Baryon

The name Baryon comes from the Greek word for “heavy”, because at the time of their nomenclature, most known particles had lower masses than the baryons. Baryons are made up of three quarks in the standard model. This class of particles includes the proton and neutron; other baryons are the lambda, sigma, xi and omega particles. Baryons are distinct from mesons in that mesons are composed of only two quarks. Baryons and mesons are included in the overall class known as hadrons, the particles which interact by strong force. While baryons are fermions, mesons are bosons.

From a technical point of view, baryons are strongly interacting fermions, i.e., they experience the strong nuclear force and are described by the Fermi- Dirac statistics, which apply to all particles obeying the Pauli exclusion principle. All members of the baryon family of particles adhere to the law of conservation of baryon family number. The family number is+1 for ordinary baryons and -1 for anti- baryons. In any particle interaction, the sum of the baryon family numbers of the interacting particles must equal the sum for the resulting particles.

In the kind of environments that we are familiar with in everyday life, the only stable baryon is the proton. Astronomers often use the term ‘Baryonic matter’ to refer to ordinary matter. It’s a bit of misnomer, as it includes electrons which are leptons and generally excludes neutrinos and anti- neutrinos which are also leptons.

Baryonic matter

Baryonic matter is mainly composed of baryons, which includes atoms of any sort. Non- baryonic matter, as implied by the name, is any sort of matter that is not primarily composed of baryons. This might include some ordinary matter such as neutrinos or free electrons; however it may also include exotic species of non- baryonic dark matter, such as supersymmetric particles, axions or black holes. The distinction between baryonic and non- baryonic matter is important in cosmology.

Baryogenesis

Experiments are consistent with the number of quarks in the universe being a constant and more specifically the number of baryons being a constant, in technical language, the total baryon number appears to be conserved. Until recently, it was believed that some experiments showed the existence of pentaquarks- exotic baryons made up of four quarks and one anti- quark. While the prevailing Standard model of particle Physics, the number of baryons may change in multiples of three due to the action of sphalerons although is rare and not been observed experimentally.

Questions:

• What is a Baryon?
• What is the matter of Baryons?