List of particles

All the particles of the Standard Model have been experimentally observed, including the Higgs boson in 2012.

[2][3] Many other hypothetical elementary particles, such as the graviton, have been proposed, but not observed experimentally.

They include the quarks and leptons, as well as any composite particles consisting of an odd number of these, such as all baryons and many atoms and nuclei.

In the Standard Model, there are 12 types of elementary fermions: six quarks and six leptons.

Their respective antiparticles are the antileptons, which are identical, except that they carry the opposite electric charge and lepton number.

The antiparticle of an electron is an antielectron, which is almost always called a "positron" for historical reasons.

In a process known as the "Higgs mechanism", the Higgs boson and the other gauge bosons in the Standard Model acquire mass via spontaneous symmetry breaking of the SU(2) gauge symmetry.

The Minimal Supersymmetric Standard Model (MSSM) predicts several Higgs bosons.

On 4 July 2012, the discovery of a new particle with a mass between 125 and 127 GeV/c2 was announced; physicists suspected that it was the Higgs boson.

Since then, the particle has been shown to behave, interact, and decay in many of the ways predicted for Higgs particles by the Standard Model, as well as having even parity and zero spin, two fundamental attributes of a Higgs boson.

(The interaction between quarks and gluons is described by the theory of quantum chromodynamics.)

In quantum hadrodynamics, mesons mediate the residual strong force between nucleons.

At one time or another, positive signatures have been reported for all of the following exotic mesons but their existences have yet to be confirmed.

Atoms are the smallest neutral particles into which matter can be divided by chemical reactions.

An atom consists of a small, heavy nucleus surrounded by a relatively large, light cloud of electrons.

Exotic atoms may be composed of particles in addition to or in place of protons, neutrons, and electrons, such as hyperons or muons.

If it exists, the graviton is expected to be massless because the gravitational force has a very long range, and appears to propagate at the speed of light.

A combination of three u, d or s-quarks with a total spin of ⁠ 3 / 2 ⁠ form the so-called "baryon decuplet".
Proton quark structure: 2 up quarks and 1 down quark.
Mesons of spin 0 form a nonet.
A semi-accurate depiction of the helium atom. In the nucleus, the protons are in red and neutrons are in purple. In reality, the nucleus is also spherically symmetrical.