New Results for Ultraperipheral Heavy Ion Collisions

Abstract

We discuss diphoton semi(exclusive) production in ultraperipheral $PbPb$ collisions at energy of $\sqrt{s_{NN}}=$ 5.5 TeV (LHC). The nuclear calculations are based on equivalent photon approximation in the impact parameter space. 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 (formally three-loops). We got relatively high cross sections in $PbPb$ collisions. This opens a possibility to study the $\gamma \gamma \to \gamma \gamma$ (quasi)elastic scattering at the LHC. 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. We identify region(s) of phase space where the two-gluon exchange contribution becomes important ingredient compared to box and nonperturbative VDM-Regge mechanisms. We discuss also first results concerning production of two $e^{+}{e}^{-}$ pairs in UPCs of heavy ions. We considered only double scattering mechanism.

invited talk by A. Szczurek at the international workshop Diffraction 2016, Santa Tecla, Sicily, Italy, September 2-7, 2016, 6 pages, 7 figures, 1 table. arXiv admin note: substantial text overlap with arXiv:1610.08546, arXiv:1606.09038

References in corpus (4)

• Light-by-light scattering in ultraperipheral PbPb collisions at the Large Hadron Collider
• Exclusive muon-pair productions in ultrarelativistic heavy-ion collisions: Realistic nucleus charge form factor and differential distributions
• Two-gluon exchange contribution to elastic $\gamma \gamma \to \gamma \gamma$ scattering and production of two-photons in ultraperipheral ultrarelativistic heavy ion and proton-proton collisions
• Double scattering production of two positron-electron pairs in ultraperipheral heavy-ion collisions

Cited by in corpus (1)

• Elastic light-by-light scattering in a nonminimal Lorentz violation scenario