Photon-photon scattering in the resonance region at midrapidity at the LHC

Abstract

A study is presented to extend the measurements of photon-photon scattering in ultra-peripheral Pb-Pb collisions at the LHC into the mass region of the pseudoscalar resonances $η$ and $η'$. The elementary photon-photon scattering cross section is presented. The cross section for photon-photon scattering in Pb-Pb is derived by convoluting the elementary photon-photon cross section with the Pb-Pb photon luminosity. The main background to two-photon final states, arising from double $π^{0}$ production with two of the four decay photons escaping detection, is examined, and possible kinematical conditions are discussed to optimize the signal-to-background ratio for such measurements at mid-rapidity.

6 pages, 7 figures, to appear in Proceedings Workshop Diffraction and Low-x, aug 26-sept 1, 2018, Reggio Calabria