Central exclusive quarkonium production with tagged forward protons at RHIC

Abstract

We study the Central Exclusive Production (CEP) of chi_cJ and eta_c mesons at RHIC in proton-proton collisions. We consider the chi_cJ --> J/psi + gamma decay channels and, recalling that the J_z=0 suppression of the J=1,2 states can be compensated by their larger branchings to J/psi + gamma, present predictions of rates and distributions for chi_c(0,1,2) production. Particular attention is paid to the impact of p_t cuts applied to the outgoing protons, which can influence the relative rates significantly. The distribution in the azimuthal angle difference between the outgoing protons and the proton p_t^2 is also studied, and shown to depend sensitively on the spin and parity of the centrally produced meson, as well as being affected by the soft survival factors, S^2. Two- and four-body decays, which are particularly relevant for chi_c0 production, are also considered. We show that in the two-body case, backgrounds from `direct' QCD production based on both perturbative and non-perturbative models are expected to be under control.