with each other. "It's a bit like a scavenger hunt where each measured value is a clue that helps lead us to the next," Ruiz says.

4: The Standard Model needs at least 18 independent inputs

The Standard Model is quite a bit more complicated than the Pythagorean theorem. Whereas Pythagoras needed only two inputs to determine the length of the third side of a right triangle, the Standard Model needs values for at least 18 independent variables to predict the behaviors of subatomic particles. These inputs include factors such as the particle masses, the strength of the Higgs field, and how the various forces intersect with each other.

"It's like 18 independent knobs that each have a fixed value," Bose says. "They are free parameters that are not tied to each other."

The Standard Model funnels these independent values into equations that can predict how particles form, decay and bond to create all matter in the visible universe.

5: The Standard Model has evolved

The Standard Model needs inputs such as the masses of particles to make predictions. But some particles, such as photons and gluons, have no mass.

An early version of the Standard Model assumed that another type of particle, the neutrino, was massless as well. But when scientists discovered that was not true, theorists needed to fit this discovery into the Standard Model's equations. (And they are still working on it!)

According to Bose, the Standard Model has developed through decades of trial and error. "The initial description of the Standard Model was far from complete or correct," Bose says. "Our understanding has changed significantly over the years."

Physicists are hopeful that future discoveries will provide further insight into the big questions in physics that the Standard Model fails to address.

6. The Standard Model cannot explain all of physics

The Standard Model is a trustworthy guide when it comes to its 17 fundamental particles and three fundamental forces. But observations from astronomy and cosmology let us know that there's more to the subatomic world.

"A big open question is gravity," Bose says. "We don't have any way to account for gravity on subatomic scales."

Gravity, dark matter and many other phenomena are omitted from the Standard Model, and experimental results so far have only served to discredit promising ideas for ways to include them.

But Bose isn't worried. As the history of the Standard Model shows, just knowing where the questions lie is an important step. Interesting questions lead to intriguing answers, and intriguing answers lead to even more interesting questions.

"It's one of the greatest theories of all time-and almost a theory of everything," Bose says. "We're excited to see how new experimental results might shake things up and enable the Standard Model to keep growing and evolving."

# data[].attributes.attachment_link.title
Six fabulous facts about the Standard Model

# data[].attributes.attachment_link.description
Learn about the Standard Model of particle physics and how physicists use it to predict the (subatomic) future.

# data[].attributes.headline
Πέρα από το Καθιερωμένο Πρότυπο

# data[].attributes.subject
Πέρα από το Καθιερωμένο Πρότυπο

# data[].attributes.attachment_link.readable_text
Humans have always sought to understand the essence of the world around them. Ancient civilizations believed everything was composed of basic constituents like earth, air, water and fire; in the 1800s, these classical elements gave way to a meticulous record of over a hundred chemical elements, known today as the modern periodic table. The discovery of the electron in 1897 ushered in a new era, as scientists realized that the true building blocks of nature were even smaller than they had thought.

Since then, a slew of subatomic particles has been discovered and organized into a theory called the Standard Model, which impressively describes the properties and behavior of the matter surrounding us in a single, albeit hefty, mathematical equation.

"The Standard Model is scientists' best guess at explaining the universe," says Don Lincoln, a physicist at the US Department of Energy's Fermi National Accelerator Laboratory.

Since its formulation in the early 1970s, the Standard Model has predicted the outcome of countless experiments in particle physics with remarkable accuracy. Its most recent addition, the Higgs boson in 2012, rounded out the model by shedding light on how subatomic particles gain their mass. "It's simply the most successful theory we have for explaining the behavior of the matter we see," Lincoln says.

Why, then, are scientists so intent on discovering physics beyond the Standard Model?

"We have a precise model of only a small sliver of reality," Lincoln says. "And there are a lot of unexplained mysteries," ones that can't be understood within the Standard Model's tried-and-true mathematical framework.

Perhaps the most intriguing puzzle is the relative lack of antimatter found in the universe. Antimatter is composed of particles with certain properties, like charge and spin, flipped from their ordinary matter counterparts. According to the interactions of the Standard Model, the birth of our universe should have produced matter and antimatter in equal amounts-but somehow, that balance was tipped to create the matter-dominated world we live in today.

Another hint that there is physics beyond the Standard Model is that the theory does not account for dark matter, which physicists believe to be five times more prevalent than visible matter in the universe. While dark matter has never been directly observed, ample evidence of its presence exists. For example, scientists think the gravitational pull of dark matter causes galaxies to rotate at speeds unexplainable by the influence of the matter we can see.

"It's what holds the universe together," says Marcela Carena, a theoretical particle physicist at Fermilab. "But we have no clue what it's made of, or why it is there at all."

Attempts to decipher these mysteries require deep collaboration between the theoretical and experimental sides of particle physics, says Flip Tanedo, a physicist at the University of California, Riverside who works on understanding the nature of dark matter.

Many physicists think that new additions to the Standard Model will be part of a hidden "dark sector" of particles that interact only rarely, if at all, with the matter we are familiar with. But proving this hypothesis will take concrete experimental evidence. Any observation that doesn't agree with Standard Model predictions is a clue. But only after scientists make rigorous checks-to confirm that it cannot be explained away by a fluke in the data or an error in theoretical calculations-is it a smoking gun. Once both of those paths have been ruled out, Carena says, "then the explanation for the discrepancy must be something new."

"We are at an amazing time in history," Carena says, because of the sophisticated technology available to explore past the limits of current understanding. "We have such amazing tools, and very powerful mathematical methods, to learn about our universe and about ourselves."

Nonetheless, it's improbable that physics will ever reach a point so far beyond the Standard Model that the theory gets replaced entirely by something new. "There are pieces missing in the puzzle," she says. "But we're not going to throw away all the pieces that already fit so well together."

Tanedo agrees: "A theory is a model of nature, not a definition of what nature is," he says.

What's more likely is that the Standard Model will be regarded as effective at only certain scales and energies, similar to how chemistry describes atomic structure without much need for the mathematics of particle physics. "I wouldn't pick up a subatomic particle physics textbook to understand the periodic table of elements," Tanedo says.

With so much of the matter and energy in our universe left to unravel, the search for physics beyond the Standard Model is a journey ripe for discovery. "The ocean of what we don't understand is far more vast than the little pond in which we've explored," Lincoln says. "Anyone who wishes to explore this sea of knowledge can get on a boat and sail away."

# data[].attributes.attachment_link.description
The Standard Model is one of the most well-tested theories in particle physics. But scientists are searching for new physics beyond it.

# data[].attributes.headline
Τρόποι ζύγισης νετρίνου

# data[].attributes.subject
Τρόποι ζύγισης νετρίνου

# data[].attributes.attachment_link.readable_text
In 1980, Hamish Robertson was a tenured professor at Michigan State. He'd been there since his postdoc in 1971, and he was content. "I want to stress how valued and happy I felt there," he says. "It was, and still is, an outstanding place."

But he and his friend and colleague, Tom Bowles, had begun to hatch an idea that would take him far from MSU. They were devising a new experiment to measure the mass of the elusive and perplexingly light neutrino.

Neutrinos are the only fundamental particles whose mass we still don't know. As their name implies, neutrinos are very, very small. But they outnumber the other fundamental particles by a factor of 10 billion.

Their collective abundance makes it likely that they influenced the formation of structures in the early universe, so knowing their mass is critical to closing gaps in our understanding of the cosmos.

But how do you measure something with a mass so small it approaches zero? Hundreds of physicists, including Robertson, have devoted their careers to solving this problem, and they're seeing progress. Research projects underway in Europe and the United States fuel a sense of optimism that the task can be accomplished.

To measure directly or indirectly, that is the question

If you were asked to weigh something-your dog for example-how would you do it?

You could set the dog in your car, watch the compression, measure how many inches the car is displaced, then convert that into a measurement of the dog's mass. You'd need to know the weight of the car, the technical specifications of the shocks, how much air is in the tires, and something about spring constants. That's an indirect (and hard) way.

Alternatively, you could simply set the dog on a bathroom scale.

The decision on which approach to use, direct versus indirect, depends on what resources you have available. If you don't have a bathroom scale, an indirect measurement using your car could hypothetically be your best option.

When it comes to neutrinos, scientists have faced a similar situation.

In 1987, astrophysicists interested in the mass of neutrinos got an assist from a rare nearby supernova. The spectral data they collected from the stellar explosion helped them make an indirect measurement that gave them an upper limit on the neutrino mass. As in the car example, they used mathematical models, known quantities, and interactions between many parts of a system to make a calculation.

Cosmologists have also made an indirect measurement by looking for the imprint of neutrino mass on faint radiation in space called the cosmic microwave background, says Diana Parno, an associate professor at Carnegie Mellon University and US spokesperson for the Karlsruhe Tritium Neutrino direct mass experiment, or KATRIN.

"What we would ideally like is an Earth-based measurement of the neutrino mass, and then we can compare that against the cosmological measurement," Parno says.

So, while cosmologists and astrophysicists look to the sky, experimentalists like Robertson, Bowles and Parno take the direct approach to searching for the neutrino mass. It's tough-the ghostly particles don't interact with electromagnetic fields or the nuclear strong force, and they're so light that gravity barely pulls on them. Experimentalists have to get creative.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Building a bathroom scale for neutrinos

Back in 1980, Robertson and Bowles developed a new idea for making a direct neutrino mass measurement.

But there were only a few places that had the equipment, the funding and other resources required for the experiment they wanted to propose. The US Department of Energy's Los Alamos National Laboratory was one of them.

Bowles already worked in Los Alamos, and he wanted Robertson to join him. Robertson was tempted. "Since I first was aware of science as a child, I knew about Los Alamos. I always thought it would be the most extraordinary place to be," he says.

To convince Robertson to take the dive, Bowles invited him to visit the lab. One night he treated Robertson to dinner at Southwest restaurant Rancho de Chimayo. "On the way back, we stopped the car and turned off the lights," Robertson says. "We got out so I could marvel at the spectacular carpet of stars in the clear mountain air."

Robertson was sold. He was ready to embark on the journey to measure neutrino mass.

So how does one go about building a bathroom scale for neutrinos? If you have a squirmy dog that won't sit on the scale, you can weigh yourself alone, then weigh yourself with your pet. The difference between the two is the weight of the dog. Neutrino researchers use that same idea, taking advantage of processes that produce neutrinos.

In a process called beta decay, a neutron in an unstable nucleus transforms into a proton to restore balance. As the neutron becomes a proton, it emits a negatively charged electron-and a neutrino.

Another process that produces a neutrino is electron capture: A proton in an unstable nucleus captures an electron from the inner shell, converts to a neutron, and ejects a neutrino.

In both cases the events produce a very specific amount of energy-you can look it up in a table. That exact amount of energy is the difference between the mass of the parent atom and the mass of the daughter atom. And that energy is shared between the products: the neutrino and the electron in beta decay, or the neutrino and the excited daughter atom in electron capture.

Experimentalists measure energies, hence they can determine the energy taken by the neutrino. Then they take advantage of that old reliable equation E = mc² and convert the neutrino's energy to mass.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Awkward space in the Standard Model

Why is investigating the mass of neutrinos so alluring to scientists like Robertson and Bowles? Because the unresolved problem has shaken scientists' understanding of the universe.

The Standard Model of particle physics-our current best explanation of the fundamental forces and particles that make up everything-predicts that neutrinos should have no mass. But oscillation experiments in the 1990s showed that they must have mass.

"Neutrino mass is our first laboratory evidence for physics beyond the Standard Model, and that's so cool," Parno says.

As Robertson explains: "Neutrinos are the only matter particles for which the Standard Model made a prediction for what its mass would be. And that prediction was wrong.

"We have examples of things that are not in the Standard Model. Gravity is not in the Standard Model. The mass of quarks is not predicted. But there is only this one case where the Standard Model actually made a prediction, and it got it wrong."

The upper limit for the neutrino mass, as determined indirectly by cosmology, is roughly one millionth the mass of the next lightest particle, the electron. That's like the gap between one mouse, which weighs roughly 25 grams, and five elephants, which together weigh roughly 25,000 kilograms. "That's an enormous gap," says Parno. "It's awkward to have this empty space in the Standard Model."

The gap means that neutrino masses might be special. Or they might not be. But until we have a measurement to work with, we can't really say anything definitive. So making that measurement is a crucial first step.

Even if researchers achieved a result for the mass of the neutrino, the work would not be done. It would help rule out some theories and models, but there would still be questions, says Patrick Huber, neutrino theorist and director of the Center for Neutrino Physics at Virginia Tech.

"It's not like once you have the measurement, you immediately select the right model," he says. "It's not like every theorist has predicted a certain neutrino mass, and somebody has the right theory once it's measured. But it would lead to a whole bunch of broader questions."

Huber has dedicated his career to neutrinos for this exact reason. "If they see the neutrino mass, this will be very exciting. But what would be even more exciting is if they're not seeing the neutrino mass where they should have seen it, because that means something new is happening," he says. "Then we are forced to really start thinking anew."

A ghost worth chasing

Back to the 1980s-Bowles's persuasion had worked. "The siren song of Los Alamos was too strong to resist," Robertson says.

Robertson's wife was also interested in heading out west. As a female nuclear physicist in a male-dominated lab in the '70s, she had faced an uphill battle to navigate her career. Together, husband and wife secured jobs at the lab and flew down to buy a house. "On the glide path into Albuquerque, I still remember the feeling of elation," Robertson says. "It was a new beginning."

