baryonnumbercarrying

Baryon-number carrying refers to any particle or system that has nonzero baryon number, a quantum number that counts baryons minus antibaryons. In the Standard Model, baryon number B is assigned as B = 1 for baryons (such as protons and neutrons), B = −1 for antibaryons, and B = 0 for mesons. Quarks carry fractional baryon number, B = 1/3, and antiquarks carry B = −1/3; the total baryon number of a composite particle is the sum of its constituents’ baryon numbers. This makes baryon-number carrying states the basic carriers of the baryon number carried by matter.

Baryon number is an approximately conserved quantity in perturbative processes of the Standard Model, meaning that in ordinary reactions the total B before and after is the same. Some non-perturbative effects in the electroweak sector can violate B while preserving B−L, but such processes are highly suppressed at low energies. Observationally, no confirmed cases of baryon-number violation have been detected, and proton decay searches place stringent limits on B-violating interactions. Proton and neutron oscillations into states with different baryon numbers are also subjects of experimental scrutiny.

The concept is central to topics such as baryogenesis, which seeks to explain the matter–antimatter asymmetry of the universe by mechanisms that involve B (and often L and CP) violation in the early universe. In addition, theories beyond the Standard Model sometimes posit new, baryon-number-carrying particles (for example, certain dark matter scenarios) or novel states of baryonic matter under extreme conditions.

See also: baryon number, baryogenesis, proton decay, sphaleron, grand unified theories.