Photoproduction of $J/\psi$ with neutron tagging in ultra-peripheral collisions of nuclei at RHIC and the LHC

TL;DR

This paper predicts cross sections for $J/psi$ photoproduction with neutron tagging in ultra-peripheral collisions at RHIC and LHC, highlighting the impact of different neutron emission sources on event classification.

Contribution

It introduces a detailed analysis of neutron emission sources in $J/psi$ photoproduction, improving understanding of nuclear shadowing effects in incoherent processes.

Findings

Neutron emission probabilities are significantly affected by additional sources beyond electromagnetic dissociation.

Incoherent $J/psi$ photoproduction processes influence neutron emission patterns.

The study enables exploration of nuclear shadowing at very low Bjorken-$x$ values.

Abstract

We present predictions for the cross sections of the coherent and incoherent $J/\psi$ photoproduction in ultra-peripheral collisions at RHIC and at the LHC calculated for different classes of events depending on the presence of neutrons emitted by colliding nuclei. Since strong nucleus-nucleus interactions in UPCs are suppressed, it is usually assumed that neutrons at forward rapidities originate mainly from the electromagnetic dissociation of colliding nuclei caused by additional photon exchanges. This is a reasonable assumption for the coherent photoproduction where the state of the target nucleus remains intact. We consider additional sources of neutrons in the incoherent quasielastic and nucleon dissociative $J/\psi$ photoproduction and show that these processes significantly change probabilities of neutron emission compared to calculations when only neutrons from electromagnetic dissociation of nuclei are considered. Such studies should allow one to explore the dynamics of nuclear shadowing in the incoherent $J/\psi$ photoproduction down to $x \sim 10^{-5}$.