A few months later, they officially made the move, with their 6-month-old son in tow.

In 1972 a Swedish physicist named Karl-Erik Bergkvist had declared a new neutrino mass limit: 55 electronvolts. Robertson, Bowles and their colleagues thought they could do better. Their idea was to study beta decay using tritium, a radioactive isotope of hydrogen. Bergkvist had also used tritium, but it was a form implanted into aluminum. Robertson and Bowles wanted to use it in a more pure, gaseous form.

The lab administration was open to their project. "They said, 'How much money do you need?' Well, I had no idea," Robertson says. So he threw out a number. "They said, 'Okay, fine.' So that was it. Off we went."

With that funding-which in the end wasn't quite enough, but at least got them started-they pushed the limit down to about 10 electronvolts. Importantly, they had proved that tritium decay experiments could work.

In 1988, Robertson shifted gears and joined the Sudbury Neutrino Observatory. In 2001 the group demonstrated neutrino oscillation-a finding that proved neutrinos have mass and that eventually earned the 2015 Nobel Prize in Physics.

Having confirmed that neutrinos have mass, scientists returned to the quest to build a bathroom scale for neutrinos. The KATRIN experiment was forming, and the collaboration members asked everyone who had worked on a tritium experiment in the past to join. Robertson had moved to the University of Washington by then, but he joined the collaboration happily, even offering to design and provide the detector system for the project.

Nestled in Karlsruhe, Germany, the KATRIN experiment now relies on contributions from 150 researchers from seven countries.

Parno is one of those researchers. Like others, she was drawn to the experiment by the thrill of chasing something unknown. "Neutrinos are really weird," she says. "They keep on surprising and confusing us. I think neutrinos still have a lot to teach us."

KATRIN is the most advanced direct mass measurement experiment. The KATRIN collaboration published an exciting result in February 2022: Neutrinos must weigh less than 0.8 electronvolts. Oscillation experiments provided a floor, and the KATRIN result provides a ceiling. "We are closing in," Robertson says.

This range is much tighter than the one from the indirect astrophysical supernova measurement. "The supernova limit is about 5.7 electronvolts, about seven times looser than the current KATRIN limit," Parno says.

And it's close to the limit from cosmological indirect measurements, which is somewhere in the range 0.12 to 0.5 electronvolts, depending which parameters are used in the model, Robertson says.

KATRIN's 0.8 electronvolt number is the new benchmark for all direct mass experiments, but other inventive scientists are on KATRIN's heels.

New approaches

In 2009, Joe Formaggio, a professor at the Massachusetts Institute of Technology, and Benjamin Monreal, an associate professor at Case Western Reserve University, had another tritium-based idea, which became the foundation of the neutrino mass experiment known as Project 8.

"They proposed just a really beautiful idea," Robertson says. "It's one of those ideas where you say: Oh yeah, I wish I thought of that!"

Robertson has worked with the Project 8 team since its inception. The experiment also uses tritium decay, but Project 8 determines the energy of the emitted electron differently. They measure the frequency of the electron's cyclotron radiation-the microwave radiation that escapes from charged particles in circular orbit in a magnetic field.

"The amount of power radiated is really very small, but you can measure it," Robertson says.

Various aspects of the experiment are still being developed and tested. If the new approach works as planned, the Project 8 team hopes to measure the neutrino mass with a sensitivity of approximately 0.04 electronvolts.

The third technique currently under investigation as a way to directly measure neutrino mass uses molecules of the holmium isotope ¹⁶³Ho. It's challenging as well, says researcher Loredana Gastaldo, Junior Professor at the Kirchhoff Institute for Physics at the University of Heidelberg and spokesperson of the Electron Capture ¹⁶³ Ho, or ECHo, experiment.

"If you want to learn more about neutrinos, you need to be creative, to find an original and clever method that allows you to really learn something about them," she says. "The neutrinos don't give anything up as a present, so you need to sweat a lot to gain a little bit more understanding."

The ECHo experiment relies on electron capture events in ¹⁶³Ho. Scientists implant ¹⁶³ Ho ions in microcalorimeters, a totally different type of detector than the ones used in KATRIN and Project 8. "The idea is that if energy is deposited into the detector, there is an increase of temperature ... and we can measure this extremely small increase in temperature with very precise thermometers," Gastaldo says.

Each project is different, but through human ingenuity (and persistence), direct mass measurement experiments are making strides.

Let's get together

Robertson, who is now a professor emeritus at the Center for Experimental Nuclear Physics and Astrophysics at the University of Washington in Seattle, officially retired in 2017. But he's still working on Project 8.

The collaboration is younger than KATRIN and, so far, has done only proof-of-concept experiments. The next step is to create a full-blown large-scale detector.

"Some days you get up and you learn something that is just not going to work," Robertson says. "And you say: Oh my goodness, we're doomed.

"And then you work for another week or two-or a month or a year-and you talk to your friends, and somebody has an idea, and suddenly the sun comes out again, and that problem is solved, and you move on.

"I still work at this 24/7 because I really love this experiment."

And he's not alone. Parno, Gastaldo and Huber are just a few of the hundreds of other neutrino experts who have dedicated their careers to finding the mass of the neutrino. And they all rely on each other.

"We are all learning from all the other groups," Gastaldo says. "And this makes the collaborations really alive and with super interesting discussions in which all of us are gaining a lot of knowledge."

To maximize neutrino physicists' ability to learn from each other, Gastaldo organized a conference, called NuMass, in 2016. The inaugural meeting was a gathering of 40 scientists from the US and Europe, all with different expertise. "The discussions were so deep it was unbelievable," Gastaldo says.

The group repeated the conference in 2018, 2020 and 2022.

"I think it's fantastically interesting to have so many different fields of knowledge that turn out to be necessary in order to unlock the secrets of this incredibly lightweight, incredibly rarely interacting particle that somehow shaped the universe," Parno says.

The optimism of neutrino mass researchers is infectious. They continue, with tangible passion, to push the limits of human ingenuity.

And there's always room for newcomers.

"You have to have young people because they're the people who actually can get stuff done," Robertson says. "There's this huge group of people. I'm just wandering along jumping from the shoulder of one giant to another. That's part of what makes science fun."

In 1980, Hamish Robertson was a tenured professor at Michigan State. He'd been there since his postdoc in 1971, and he was content. "I want to stress how valued and happy I felt there," he says. "It was, and still is, an outstanding place."

But he and his friend and colleague, Tom Bowles, had begun to hatch an idea that would take him far from MSU. They were devising a new experiment to measure the mass of the elusive and perplexingly light neutrino.

Neutrinos are the only fundamental particles whose mass we still don't know. As their name implies, neutrinos are very, very small. But they outnumber the other fundamental particles by a factor of 10 billion.

Their collective abundance makes it likely that they influenced the formation of structures in the early universe, so knowing their mass is critical to closing gaps in our understanding of the cosmos.

But how do you measure something with a mass so small it approaches zero? Hundreds of physicists, including Robertson, have devoted their careers to solving this problem, and they're seeing progress. Research projects underway in Europe and the United States fuel a sense of optimism that the task can be accomplished.

To measure directly or indirectly, that is the question

If you were asked to weigh something-your dog for example-how would you do it?

You could set the dog in your car, watch the compression, measure how many inches the car is displaced, then convert that into a measurement of the dog's mass. You'd need to know the weight of the car, the technical specifications of the shocks, how much air is in the tires, and something about spring constants. That's an indirect (and hard) way.

Alternatively, you could simply set the dog on a bathroom scale.

The decision on which approach to use, direct versus indirect, depends on what resources you have available. If you don't have a bathroom scale, an indirect measurement using your car could hypothetically be your best option.

When it comes to neutrinos, scientists have faced a similar situation.

In 1987, astrophysicists interested in the mass of neutrinos got an assist from a rare nearby supernova. The spectral data they collected from the stellar explosion helped them make an indirect measurement that gave them an upper limit on the neutrino mass. As in the car example, they used mathematical models, known quantities, and interactions between many parts of a system to make a calculation.

Cosmologists have also made an indirect measurement by looking for the imprint of neutrino mass on faint radiation in space called the cosmic microwave background, says Diana Parno, an associate professor at Carnegie Mellon University and US spokesperson for the Karlsruhe Tritium Neutrino direct mass experiment, or KATRIN.

"What we would ideally like is an Earth-based measurement of the neutrino mass, and then we can compare that against the cosmological measurement," Parno says.

So, while cosmologists and astrophysicists look to the sky, experimentalists like Robertson, Bowles and Parno take the direct approach to searching for the neutrino mass. It's tough-the ghostly particles don't interact with electromagnetic fields or the nuclear strong force, and they're so light that gravity barely pulls on them. Experimentalists have to get creative.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Building a bathroom scale for neutrinos

Back in 1980, Robertson and Bowles developed a new idea for making a direct neutrino mass measurement.

But there were only a few places that had the equipment, the funding and other resources required for the experiment they wanted to propose. The US Department of Energy's Los Alamos National Laboratory was one of them.

Bowles already worked in Los Alamos, and he wanted Robertson to join him. Robertson was tempted. "Since I first was aware of science as a child, I knew about Los Alamos. I always thought it would be the most extraordinary place to be," he says.

To convince Robertson to take the dive, Bowles invited him to visit the lab. One night he treated Robertson to dinner at Southwest restaurant Rancho de Chimayo. "On the way back, we stopped the car and turned off the lights," Robertson says. "We got out so I could marvel at the spectacular carpet of stars in the clear mountain air."

Robertson was sold. He was ready to embark on the journey to measure neutrino mass.

So how does one go about building a bathroom scale for neutrinos? If you have a squirmy dog that won't sit on the scale, you can weigh yourself alone, then weigh yourself with your pet. The difference between the two is the weight of the dog. Neutrino researchers use that same idea, taking advantage of processes that produce neutrinos.

In a process called beta decay, a neutron in an unstable nucleus transforms into a proton to restore balance. As the neutron becomes a proton, it emits a negatively charged electron-and a neutrino.

Another process that produces a neutrino is electron capture: A proton in an unstable nucleus captures an electron from the inner shell, converts to a neutron, and ejects a neutrino.

In both cases the events produce a very specific amount of energy-you can look it up in a table. That exact amount of energy is the difference between the mass of the parent atom and the mass of the daughter atom. And that energy is shared between the products: the neutrino and the electron in beta decay, or the neutrino and the excited daughter atom in electron capture.

Experimentalists measure energies, hence they can determine the energy taken by the neutrino. Then they take advantage of that old reliable equation E = mc² and convert the neutrino's energy to mass.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Awkward space in the Standard Model

Why is investigating the mass of neutrinos so alluring to scientists like Robertson and Bowles? Because the unresolved problem has shaken scientists' understanding of the universe.

The Standard Model of particle physics-our current best explanation of the fundamental forces and particles that make up everything-predicts that neutrinos should have no mass. But oscillation experiments in the 1990s showed that they must have mass.

"Neutrino mass is our first laboratory evidence for physics beyond the Standard Model, and that's so cool," Parno says.

As Robertson explains: "Neutrinos are the only matter particles for which the Standard Model made a prediction for what its mass would be. And that prediction was wrong.

"We have examples of things that are not in the Standard Model. Gravity is not in the Standard Model. The mass of quarks is not predicted. But there is only this one case where the Standard Model actually made a prediction, and it got it wrong."

The upper limit for the neutrino mass, as determined indirectly by cosmology, is roughly one millionth the mass of the next lightest particle, the electron. That's like the gap between one mouse, which weighs roughly 25 grams, and five elephants, which together weigh roughly 25,000 kilograms. "That's an enormous gap," says Parno. "It's awkward to have this empty space in the Standard Model."

The gap means that neutrino masses might be special. Or they might not be. But until we have a measurement to work with, we can't really say anything definitive. So making that measurement is a crucial first step.

Even if researchers achieved a result for the mass of the neutrino, the work would not be done. It would help rule out some theories and models, but there would still be questions, says Patrick Huber, neutrino theorist and director of the Center for Neutrino Physics at Virginia Tech.

"It's not like once you have the measurement, you immediately select the right model," he says. "It's not like every theorist has predicted a certain neutrino mass, and somebody has the right theory once it's measured. But it would lead to a whole bunch of broader questions."

Huber has dedicated his career to neutrinos for this exact reason. "If they see the neutrino mass, this will be very exciting. But what would be even more exciting is if they're not seeing the neutrino mass where they should have seen it, because that means something new is happening," he says. "Then we are forced to really start thinking anew."

A ghost worth chasing

Back to the 1980s-Bowles's persuasion had worked. "The siren song of Los Alamos was too strong to resist," Robertson says.

Robertson's wife was also interested in heading out west. As a female nuclear physicist in a male-dominated lab in the '70s, she had faced an uphill battle to navigate her career. Together, husband and wife secured jobs at the lab and flew down to buy a house. "On the glide path into Albuquerque, I still remember the feeling of elation," Robertson says. "It was a new beginning."

A few months later, they officially made the move, with their 6-month-old son in tow.

In 1972 a Swedish physicist named Karl-Erik Bergkvist had declared a new neutrino mass limit: 55 electronvolts. Robertson, Bowles and their colleagues thought they could do better. Their idea was to study beta decay using tritium, a radioactive isotope of hydrogen. Bergkvist had also used tritium, but it was a form implanted into aluminum. Robertson and Bowles wanted to use it in a more pure, gaseous form.

