Charmed Baryons - Charmed Sigma Quark Content

Charmed Sigma Quark Content

As noted above, charmed Sigma particles, like Λ+
c particles, comprise a charm quark and two light up, down, strange) quarks. However, Σ
c particles have isospin 1. This is equivalent to saying that they can exist in three charged states, the doubly charged, the singly charged, and the neutral. The situation is directly analogous to the strange baryon nomenclature. The ground state (that is, with no orbital angular momentum) baryons can also be pictured thus. Each quark is a spin 1/2 particle. The spins can be pointed up, or down. In Λ+
c ground state, the two light quarks point up-down to give a zero spin diquark. This then combines with the charm quark to give a spin 1/2 particle. In the Σ
c, the two light quarks combine to give a spin 1 diquark, which then combines with the charm quark to give either a spin 1/2 particle, or a spin 3/2 particle (normally known as a Σ∗
c). It is the rules of quantum mechanics that make it possible for a Λ
c to exist only with three different quarks (that is cud quarks), whereas the Σ
c can exist as cuu, cud or cdd (thus the three different charges).

All Σ
c particles decay by the strong force. Typically this mean the emission of a pion as it decays down to the comparatively stable Λ+
c. Thus their masses are not usually measured directly, but in terms of their mass differences, m(Σ
c)−m(Λ+
c). This is experimentally easier to measure precisely, and theoretically easier to predict, than the absolute value of the mass.