quark-top quark-charm quark-up lepton-tau lepton-muon lepton-electron lepton-tn lepton-mn lepton-en quark-bottom quark-strange bosons-photon bosons-w higgs bosons-z bosons-gluon quark-down Standard Model Key

The Standard Model of Particle Physics

The Standard Model is a kind of periodic table of the elements for particle physics. But instead of listing the chemical elements, it lists the fundamental particles that make up the atoms that make up the chemical elements, along with any other particles that cannot be broken down into any smaller pieces.

The complete Standard Model took a long time to build. Physicist J.J. Thomson discovered the electron in 1897, and scientists at the Large Hadron Collider found the final piece of the puzzle, the Higgs boson, in 2012.

Use this interactive graphic to explore the different particles that make up the building blocks of our universe.

Up Quark

Discovered in:

1968

Mass:

2.3 MeV

Generation:

First

Discovered at:

SLAC

Charge:

2/3

Spin:

1/2

About:

Up and down quarks make up protons and neutrons, which make up the nucleus of every atom.

Charm Quark

Discovered in:

1974

Mass:

1.275 GeV

Generation:

Second

Discovered at:

Brookhaven & SLAC

Charge:

2/3

Spin:

1/2

About:

In 1974, two independent research groups conducting experiments at two independent labs discovered the charm quark, the fourth quark to be found. The surprising discovery forced physicists to reconsider how the universe works at the smallest scale.

Top Quark

Discovered in:

1995

Mass:

173.21 GeV

Generation:

Third

Discovered at:

Fermilab

Charge:

2/3

Spin:

1/2

About:

The top quark is the heaviest quark discovered so far. It has about the same weight as a gold atom. But unlike an atom, it is a fundamental, or elementary, particle; as far as we know, it is not made of smaller building blocks.

Down Quark

Discovered in:

1968

Mass:

4.8 MeV

Generation:

First

Discovered at:

SLAC

Charge:

-1/3

Spin:

1/2

About:

Nobody knows why, but a down quark is a just a little bit heavier than an up quark. If that weren’t the case, the protons inside every atom would decay and the universe would look very different.

Strange Quark

Discovered in:

1947

Mass:

95 MeV

Generation:

Second

Discovered at:

Manchester University

Charge:

-1/3

Spin:

1/2

About:

Scientists discovered particles with “strange" properties many years before it became clear that those strange properties were due to the fact that they all contained a new, “strange” kind of quark. Theorist Murray Gell-Mann was awarded the Nobel Prize for introducing the concepts of strangeness and quarks.

Bottom Quark

Discovered in:

1977

Mass:

4.18 GeV

Generation:

Third

Discovered at:

Fermilab

Charge:

-1/3

Spin:

1/2

About:

This particle is a heavier cousin of the down and strange quarks. Its discovery confirmed that all elementary building blocks of ordinary matter come in three different versions.

Electron

Discovered in:

1897

Mass:

0.511 MeV

Generation:

First

Discovered at:

Cavendish Laboratory

Charge:

-1

Spin:

1/2

About:

The electron powers the world. It is the lightest particle with an electric charge and a building block of all atoms. The electron belongs to the family of charged leptons.

Muon

Discovered in:

1937

Mass:

105.66 MeV

Generation:

Second

Discovered at:

Caltech & Harvard

Charge:

-1

Spin:

1/2

About:

The muon is a heavier version of the electron. It rains down on us as it is created in collisions of cosmic rays with the Earth’s atmosphere. When it was discovered in 1937, a physicist asked, “Who ordered that?”

Tau

Discovered in:

1976

Mass:

1776.82 MeV

Generation:

Third

Discovered at:

SLAC

Charge:

-1

Spin:

1/2

About:

The discovery of this particle in 1976 completely surprised scientists. It was the first discovery of a particle of the so-called third generation. It is the third and heaviest of the charged leptons, heavier than both the electron and the muon.

Electron Neutrino

Discovered in:

1956

Mass:

<2 eV

Generation:

First

Discovered at:

Savannah River Plant

Charge:

0

Spin:

1/2

About:

Measurements and calculations in the 1920s led to the prediction of the existence of an elusive particle without electric charge, the neutrino. But it wasn’t until 1956 that scientists observed the signal of an electron neutrino interacting with other particles. Nuclear reactions in the sun and in nuclear power plants produce electron antineutrinos.

Muon Neutrino

Discovered in:

1962

Mass:

<0.19 MeV

Generation:

Second

Discovered at:

Brookhaven

Charge:

0

Spin:

1/2

About:

Neutrinos come in three flavors. The muon neutrino was first discovered in 1962. Neutrino beams from accelerators are typically made up of muon neutrinos and muon antineutrinos.

Tau Neutrino

Discovered in:

2000

Mass:

<18.2 MeV

Generation:

Third

Discovered at:

Fermilab

Charge:

0

Spin:

1/2

About:

Based on theoretical models and indirect observations, scientists expected to find a third generation of neutrino. But it took until 2000 for scientists to develop the technologies to identify the particle tracks created by tau neutrino interactions.

Photon

Discovered in:

1923

Mass:

<1x10-18 eV

Discovered at:

Washington University

Charge:

0

Spin:

1

About:

The photon is the only elementary particle visible to the human eye—but only if it has the right energy and frequency (color). It transmits the electromagnetic force between charged particles.

Gluon

Discovered in:

1979

Mass:

0

Discovered at:

DESY

Charge:

0

Spin:

1

About:

The gluon is the glue that holds together quarks to form protons, neutrons and other particles. It mediates the strong nuclear force.

Z Boson

Discovered in:

1983

Mass:

91.1876 GeV

Discovered at:

CERN

Charge:

0

Spin:

1

About:

The Z boson is the electrically neutral cousin of the W boson and a heavy relative of the photon. Together, these particles explain the electroweak force.

W Boson

Discovered in:

1983

Mass:

80.385 GeV

Discovered at:

CERN

Charge:

±1

Spin:

1

About:

The W boson is the only force carrier that has an electric charge. It’s essential for weak nuclear reactions: Without it, the sun would not shine.

Higgs Boson

Discovered in:

2012

Mass:

125.7 GeV

Discovered at:

CERN

Charge:

0

Spin:

0

About:

Discovered in 2012, the Higgs boson was the last missing piece of the Standard Model puzzle. It is a different kind of force carrier from the other elementary forces, and it gives mass to quarks as well as the W and Z bosons. Whether it also gives mass to neutrinos remains to be discovered.