The lab administration was open to their project. "They said, 'How much money do you need?' Well, I had no idea," Robertson says. So he threw out a number. "They said, 'Okay, fine.' So that was it. Off we went."

With that funding-which in the end wasn't quite enough, but at least got them started-they pushed the limit down to about 10 electronvolts. Importantly, they had proved that tritium decay experiments could work.

In 1988, Robertson shifted gears and joined the Sudbury Neutrino Observatory. In 2001 the group demonstrated neutrino oscillation-a finding that proved neutrinos have mass and that eventually earned the 2015 Nobel Prize in Physics.

Having confirmed that neutrinos have mass, scientists returned to the quest to build a bathroom scale for neutrinos. The KATRIN experiment was forming, and the collaboration members asked everyone who had worked on a tritium experiment in the past to join. Robertson had moved to the University of Washington by then, but he joined the collaboration happily, even offering to design and provide the detector system for the project.

Nestled in Karlsruhe, Germany, the KATRIN experiment now relies on contributions from 150 researchers from seven countries.

Parno is one of those researchers. Like others, she was drawn to the experiment by the thrill of chasing something unknown. "Neutrinos are really weird," she says. "They keep on surprising and confusing us. I think neutrinos still have a lot to teach us."

KATRIN is the most advanced direct mass measurement experiment. The KATRIN collaboration published an exciting result in February 2022: Neutrinos must weigh less than 0.8 electronvolts. Oscillation experiments provided a floor, and the KATRIN result provides a ceiling. "We are closing in," Robertson says.

This range is much tighter than the one from the indirect astrophysical supernova measurement. "The supernova limit is about 5.7 electronvolts, about seven times looser than the current KATRIN limit," Parno says.

And it's close to the limit from cosmological indirect measurements, which is somewhere in the range 0.12 to 0.5 electronvolts, depending which parameters are used in the model, Robertson says.

KATRIN's 0.8 electronvolt number is the new benchmark for all direct mass experiments, but other inventive scientists are on KATRIN's heels.

New approaches

In 2009, Joe Formaggio, a professor at the Massachusetts Institute of Technology, and Benjamin Monreal, an associate professor at Case Western Reserve University, had another tritium-based idea, which became the foundation of the neutrino mass experiment known as Project 8.

"They proposed just a really beautiful idea," Robertson says. "It's one of those ideas where you say: Oh yeah, I wish I thought of that!"

Robertson has worked with the Project 8 team since its inception. The experiment also uses tritium decay, but Project 8 determines the energy of the emitted electron differently. They measure the frequency of the electron's cyclotron radiation-the microwave radiation that escapes from charged particles in circular orbit in a magnetic field.

"The amount of power radiated is really very small, but you can measure it," Robertson says.

Various aspects of the experiment are still being developed and tested. If the new approach works as planned, the Project 8 team hopes to measure the neutrino mass with a sensitivity of approximately 0.04 electronvolts.

The third technique currently under investigation as a way to directly measure neutrino mass uses molecules of the holmium isotope ¹⁶³Ho. It's challenging as well, says researcher Loredana Gastaldo, Junior Professor at the Kirchhoff Institute for Physics at the University of Heidelberg and spokesperson of the Electron Capture ¹⁶³ Ho, or ECHo, experiment.

"If you want to learn more about neutrinos, you need to be creative, to find an original and clever method that allows you to really learn something about them," she says. "The neutrinos don't give anything up as a present, so you need to sweat a lot to gain a little bit more understanding."

The ECHo experiment relies on electron capture events in ¹⁶³Ho. Scientists implant ¹⁶³ Ho ions in microcalorimeters, a totally different type of detector than the ones used in KATRIN and Project 8. "The idea is that if energy is deposited into the detector, there is an increase of temperature ... and we can measure this extremely small increase in temperature with very precise thermometers," Gastaldo says.

Each project is different, but through human ingenuity (and persistence), direct mass measurement experiments are making strides.

Let's get together

Robertson, who is now a professor emeritus at the Center for Experimental Nuclear Physics and Astrophysics at the University of Washington in Seattle, officially retired in 2017. But he's still working on Project 8.

The collaboration is younger than KATRIN and, so far, has done only proof-of-concept experiments. The next step is to create a full-blown large-scale detector.

"Some days you get up and you learn something that is just not going to work," Robertson says. "And you say: Oh my goodness, we're doomed.

"And then you work for another week or two-or a month or a year-and you talk to your friends, and somebody has an idea, and suddenly the sun comes out again, and that problem is solved, and you move on.

"I still work at this 24/7 because I really love this experiment."

And he's not alone. Parno, Gastaldo and Huber are just a few of the hundreds of other neutrino experts who have dedicated their careers to finding the mass of the neutrino. And they all rely on each other.

"We are all learning from all the other groups," Gastaldo says. "And this makes the collaborations really alive and with super interesting discussions in which all of us are gaining a lot of knowledge."

To maximize neutrino physicists' ability to learn from each other, Gastaldo organized a conference, called NuMass, in 2016. The inaugural meeting was a gathering of 40 scientists from the US and Europe, all with different expertise. "The discussions were so deep it was unbelievable," Gastaldo says.

The group repeated the conference in 2018, 2020 and 2022.

"I think it's fantastically interesting to have so many different fields of knowledge that turn out to be necessary in order to unlock the secrets of this incredibly lightweight, incredibly rarely interacting particle that somehow shaped the universe," Parno says.

The optimism of neutrino mass researchers is infectious. They continue, with tangible passion, to push the limits of human ingenuity.

And there's always room for newcomers.

"You have to have young people because they're the people who actually can get stuff done," Robertson says. "There's this huge group of people. I'm just wandering along jumping from the shoulder of one giant to another. That's part of what makes science fun."

# data[].attributes.attachment_link.description
For decades scientists have tried to find a way to measure the mass of the lightest matter particle known to exist. Three new approaches now have a chance to succeed.

# data[].attributes.headline
Είστε ειδικός του Higgs; Κάντε αυτό το κουίζ για να μάθετε!

# data[].attributes.subject
Είστε ειδικός του Higgs; Κάντε αυτό το κουίζ για να μάθετε!

# data[].attributes.attachment_link.title
Are you a Higgs expert? Take this quiz to find out!

# data[].attributes.attachment_link.description
I took the Higgs quiz! How much do you know about the Higgs boson?

# data[].attributes.headline
Η αντιύλη χρησιμοποιεί

# data[].attributes.body
Η αντιύλη χρησιμοποιείται στην ιατρική.

Το PET (τομογραφία εκπομπής ποζιτρονίων) χρησιμοποιεί ποζιτρόνια για την παραγωγή εικόνων υψηλής ανάλυσης του σώματος.

# data[].attributes.attachment_link.readable_text
Antimatter is the stuff of science fiction. In the book and film Angels and Demons, Professor Langdon tries to save Vatican City from an antimatter bomb. Star Trek 's starship Enterprise uses matter-antimatter annihilation propulsion for faster-than-light travel.

But antimatter is also the stuff of reality. Antimatter particles are almost identical to their matter counterparts except that they carry the opposite charge and spin. When antimatter meets matter, they immediately annihilate into energy.

While antimatter bombs and antimatter-powered spaceships are far-fetched, there are still many facts about antimatter that will tickle your brain cells.

1. Antimatter should have annihilated all of the matter in the universe after the big bang.

According to theory, the big bang should have created matter and antimatter in equal amounts. When matter and antimatter meet, they annihilate, leaving nothing but energy behind. So in principle, none of us should exist.

But we do. And as far as physicists can tell, it's only because, in the end, there was one extra matter particle for every billion matter-antimatter pairs. Physicists are hard at work trying to explain this asymmetry.

2. Antimatter is closer to you than you think.

Small amounts of antimatter constantly rain down on the Earth in the form of cosmic rays, energetic particles from space. These antimatter particles reach our atmosphere at a rate ranging from less than one per square meter to more than 100 per square meter. Scientists have also seen evidence of antimatter production above thunderstorms.

But other antimatter sources are even closer to home. For example, bananas produce antimatter, releasing one positron-the antimatter equivalent of an electron-about every 75 minutes. This occurs because bananas contain a small amount of potassium-40, a naturally occurring isotope of potassium. As potassium-40 decays, it occasionally spits out a positron in the process.

Our bodies also contain potassium-40, which means positrons are being emitted from you, too. Antimatter annihilates immediately on contact with matter, so these antimatter particles are very short-lived.

3. Humans have created only a tiny amount of antimatter.

Antimatter-matter annihilations have the potential to release a huge amount of energy. A gram of antimatter could produce an explosion the size of a nuclear bomb. However, humans have produced only a minuscule amount of antimatter.

All of the antiprotons created at Fermilab's Tevatron particle accelerator add up to only 15 nanograms. Those made at CERN amount to about 1 nanogram. At DESY in Germany, approximately 2 nanograms of positrons have been produced to date.

If all the antimatter ever made by humans were annihilated at once, the energy produced wouldn't even be enough to boil a cup of tea.

The problem lies in the efficiency and cost of antimatter production and storage. Making 1 gram of antimatter would require approximately 25 million billion kilowatt-hours of energy and cost over a million billion dollars.

4. There is such a thing as an antimatter trap.

To study antimatter, you need to prevent it from annihilating with matter. Scientists have created ways to do just that.

Charged antimatter particles such as positrons and antiprotons can be held in devices called Penning traps. These are comparable to tiny accelerators. Inside, particles spiral around as the magnetic and electric fields keep them from colliding with the walls of the trap.

But Penning traps won't work on neutral particles such as antihydrogen. Because they have no charge, these particles cannot be confined by electric fields. Instead, they are held in Ioffe traps, which work by creating a region of space where the magnetic field gets larger in all directions. The particle gets stuck in the area with the weakest magnetic field, much like a marble rolling around the bottom of a bowl.

Earth's magnetic field can also act as a sort of antimatter trap. Antiprotons have been found in zones around the Earth called Van Allen radiation belts.

5. Antimatter might fall up.

Antimatter and matter particles have the same mass but differ in properties such as electric charge and spin. The Standard Model predicts that gravity should have the same effect on matter and antimatter; however, this has yet to be seen. Experiments such as AEGIS, ALPHA and GBAR are hard at work trying to find out.

Observing gravity's effect on antimatter is not quite as easy as watching an apple fall from a tree. These experiments need to hold antimatter in a trap or slow it down by cooling it to temperatures just above absolute zero. And because gravity is the weakest of the fundamental forces, physicists must use neutral antimatter particles in these experiments to prevent interference by the more powerful electrical force.

Editor's note: In 2023, the ALPHA experiment published results indicating that antimatter does indeed fall down.

6. Antimatter is studied in particle decelerators.

You've heard of particle accelerators, but did you know there were also particle decelerators? CERN houses a machine called the Antiproton Decelerator, a storage ring that can capture and slow antiprotons to study their properties and behavior.

In circular particle accelerators like the Large Hadron Collider, particles get a kick of energy each time they complete a rotation. Decelerators work in reverse; instead of an energy boost, particles get a kick backward to slow their speeds.

7. Neutrinos might be their own antiparticles.

A matter particle and its antimatter partner carry opposite charges, making them easy to distinguish. Neutrinos, nearly massless particles that rarely interact with matter, have no charge. Scientists believe that they may be Majorana particles, a hypothetical class of particles that are their own antiparticles.

Projects such as the Majorana Demonstrator and EXO-200 are aimed at determining whether neutrinos are Majorana particles by looking for a behavior called neutrinoless double-beta decay.

Some radioactive nuclei simultaneously decay, releasing two electrons and two neutrinos. If neutrinos were their own antiparticles, they would annihilate each other in the aftermath of the double decay, and scientists would observe only electrons.

Finding Majorana neutrinos could help explain why antimatter-matter asymmetry exists. Physicists hypothesize that Majorana neutrinos can either be heavy or light. The light ones exist today, and the heavy ones would have only existed right after the big bang. These heavy Majorana neutrinos would have decayed asymmetrically, leading to the tiny matter excess that allowed our universe to exist.

8. Antimatter is used in medicine.

PET (positron emission tomography) uses positrons to produce high-resolution images of the body. Positron-emitting radioactive isotopes (like the ones found in bananas) are attached to chemical substances such as glucose that are used naturally by the body. These are injected into the bloodstream, where they are naturally broken down, releasing positrons that meet electrons in the body and annihilate. The annihilations produce gamma rays that are used to construct images.

Scientists on CERN's ACE project have studied antimatter as a potential candidate for cancer therapy. Physicians have already discovered that they can target tumors with beams of particles that will release their energy only after safely passing through healthy tissue. Using antiprotons adds an extra burst of energy. The technique was found to be effective in hamster cells, but researchers have yet to conduct studies in human cells.

9. The antimatter that should have prevented us from existing might still be lurking in space.

One way that scientists are trying to solve the antimatter-matter asymmetry problem is by looking for antimatter left over from the big bang.

The Alpha Magnetic Spectrometer is a particle detector that sits atop the International Space Station searching for these particles. AMS contains magnetic fields that bend the path of cosmic particles to separate matter from antimatter. Its detectors assess and identify the particles as they pass through.

Cosmic ray collisions routinely produce positrons and antiprotons, but the probability of creating an antihelium atom is extremely low because of the huge amount of energy it would require. This means the observation of even a single antihelium nucleus would be strong evidence for the existence a large amount of antimatter somewhere else in the universe.

