J/Psi Production by Charm Quark Coalescence

Abstract

Production of $c\bar c$ pairs in elementary hadron-hadron collisions is introduced in a simulation of relativistic heavy ion collisions. Coalescence of charmed quarks and antiquarks into various charmonium states is performed and the results are compared to PHENIX J$/\psi$ Au+Au data. The $\chi$ and $\psi$' bound states must be included as well as the ground state J$/\psi$, given the appreciable feeding from the excited states down to the J$/\psi$ via gamma decays. Charmonium coalescence is found to take place at relatively late times: generally after $c$($\bar c$)-medium interactions have ceased. Direct production of charmonia through hadron-hadron interactions, {\it ie.} without explicit presence of charm quarks, occurring only at early times, is suppressed by collisions with comoving particles and accounts for some $\sim 5\%$ of the total J$/\psi$ production. Coalescence is especially sensitive to the level of open charm production, scaling naively as $n_{c\bar c}^2$. The J$/\psi$ transverse momentum distribution is dependent on the charm quark transverse momentum distribution and early charm quark-medium interaction, thus providing a glimpse of the initial collision history.