Probing the gluonic structure of the deuteron with $J/\psi$ photoproduction in d+Au ultra-peripheral collisions

TL;DR

This paper reports the first measurement of $J/\psi$ photoproduction in ultra-peripheral d+Au collisions at RHIC, providing new insights into the gluonic structure of the deuteron and testing saturation models against experimental data.

Contribution

It presents the first experimental measurement of $J/\psi$ photoproduction off the deuteron in UPCs, comparing data with theoretical models to explore gluon distributions.

Findings

Data agrees better with the Color Glass Condensate saturation model.

Results are sensitive to the gluon density distribution of the deuteron.

First investigation of neutron-tagged events in this context.

Abstract

Understanding gluon density distributions and how they are modified in nuclei are among the most important goals in nuclear physics. In recent years, diffractive vector meson production measured in ultra-peripheral collisions (UPCs) at heavy-ion colliders has provided a new tool for probing the gluon density. In this Letter, we report the first measurement of $J/\psi$ photoproduction off the deuteron in UPCs at the center-of-mass energy $\sqrt{s_{_{\rm NN}}}=200~\rm GeV$ in d$+$Au collisions. The differential cross section as a function of momentum transfer $-t$ is measured. In addition, data with a neutron tagged in the deuteron-going Zero-Degree Calorimeter is investigated for the first time, which is found to be consistent with the expectation of incoherent diffractive scattering at low momentum transfer. Theoretical predictions based on the Color Glass Condensate saturation model and the gluon shadowing model are compared with the data quantitatively. A better agreement with the saturation model has been observed. With the current measurement, the results are found to be directly sensitive to the gluon density distribution of the deuteron and the deuteron breakup, which provides insights into the nuclear gluonic structure.