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:
A new class of particles with “strange” properties were discovered in the 1960s, many years before it became clear that those properties were due to the fact that the particles all contained a new, “strange” kind of quark.
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.
