New results on ultra-peripheral collisions with ALICE

About

Photon-induced reactions in ultra-peripheral collisions (UPCs) of Pb-emphasized textPb nuclei at the LHC have been studied using the ALICE detector for several years. The ALICE detector can measure the photoproduction cross section for vector mesons at various rapidities, centre-of-mass energies and collision systems. This process allows us to study the energy evolution of the gluon content of the different targets: protons and Pb nuclei.

First measurements of the $\rm{\rho^0}$ photoproduction cross section in Xe-Xe UPCs and the t-dependent photonuclear cross section of $\rm{J/\psi}$ in Pb-Pb UPCs, both at midrapidity, unveil new routes to disentangle the different $\gamma$-$\rm{Pb}$ contributions to the UPCs cross sections and to understand the high-energy limit of QCD via shadowing or saturation, respectively.

Additionally, new ALICE results on rapidity-differential cross section measurements for different nuclear-breakup classes in Pb-Pb at $\sqrt{s_{\rm NN}}$=5.02 TeV will be presented. The results on $\rm{J/\psi}$ and $\rm{\psi'}$ cross sections at midrapidity are complementary to previous findings in the forward rapidity region..

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