10. People are actually studying how to fuel spacecraft with antimatter.

Just a handful of antimatter can produce a huge amount of power, making it a popular fuel for futuristic vehicles in science fiction.

Antimatter rocket propulsion is hypothetically possible; the major limitation is gathering enough antimatter to make it happen.

There is currently no technology available to mass-produce or collect antimatter in the volume needed for this application. However, a small number of researchers have conducted simulation studies on propulsion and storage. These include Ronan Keane and Wei-Ming Zhang, who did their work at Western Reserve Academy and Kent State University, respectively, and Marc Weber and his colleagues at Washington State University. One day, if we can figure out a way to create or collect large amounts of antimatter, their studies might help antimatter-propelled interstellar travel become a reality.
For more antimatter facts, see Four (more) things you might not know about antimatter.

# data[].attributes.attachment_link.title
Ten things you might not know about antimatter

# data[].attributes.attachment_link.description
Antimatter has fueled many a supernatural tale. It's also fascinating all by itself.

# data[].attributes.headline
Τα 6 γκλουόνια φτιάχνο

# data[].attributes.body
Τα 6 γκλουόνια φτιάχνονται από ένα "χρώμα" και ένα "αντι-χρώμα" (όχι όμως του αντίστοιχου χρώματος). Τα άλλα δύο φτιάχνονται με κατάλληλους συνδυασμούς όλων των χρωμάτων και αντι-χρωμάτων, τους οποίους ορίζει επακριβώς το μαθηματικό υπόβαθρο.

# data[].attributes.attachment_link.readable_text
Antimatter: It's the opposite of the matter we're used to; it's mysteriously elusive; and when it gets too close to ordinary matter, the two annihilate on contact.

But there's even more to the extraordinary stuff, including these four fascinating facts.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

All atoms contain antimatter

The first three subatomic particles you ever learned about were likely the proton, neutron and electron. These particles make up the atoms that form our bodies and the world around us.

Of the group, only the electron is elementary, which means it is not made up of any smaller components. Protons and neutrons, on the other hand, are each made up of elementary particles called quarks and gluons.

Protons and neutrons are usually described as being composed of three quarks. But the reality is much messier than that. Protons and neutrons contain whole seas of quarks, antiquarks and gluons. Inside a proton or a neutron, particles and antiparticles constantly collide and annihilate one another.

Protons and neutrons are described as being made up of just three quarks because, within this maelstrom of appearing and disappearing particles, three quarks remain without an antimatter counterpart, says Beatriz Gato-Rivera, a researcher at the Spanish National Research Council and author of a book about antimatter. The antimatter versions of protons-antiprotons-contain three unpaired antiquarks instead.

Antimatter is all around you, inside every one of your atoms, along with the atoms of everything around you.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Antimatter was originally predicted through math

In 1928, British physicist Paul Dirac was faced with a puzzle. To describe the behavior of electrons, he had formulated a theory that combined Einstein's special relativity and quantum mechanics. But for his mathematical equations to work, he needed a particle that, at least at the time, wasn't known to exist. The new particle needed to have the same mass as an electron but the opposite charge.

Three years later, he finally proposed the existence of such a particle, which he called an "anti-electron."

That same year, the American physicist Carl Anderson, at the California Institute of Technology, was taking pictures of strange particle tracks left by cosmic rays traversing a particle detector known as a cloud chamber. In 1932, Anderson confirmed that the tracks came from the particles Dirac had predicted, produced when cosmic rays collided with Earth's atmosphere. Anderson dubbed the particles "positrons." This was the first confirmed observation of antimatter.

Unbalanced mathematical equations have led to the prediction of other particles as well. During the early 20th century, the masses and stability of atoms could not be explained by their protons and electrons alone. Ernest Rutherford proposed that another, neutral particle must be adding to their weight-the neutron. And in 1930, scientists needed something to explain why nuclei that emitted energy in the form of beta particles during radioactive decay didn't recoil straight back, but at an angle. Wolfgang Pauli proposed that the decay must be emitting another, invisible particle at the same time-a particle later named the neutrino.

Scientists are currently searching for other particles, including axions, supersymmetric particles and dark matter particles, that could explain many longstanding puzzles in particle physics and cosmology.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Scientists can create hybrid atoms made partially out of antimatter

By slowing antiprotons in a particle decelerator and then combining them with cryogenic helium, scientists can produce a metastable hybrid atom called anti-protonic helium.

Hybrid atoms like this are called "exotic" atoms. Generally speaking, an exotic atom has a constituent particle swapped out for another particle with the same charge. In some cases, the new particle is a form of antimatter. In anti-protonic helium, a helium atom's electron is replaced with an antiproton. Other examples include muonium (which contains an antimuon and an electron) and positronium (which contains an electron and a positron).

Exotic atoms are used to study interactions between matter and antimatter on a minuscule scale. The short-scale interactions between the particles and antiparticles within atoms enable researchers to study phenomena that may not be investigated otherwise.

"These short-scale interactions are an important tool in searching for new physics," says Anna Soter, a particle physicist at ETH Zurich.

Scientists are probing exotic atoms to search for signs of an unusual "fifth force" between the antiproton and the electron. Scientists also use exotic atoms to gather very precise measurements of particles' properties. This enables them to test symmetries in the Standard Model, such as the prediction that particles and their antiparticles should have exactly the same mass and charge (although with the opposite sign).

"To date, the metastable antiprotonic helium atom is the largest antimatter-containing exotic atom that scientists have been able to study using laser spectroscopy," Soter says. "But simpler systems, like muonium and positronium, are also exciting to study. These atoms consist of only elementary particles, in the absence of strong interaction."

In addition to creating hybrid particles, scientists can also create anti-atoms. For example, by combining antiprotons and positrons, scientists at CERN are producing anti-hydrogen.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Scientists have found more antimatter in our galaxy than they can currently explain

In the 1970s, the European Space Agency's INTEGRAL mission detected a gamma ray signal in the center of the Milky Way. The brightness and distribution of this signal indicated that the equivalent of 9 trillion kilograms of positrons (that's 10 ⁴³ positrons) within our galaxy's core were being annihilated each second-much more than scientists expected.

Where all these positrons come from is an open question. Some candidates include the supermassive black hole at the center of the galaxy, other massive black holes in the vicinity, rapidly spinning neutron stars called pulsars, and annihilations between dark matter particles.

Several experiments aim to locate the source of the gamma-rays in the center of our galaxy. The Compton Spectrometer and Imager (COSI), for example, is a gamma-ray telescope that will image our galaxy's core to probe for the source of these positrons. Other efforts, such as the proposed All-sky Medium Energy Gamma-ray Observatory (AMEGO), also aim to shed light on this mystery.

More recently, scientists detected a second excess of positrons, this one at much higher energy. The cosmic-ray detector PAMELA, on board a Russian satellite, discovered in 2008 that more antimatter particles were traveling past Earth than scientists had originally predicted. Other experiments, such as AMS-02, installed on the International Space Station in 2011, have confirmed the PAMELA collaboration's finding.

Where do these extra positrons come from? Several hypotheses have been put forward. According to Tim Linden, an astronomer at Stockholm University, the strongest contenders may be pulsars.

Scientists have been studying gamma rays from pulsars to figure out how many positrons the stars release. "We're getting numbers that match very well with models where pulsars would produce the excess positrons that we see," Linden says.
For more antimatter facts, see Ten things you might not know about antimatter.

Antimatter: It's the opposite of the matter we're used to; it's mysteriously elusive; and when it gets too close to ordinary matter, the two annihilate on contact.

But there's even more to the extraordinary stuff, including these four fascinating facts.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

All atoms contain antimatter

The first three subatomic particles you ever learned about were likely the proton, neutron and electron. These particles make up the atoms that form our bodies and the world around us.

Of the group, only the electron is elementary, which means it is not made up of any smaller components. Protons and neutrons, on the other hand, are each made up of elementary particles called quarks and gluons.

Protons and neutrons are usually described as being composed of three quarks. But the reality is much messier than that. Protons and neutrons contain whole seas of quarks, antiquarks and gluons. Inside a proton or a neutron, particles and antiparticles constantly collide and annihilate one another.

Protons and neutrons are described as being made up of just three quarks because, within this maelstrom of appearing and disappearing particles, three quarks remain without an antimatter counterpart, says Beatriz Gato-Rivera, a researcher at the Spanish National Research Council and author of a book about antimatter. The antimatter versions of protons-antiprotons-contain three unpaired antiquarks instead.

Antimatter is all around you, inside every one of your atoms, along with the atoms of everything around you.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Antimatter was originally predicted through math

In 1928, British physicist Paul Dirac was faced with a puzzle. To describe the behavior of electrons, he had formulated a theory that combined Einstein's special relativity and quantum mechanics. But for his mathematical equations to work, he needed a particle that, at least at the time, wasn't known to exist. The new particle needed to have the same mass as an electron but the opposite charge.

Three years later, he finally proposed the existence of such a particle, which he called an "anti-electron."

That same year, the American physicist Carl Anderson, at the California Institute of Technology, was taking pictures of strange particle tracks left by cosmic rays traversing a particle detector known as a cloud chamber. In 1932, Anderson confirmed that the tracks came from the particles Dirac had predicted, produced when cosmic rays collided with Earth's atmosphere. Anderson dubbed the particles "positrons." This was the first confirmed observation of antimatter.

Unbalanced mathematical equations have led to the prediction of other particles as well. During the early 20th century, the masses and stability of atoms could not be explained by their protons and electrons alone. Ernest Rutherford proposed that another, neutral particle must be adding to their weight-the neutron. And in 1930, scientists needed something to explain why nuclei that emitted energy in the form of beta particles during radioactive decay didn't recoil straight back, but at an angle. Wolfgang Pauli proposed that the decay must be emitting another, invisible particle at the same time-a particle later named the neutrino.

Scientists are currently searching for other particles, including axions, supersymmetric particles and dark matter particles, that could explain many longstanding puzzles in particle physics and cosmology.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Scientists can create hybrid atoms made partially out of antimatter

By slowing antiprotons in a particle decelerator and then combining them with cryogenic helium, scientists can produce a metastable hybrid atom called anti-protonic helium.

Hybrid atoms like this are called "exotic" atoms. Generally speaking, an exotic atom has a constituent particle swapped out for another particle with the same charge. In some cases, the new particle is a form of antimatter. In anti-protonic helium, a helium atom's electron is replaced with an antiproton. Other examples include muonium (which contains an antimuon and an electron) and positronium (which contains an electron and a positron).

Exotic atoms are used to study interactions between matter and antimatter on a minuscule scale. The short-scale interactions between the particles and antiparticles within atoms enable researchers to study phenomena that may not be investigated otherwise.

"These short-scale interactions are an important tool in searching for new physics," says Anna Soter, a particle physicist at ETH Zurich.

Scientists are probing exotic atoms to search for signs of an unusual "fifth force" between the antiproton and the electron. Scientists also use exotic atoms to gather very precise measurements of particles' properties. This enables them to test symmetries in the Standard Model, such as the prediction that particles and their antiparticles should have exactly the same mass and charge (although with the opposite sign).

"To date, the metastable antiprotonic helium atom is the largest antimatter-containing exotic atom that scientists have been able to study using laser spectroscopy," Soter says. "But simpler systems, like muonium and positronium, are also exciting to study. These atoms consist of only elementary particles, in the absence of strong interaction."

In addition to creating hybrid particles, scientists can also create anti-atoms. For example, by combining antiprotons and positrons, scientists at CERN are producing anti-hydrogen.

Illustration by Sandbox Studio, Chicago with Kimberly Boustead

Scientists have found more antimatter in our galaxy than they can currently explain

In the 1970s, the European Space Agency's INTEGRAL mission detected a gamma ray signal in the center of the Milky Way. The brightness and distribution of this signal indicated that the equivalent of 9 trillion kilograms of positrons (that's 10 ⁴³ positrons) within our galaxy's core were being annihilated each second-much more than scientists expected.

Where all these positrons come from is an open question. Some candidates include the supermassive black hole at the center of the galaxy, other massive black holes in the vicinity, rapidly spinning neutron stars called pulsars, and annihilations between dark matter particles.

Several experiments aim to locate the source of the gamma-rays in the center of our galaxy. The Compton Spectrometer and Imager (COSI), for example, is a gamma-ray telescope that will image our galaxy's core to probe for the source of these positrons. Other efforts, such as the proposed All-sky Medium Energy Gamma-ray Observatory (AMEGO), also aim to shed light on this mystery.

More recently, scientists detected a second excess of positrons, this one at much higher energy. The cosmic-ray detector PAMELA, on board a Russian satellite, discovered in 2008 that more antimatter particles were traveling past Earth than scientists had originally predicted. Other experiments, such as AMS-02, installed on the International Space Station in 2011, have confirmed the PAMELA collaboration's finding.

Where do these extra positrons come from? Several hypotheses have been put forward. According to Tim Linden, an astronomer at Stockholm University, the strongest contenders may be pulsars.

Scientists have been studying gamma rays from pulsars to figure out how many positrons the stars release. "We're getting numbers that match very well with models where pulsars would produce the excess positrons that we see," Linden says.
For more antimatter facts, see Ten things you might not know about antimatter.

# data[].attributes.attachment_link.title
Four (more) things you might not know about antimatter

# data[].attributes.attachment_link.description
It's around you, it's a part of you, and scientists are still trying to figure it out.

