This article includes a list of the different
types of atomic- and sub-atomic particles
found or hypothesized to exist in the whole
of the universe categorized by type.
Properties of the various particles listed
are also given, as well as the laws that the
particles follow.
For individual lists of the different particles,
see the list below.
== 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 particles of the Standard Model have
been experimentally observed, recently including
the Higgs boson.
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 ​1⁄2.
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 interaction.
Quarks are the only known carriers of fractional
charge, but because they combine in groups
of three (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 +​2⁄3, while
the up antiquark carries charge −​2⁄3),
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".
==== 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 nearly 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, rather they exist in a superposition
of mass eigenstates.
The hypothetical heavy right-handed neutrino,
called a "sterile neutrino", has been left
off the list.
=== Bosons ===
Bosons are one of the two fundamental classes
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:
The Higgs boson is postulated by the electroweak
theory primarily to explain the origin of
particle masses.
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.
A new particle expected to be the Higgs boson
was observed at the CERN/LHC on 14 March 2013,
around the energy of 126.5 GeV with an accuracy
of close to five sigma (99.9999%, which is
accepted as definitive).
The Higgs mechanism giving mass to other particles
has not been observed.
Elementary bosons responsible for the four
fundamental forces of nature are called force
particles (gauge bosons).
Strong interaction is mediated by the gluon,
weak interaction is mediated by the W and
Z bosons.
The graviton, listed separately above, is
a hypothetical particle that has been included
in some extensions to the standard model to
mediate the gravitational force.
It is in a peculiar category between known
and hypothetical particles: As an unobserved
particle that is not predicted by, nor required
for the Standard Model, it belongs in the
table of hypothetical particles, below.
But gravitational force itself is a certainty,
and expressing that known force in the framework
of a quantum field theory requires a boson
to mediate it.
=== Hypothetical particles ===
Supersymmetric theories predict the existence
of more particles, none of which have been
confirmed experimentally as of 2018:
Note: just as the photon, Z boson and W±
bosons are superpositions of the B0, W0, W1,
and W2 fields – the photino, zino, and wino±
are superpositions of the bino0, wino0, wino1,
and wino2 by definition.No matter if one uses
the original gauginos or this superpositions
as a basis, the only predicted physical particles
are neutralinos and charginos as a superposition
of them together with the Higgsinos.
Other theories predict the existence of additional
bosons:
Mirror particles are predicted by theories
that restore parity symmetry.
"Magnetic monopole" is a generic name for
particles with non-zero magnetic charge.
They are predicted by some GUTs.
"Tachyon" is a generic name for hypothetical
particles that travel faster than the speed
of light (and so paradoxically experience
time in reverse due to inversal of Theory
of relativity) and have an imaginary rest
mass.
Preons were suggested as subparticles of quarks
and leptons, but modern collider experiments
have all but ruled out their existence.
Kaluza–Klein towers of particles are predicted
by some models of extra dimensions.
The extra-dimensional momentum is manifested
as extra mass in four-dimensional spacetime.
== Composite particles ==
=== 
Hadrons ===
Hadrons are defined as strongly interacting
composite particles.
Hadrons are either:
Composite fermions (especially 3 quarks),
in which case they are called baryons.
Composite bosons (especially 2 quarks), in
which case they are called mesons.Quark models,
first proposed in 1964 independently by Murray
Gell-Mann and George Zweig (who called quarks
"aces"), describe the known hadrons as composed
of valence quarks and/or antiquarks, tightly
bound by the color force, which is mediated
by gluons.
A "sea" of virtual quark-antiquark pairs is
also present in each hadron.
==== Baryons ====
Ordinary baryons (composite fermions) contain
three valence quarks or three valence antiquarks
each.
Nucleons are the fermionic constituents of
normal atomic nuclei:
Protons, composed of two up and one down quark
(uud)
Neutrons, composed of two down and one up
quark (ddu)
Hyperons, such as the Λ, Σ, Ξ, and Ω particles,
which contain one or more strange quarks,
are short-lived and heavier than nucleons.
Although not normally present in atomic nuclei,
they can appear in short-lived hypernuclei.
A number of charmed and bottom baryons have
also been observed.
Pentaquarks consist of four valence quarks
and one valence antiquark.
Other exotic baryons may also exist.
==== Mesons ====
Ordinary mesons are made up of a valence quark
and a valence antiquark.
Because mesons have spin of 0 or 1 and are
not themselves elementary particles, they
are "composite" bosons.
