Subnucleon fluctuations in coherent and incoherent ultra-peripheral AA collisions at LHC and RHIC with the Sartre event generator

TL;DR

This paper enhances the Sartre event generator by incorporating subnucleon fluctuations to better match ultra-peripheral collision data at LHC and RHIC, providing insights into gluon fluctuations and QCD dynamics.

Contribution

The paper introduces subnucleon fluctuations into the Sartre model, improving its ability to describe incoherent ultra-peripheral collisions at high energies.

Findings

Adding subnucleon fluctuations improves data agreement

Current models may not fully capture high-momentum transfer gluon fluctuations

Future measurements can reveal gluon vacuum fluctuations in QCD

Abstract

Sartre has been extensively used for describing photon-nuclei processes at the electron-ion collider (EIC) as well as ultra-peripheral collisions (UPC) at LHC and RHIC. Sartre is an event generator which implements the dipole model for DIS, and models the transverse geometry of the target nucleus or proton in coordinate space. It uses the Good-Walker mechanism for simulating fluctuations which contribute to the incoherent cross section for which the target breaks up after the interaction. With improved precision of UPC measurements in the last years, a detailed test of the dipole model has become possible, and Sartre's model was found lacking. In these proceedings we add subnucleon fluctuations to the nucleus and show that this is sufficient for describing the vast majority of the present measurements. We also find that for larger momentum transfers in the nucleus, which probes gluon fluctuations at higher resolution, the current complexity of the model may not suffice. Future measurements at the LHC, RHIC and especially the EIC has the potential to reveal these gluon vacuum fluctuations and glean novel insights into the self-interacting quantum field of QCD.