# data[].attributes.headline
Ποιο σωματίδιο του Καθιερωμένου Προτύπου δεν έχει ανιχνευτεί ακόμα;

# data[].attributes.subject
Ποιο σωματίδιο του Καθιερωμένου Προτύπου δεν έχει ανιχνευτεί ακόμα;

# data[].attributes.attachment_link.readable_text
Το μποζόνιο Χιγκς ανιχνεύθηκε το 2012. Ήταν το τελευταίο στοιχειώδες σωματίδιο του Καθιερωμένου Προτύπου που ανακαλύφθηκε πειραματικά; Aυτό νομίζει ο περισσότερος κόσμος.

Κι όμως υπάρχει ένα ακόμα στοιχειώδες σωματίδιο της καθιερωμένης θεωρίας που οι φυσικοί δεν κατόρθωσαν να το ανιχνεύσουν μέχρι σήμερα. Είναι το αντινετρίνο του σωματιδίου ταυ.
Σύμφωνα με το Καθιερωμένο Πρότυπο των στοιχειωδών σωματιδίων, υπάρχουν τρία είδη νετρίνων - τα νετρίνo του ηλεκτρονίου ( ), το νετρίνo του μιονίου ( ), το νετρίνo του ταυ ( ), και τα αντίστοιχα τα τρία είδη αντινετρίνων, αντινετρίνο του ηλεκτρονίου ( ), αντινετρίνο του μιονίου ( ) και αντινετρίνο του ταυ ( ). Τα αντινετρίνα διακρίνονται από τα αντίστοιχα νετρίνα γιατί έχουν αντίθετο λεπτονικό αριθμό, αντίθετη χειραλικότητα (και κατά συνέπεια αντίθετο πρόσημο ασθενούς ισοσπίν).
Τα νετρίνα είναι πολύ δύσκολο να παρατηρηθούν γιατί αλληλεπιδρούν ελάχιστα με την ύλη. Ενδεικτικά, θα μπορούσαν να διασχίσουν μόλυβδο πάχους ενός έτους φωτός πριν σκεδαστούν.

Το νετρίνο του ταυ ανιχνεύθηκε για πρώτη φορά από το πείραμα DONUT το 2000 [ Observation of Tau Neutrino Interactions]. Νετρίνα του ταυ ανίχνευσε και το πείραμα OPERA το 2011. Kαι τα δύο πειράματα ανίχνευσαν πολύ μικρό αριθμό νετρίνων ταυ - δέκα γεγονότα το καθένα. Δεδομένου ότι η ενεργός διατομή σκέδασης των αντινετρίνων ταυ είναι πολύ μικρότερη των νετρίνων ταυ, είναι φανερό γιατί δεν παρατηρήθηκαν αντινετρίνα του ταυ.

Σε ποιό εργαστήριο είναι πιθανό να παρατηρηθεί για πρώτη φορά το αντινετρίνο ταυ; Μάλλον στον Μεγάλο Επιταχυντή Αδρονίων στο CERN, όπου μπορεί να παραχθεί μεγάλος αριθμός (αντι)νετρίνων και κάποια από αυτά να ταυτοποιηθούν από τον ανιχνευτή FASER.

Περισσότερες λεπτομέρειες σχετικά με το μοναδικό σωματίδιο του Καθιερωμένου Προτύπου που δεν ανιχνεύθηκε ακόμα, στο βίντεο που ακολουθεί:

Κατηγορίες: ΣΤΟΙΧΕΙΩΔΗ ΣΩΜΑΤΙΑ

Ετικέτες: ΑΝΤΙΝΕΤΡΙΝΟ, ΝΕΤΡΙΝΟ, PHYSICS

# data[].attributes.attachment_link.title
Ποιό σωματίδιο του Καθιερωμένου Προτύπου δεν έχει ανιχνευθεί ακόμα;

# data[].attributes.attachment_link.description
Το μποζόνιο Χιγκς ανιχνεύθηκε το 2012. Ήταν το τελευταίο στοιχειώδες σωματίδιο του Καθιερωμένου Προτύπου που ανακαλύφθηκε πειραματικά; Aυτό νομίζει ο περισσότερος κόσμος. Κι όμως υπάρχει ένα ακόμα στοιχειώδες σωματίδιο της καθιερωμένης θεωρίας που οι φυσικοί δεν κατόρθωσαν να το ανιχνεύσουν μέχρι σήμερα. Είναι το αντινετρίνο του σωματιδίου ταυ.

# data[].attributes.attachment_link.description
All matter around us is made of elementary particles, the building blocks of matter. These particles occur in two basic types called quarks and leptons. Each group consists of six particles, which are related in pairs, or “generations”. The lightest and most stable particles make up the first genera…

# data[].attributes.attachment_link.readable_text
για τα στοιχειώδη σωματίδια και δεν τολμούσατε να ρωτήσετε!(μια προσπάθεια παρουσίασης της έρευνας στην περιοχή των στοιχειωδών σωματιδίων για μη ειδικούς)

Από τις αρχές του 2021, σχεδόν όλοι οι browsers δεν επιτρέπουν την εκτέλεση των αρχείων/animations που έχουν συνταχθεί με το λογισμικό Flash της Adobe, κυρίως για λόγους ασφαλείας του διαδικτύου. Δυστυχώς, τα περισσότερα από τα animations αυτού του ιστοτόπου έχουν συνταχθεί με το Flash. Γίνεται προσπάθεια να ξαναγραφτούν με άλλο λογισμικό. Ζητάμε την κατανόησή σας.

Από τις 15 Φεβρουαρίου 1999 έχουν επισκεφθεί την σελίδα αυτή φορές
(Information supplied by the page Web-Counter)

# data[].attributes.attachment_link.title
ΕΛΛΗΝΙΚΗ ΟΜΑΔΑ ΕΚΛΑΪΚΕΥΣΗΣ

# data[].attributes.attachment_link.description
για τα στοιχειώδη σωματίδια και δεν τολμούσατε να ρωτήσετε! (μια προσπάθεια παρουσίασης της έρευνας στην περιοχή των στοιχειωδών σωματιδίων για μη ειδικούς) Από τις αρχές του 2021, σχεδόν όλοι οι browsers δεν επιτρέπουν την εκτέλεση των αρχείων/animations που έχουν συνταχθεί με το λογισμικό Flash της Adobe, κυρίως για λόγους ασφαλείας του διαδικτύου.

# data[].attributes.attachment_link.readable_text
Facebook-Seite

LHC Livescreen

ATLAS Webseite

LHC@InternationalMasterclasses

Έλα μαζί μας σ' ένα ταξίδι στα απειροελάχιστα συστατικά της ύλης! Μάθε τι ακριβώς γίνεται 100 μέτρα κάτω από την επιφάνεια της γης, στο CERN, τον Ευρωπαϊκό Οργανισμό για την Πυρηνική Έρευνα. Τα τέσσερα πειράματα, ALICE, ATLAS, CMS και LHCb, τοποθετημένα στην 27 χιλιομέτρων περιφέρεια του Μεγάλου Αδρονικού Επιταχυντή (Large Hadron Collider, LHC), ήδη λειτουργούν. Το σύντομο video που ακολουθεί αποτελεί μια ματιά στην έναρξη αυτού του συναρπαστικού ταξιδιού για την κατανόηση της καταγωγής της μάζας, της Σκοτεινής 'Υλης και νέων φαινομένων, όπως της Υπερσυμμετρίας και των Επιπλέον Διαστάσεων.

Η έρευνα στη Φυσική των Σωματιδίων είναι συναρπαστική! Στις επόμενες σελίδες μπορείς να πάρεις και εσύ μέρος σ' αυτή την έρευνα. Η ανάλυση των δεδομένων που έχουν καταγραφεί το 2011 από τον ανιχνευτή ATLAS σε περιμένει. Στο επάνω μενού μπορείς να επιλέξεις μεταξύ δύο διαφορετικών συνόλων δεδομένων, από τα πραγματικά δεδομένα του πειράματος ATLAS. Τα ονομάζουμε "W-διαδρομές" και "Z-διαδρομές". Η διαδικασία για κάθε σύνολο απαιτεί περίπου 45 λεπτά. Στην αρχή κάθε διαδικασίας θα βρεις μια θεωρητική εισαγωγή. Ακολουθούν οι ασκήσεις και οι πραγματικές μετρήσεις. Στο τέλος θα μπορείς να υπολογίσεις και να ερμηνεύσεις τα αποτελέσματά σου.

Παρακαλώ, να επιλέξεις είτε τις "W-Διαδρομές" ή τις "Z-Διαδρομές". Ξεκίνα τη σωματιδιακή φυσική του 21ου αιώνα!

# data[].attributes.attachment_link.description
Facebook-Seite LHC Livescreen ATLAS Webseite LHC@InternationalMasterclasses Έλα μαζί μας σ' ένα ταξίδι στα απειροελάχιστα συστατικά της ύλης! Μάθε τι ακριβώς γίνεται 100 μέτρα κάτω από την επιφάνεια της γης, στο CERN, τον Ευρωπαϊκό Οργανισμό για την Πυρηνική Έρευνα. Τα τέσσερα πειράματα, ALICE, ATLAS, CMS και LHCb, τοποθετημένα στην 27 χιλιομέτρων περιφέρεια του Μεγάλου Αδρονικού Επιταχυντή (Large Hadron Collider, LHC), ήδη λειτουργούν.

# data[].attributes.attachment_link.description
CERN, the European Organization for Nuclear Research, is one of the world's largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works.

# data[].attributes.headline
Σ' αυτή την προσπάθεια

# data[].attributes.body
Σ' αυτή την προσπάθεια, βασικές πηγές γνώσης και αναφοράς ήταν:

Το Ευρωπαϊκό Εργαστήριο Φυσικής Σωματιδίων - CERN

Η Ελληνική Ομάδα Εκλαϊκευσης ,τμήμα της ΙNTERNATIONAL PARTICLE PHYSICS OUTREACH GROUP (IPPOG)

Τα LHC@InternationalMasterclasses

και τα αντίστοιχα λήματα της Wikipedia

# data[].attributes.body
Ινδός μαθηματικός και φυσικός με ειδίκευση στη θεωρητική φυσική . Είναι περισσότερο γνωστός για την εργασία του στην κβαντομηχανική στις αρχές της δεκαετίας του 1920 και τη συνεργασία με τον Άλμπερτ Αϊνστάιν για την ανάπτυξη της στατιστικής Bose-Einstein και τη θεωρία του συμπυκνώματος Bose-Einstein .

# data[].attributes.body
Ιταλός θεωρητικός και πειραματικός φυσικός.

Νόμπελ Φυσικής το 1938 για την τεχνητή ραδιενέργεια που παράγεται από την ακτινοβολία νετρονίων και για τη σχετική ανακάλυψη πυρηνικών αντιδράσεων που προκαλούνται από αργά νετρόνια.

Το 1942 κατασκεύασε τον πρώτο ατομικό αντιδραστήρα (Chicago Pile-1), στο Σικάγο των Η.Π.Α., με τον οποίο πέτυχε την πρώτη τεχνητή αλυσιδωτή πυρηνική αντίδραση. Είχε συμμετοχή στο Manhattan Project και στην κατασκευή της πρώτης ατομικής βόμβας. Θεωρείται ο "αρχιτέκτονας" της πυρηνικής φυσικής.

# data[].attributes.headline
Πηγή φωτογραφίας:

# data[].attributes.subject
Πηγή φωτογραφίας:

# data[].attributes.attachment_link.readable_text
Larger

Fermi, Enrico

I: Individuals and Groups

Painting (photograph copy) of physicist Enrico Fermi by artist Martyl Schweig Langsdorf, and unveiled 18 November 1955 in the Enrico Fermi Institute for Nuclear Research at the University of Chicago.

Fermi, Enrico, 1901-1954 | Nobel Prize winners | Physicists | Paintings (Visual works)

Photographic prints; 17.7 x 13.0 cm

Langsdorf, Martyl Schweig, 1917-2003

Archival Photographic Files

University of Chicago Library, Special Collections Research Center

# data[].attributes.attachment_link.description
The Photographic Archive contains more than 60,000 images documenting the history of the University of Chicago.

# data[].attributes.headline
        Αφίσα:  Το Καθιερωμένο Πρότυπο και τα Στοιχειώδη Σωματίδια

# data[].attributes.subject
        Αφίσα:  Το Καθιερωμένο Πρότυπο και τα Στοιχειώδη Σωματίδια

# data[].attributes.attachment_link.title
ΑΦΙΣΑ ΙΙΙ Καθιερωμένο Πρότυπο

# data[].attributes.attachment_link.readable_text
The long-awaited first results from the Muon g-2 experiment at the US Department of Energy's Fermi National Accelerator Laboratory show fundamental particles called muons behaving in a way that is not predicted by scientists' best theory, the Standard Model of particle physics. This landmark result, made with unprecedented precision, confirms a discrepancy that has been gnawing at researchers for decades.

The strong evidence that muons deviate from the Standard Model calculation might hint at exciting new physics. Muons act as a window into the subatomic world and could be interacting with yet undiscovered particles or forces.

"Today is an extraordinary day, long awaited not only by us but by the whole international physics community," says Graziano Venanzoni, co-spokesperson of the Muon g-2 experiment and physicist at the Italian National Institute for Nuclear Physics. "A large amount of credit goes to our young researchers who, with their talent, ideas and enthusiasm, have allowed us to achieve this incredible result."

