Light-by-light scattering in ultraperipheral collisions of heavy ions at two future detectors

Abstract

We discuss possible future studies of photon-photon (light-by-light) scattering using a planned FoCal and ALICE 3 detectors. We include different mechanisms of γγ→γγ scattering such as double-hadronic photon fluctuations, t/u-channel neutral pion exchange or resonance excitations (γγ→R) and deexcitation (R→γγ). The broad range of (pseudo)rapidities and lower cuts on transverse momenta open a necessity to consider not only dominant box contributions but also other subleading contributions. Here we include low mass resonant R=π0, η, η′ contributions. The resonance contributions give intermediate photon transverse momenta. However, these contributions can be eliminated by imposing windows on diphoton invariant mass. We study and quantify individual box contributions (leptonic, quarkish). The electron/positron boxes dominate at low Mγγ<1 GeV diphoton invariant masses. The PbPb→PbPbγγ cross section is calculated within equivalent photon approximation in the impact parameter space. Several differential distributions are presented and discussed. We consider four different kinematic regions. We predict a cross section in the (mb-b) range for typical ALICE 3 cuts, a few orders of magnitude larger than for the current ATLAS or CMS experiments. We also consider the two-π0 background which can, in principle, be eliminated at the new kinematical range for the ALICE 3 measurements by imposing dedicated cuts on diphoton transverse momentum and/or so-called vector asymmetry. Published by the American Physical Society 2024