This is a list of known and hypothesized molecular, atomic, and subatomic particles in particle physics, condensed matter physics and cosmology.
Standard Model elementary particles
Elementary particles are particles with no measurable internal structure; that is, it is unknown whether they are composed of other particles. They are the fundamental objects of quantum field theory. Many families and sub-families of elementary particles exist. Elementary particles are classified according to their spin. Fermions have half-integer spin while bosons have integer spin. All the elementary particles of the Standard Model have been experimentally observed, including the Higgs boson in 2012. Many other hypothetical elementary particles, such as the graviton, have been proposed, but not observed experimentally.
Fermions
Fermions are one of the two fundamental classes of particles, the other being bosons. Fermion particles are described by Fermi–Dirac statistics and have quantum numbers described by the Pauli exclusion principle. 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.
Fermions have half-integer spin; for all known elementary fermions this is ħ. All known fermions except neutrinos, are also Dirac fermions; that is, each known fermion has its own distinct antiparticle. It is not known whether the neutrino is a Dirac fermion or a Majorana fermion. Fermions are the basic building blocks of all matter. They are classified according to whether they interact via the strong interaction or not. In the Standard Model, there are 12 types of elementary fermions: six quarks and six leptons.
Quarks
Quarks are the fundamental constituents of hadrons and interact via the strong force. Quarks are the only known carriers of fractional charge, but because they combine in groups of three quarks (baryons) or in pairs of one quark and one antiquark (mesons), only integer charge is observed in nature. Their respective antiparticles are the antiquarks, which are identical except that they carry the opposite electric charge (for example the up quark carries charge +e, while the up antiquark carries charge −e), color charge, and baryon number. There are six flavors of quarks; the three positively charged quarks are called "up-type quarks" while the three negatively charged quarks are called "down-type quarks".
{|class="wikitable sortable" style="margin:1em auto; text-align:center"
|+Quarks
|-
! Generation !! Name !! Symbol !! Antiparticle !! Spin !! Charge !! data-sort-type="number"|Mass
|-
|rowspan=2| 1
| up || u ||
|data-sort-value="1"| || + ||
|-
| down || d ||
|data-sort-value="2"| || − ||
|-
|rowspan=2| 2
| charm || c ||
|data-sort-value="3"| || + ||
|-
| strange || s ||
|data-sort-value="4"| || − ||
|-
|rowspan=2| 3
| top || t ||
|data-sort-value="5"| || + ||
|-
| bottom || b ||
|data-sort-value="6"| || − ||
|}
Leptons
Leptons do not interact via the strong interaction. 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. There are six leptons in total; the three charged leptons are called "electron-like leptons", while the neutral leptons are called "neutrinos". Neutrinos are known to oscillate, so that neutrinos of definite flavor do not have definite mass: instead, they exist in a superposition of mass eigenstates. The hypothetical heavy right-handed neutrino, called a "sterile neutrino", has been omitted.
{|class="wikitable sortable" style="margin:1em auto; text-align:center"
|+Leptons
|-
! Generation !! Name !! Symbol !! Antiparticle !! Spin !! Charge !! Mass
|-
|rowspan=2| 1
| electron || ||
|data-sort-value="4"| || −1 || 0.511
|-
| electron neutrino || ||
|data-sort-value="1"| ||  0 ||
|-
|rowspan=2| 2
| muon || ||
|data-sort-value="5"| || −1 || 105.7
|-
| muon neutrino || ||
|data-sort-value="2"| ||  0 ||
|-
|rowspan=2| 3
| tau || ||
|data-sort-value="3"| || −1 ||
|-
| tau neutrino || ||
|data-sort-value="6"| ||  0 ||
|}
Bosons
Bosons are one of the two fundamental particles having integral spinclasses of particles, the other being fermions. Bosons are characterized by Bose–Einstein statistics and all have integer spins. Bosons may be either elementary, like photons and gluons, or composite, like mesons.
According to the Standard Model, the elementary bosons are:
{| class="wikitable sortable" style="margin:1em auto; align: center; text-align: center;"
! Name !! Symbol !! Antiparticle !! Spin !! Charge !! Mass
Dark matter candidates
Many hypothetical particle candidates for dark matter have been proposed like weakly interacting massive particles (WIMP), weakly interacting slender particles (WISP), or feebly interacting particles (FIP).
Dark energy candidates
Hypothetical particle candidates to explain dark energy include the chameleon particle and the acceleron.
Auxiliary particles
Virtual particles are mathematical tools used in calculations that exhibits some of the characteristics of an ordinary particle but do not obey the mass-shell relation. These particles are unphysical and unobservable. These include:
- Ghost particles, like Faddeev–Popov ghosts and Pauli–Villars ghosts
- Spurions, auxiliary field in a quantum field theory that can be used to parameterize any symmetry
- Soft photons, photons with energies below detectable in experiment.
There are also instantons, field configurations which are a local minimum of the Yang–Mills field equation. Instantons are used in nonperturbative calculations of tunneling rates. Instantons have properties similar to particles, specific examples include:
- Calorons, finite temperature generalization of instantons.
- Merons, a field configuration which is a non-self-dual solution of the Yang–Mills field equation. The instanton is believed to be composed of two merons.
- Sphalerons are a field configuration which is a saddle point of the Yang–Mills field equations. Sphalerons are used in nonperturbative calculations of non-tunneling rates.
- Renormalons, a possible type of singularity arising when using Borel summation. It is a counterpart of an instanton singularity.
Classification by speed
- A bradyon (or tardyon) travels slower than the speed of light in vacuum and has a non-zero, real rest mass.
- A luxon travels as fast as light in vacuum and has no rest mass.
- A tachyon is a hypothetical particle that travels faster than the speed of light so they would paradoxically experience time in reverse (due to inversion of the theory of relativity) and would violate the known laws of causality. A tachyon has an imaginary rest mass.