A muon is about 200 times as massive as its cousin, the electron. Muons occur naturally when cosmic rays strike Earth's atmosphere, and particle accelerators at Fermilab can produce them in large numbers. Like electrons, muons act as if they have a tiny internal magnet. In a strong magnetic field, the direction of the muon's magnet precesses, or wobbles, much like the axis of a spinning top or gyroscope. The strength of the internal magnet determines the rate that the muon precesses in an external magnetic field and is described by a number that physicists call the g-factor. This number can be calculated with ultra-high precision.

As the muons circulate in the Muon g-2 magnet, they also interact with a quantum foam of subatomic particles popping in and out of existence. Interactions with these short-lived particles affect the value of the g-factor, causing the muons' precession to speed up or slow down very slightly. The Standard Model predicts this so-called anomalous magnetic moment extremely precisely. But if the quantum foam contains additional forces or particles not accounted for by the Standard Model, that would tweak the muon g-factor further.

"This quantity we measure reflects the interactions of the muon with everything else in the universe. But when the theorists calculate the same quantity, using all of the known forces and particles in the Standard Model, we don't get the same answer," says Renee Fatemi, a physicist at the University of Kentucky and the simulations manager for the Muon g-2 experiment. "This is strong evidence that the muon is sensitive to something that is not in our best theory."

The predecessor experiment at DOE's Brookhaven National Laboratory, which concluded in 2001, offered hints that the muon's behavior disagreed with the Standard Model. The new measurement from the Muon g-2 experiment at Fermilab strongly agrees with the value found at Brookhaven and diverges from theory with the most precise measurement to date.

The accepted theoretical values for the muon are:

g-factor: 2.00233183620(86) [uncertainty in parentheses]

anomalous magnetic moment: 0.00116591810(43)

The new experimental world-average results announced by the Muon g-2 collaboration today are:

g-factor: 2.00233184122(82)

anomalous magnetic moment: 0.00116592061(41)

The first result of the Muon g-2 experiment at Fermilab confirms the result from the experiment performed at Brookhaven National Lab two decades ago. Together, the two results show strong evidence that muons diverge from the Standard Model prediction.

The combined results from Fermilab and Brookhaven show a difference with theory at a significance of 4.2 sigma, a little shy of the 5 sigma (or standard deviations) that scientists require to claim a discovery but still compelling evidence of new physics. The chance that the results are a statistical fluctuation is about 1 in 40,000.

The Fermilab experiment reuses the main component from the Brookhaven experiment, a 50-foot-diameter superconducting magnetic storage ring. In 2013, it was transported 3200 miles by land and sea from Long Island to the Chicago suburbs, where scientists could take advantage of Fermilab's particle accelerator and produce the most intense beam of muons in the United States. Over the next four years, researchers assembled the experiment; tuned and calibrated an incredibly uniform magnetic field; developed new techniques, instrumentation, and simulations; and thoroughly tested the entire system.

The Muon g-2 experiment sends a beam of muons into the storage ring, where they circulate thousands of times at nearly the speed of light. Detectors lining the ring allow scientists to determine how fast the muons are precessing.

In its first year of operation, in 2018, the Fermilab experiment collected more data than all prior muon g-factor experiments combined. With more than 200 scientists from 35 institutions in seven countries, the Muon g-2 collaboration has now finished analyzing the motion of more than 8 billion muons from that first run.

"After the 20 years that have passed since the Brookhaven experiment ended, it is so gratifying to finally be resolving this mystery," says Fermilab scientist Chris Polly, who is a co-spokesperson for the current experiment and was a lead graduate student on the Brookhaven experiment.

Data analysis on the second and third runs of the experiment is under way, the fourth run is ongoing, and a fifth run is planned. Combining the results from all five runs will give scientists an even more precise measurement of the muon's wobble, revealing with greater certainty whether new physics is hiding within the quantum foam.

"So far we have analyzed less than 6% of the data that the experiment will eventually collect. Although these first results are telling us that there is an intriguing difference with the Standard Model, we will learn much more in the next couple of years," Polly says.

"Pinning down the subtle behavior of muons is a remarkable achievement that will guide the search for physics beyond the Standard Model for years to come," says Fermilab Deputy Director of Research Joe Lykken. "This is an exciting time for particle physics research, and Fermilab is at the forefront."
Editor's note: This article was originally published as a Fermilab press release.

# data[].attributes.attachment_link.title
First results from Fermilab's Muon g-2 experiment strengthen evidence of new physics

# data[].attributes.attachment_link.description
The long-awaited first results from the Muon g-2 experiment at the US Department of Energy's Fermi National Accelerator Laboratory show fundamental particles called muons behaving in a way that is not predicted by scientists' best theory, the Standard Model of particle physics.

# data[].attributes.headline
Τα πρώτα αποτελέσματα

# data[].attributes.body
Τα πρώτα αποτελέσματα από το πείραμα Muon g-2 του Fermilab ενισχύουν τα στοιχεία της νέας φυσικής

# data[].attributes.headline
Το «ανυπάκουο» μιόνιο και το Καθιερωμένο Πρότυπο Φυσικής

# data[].attributes.subject
Το «ανυπάκουο» μιόνιο και το Καθιερωμένο Πρότυπο Φυσικής

# data[].attributes.attachment_link.title
Μία "ρωγμή" στους νόμους της Φυσικής: Πώς ένα ανυπάκουο σωματίδιο μπορεί να αλλάξει την αντίληψή μας για το Σύμπαν | LiFO

# data[].attributes.attachment_link.description
Επιστήμονες συγκεντρώνουν όλο και περισσότερες ενδείξεις στα πειράματά τους για μία "ρωγμή" στο καθιερωμένο μοντέλο της Φυσικής και την αντίληψή μας για τον

# data[].attributes.attachment_link.readable_text
Το πρώτο τεύχος μιας συνεργασίας για την εξωστρέφεια της αρχιτεκτονικής και του design

Σπύρος Στάβερης: "Φωτογραφία είναι η συνέχιση της πολιτικής με άλλα μέσα"

Όταν ο όχλος του Ίντερνετ επιτέθηκε και σε μένα

# data[].attributes.attachment_link.title
Μπορεί ένα "ανυπάκουο" σωματίδιο να ανατρέψει την αντίληψή μας για το Σύμπαν; | LiFO

# data[].attributes.attachment_link.description
Σύντομο μάθημα Φυσικής των Στοιχειωδών Σωματιδίων από τον καθηγητή του ΕΜΠ Νίκο Τράκα, με αφορμή τις νέες μετρήσεις από το πείραμα Muon g−2 στο Fermilab του Ιλινόι, που ίσως να οδηγήσουν σε μια ιστορική ανακάλυψη.

# data[].attributes.headline
Το νετρίνο του μιονίου μέσα στο σύμπαν, μια και αποτελεί ένα από τα κυριότερα συστατικά του.

# data[].attributes.subject
Το νετρίνο του μιονίου μέσα στο σύμπαν, μια και αποτελεί ένα από τα κυριότερα συστατικά του.

# data[].attributes.body
Έργο ζωγραφικής από την Έλενα Γιαννοπούλου
(Απρίλιος 2020)

# data[].attributes.headline
Διαγράμματα  Feynman

# data[].attributes.subject
Διαγράμματα  Feynman

# data[].attributes.body
Αποτελούν επινόηση του Richard Feynman και αποτελούν έναν τρόπο οπτικής παράστασης των αλληλοεπιδράσεων των στοιχειωδών σωματιδίων, απλοποιώντας έτσι τις πολύπλοκες μαθηματικές σχέσεις που τις περιγράφουν.

# data[].attributes.body
O Richard  Feynman (1918 - 1988) ήταν ένας από τους σημαντικούς φυσικούς του 20ου αιώνα. Θεωρητικός φυσικός αλλά και χαρισματικός δάσκαλος, το 1965 τιμήθηκε με το Νόμπελ Φυσικής για την εργασία του στην Κβαντική Ηλεκτροδυναμική (QED), τη θεωρία που εξηγεί τον τρόπο αλληλεπίδρασης της ύλης με το φως.

# data[].attributes.headline
Σ' αυτό το διάγραμμα

# data[].attributes.body
Σ' αυτό το διάγραμμα Feynman, ένα ηλεκτρόνιο (e⁻)  και ένα ποζιτρόνιο(e⁺) εξαϋλώνονται παράγοντας ένα φωτόνιο (γ), το οποίο μετατρέπεται σε ζεύγος quark  και antiquark  με το antiquark να ακτινοβολεί ένα γκλουόνιο (g)

# data[].attributes.attachment_link.readable_text
From Wikipedia, the free encyclopedia

File history

More than 100 pages use this file. The following list shows the first 100 pages that use this file only. A full list is available.

View more links to this file.

Global file usage

The following other wikis use this file:

Usage on ar.wikipedia.org

Usage on bn.wikipedia.org

Usage on ca.wikipedia.org

Usage on de.wikipedia.org

Usage on el.wikipedia.org

View more global usage of this file.

# data[].attributes.attachment_link.description
From Wikipedia, the free encyclopedia More than 100 pages use this file. The following list shows the first 100 pages that use this file only. A full list is available. View more links to this file.

# data[].attributes.headline
Διάγραμμα Feynman τη

# data[].attributes.body
Διάγραμμα Feynman της εξαΰλωσης ηλεκτρονίου (e⁻)  και ποζιτρονίου (e⁺) με δημιουργία 2 φωτονίων (γ).

# data[].attributes.attachment_link.title
File:Feynman EP Annihilation.svg - Wikipedia

# data[].attributes.attachment_link.description
Information |Description={{en|1=Feynman diagram showing Space-Time vectors of Electron-Positron Annihilation}} |Source=My creation; reimplementation of PNG on Wikipedia |Author=bitwise |Date=2010-03-07 |Permission= |other_versions= }} [[Category:Physic

# data[].attributes.attachment_link.readable_text
Τα διαγράμματα Feynman είναι μια εικονική αναπαράσταση που περιγράφει την συμπεριφορά και την αλληλεπίδραση των στοιχειωδών σωματιδίων. Τα παρουσίασε για πρώτη φορά ο Richard Feynman το 1948 οπτικοποιώντας τις πολύπλοκες εξισώσεις που περιγράφουν τις αντίστοιχες αλληλεπιδράσεις των σωματιδίων που συμμετέχουν σ' αυτές. Ενώ τα διαγράμματα εφαρμόζονται κυρίως στην κβαντική θεωρία πεδίου, μπορούν επίσης να χρησιμοποιηθούν και σε άλλους τομείς, όπως στην φυσική στερεάς κατάστασης.

Το βίντεο που ακολουθεί περιγράφει αυτά που πρέπει να ξέρουμε ώστε να κατανοούμε στοιχειωδώς τα διαγράμματα Feynman:

# data[].attributes.attachment_link.title
Πώς διαβάζονται τα διαγράμματα Feynman

# data[].attributes.attachment_link.description
Τα διαγράμματα Feynman είναι μια εικονική αναπαράσταση που περιγράφει την συμπεριφορά και την αλληλεπίδραση των στοιχειωδών σωματιδίων. Τα παρουσίασε για πρώτη φορά ο Richard Feynman το 1948 οπτικοποιώντας τις πολύπλοκες εξισώσεις που περιγράφουν τις αντίστοιχες αλληλεπιδράσεις των σωματιδίων που συμμετέχουν σ' αυτές. Ενώ τα διαγράμματα εφαρμόζονται κυρίως στην κβαντική θεωρία πεδίου, μπορούν επίσης να χρησιμοποιηθούν...

# data[].attributes.headline
         Δοκιμάστε τις γνώσεις σας

# data[].attributes.subject
         Δοκιμάστε τις γνώσεις σας

# data[].attributes.attachment_link.title
Quiz: Στοιχειώδη Σωμάτια και Υποατομικά Σωματίδια

# data[].attributes.attachment_link.description
Quiz: Στοιχειώδη Σωμάτια και Υποατομικά Σωματίδια

# data[].attributes.headline
Πως ζωγραφίζουμε ένα στοιχειώδες σωματίδιο;

# data[].attributes.subject
Πως ζωγραφίζουμε ένα στοιχειώδες σωματίδιο;

# data[].attributes.headline
Το χρονικό των ανακαλύψεων των  στοιχειωδών σωματιδίων

# data[].attributes.subject
Το χρονικό των ανακαλύψεων των  στοιχειωδών σωματιδίων

# data[].attributes.body
Ονομάστηκε έτσι γιατί οι φυσικοί πίστευαν ότι ήταν το τελευταίο σωματίδιο που θα ανακάλυπταν και έτσι του
έδωσαν το τελευταίο γράμμα της αλφαβήτου.

# data[].attributes.headline
Τα νετρίνα αλλάζουν 

# data[].attributes.body
Τα νετρίνα αλλάζουν "γεύση".

Ταλαντώνονται από τη μια μορφή στην άλλη ...

# data[].attributes.body
Όλα τα σωματίδια που αλληλεπιδρούν με την ισχυρή πυρηνική δύναμη. Συντίθενται από τα κουάρκ. Τα πρωτόνια και τα νετρόνια καθώς και τα μεσόνια είναι αδρόνια.

# data[].attributes.headline
Σωμάτια  ή  σύνθετα σωματίδια (Composite particles)

# data[].attributes.subject
Σωμάτια  ή  σύνθετα σωματίδια (Composite particles)

# data[].attributes.body
Είναι υποατομικά σωματίδια που κατασκευάζονται

από περισσότερα από ένα κουάρκ .
Τα πρωτόνια και τα νετρόνια είναι σωμάτια.

