Exclusive Photoproduction of Upsilon in pPb collisions with the CMS

TL;DR

This paper reports on the measurement of exclusive Upsilon photoproduction in proton-lead ultraperipheral collisions at the CMS experiment, providing insights into gluon distributions at small x values.

Contribution

It presents the first detailed measurements of Upsilon states in pPb UPCs at 5.02 TeV, including cross sections and t-distributions, compared with theoretical models.

Findings

Measured total Upsilon photoproduction cross sections at various energies.

Compared experimental results with theoretical predictions and previous data.

Provided data on gluon distribution at small x in proton and lead nuclei.

Abstract

Results of exclusive photoproduction of Upsilon states in Ultraperipheral collisions (UPC) of protons and ions with the CMS experiment are presented, which provides a clean probe of the gluon distribution at small values of parton fractional momenta $x \approx 10^{-2} 10^{4}$ at central rapidities (|y| $< 2.5$). The three Upsilon states (1S, 2S, 3S) are measured in the dimuon decay channel along with the photon-photon decaying to dimuon QED continuum at $\sqrt{s_{NN}}=5.02$~TeV for integrated luminosity of $L_{int} = 35$ nb$^{-1}$. The total Upsilon photoproduction cross sections at different photon-proton center of mass energy $W_{\gamma p}$ and t-differential distributions are presented and compared with other experimental results as well as theoretical predictions.