Charmonium production from nonequilibrium charm and anticharm quarks in   quark-gluon plasma
  Parameterizing the charm and anticharm quark momentum distributions by the Tsallis distribution, we study the nonequilibrium effect on the charmonium production rate in a quark-gluon plasma up to the next-to-leading order in perturbative QCD. We find that nonequilibrium charm and anticharm quarks suppress the charmonium production rate compared to that from equilibrated ones. We further show that the suppression factor calculated with the charm quark relaxation time, which has been frequently used in the literature, is close to our results. 
Taesoo Song, Kyong Chol Han, Che Ming Ko
nucl-th