# data[].attributes.headline
                           Ασθενής πυρηνική αλληλεπίδραση 

# data[].attributes.subject
                           Ασθενής πυρηνική αλληλεπίδραση 

# data[].attributes.body
·        Είναι η δεύτερη αλληλεπίδραση που δεν είναι άμεσα αντιληπτή. Όσα σωματίδια αισθάνονται την ασθενή αλλά όχι την ισχυρή αλληλεπίδραση τα ονομάζουμε λεπτόνια.

·        Είναι αναγκαία για την κατασκευή των βαρέων πυρήνων.

·        Ευθύνεται για τις ραδιενεργές διασπάσεις των πυρήνων, τις μετατροπές των νετρονίων σε πρωτόνια μέσω των διασπάσεων β.

·        Σε αυτή την αλληλεπίδραση οφείλεται μια από τις βασικές πυρηνικές αντιδράσεις που γίνονται στον ήλιο και τον κάνουν να μας φωτίζει.

·        Έχει σχετική ισχύ  10 ⁻⁶( είναι η τρίτη σε μέγεθος δύναμη)

·        Η εμβέλειά της είναι   10 ⁻¹⁸ m.

·        Φορείς αλληλεπίδρασής της είναι τα μποζόνια  W⁺ , W− και   Ζ ⁰

# data[].attributes.headline
                              Ισχυρή πυρηνική αλληλεπίδραση 

# data[].attributes.subject
                              Ισχυρή πυρηνική αλληλεπίδραση 

# data[].attributes.body
•        Είναι η πρώτη από τις αλληλεπιδράσεις που δεν εμφανίζεται άμεσα στη καθημερινή μας ζωή, είναι όμως υπεύθυνη για την συγκρότηση των πυρήνων των ατόμων. Αυτή συγκρατεί τα πρωτόνια και τα νετρόνια ώστε να σχηματίσουν τον πυρήνα.

•        Δεν κάνει διάκριση μεταξύ πρωτονίων και νετρονίων.

•        Είναι η πιο ισχυρή από τις 4 δυνάμεις. Έχει σχετική ισχύ 1.

•        Δρα μόνο μεταξύ των γειτονικών νουκλεονίων, και εμφανίζεται μεταξύ των κουάρκ από τα οποία αυτά αποτελούνται. Η εμβέλειά της είναι  10 ⁻¹⁵m  (διάμετρος του πυρήνα των ατόμων).

•        Έχει ως φορείς αλληλεπίδρασης τα γκλουόνια (8 διαφορετικά)

# data[].attributes.headline
                                  Βαρυτική αλληλεπίδραση 

# data[].attributes.subject
                                  Βαρυτική αλληλεπίδραση 

# data[].attributes.body
·        Είναι υπεύθυνη για τη συγκρότηση των γαλαξιών και για την  περιφορά της Γης και των άλλων πλανητών γύρω από τον Ήλιο.

Είναι η ελκτική δύναμη μεταξύ όλων των μαζών στο σύμπαν. Η βαρύτητα μελετήθηκε για πρώτη φορά από τον Νεύτωνα και αργότερα με την Γενική Θεωρία της Σχετικότητας του Einstein.

Είναι η πιο αδύναμη των δυνάμεων. Έχει σχετική ισχύ  . Λόγω της πολύ μικρής ισχύος της δεν την λαμβάνουμε υπόψη στη μελέτη του μικρόκοσμου.

Έχει θεωρητικά άπειρη εμβέλεια (δρα σε ολόκληρο το σύμπαν).

Το σωματίδιο που μεταφέρει τη δύναμη (φορέας αλληλεπίδρασης) ονομάζεται βαρυτόνιο /graviton

Το βαρυτόνιο έχει θεωρητικά μηδενική μάζα και  φορτίο, αλλά δεν έχει ακόμα βρεθεί.

# data[].attributes.headline
                           Ηλεκτρομαγνητική αλληλεπίδραση 

# data[].attributes.subject
                           Ηλεκτρομαγνητική αλληλεπίδραση 

# data[].attributes.body
·        Είναι υπεύθυνη για το "τίναγμα" που αισθανόμαστε όταν, περπατώντας πάνω σ' ένα χαλί, ακουμπάμε ένα σιδερένιο αντικείμενο, για τη λειτουργία όλων των ηλεκτρικών μηχανών αλλά και για τη συγκρότηση των ατόμων: τα ηλεκτρόνια περιφέρονται γύρω από τον πυρήνα του ατόμου συγκρατούμενα από την ηλεκτρομαγνητική αλληλεπίδραση.

·        Ασκείται μεταξύ όλων των σωμάτων που έχουν ηλεκτρικό φορτίο.

·        Σε αυτή οφείλεται η συνοχή των ατόμων και η σύνθεση των ατόμων σε μόρια – άρα, σε αυτήν οφείλεται η σύνθεση της συνήθους μοριακής ύλης (όλα τα υλικά αντικείμενα γύρω μας καθώς και η έμβια ύλη).

·        Είναι η δεύτερη μεγαλύτερη. Έχει σχετική ισχύ 1/137

·        Έχει θεωρητικά άπειρη εμβέλεια (δρα σε ολόκληρο το σύμπαν).

·        Φορέας αλληλεπίδρασής της είναι  το φωτόνιο.

# data[].attributes.headline
     Οι 4 Θεμελιώδεις δυνάμεις (Fundamental Forces)    

# data[].attributes.subject
     Οι 4 Θεμελιώδεις δυνάμεις (Fundamental Forces)    

# data[].attributes.headline
    Τα σωματίδια -  φορείς των δυνάμεων

# data[].attributes.subject
    Τα σωματίδια -  φορείς των δυνάμεων

# data[].attributes.headline
          Τα φερμιόνια : Κουάρκ και Λεπτόνια

# data[].attributes.subject
          Τα φερμιόνια : Κουάρκ και Λεπτόνια

# data[].attributes.headline
                            Higgs  boson

# data[].attributes.subject
                            Higgs  boson

# data[].attributes.attachment_link.title
νετρίνο μιονίου (2)

# data[].attributes.headline
    Νετρίνο μιονίου

# data[].attributes.subject
    Νετρίνο μιονίου

# data[].attributes.headline
Νετρίνο ηλεκτρονίου

# data[].attributes.subject
Νετρίνο ηλεκτρονίου

# data[].attributes.headline
        Νετρίνο ταυ

# data[].attributes.subject
        Νετρίνο ταυ

# data[].attributes.headline
Μαθηματική αναπαράσταση του Καθιερωμένου Προτύπου με την Λαγκρανζιανή συνάρτηση

# data[].attributes.subject
Μαθηματική αναπαράσταση του Καθιερωμένου Προτύπου με την Λαγκρανζιανή συνάρτηση

# data[].attributes.body
Η 1η γραμμή περιγράφει τις δυνάμεις (εκτός από τη βαρύτητα).

Η 2η γραμμή δείχνει πως οι δυνάμεις δρουν στα στοιχειώδη σωματίδια (κουάρκ και λεπτόνια).

Η 3η και η 4η γραμμή περιγράφουν το μποζόνιο Higgs και τον μηχανισμό με τον οποίο τα σωματίδια αποκτούν τη μάζα τους.

# data[].attributes.headline
Το "Καθιερωμένο Πρότ

# data[].attributes.body
Το "Καθιερωμένο Πρότυπο" ολοκληρώθηκε την δεκαετία του 1970 και μια μεγάλη σειρά πειραμάτων αργότερα, επιβεβαίωσαν όλες τις προβλέψεις του (εκτός του ότι τα νετρίνα δεν έχουν μάζα). Η οριστική επιβεβαίωση ήρθε το 2013 με την ανακάλυψη του μποζονίου Higgs.
Αδυναμία του Καθιερωμένου Προτύπου είναι η περιγραφή της "Σκοτεινής ύλης" και της βαρύτητας  που να συμφωνεί με την καμπύλωση του χωροχρόνου της γενικής σχετικότητας.

# data[].attributes.headline
Το Καθιερωμένο Πρότυ

# data[].attributes.body
Το Καθιερωμένο Πρότυπο της Σωματιδιακής Φυσικής διατυπώθηκε πριν από αρκετές δεκαετίες για να περιγράψει τις ιδιότητες και τις αλληλεπιδράσεις των στοιχειωδών σωματιδίων.
Η θεωρία του επεκτάθηκε και τροποποιήθηκε πολλές φορές στο πέρασμα του χρόνου και τα πειράματα έχουν ενισχύσει την εμπιστοσύνη των φυσικών σ’ αυτό.

Κι όμως, οι επιστήμονες γνωρίζουν ότι το Καθιερωμένο Πρότυπο είναι ελλιπές. Δεν μπορεί να προβλέψει τις μάζες συγκεκριμένων σωματιδίων, ούτε μπορεί να εξηγήσει τι είναι η σκοτεινή ενέργεια και η σκοτεινή ύλη, περίπου το 95% του περιεχομένου του σύμπαντος.
Για να ανακαλύψουν τι κρύβεται πέρα από το Καθιερωμένο Πρότυπο οι φυσικοί ψάχνουν για τις ατέλειές του ...

# data[].attributes.attachment_link.readable_text
To 1998, oι φυσικοί έκαναν μια ανακάλυψη που κλόνισε την καθιερωμένη θεωρία τους για τα στοιχειώδη σωματίδια και έφερε στο προσκήνιο για τις επόμενες δεκαετίες ένα ταπεινό σωματίδιο.

Το Καθιερωμένο Πρότυπο, η θεωρία που περιγράφει την φυσική των θεμελιωδών σωματιδίων της ύλης από την οποία είμαστε φτιαγμένοι, προέβλεπε ότι η μάζα των σωματιδίων που ονομάζονται νετρίνα δεν έχουν μάζα. Τα πειράματα έδειχναν πως τα νετρίνα κινούνται με την ταχύτητα του φωτός, κάτι που μόνο ένα σωματίδιο με μάζα ηρεμίας μηδέν μπορούσε να το πετύχει.

Όμως οι φυσικοί του ανιχνευτή νετρίνων Super-Kamiokande στην Ιαπωνία από τα πρώτα δεδομένα που συνέλεξαν έβλεπαν πως τα νετρίνα είχαν μια πολύ μικρή μάζα, αλλά ασφαλώς όχι μηδενική. Το γεγονός αυτό τους έφερε σε αμηχανία γιατί δεν μπορούσαν να το εξηγήσουν. Προφανώς κάτι έλειπε από την μέχρι τότε αποδεκτή θεωρία.

Τώρα γνωρίζουμε. Τα νετρίνα έχουν μάζα. Είναι απίστευτα ελαφρά - ένα εκατομμύριο φορές ελαφρότερα από το αμέσως επόμενο ελαφρύτερο σωματίδιο, το ηλεκτρόνιο. Τρισεκατομμύρια νετρίνα διασχίζουν το σώμα μας κάθε δευτερόλεπτο, και αλληλεπιδρούν πολύ σπάνια με την ύλη.

Επειδή τα νετρίνα αλληλεπιδρούν ασθενέστατα με την ύλη, τα πειράματα που διερευνούν τις ιδιότητές του είναι πολύ δύσκολα, και οι γνώσεις μας γι' αυτά είναι περιορισμένες, σε σχέση με τα άλλα σωματίδια του Καθιερωμένου Προτύπου.

Τι γνωρίζουμε για τα νετρίνα;

Γνωρίζουμε ότι εμφανίζονται με τρεις γεύσεις. Και όχι με μόνο μια από αυτές. Καθώς κινούνται στον χώρο μεταπίπτουν από την μια γεύση στην άλλη - ένα φαινόμενο γνωστό με το όνομα ταλαντώσεις νετρίνων. Αυτό το φαινόμενο είναι δεν θα ήταν δυνατό αν τα νετρίνα είχαν μηδενική μάζα.

Αλλά από πού προέρχεται αυτή η μάζα;

Τα νετρίνα ανήκουν στην κατηγορία των στοιχειωδών σωματιδίων που ονομάζονται φερμιόνια[1]. Όλα τα άλλα φερμιόνια, όπως τα λεπτόνια και τα κουάρκ "κερδίζουν" την μάζα τους μέσα από την αλληλεπίδρασή τους με το μποζόνιο Higgs. Όμως τα νετρίνα δεν φαίνεται να ακολουθούν τον ίδιο δρόμο.

Οι φυσικοί έχουν προτείνει εκατοντάδες θεωρίες για το πώς τα νετρίνα αποκτούν την μάζα τους και ο καθένας έχει την προτίμησή του. Ίσως υπάρχει μια άλλη πηγή μάζας την οποία δεν γνωρίζουμε. Ίσως η μάζα των νετρίνων να προκύπτει από την αλληλεπίδραση του μποζονίου Higgs και αυτής της άγνωστης πηγής μάζας.

Υπάρχουν πολλές προτάσεις-απαντήσεις, κι αν είμαστε τυχεροί η ερώτηση γίνεται: ποια είναι η σωστή απάντηση; Το σίγουρο είναι ότι στο ερώτημα, "ποιος είναι ο τρόπος με τον οποίο η φύση επιλέγει να δώσει μάζα στα νετρίνα;" δεν έχει ακόμα απαντηθεί οριστικά.

