Baryon

The most stable baryons are the proton (the lightest of the baryons) and the neutron (together they form a group of nucleons ). The first of them, as far as it is known today, is stable, the second experiences beta decay with a lifetime close to 1000 s. Heavier baryons decay in time from 10 ⁻²³ to 10 ⁻¹⁰ s.

Nucleons have the quark composition uud (proton) and udd (neutron). Their spin is 1/2, the oddity is zero. The mass is close to 940 MeV. Together with their short-lived excited states, nucleons belong to the group of N-baryons .

Baryons containing at least one strange quark (but not containing heavier quarks) are called hyperons .

In the baryon family, in addition to nucleons, groups of Δ-, Λ-, Σ-, Ξ- and Ω-baryons are distinguished.

• Δ-baryons (Δ ⁺⁺ , Δ ⁺ , Δ ⁰ , Δ ^- ), like nucleons, consist of u- and d-quarks , but, unlike nucleons, their spin is 3/2. They decay mainly on a nucleon and a peony . The lifetime of Δ-baryons is close to 10 ⁻²³ s.

• Λ-baryons (Λ ⁰ ) are neutral (but not truly neutral) particles with spin 1/2 and strangeness −1 (that is, they can be called Λ-hyperons), consisting of u-, d- and s-quarks . In them, u- and d-quarks are in the isospin singlet state ( I = 0). Mass 1117 MeV . They decay mainly into a proton and a negative pion, or into a neutron and a neutral pion with a lifetime of 2.6 × ^{10 −10} s. Heavy Λ-baryons (Λ ⁺ _c and Λ ⁰ _b ) are also discovered, in which a strange quark is replaced by a charmed ( c-quark ) or a beautiful ( b-quark ).

• Σ-baryons (Σ ⁺ , Σ ⁰ , Σ ^- ) have spin 1/2, the strangeness −1. Like the Λ-baryon, they consist of u-, d- and s-quarks , but are triplet in isospin ( I = 1). The neutral Σ ⁰ baryon has the same quark composition as the Λ ⁰ baryon (uds), but is heavier; therefore, it decays very quickly at Λ ⁰ with the release of the photon (the lifetime is only 6⋅10 ⁻²⁰ s, since decay occurs due to electromagnetic interaction). Σ ⁺ (uus) and Σ ^- (dds) decay in about 10 ⁻¹⁰ s into a pion and nucleon. It should be noted that Σ ⁺ and Σ ^- are not particles and antiparticles - they are independent particles, each of them (as, by the way, Σ ⁰ ) has its own antiparticle. The masses of Σ-hyperons are about 1200 MeV. Heavy Σ-baryons that are not hyperons (that is, containing a heavier quark instead of an s-quark) were also found.

• Ξ-baryons (Ξ ⁰ and Ξ ^- ) have spin 1/2, the oddity is −2. They contain two strange quarks; quark composition uss (Ξ ⁰ ) and dss (Ξ ^- ). Their mass is close to 1.3 GeV. They decompose (with a lifetime of about 10 ⁻¹⁰ s) into pion and Λ ⁰ hyperon. There are heavy Ξ-baryons that are not hyperons (one of the strange quarks is replaced by a c- or b-quark).

• Ω-baryons (there is only one type of these particles, Ω ^- hyperon) have spin 3/2 and strangeness −3, consist of 3 strange quarks (sss). Particle mass 1,672 GeV. The predominant decay modes are into Λ ⁰ hyperon and negative kaon, or into Ξ ⁰ and negative pion (lifetime of about 10 ⁻¹⁰ s). Some heavy Ω-baryons are discovered, characterized by the replacement of one of the s-quarks with a heavy quark.

There is also a wide range of short-lived excited states of these baryons.

Most light baryons in the ground state decay due to weak interaction; therefore, their lifetime is relatively long (the exception is, as noted above, Σ ⁰ hyperon).

Light baryons (hyperons, Δ-baryons and nucleons), depending on the spin, are part of one of two multiplets : a 3/2 spinuplet (Δ-baryons, Ω-hyperons and excited states of Σ- and Ξ-hyperons) and an octet with spin 1/2 (nucleons, Σ-, Λ- and Ξ-hyperons).

Baryonic matter is matter consisting of baryons (neutrons, protons) and electrons . That is, the usual form of matter, substance .
There is also baryonic antimatter , or antimatter . According to modern concepts, 7% of its mass is contained in stars, 7% cold and hot gas inside galaxies, 4% gas in galactic clusters, 28% cold intergalactic gas, 15% warm intergalactic gas, 40% in a rarefied gas with a fibrous structure ^{[4 ] [5]} .

Baryons obey the empirically established law of conservation of the baryon number: in a closed system, a value equal to the difference in the number of baryons and the number of antibaryons is preserved. This quantity is called the baryon number . The reasons for the conservation of the baryon number are still unknown (in any case, there is no calibration field associated with it, as with an electric charge), but in many versions of modern (not yet confirmed) theories that expand the Standard Model, this law may be violated. If the baryon number is not conserved, then the proton (the lightest of the baryons) can decay; however, no proton decay has yet been detected — only the lower limit on the proton lifetime has been established (from 10 ²⁹ to 10 ³³ years, depending on the decay channel). Other processes that do not preserve the baryon number, such as neutron-antineutron oscillations , are predicted.

• Baryon list
• Hyperons

• Jean Letessier, Johann Rafelski, T. Ericson, PY Landshoff. Hadrons and Quark-Gluon Plasma. - Cambridge University Press , 2002 .-- 415 p. - ISBN 9780511037276 .