Sigma baryon

Sigma - baryon ( Σ )

Σ0

Σ -

The three Σ - baryons, also sigma baryons are baryons, which consist of a strange quark and all pair combinations of up-and down - quark. They have spin 1 /2, isospin 1 and are characterized by their electric charge: Σ , Σ0 and Σ -.

The Σ - baryons are among the hyperons.

Description

The Σ - baryons belong to the SU (3) octet.

The charged Σ - baryon decay to almost 100 % in a nucleon and a pion. Here, the Σ - because of its negative charge only into a neutron and a π - decay, whereas the Σ decays with equal probability into a neutron and a π as a proton and a π0.

The uncharged Σ0 decays with almost 100% probability in a Λ - baryon and a photon. This decay takes place by means of the electromagnetic interaction, so that this particle is much shorter-lived than the charged Σ - baryons.

Excited States

The Σ - baryons have excited states, which are called Σ * baryons. They have the same quark content as the Σ - baryons, however, spin 3/2, and are part of the baryon Dekupletts. They are slightly heavier than the Σ - baryons ( Σ - * ≈ 1387 MeV/c2, Σ0 * ≈ 1384 MeV/c2, Σ * ≈ 1383 MeV/c2 ).

The Σ * baryons decay for the most part under the strong nuclear force in a pion and a Σ - baryon or into a pion and a Λ - baryon. A small portion ( ≈ 1.3%) decomposes the Σ0 * baryon in a Λ - baryon and a photon.