# data[].attributes.attachment_link.title
The 2,400-year search for the atom - Theresa Doud

# data[].attributes.headline
1897: JJ Thompson discovers the electron

# data[].attributes.subject
1897: JJ Thompson discovers the electron

# data[].attributes.attachment_link.title
In search of giants - the building blocks of matter 1/2

# data[].attributes.headline
1905: Einstein proposes the existence of discrete energy packets, later named photons, in his explanation of the photoelectric effect.

# data[].attributes.subject
1905: Einstein proposes the existence of discrete energy packets, later named photons, in his explanation of the photoelectric effect.

# data[].attributes.body
Investigate the photoelectric effect using PhET.

# data[].attributes.attachment_link.description
See how light knocks electrons off a metal target, and recreate the experiment that spawned the field of quantum mechanics.

# data[].attributes.headline
1909: Robert Millikan and the oil drop experiment.

# data[].attributes.subject
1909: Robert Millikan and the oil drop experiment.

# data[].attributes.body
Measured the charge of an electron using oil droplets.
Investigate yourself by clicking the link.

# data[].attributes.attachment_link.readable_text
In this lab you will be looking for oil drops that can caught in the electric field between two capacitor plates. Some drops will fall out of your field of view as the gravitational force on them is larger than the electric force. Other drops will rise out of your field of view as the gravitational force is too small for the electrical force.

When you find a drop that is remaining at rest between the plates, use your magnifier to zoom in on the drop to determine it's size. Distances have not been drawn to scale to help make the physics of the experiment more noticeable.

When you are ready to start the experiment, click on the begin button

# data[].attributes.attachment_link.description
In this lab you will be looking for oil drops that can caught in the electric field between two capacitor plates. Some drops will fall out of your field of view as the gravitational force on them is larger than the electric force.

# data[].attributes.headline
1911: Ernest Rutherford's gold foil experiment.

# data[].attributes.subject
1911: Ernest Rutherford's gold foil experiment.

# data[].attributes.body
Most of the atom is empty space.
Nucleus is dense and positively charged.
The proton is discovered.
Try the PhET simulation link.

# data[].attributes.headline
1912: Cloud chamber invented by Charles TR Wilson.

# data[].attributes.subject
1912: Cloud chamber invented by Charles TR Wilson.

# data[].attributes.body
See how to build a cloud chamber in this video clip.

# data[].attributes.attachment_link.title
Brian Cox Builds a Cloud Chamber - Wonders of Life - Series 1 Episode 3 Preview - BBC Two

# data[].attributes.headline
1920s: de Broglie, Schrodinger and Heisenberg's quantum mechanical model of the atom

# data[].attributes.subject
1920s: de Broglie, Schrodinger and Heisenberg's quantum mechanical model of the atom

# data[].attributes.attachment_link.title
Modern Atomic Theory: De Broglie's, Schrodinger's & Heisenberg's Contributions

# data[].attributes.headline
1923: Photon discovered experimentally by Arthur Compton.

# data[].attributes.subject
1923: Photon discovered experimentally by Arthur Compton.

# data[].attributes.body
He demonstrated the particle nature of electromagnetic radiation.

# data[].attributes.headline
1928: Paul Dirac predicts anti-particles

# data[].attributes.subject
1928: Paul Dirac predicts anti-particles

# data[].attributes.headline
1930: Wolfgang Pauli predicts the neutrino.

# data[].attributes.subject
1930: Wolfgang Pauli predicts the neutrino.

# data[].attributes.headline
1932: James Chadwick discovers the neutron.

# data[].attributes.subject
1932: James Chadwick discovers the neutron.

# data[].attributes.headline
1932: Positron discovered (anti-particle of electron) by Carl Anderson.

# data[].attributes.subject
1932: Positron discovered (anti-particle of electron) by Carl Anderson.

# data[].attributes.headline
1937: Muon discovered by Carl D Anderson & Seth Neddermeyer.

# data[].attributes.subject
1937: Muon discovered by Carl D Anderson & Seth Neddermeyer.

# data[].attributes.body
Stroll through CERN!

# data[].attributes.attachment_link.title
A stroll through CERN’s underground spaces - Google Arts & Culture

# data[].attributes.attachment_link.description
Google Arts & Culture features content from over 2000 leading museums and archives who have partnered with the Google Cultural Institute to bring the world’s treasures online.

# data[].attributes.headline
1955: Antiproton discovered by Emilio Segre & Owen Chamberlain.

# data[].attributes.subject
1955: Antiproton discovered by Emilio Segre & Owen Chamberlain.

# data[].attributes.body
Bombarded a copper target with high-energy protons from the proton synchrotron at the University of California.

