J/ψproduction and elliptic flow in relativistic heavy-ion collisions

Abstract

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 study the nuclear modification factor ${R}_{\mathit{AA}}$ and elliptic flow ${v}_{2}$ of $J/\ensuremath{\psi}$ in relativistic heavy-ion collisions. For the expansion dynamics of produced hot, dense matter, we introduce a schematic fireball model with its transverse acceleration determined from the pressure gradient inside the fireball and azimuthally anisotropic expansion parametrized to reproduce measured ${v}_{2}$ of light hadrons. We assume that light hadrons freeze out at the temperature of 120 MeV while charmonia freeze out at 160 MeV, 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 use the screening mass between their charm and anticharm quarks and their dissociation cross sections given by the perturbative quantum chromodynamical (pQCD) calculations 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 also use 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 find that this effect is small for the ${R}_{\mathit{AA}}$ of $J/\ensuremath{\psi}$ as they suppress the number of initially produced $J/\ensuremath{\psi}$ but enhance the number of regenerated ones. The higher-order corrections increase, however, the ${v}_{2}$ of $J/\ensuremath{\psi}$. Our results suggest that the ${v}_{2}$ of $J/\ensuremath{\psi}$ can play an important role in discriminating between $J/\ensuremath{\psi}$ production from initial hard collisions and from regeneration in the quark-gluon plasma.