Examples of mesons include the pion, kaon,
and the J/ψ.
In quantum hydrodynamic models, 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.
A tetraquark consists of two valence quarks
and two valence antiquarks;
A glueball is a bound state of gluons with
no valence quarks;
Hybrid mesons consist of one or more valence
quark-antiquark pairs and one or more real
gluons.
=== Atomic nuclei ===
Atomic nuclei consist of protons and neutrons.
Each type of nucleus contains a specific number
of protons and a specific number of neutrons,
and is called a "nuclide" or "isotope".
Nuclear reactions can change one nuclide into
another.
See table of nuclides for a complete list
of isotopes.
=== Atoms ===
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.
Each type of atom corresponds to a specific
chemical element.
To date, 118 elements have been discovered
or created.
The atomic nucleus consists of protons and
neutrons.
Protons and neutrons are, in turn, made of
quarks.
=== Molecules ===
Molecules are the smallest particles into
which a non-elemental substance can be divided
while maintaining the physical properties
of the substance.
Each type of molecule corresponds to a specific
chemical compound.
Molecules are a composite of two or more atoms.
See list of compounds for a list of molecules.
A molecule is generally combined in a fixed
proportion.
It is the most basic unit of matter and is
homogenous.
== Quasiparticles ==
Quasiparticles are effective particles that
exist in many particle systems.
The field equations of condensed matter physics
are remarkably similar to those of high energy
particle physics.
As a result, much of the theory of particle
physics applies to condensed matter physics
as well; in particular, there are a selection
of field excitations, called quasi-particles,
that can be created and explored.
These include:
Phonons are vibrational modes in a crystal
lattice.
Excitons are bound states of an electron and
a hole.
Plasmons are coherent excitations of a plasma.
Polaritons are mixtures of photons with other
quasi-particles.
Polarons are moving, charged (quasi-) particles
that are surrounded by ions in a material.
Magnons are coherent excitations of electron
spins in a material.
== Other ==
Accelerons are hypothetical particles postulated
to relate neutrino mass to dark energy, and
are named for the role they play in the accelerating
expansion of the universe
An anyon is a generalization of fermion and
boson in two-dimensional systems like sheets
of graphene that obeys braid statistics.
A plekton is a theoretical kind of particle
discussed as a generalization of the braid
statistics of the anyon to dimension > 2.
A WIMP (weakly interacting massive particle)
is any one of a number of particles that might
explain dark matter (such as the neutralino
or the axion).
A GIMP (gravitationally interacting massive
particle) is a particle which provides an
alternative explanation of dark matter, instead
of the aforementioned WIMP.
The pomeron, used to explain the elastic scattering
of hadrons and the location of Regge poles
in Regge theory.
The skyrmion, a topological solution of the
pion field, used to model the low-energy properties
of the nucleon, such as the axial vector current
coupling and the mass.
A genon is a particle existing in a closed
timelike world line where spacetime is curled
as in a Frank Tipler or Ronald Mallett time
machine.
A goldstone boson is a massless excitation
of a field that has been spontaneously broken.
The pions are quasi-goldstone bosons (quasi-
because they are not exactly massless) of
the broken chiral isospin symmetry of quantum
chromodynamics.
A goldstino is a goldstone fermion produced
by the spontaneous breaking of supersymmetry.
An instanton is a field configuration which
is a local minimum of the Euclidean action.
Instantons are used in nonperturbative calculations
of tunneling rates.
A dyon is a hypothetical particle with both
electric and magnetic charges.
A geon is an electromagnetic or gravitational
wave which is held together in a confined
region by the gravitational attraction of
its own field of energy.
An inflaton is the generic name for an unidentified
scalar particle responsible for the cosmic
inflation.
A spurion is the name given to a "particle"
inserted mathematically into an isospin-violating
decay in order to analyze it as though it
conserved isospin.
What is called "true muonium", a bound state
of a muon and an antimuon, is a theoretical
exotic atom which has never been observed.
An ion (a charged atom or molecule) is either
an anion or a cation.
A dislon is a localized collective excitation
of a crystal dislocation around the static
displacement.
== Classification by speed ==
A tardyon or bradyon travels slower than light
and has a non-zero rest mass.
A luxon travels at the speed of light and
has no rest mass.
A tachyon (mentioned above) is a hypothetical
particle that travels faster than the speed
of light and has an imaginary rest mass.
== See also
