Photoproduction cross section measurements in ultra-peripheral Pb-Pb and p-Pb collisions at the LHC with ALICE

Abstract

Ultra-peripheral collisions of ultra-relativistic lead ions are a tool for studying g-nucleus or gg interactions at the LHC. Beams of lead ions at the LHC are a source of intense photon fluxes with very high energies, due to the effect of Lorentz contraction and the fact that the equivalent flux of almost real photons around lead ions is proportional to the square of their charge. Since in ultra-peripheral collisions the impact parameter is greater than the sum of the nuclear radii, hadronic interactions are suppressed and electromagnetic interactions dominate. Experimentally, ultra-peripheral collision events are characterized by very low multiplicities in the central rapidity region and rapidity gaps outside central rapidity. In this thesis, photoproduction cross section measurements performed by ALICE (A Large Ion Collider Experiment) in ultra-peripheral collisions are summarized. After a review of ultraperipheral physics in this section, the sub-detectors of ALICE used in ultra-peripheral analyses are described in section 2. Section 3 contains a review of ALICE measurements of r0 photoproduction in Pb-Pb collisions at psNN = 2:76 and 5:02 TeV, and section 4 summarizes ALICE measurements of continuum γγ → e+e- photoproduction in Pb-Pb collisions at psNN = 2:76 TeV. ALICE measurements of J/y photoproduction in Pb-Pb collisions at psNN = 2:76 TeV and in p-Pb collisions at psNN = 5:02 TeV are discussed in section 5. In section 6 detector upgrades for LHC run 3 and 4, and prospects for ultra-peripheral measurements in run 3 and 4 are described. The last section contains a summary and conclusions.