Το κρυμμένο νετρίνο

Σύμφωνα με τα πειραματικά δεδομένα, τα νετρίνα δεν μπορούν να αλληλεπιδράσουν με το πεδίο Higgs, διότι δεν είναι δεξιόστροφα. Τα σωματίδια μπορούν να είναι ή αριστερόστροφα ή δεξιόστροφα. Οι ονομασίες αυτές δείχνουν τον προσανατολισμό του σπιν τους σε σχέση με την κατεύθυνση της ορμής τους. Η ιδιότητα προσανατολισμού, δεξιόστροφη ή αριστερόστροφη ονομάζεται "χειραλικότητα".

Μπορείτε να θεωρήσετε τα περισσότερα σωματίδια αμφιδέξια. Εμφανίζονται τόσο ως αριστερόμορφα όσο και ως δεξιόμορφα. Όταν ένα σωματίδιο αλληλεπιδρά με το πεδίο Higgs, αλλάζει χειραλικότητα από αριστερά προς δεξιά ή δεξιά προς αριστερά. Αυτή η αλλαγή πρέπει να συμβεί ώστε το πεδίο να δώσει μάζα στα σωματίδια.

Τα αριστερόστροφα σωματίδια συμπεριφέρονται πολύ διαφορετικά από τα δεξιόστροφα σωματίδια. Άρα χρειάζεστε κάτι για να τα κολλήσετε μαζί, κι αυτό είναι το μποζόνιο Higgs.

Αλλά στην περίπτωση των νετρίνων, αυτό είναι πιο περίπλοκο. Τούτο συμβαίνει επειδή, όλα τα νετρίνα φαίνεται πως είναι αριστερόστροφα.

Η έλλειψη δεξιόστροφου νετρίνου αποτελεί το βασικότερο μυστήριο των νετρίνων. Δεν γνωρίζουμε αν ένα τέτοιο σωματίδιο υπάρχει στην πραγματικότητα. Και εάν υπάρχει το δεξιόστροφο νετρίνο, πρέπει να είναι τόσο αδρανές, ώστε να αλληλεπιδρά μόνο με το μποζόνιο Higgs, και γιαυτό ιδιαίτερα δύσκολο να εντοπιστεί.

Το νετρίνο ως το αντισωματίδιό του

Παρόλο που οι επιστήμονες δεν έχουν ακόμη ανιχνεύσει δεξιόστροφα νετρίνα, γνωρίζουν ήδη μια διαφορετική ομάδα δεξιόστροφων σωματιδίων στο οικοσύστημα των νετρίνων: τα αντινετρίνα. Αυτό μας συνδέει με την επόμενη θεωρία: Είναι πιθανό ένα νετρίνο να είναι στην πραγματικότητα και το αντισωματίδιό του.

Κάθε θεμελιώδες σωματίδιο αντιστοιχεί σε ένα αντισωματίδιο με ορισμένα κατοπτρικά χαρακτηριστικά, όπως αντίθετο φορτίο (για παράδειγμα, το αρνητικά φορτισμένο ηλεκτρόνιο και το θετικά φορτισμένο αντισωματίδιό του, το ποζιτρόνιο). Τα αντισωματίδια αποκτούν την μάζα τους όπως ακριβώς και τα αντίστοιχά τους σωματίδια.

Το νετρίνο και το αντινετρίνο, είναι και τα δύο ηλεκτρικά ουδέτερα σωματίδια. Εδώ λοιπόν προκύπτει ένας γρίφος: Αν μοιάζει με νετρίνο και δρα σαν νετρίνο, δεν σημαίνει ότι το αντινετρίνο μπορεί να είναι το ίδιο σωματίδιο με το νετρίνο;

Εάν το αντινετρίνο και το νετρίνο είναι απλώς δεξιόστροφες και αριστερόστροφες εκδοχές του ίδιου σωματιδίου, τότε θα πρέπει να μπορούν να αλληλεπιδρούν ώστε να αποκτήσουν μάζα. Που σημαίνει ότι τα νετρίνα είναι αυτό που ονομάζουμε φερμιόνια Majorana, το οποίο μπορεί να προκύψει μόνο όταν τόσο το σωματίδιο όσο και το αντισωματίδιο είναι πανομοιότυπα.

Σε αυτό το σενάριο, το νετρίνο θα πάρει τη μάζα του μέσω μιας αλληλεπίδρασης με το αντινετρίνο του. Για να γίνει αυτό, οι θεωρητικοί θα πρέπει να εφεύρουν κάτι άλλο, όπως μια μοναδική μορφή του μποζονίου Higgs ειδική για την αλληλεπίδραση νετρίνων.

Μια εναλλακτική θεωρία χωρίς το Higgs

Η πιο δημοφιλής θεωρία προτείνει έναν εντελώς νέο μηχανισμό για την μάζα των νετρίνων, εισάγοντας ένα νέο σωματίδιο πέραν του Καθιερωμένου Προτύπου.

Σύμφωνα με αυτή τη θεωρία, η νέα αυτή οντότητα θα μπορούσε να είναι ένα πολύ βαρύ σωματίδιο, που μοιάζει με δεξιόστροφο νετρίνο, αλλά με διαφορετική μάζα. Θα μπορούσε να είναι κάτι που μοιάζει με το μποζόνιο Higgs ή ένα είδος σωματιδίου σαν το ηλεκτρόνιο ή πολλά σωματίδια η συλλογική δράση των οποίων δίνει την μάζα στα νετρίνα. Μια μορφή αυτής της θεωρίας, αρκετά δημοφιλής, είναι ο μηχανισμός Seesaw, οποίος επιβεβαιώνει τις πολύ μικρές μάζες των νετρίνων.

Αν το σωματίδιο που δημιουργεί την μάζα των νετρίνων είναι πολύ βαρύ, η μεγάλη του μάζα είναι που κάνει τα νετρίνα να έχουν πολύ μικρή μάζα.

Τα πειράματα νετρίνων

Οι φυσικοί δοκιμάζουν αυτές τις θεωρίες με πειράματα. Η πρώτη και πιο σημαντική ερώτηση που πρέπει να απαντηθεί είναι, "αν τα νετρίνα Majorana είναι φερμιόνια;". Πειράματα όπως το GERDA (GERmanium Detector Array) στο υπόγειο εργαστήριο του Gran Sasso στην Ιταλία προσπαθούν να προσδιορίσουν αν τα νετρίνα ταυτίζονται με τα αντισωμτίδιά τους, αναζητώντας ένα φαινόμενο που ονομάζεται διπλή βήτα διάσπαση.

Σ' αυτή την διαδικασία, ένα νετρόνιο στον πυρήνα ενός ισοτόπου, στην περίπτωση αυτή ένα ισότοπο γερμανίου, διασπάται σε ένα ηλεκτρόνιο και ένα νετρίνο. Αν δυο νετρόνια στον πυρήνα του ισοτόπου διασπαστούν ταυτόχρονα, τότε προκύπτει αυτό που ονομάζεται διπλή βήτα διάσπαση. Οι φυσικοί ψάχνουν μια διπλή βήτα διάσπαση όπου ο πυρήνας δεν εκπέμπει νετρίνα, αλλά φαίνεται να εκπέμπει μόνο δυο ηλεκτρόνια, αφού τα νετρίνα (τύπου Majorana) που εκπέμπονται εξαϋλώνονται.

Κι αν η παρατήρηση της διπλής βήτα διάσπασης είναι εξαιρετικά σπάνια, τότε η χωρίς νετρίνα διπλή διάσπαση βήτα θα είναι πολύ σπανιότερη. Αλλά, οι φυσικοί περιμένουν να δοθεί πειραματική απάντηση στο πρόβλημα σε περίπου δέκα χρόνια.

Οι καρποί αυτής της έρευνας δεν τελειώνουν με τα νετρίνα. Αν κατανοήσουμε περισσότερο τα νετρίνα τότε θα μπορούμε να απαντήσουμε κι άλλες ανοιχτές ερωτήσεις στην σωματιδιακή φυσική. Ερωτήσεις όπως: Γιατί η ύλη στο σύμπαν κυριαρχεί συντριπτικά έναντι της αντιύλης; Γιατί η διαστολή του σύμπαντος επιταχύνεται; Τι είναι η σκοτεινή ύλη;

Το βέβαιο είναι πως η συλλογή όσο το δυνατόν περισσότερων πειραματικών δεδομένων σχετικά με την μάζα των νετρίνων θα μας βοηθήσει να κατανοήσουμε περισσότερο την φυσική των στοιχειωδών σωματιδίων - ή που είναι το ίδιο, να κατανοήσουμε καλύτερα τον εαυτό μας και τον κόσμο που μας περιβάλλει.

πηγή: https://www.symmetrymagazine.org/article/how-do-neutrinos-get-their-mass

[1] =τα σωματίδια που υπακούουν στην απαγορευτική αρχή του Pauli και έχουν ημιακέραιο σπιν, μποζόνια=δεν υπακούουν στην απαγορευτική αρχή του Pauli και έχουν ακέραιο σπιν

# data[].attributes.attachment_link.title
Τι συμβαίνει με την μάζα των νετρίνων;

# data[].attributes.attachment_link.description
To 1998, oι φυσικοί έκαναν μια ανακάλυψη που κλόνισε την καθιερωμένη θεωρία τους για τα στοιχειώδη σωματίδια και έφερε στο προσκήνιο για τις επόμενες δεκαετίες ένα ταπεινό σωματίδιο. Το Καθιερωμένο Πρότυπο, η θεωρία που περιγράφει την φυσική των θεμελιωδών σωματιδίων της ύλης από την οποία είμαστε φτιαγμένοι, προέβλεπε ότι η μάζα των σωματιδίων που ονομάζονται...

# data[].attributes.headline
      ΑΝΤΙΥΛΗ

# data[].attributes.subject
      ΑΝΤΙΥΛΗ

# data[].attributes.body
Για κάθε σωματίδιο υπάρχει και το αντισωματίδιό του

# data[].attributes.body
H  ονομασία bottom  χρησιμοποιήθηκε για 1η φορά το 1975 από τον Haim Harasi.
Πολλές φορές χρησιμοποιείται και το όνομα beauty (ομορφιά), ίσως γιατί όταν ανακαλύφθηκε οι φυσικοί κατάλαβαν ότι μια ομάδα 6 κουάρκ έκαναν τη θεωρία όμορφη.

# data[].attributes.body
Ονομάστηκε έτσι γιατί όταν ανακαλύφθηκε, οι μαθηματικοί υπολογισμοί της θεωρίας ήταν γοητευτικοί.

# data[].attributes.body
Ονομάστηκε έτσι, γιατί είναι το βαρύτερο από όλα τα κουάρκ και τα λεπτόνια.

# data[].attributes.body
Ονομάστηκε παράξενο γιατί την 1η φορά που ανιχνεύτηκε οι φυσικοί δεν καταλάβαιναν τι ήταν.

# data[].attributes.headline
Το όνομα λεπτόνια πρ

# data[].attributes.body
Το όνομα λεπτόνια προέρχεται από την ελληνική λέξη  "λεπτός" που σημαίνει ελαφρύς.
Το όνομα αυτό δόθηκε γιατί το πρώτο λεπτόνιο που ανακαλύφθηκε, το ηλεκτρόνιο, ήταν πολύ ελαφρύτερο από το πρωτόνιο.

# data[].attributes.headline
Τα φερμιόνια δημιουργούν και αλληλεπιδρούν με 4 πεδία δυνάμεων.                                                                  Τα μποζόνια είναι η σωματιδιακή έκφραση αυτών των πεδίων (κβαντική θεωρία πεδίου). 

# data[].attributes.subject
Τα φερμιόνια δημιουργούν και αλληλεπιδρούν με 4 πεδία δυνάμεων.                                                                  Τα μποζόνια είναι η σωματιδιακή έκφραση αυτών των πεδίων (κβαντική θεωρία πεδίου). 

# data[].attributes.headline
Η ανακάλυψη του σωματίου Higgs μετά από σχεδόν 50 χρόνια αναζήτησης ολοκλήρωσε το Καθιερωμένο Πρότυπο ως βασική θεωρία ερμηνείας των ιδιοτήτων όλων των στοιχειωδών σωματίων που γνωρίζουμε σήμερα και των θεμελιωδών αλληλεπιδράσεών τους.

# data[].attributes.subject
Η ανακάλυψη του σωματίου Higgs μετά από σχεδόν 50 χρόνια αναζήτησης ολοκλήρωσε το Καθιερωμένο Πρότυπο ως βασική θεωρία ερμηνείας των ιδιοτήτων όλων των στοιχειωδών σωματίων που γνωρίζουμε σήμερα και των θεμελιωδών αλληλεπιδράσεών τους.

# data[].attributes.headline
                                                  Το πεδίο Higgs

# data[].attributes.subject
                                                  Το πεδίο Higgs

# data[].attributes.body
Το Καθιερωμένο Πρότυπο απαιτεί την ύπαρξη ενός σωματίου χωρίς φορτίο και σπιν (μποζόνιο), το οποίο δημιουργείται από ένα  κβαντικό πεδίο που γεμίζει το Σύμπαν και δίνει μάζα στα άλλα στοιχειώδη σωμάτια.
Το σωμάτιο αυτό ονομάζεται σωμάτιο Higgs (το αντίστοιχο πεδίο ονομάζεται πεδίο Higgs) και παρατηρήθηκε στις 4 Ιουλίου του 2012 από τα πειράματα ATLAS και CMS του μεγάλου επιταχυντή αδρονίων LHC.