Baryons are composite particles made of three quarks, as opposed to mesons, which are composite
particles made of one quark and one antiquark.
Baryons and mesons are both hadrons, which are particles composed solely of quarks or
both quarks and antiquarks.
The term baryon is derived from the Greek "βαρύς" (barys), meaning "heavy", because,
at the time of their naming, it was believed that baryons were characterized by having
greater masses than other particles that were classed as matter.
Until a few years ago, it was believed that some experiments showed the existence of pentaquarks
– baryons made of four quarks and one antiquark.
The particle physics community as a whole did not view their existence as likely by
2006.
On 13 July 2015, the LHCb collaboration at CERN reported results consistent with pentaquark
states in the decay of bottom Lambda baryons (Λ0b).Since baryons are composed of quarks,
they participate in the strong interaction.
Leptons, on the other hand, are not composed of quarks and as such do not participate in
the strong interaction.
The most famous baryons are the protons and neutrons that make up most of the mass of
the visible matter in the universe, whereas electrons, the other major component of atoms,
are leptons.
Each baryon has a corresponding antiparticle known as an antibaryon in which quarks are
replaced by their corresponding antiquarks.
For example, a proton is made of two up quarks and one down quark, while its corresponding
antiparticle, the antiproton, is made of two up antiquarks and one down antiquark.
== Lists of baryons == These lists detail all known and predicted
baryons in total angular momentum J = ​1⁄2 and J = ​3⁄2 configurations with positive
parity.
Baryons composed of one type of quark (uuu, ddd, ...) can exist in J = ​3⁄2 configuration,
but J = ​1⁄2 is forbidden by the Pauli exclusion principle.
Baryons composed of two types of quarks (uud, uus, ...) can exist in both J = ​1⁄2 and
J = ​3⁄2 configurations.
Baryons composed of three types of quarks (uds, udc, ...) can exist in both J = ​1⁄2
and J = ​3⁄2 configurations.
Two J = ​1⁄2 configurations are possible for these baryons.The symbols encountered
in these lists are: I (isospin), J (total angular momentum), P (parity), u (up quark),
d (down quark), s (strange quark), c (charm quark), b (bottom quark), Q (charge), B (baryon
number), S (strangeness), C (charm), B′ (bottomness), as well as a wide array of subatomic
particles (hover for name).
(See the baryon article for a detailed explanation of these symbols.)
Antibaryons are not listed in the tables; however, they simply would have all quarks
changed to antiquarks, and Q, B, S, C, B′, would be of opposite signs.
Particles with † next to their names have been predicted by the Standard Model but not
yet observed.
Values in red have not been firmly established by experiments, but are predicted by the quark
model and are consistent with the measurements.
=== JP = ​1⁄2+ baryons === †^ Particle has not yet been observed.[a]
^ The masses of the proton and neutron are known with much better precision in atomic
mass units (u) than in MeV/c2, due to the relatively poorly known value of the elementary
charge.
In atomic mass units, the mass of the proton is 1.007276466812(90) u whereas that of the
neutron is 1.00866491600(43) u.
[b] ^ At least 1035 years.
See proton decay.[c] ^ For free neutrons; in most common nuclei, neutrons are stable.[d]
^ PDG reports the resonance width (Γ).
Here the conversion τ = ​ħ⁄Γ is given instead.
[e] ^ There is a controversial discovery claim, disfavored by other experimental data.
=== JP = ​3⁄2+ baryons === †^ Particle has not yet been observed.[h]
^ PDG reports the resonance width (Γ).
Here the conversion τ = ​ħ⁄Γ is given instead.
=== Baryon resonance particles === This table gives the name, quantum numbers
(where known), and experimental status of baryons resonances confirmed by the PDG.
Baryon resonance particles are excited baryon states with short half lives and higher masses.
Despite significant research, the fundamental degrees of freedom behind baryon excitation
spectra are still poorly understood.
The spin-parity JP (when known) is given with each particle.
For the strongly decaying particles, the JP values are considered to be part of the names,
as is the mass for all resonances.
== See also == Eightfold way (physics)
List of mesons List of particles
Roper resonance Timeline of particle discoveries