UPC contribution to forward rapidity gap distribution in pPb collisions at the LHC

TL;DR

This paper analyzes the forward rapidity gap distribution in proton-lead collisions at the LHC, demonstrating the dominance of electromagnetic mechanisms and providing a semi-quantitative explanation of CMS data, with predictions for future runs.

Contribution

It explicitly shows the dominance of electromagnetic mechanisms in proton-nucleus diffraction and offers a semi-quantitative model matching CMS data.

Findings

Electromagnetic mechanisms dominate in pPb diffraction.

The model reproduces the shape and magnitude of CMS data.

Predictions are made for proton-oxygen collisions.

Abstract

In this Letter, we consider strong and electromagnetic (ultraperipheral) mechanisms in proton-nucleus coherent diffraction at the CERN Large Hadron Collider. We explicitly demonstrate the dominance of the latter and explain the CMS data on the forward rapidity gap distribution in $pPb$ collisions at $\sqrt{s_{NN}}=8.16$ TeV. In particular, we provide simple estimates, which give a good, semi-quantitative description of both magnitude and shape of the $\Delta \eta^F$ distribution in the Pomeron-proton topology. We also make predictions for the proton-oxygen run.