J/ψ production by charm quark coalescence

Abstract

The production of 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/ψ Au+Au data. The χ and ψ' bound states must be included as well as the ground state J/ψ, given the appreciable feeding from the excited states down to the J/ψ via gamma decays. Charmonium coalescence is found to take place at relatively late times: generally after c()–medium interactions have ceased. Direct production of charmonia through hadron–hadron interactions, i.e. without explicit presence of charm quarks, occurring only at early times is suppressed by collisions with comoving particles and accounts for some ∼5% of the total J/ψ production. Coalescence is especially sensitive to the level of open charm production, scaling naively as . The J/ψ 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.