$J/\psi$ photoproduction: threshold to very high energy

TL;DR

This paper presents a reaction model for $J/c$ photoproduction across a wide energy range, explaining experimental data and emphasizing the need for further theoretical and experimental advancements.

Contribution

It introduces a reaction model that incorporates the photon’s $c\bar c$ content and Pomeron exchange to describe $J/\psi$ photoproduction data from threshold to high energies.

Findings

Model successfully describes differential and total cross sections.

Data suggests no immediate link to gluon distributions or pentaquark states.

Highlights need for improved theory and data accuracy.

Abstract

A reaction model for $\gamma + p \to J/\psi + p$ photoproduction, which exposes the $c \bar c$ content of the photon in making the transition $\gamma\to c\bar c + \mathbb P \to J/\psi$ and couples the intermediate $c \bar c$ system to the proton's valence quarks via Pomeron ($\mathbb P $) exchange, is used to deliver a description of available data, viz. both differential and total cross sections from near threshold, where data has newly been acquired, to invariant mass $W \approx 300\,$GeV. The study suggests that it is premature to link existing $\gamma + p \to J/\psi + p$ data with, for instance, in-proton gluon distributions, the quantum chromodynamics trace anomaly, or pentaquark production. Further developments in reaction theory and higher precision data are necessary before the validity of any such connections can be assessed.