Charmonium production and elliptic flow in relativistic heavy-ion collisions

Using the two-component model for charmonium production, which includes contributions from both initial hard nucleon-nucleon scattering and from regeneration in the quark-gluon plasma, we have studied the nuclear modification factor RAA and elliptic flow v2 of J/ in relativistic heavy-ion collisions. For the expansion dynamics of produced hot dense matter, we have introduced a schematic fire-cylinder model with its transverse acceleration determined from the pressure gradient inside the fire-cylinder and azimuthally anisotropic expansion parameterized to reproduce measured v2 of light hadrons. We have assumed that light hadrons freeze out at the temperature of 120MeV while charmonia at 160MeV, similar to the kinetic and chemical freeze-out temperatures in the statistical model, respectively. For the properties of charmonia in the quark-gluon plasma, we have used the screening mass between their charm and anticharm quarks and their dissociation cross sections given by the perturbative QCD (pQCD) in the leading order and up to the next-to-leading order, respectively. For the relaxation time of charm and anticharm quarks in the quark-gluon plasma, we have also used the one calculated in the leading order pQCD. Modeling the effect of higher-order corrections in pQCD by introducing multiplicative factors to the dissociation cross sections of charmonia and the elastic scattering cross sections of charm and anticharm quarks, we have found that this effect is small for the RAA of J/ as they suppress the number of initially produced J/ but enhance the number of regenerated ones. The higher-order corrections increase, however, the v2 of J/ . Our results thus suggest that the v2 of J/ can play an important role in discriminating between J/ production from initial hard collisions and from regeneration in the quark-gluon plasma.