Thermal quark production in ultrarelativistic nuclear collisions

We calculate thermal production of u, d, s, c, and b quarks in ultrarelativistic heavy ion collisions. The following processes are taken into account: thermal gluon decay (g→i i¯), gluon fusion (gg→i i¯) and quark-antiquark annihilation ( j¯→i ī), where i and j represent quark species. We use the thermal quark masses, ${\mathit{m}}_{\mathit{i}}^2$(T)≃${\mathit{m}}_{\mathit{i}}^2$+(2${\mathit{g}}^2$/9)${\mathit{T}}^2$, in all the rates. At small mass [${\mathit{m}}_{\mathit{i}}$(T)T], the production is largely dominated by the thermal gluon decay channel. We obtain numerical and analytic solutions of one-dimensional hydrodynamic expansion of an initially pure glue plasma. Our results show that even in a quite optimistic scenario, all quarks are far from chemical equilibrium throughout the expansion. Thermal production of light quarks (u, d, and s) is nearly independent of species. Heavy quark (c and b) production is quite independent of the transition temperature and could serve as a very good probe of the initial temperature. Thermal quark production measurements could also be used to determine the gluon damping rate, or equivalently the magnetic mass.