Photoproduction of $J/\psi$ in d+Au ultraperipheral collisions at the BNL Relativistic Heavy Ion Collider

TL;DR

This paper analyzes STAR data on $J/eta$ photoproduction in d+Au ultraperipheral collisions, showing it mainly probes elastic and nucleon-dissociative processes on free nucleons, with minimal nuclear modifications.

Contribution

It demonstrates that STAR data primarily reflects elastic and nucleon-dissociative photoproduction on free nucleons, with negligible nuclear effects, and models the $t$ dependence effectively.

Findings

STAR data mainly probes free nucleon processes.

Nuclear modifications of gluon distribution are negligible.

Model accurately describes the $t$ dependence of the cross section.

Abstract

We argue that the STAR data on $J/\psi$ photoproduction in $d+Au$ ultraperipheral collisions (UPCs) at the momentum transfer $t \neq 0$ primarily probes elastic and possibly nucleon-dissociative $J/\psi$ photoproduction on quasi-free nucleons, while being essentially insensitive to expectedly weak nuclear modifications of the gluon distribution in the deuteron. Analyzing the STAR detector capabilities for selection of UPC events, we explore the possibility that the contribution of nucleon-dissociative $J/\psi$ photoproduction is negligibly small and obtain a very good description of the $t$ dependence of the STAR total cross section.