# data[].attributes.headline
1956: Electron neutrino discovered by Cowan and Reines.

# data[].attributes.subject
1956: Electron neutrino discovered by Cowan and Reines.

# data[].attributes.body
Detected in Los Alamos National Laboratory by observing inverse beta decay.

# data[].attributes.headline
1962: Muon neutrino discovered by Steinberger, Schwartz and Ledermann.

# data[].attributes.subject
1962: Muon neutrino discovered by Steinberger, Schwartz and Ledermann.

# data[].attributes.body
Discovered in Brookhaven National Laboratory.

# data[].attributes.headline
1964: Murray Gell-Mann and George Zweig independently propose the existence of quarks.

# data[].attributes.subject
1964: Murray Gell-Mann and George Zweig independently propose the existence of quarks.

# data[].attributes.headline
1964: Peter Higgs predicts the mass generating boson, later named the Higgs Boson.

# data[].attributes.subject
1964: Peter Higgs predicts the mass generating boson, later named the Higgs Boson.

# data[].attributes.headline
1969: Quarks discovered in the Stanford Linear Accelerator Center (SLAC).

# data[].attributes.subject
1969: Quarks discovered in the Stanford Linear Accelerator Center (SLAC).

# data[].attributes.body
The discovery of particles rapidly increases from here.

# data[].attributes.attachment_link.title
CERN: The Standard Model Of Particle Physics

# data[].attributes.headline
2012: 4th of July Higgs Boson discovered in CERN.

# data[].attributes.subject
2012: 4th of July Higgs Boson discovered in CERN.

# data[].attributes.headline
2022: Pentaquarks and tetraquarks discovered in CERN.

# data[].attributes.subject
2022: Pentaquarks and tetraquarks discovered in CERN.

# data[].attributes.attachment_link.readable_text
The collaboration has observed a new kind of "pentaquark" and the first-ever pair of "tetraquarks"

The new pentaquark, illustrated here as a pair of standard hadrons loosely bound in a molecule-like structure, is made up of a charm quark and a charm antiquark and an up, a down and a strange quark (Image: CERN)

The international LHCb collaboration at the Large Hadron Collider (LHC) has observed three never-before-seen particles: a new kind of "pentaquark" and the first-ever pair of "tetraquarks", which includes a new type of tetraquark. The findings, presented today at a CERN seminar, add three new exotic members to the growing list of new hadrons found at the LHC. They will help physicists better understand how quarks bind together into these composite particles.

Quarks are elementary particles and come in six flavours: up, down, charm, strange, top and bottom. They usually combine together in groups of twos and threes to form hadrons such as the protons and neutrons that make up atomic nuclei. More rarely, however, they can also combine into four-quark and five-quark particles, or "tetraquarks" and "pentaquarks". These exotic hadrons were predicted by theorists at the same time as conventional hadrons, about six decades ago, but only relatively recently, in the past 20 years, have they been observed by LHCb and other experiments.

Most of the exotic hadrons discovered in the past two decades are tetraquarks or pentaquarks containing a charm quark and a charm antiquark, with the remaining two or three quarks being an up, down or strange quark or their antiquarks. But in the past two years, LHCb has discovered different kinds of exotic hadrons. Two years ago, the collaboration discovered a tetraquark made up of two charm quarks and two charm antiquarks, and two "open-charm" tetraquarks consisting of a charm antiquark, an up quark, a down quark and a strange antiquark. And last year it found the first-ever instance of a "double open-charm" tetraquark with two charm quarks and an up and a down antiquark. Open charm means that the particle contains a charm quark without an equivalent antiquark.

The discoveries announced today by the LHCb collaboration include new kinds of exotic hadrons. The first kind, observed in an analysis of "decays" of negatively charged B mesons, is a pentaquark made up of a charm quark and a charm antiquark and an up, a down and a strange quark. It is the first pentaquark found to contain a strange quark. The finding has a whopping statistical significance of 15 standard deviations, far beyond the 5 standard deviations that are required to claim the observation of a particle in particle physics.

The two new tetraquarks, illustrated here as single units of tightly bound quarks. One of the particles is composed of a charm quark, a strange antiquark and an up quark and a down antiquark (left), and the other is made up of a charm quark, a strange antiquark and an up antiquark and down quark (right) (Image: CERN)

The second kind is a doubly electrically charged tetraquark. It is an open-charm tetraquark composed of a charm quark, a strange antiquark, and an up quark and a down antiquark, and it was spotted together with its neutral counterpart in a joint analysis of decays of positively charged and neutral B mesons. The new tetraquarks, observed with a statistical significance of 6.5 (doubly charged particle) and 8 (neutral particle) standard deviations, represent the first time a pair of tetraquarks has been observed.

"The more analyses we perform, the more kinds of exotic hadrons we find," says LHCb physics coordinator Niels Tuning. "We're witnessing a period of discovery similar to the 1950s, when a 'particle zoo' of hadrons started being discovered and ultimately led to the quark model of conventional hadrons in the 1960s. We're creating 'particle zoo 2.0'."

"Finding new kinds of tetraquarks and pentaquarks and measuring their properties will help theorists develop a unified model of exotic hadrons, the exact nature of which is largely unknown," says LHCb spokesperson Chris Parkes. "It will also help to better understand conventional hadrons."

While some theoretical models describe exotic hadrons as single units of tightly bound quarks, other models envisage them as pairs of standard hadrons loosely bound in a molecule-like structure. Only time and more studies of exotic hadrons will tell if these particles are one, the other or both.
Further information:
Read more on the LHCb website.

Illustrations: https://cds.cern.ch/record/2814136

# data[].attributes.attachment_link.title
LHCb discovers three new exotic particles

# data[].attributes.attachment_link.description
The international LHCb collaboration at the Large Hadron Collider (LHC) has observed three never-before-seen particles: a new kind of "pentaquark" and the first-ever pair of "tetraquarks", which includes a new type of tetraquark. The findings, presented today at a CERN seminar, add three new exotic members to the growing list of new hadrons found at the LHC.

# data[].attributes.headline
Inside CERN, the world's largest particle accelerator.

# data[].attributes.subject
Inside CERN, the world's largest particle accelerator.

# data[].attributes.attachment_link.title
Inside the World's Largest Science Experiment