Central exclusive quarkonium production with tagged forward protons at RHIC

TL;DR

This paper investigates the central exclusive production of chi_cJ and eta_c mesons at RHIC, analyzing decay channels, production rates, angular distributions, and background suppression to enhance understanding of quarkonium production mechanisms.

Contribution

It provides detailed predictions for chi_cJ and eta_c production rates, distributions, and the influence of experimental cuts, including the impact of soft survival factors and decay channels, advancing the study of quarkonium CEP at RHIC.

Findings

Production rates vary significantly with p_t cuts and meson spin-parity.

Azimuthal angle distributions are sensitive to meson quantum numbers.

Backgrounds from QCD production are manageable in two-body decay channels.

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.