New theoretical results in ultrarelativistic ultraperipheral lead-lead collisions

Abstract

We study dilepton, proton-antiproton and diphoton production in ultraperipheral lead-lead collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 and 5.5 TeV. The nuclear calculations are based on equivalent photon approximation in the impact parameter space. For correct description of the $\gamma \gamma \to p\bar{p}$ Belle data we include the proton-exchange, the $f_2(1270)$ and $f_2(1950)$ s-channel exchanges, as well as the handbag mechanism. For four muon production, we take into account electromagnetic (two-photon) double-scattering production and direct $\gamma \gamma$ production of four muons in one scattering. The cross sections for elementary $\gamma \gamma \to \gamma \gamma$ subprocess are calculated including three different mechanisms: box diagrams with leptons and quarks in the loops, a VDM-Regge contribution with virtual intermediate hadronic excitations of the photons and the two-gluon exchange contribution. We find that the cross section for elastic $\gamma \gamma$ scattering could be measured in the lead-lead collisions for the diphoton invariant mass up to $W_{\gamma \gamma }\approx$ 15 - 20 GeV. Our Standard Model predictions are compared with a recent ATLAS experimental result. We discuss results for PbPb$\to$PbPb${\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$, PbPb$\to$PbPb$e^{+}{e}^{-}{e}^{+}{e}^{-}$, PbPb$\to$PbPb$p\bar{p}$ and PbPb$\to$PbPb$\gamma \gamma$ reactions at LHC energy.

Comments: 6 pages, 2 figures, talk was given by M. Klusek-Gawenda at the 17th conference on Elastic and Diffractive scattering, EDS Blois 2017, Prague, Czech Republic, June 26-30, 2017