Photonuclear vector meson production in ultra-peripheral Pb-Pb collisions studied by the ALICE experiment at the LHC

TL;DR

This paper reports on the measurement of coherent J/Psi meson photoproduction in ultra-peripheral Pb-Pb collisions at the LHC, providing insights into nuclear gluon shadowing effects.

Contribution

First measurement of J/Psi photoproduction cross section in ultra-peripheral Pb-Pb collisions at the LHC, using ALICE data and specialized triggers.

Findings

Measured cross section for coherent J/Psi production

Compared results with theoretical models

Discussed implications for nuclear gluon shadowing

Abstract

The strong electromagnetic fields surrounding the Pb-ions accelerated at the CERN Large Hadron Collider (LHC) allow two-photon and photonuclear interactions to be studied in a so far unexplored kinematic regime. Exclusive photoproduction of vector mesons can be studied in ultra-peripheral collisions, where the impact parameters are larger than the sum of the nuclear radii and hadronic interactions are strongly suppressed. During the heavy-ion runs at the LHC in 2010 and 2011, the ALICE collaboration used special triggers to select ultra-peripheral collisions. These triggers were based on the Muon spectrometer, the Time-of-Flight detector, the Silicon Pixel detector, and the VZERO scintillator array. Information from other detectors was also used in the analysis. The cross section for coherent photoproduction of J/Psi mesons at forward rapidities will be presented. The result will be compared to model calculations and its implications for nuclear gluon shadowing will be discussed.