LHC as a Photon Collider for Probing the Standard Model in Heavy Ion Collisions with ATLAS

In ultra-relativistic heavy-ion collisions, copious rates of γγ processes are expected through the interaction of the large electromagnetic fields of the heavy nuclei. These can lead to photon-induced production of particles such as lepton pairs. In ultra-peripheral collisions (UPCs), characterized by large impact parameters between the nuclei, a di-photon interaction can be the only one taking place, leading to very clean signatures in the detector. The outgoing leptons are back-to-back in the transverse plane, which allows a precise and efficient identification. This poster presents the most recent UPC-based measurement of γγ→ττ production, performed using data from the ATLAS experiment recorded in Pb+Pb collisions. The measurement is used to extract properties of the τ-lepton and probe for new physics contributions. Measured cross-sections will be presented, and the implications for these results on physics processes beyond the Standard Model will be discussed.