J/ψ photoproduction in ultra-peripheral PbPb collisions at √ sNN = 2.76 TeV with CMS

Abstract

In ultra-peripheral heavy-ion collisions, photon-induced interactions between colliding nuclei occur at large impact parameters. In this thesis, a study of J/$\psi$ photoproduction in ultra-peripheral PbPb collisions at $sqrt{s_{NN}}=2.76$ TeV is presented. This was carried out using data collected by the Compact Muon Solenoid in 2011. An integrated luminosity of 143 $mu$$b^{-1}$ was analyzed for this thesis using specifically designed triggers. The cross section for coherent J/$\psi$ photoproduction in the single sided break-up mode, $frac{dsigma^{J/\psi}}{dy}(Xn0n)$, was measured in the rapidity interval $2.0 < |y| < 2.2$ and was found to be 356 $pm$ 71 (stat) $^{+43}_{-50}$ (syst) $mu$b. The total cross section, after correcting for break-up mode, is found to be 1.80 $pm$ 0.37 (stat) $^{+0.22}_{-0.25}$ (syst) mb, in agreement with theoretical predictions and previous measurements by the ALICE collaboration. The cross section measurement is consistent with J/$\psi$ photoproduction models that contain significant nuclear gluon shadowing. In addition, the correlation between the J/$\psi$'s and neutrons rapidities was measured and found to qualitatively agree with recent theoretical calculations. The measured rapidity correlation provides a way to distinguish between coherent and incoherent J/$\psi$ photoproduction.