Speaker
Description
In ultra-relativistic heavy-ion collisions, copious rates of $\gamma\gamma$ processes are expected through the interaction of the large electromagnetic fields of the heavy nuclei. These can lead to light-by-light scattering via loop diagrams or photon-induced production of particles such as leptons or virtual axion-like particles. 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 or photons are back-to-back in the transverse plane, which allows a precise and efficient identification. This talk presents recent UPC-based measurements, performed using data from the ATLAS experiment recorded in Pb+Pb collisions. It includes measurements of the processes $\gamma\gamma \to \tau\tau$ and $\gamma\gamma \to \gamma\gamma$, which are used to extract properties of the $\tau$-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.
| Category | Experiment |
|---|---|
| Collaboration (if applicable) | ATLAS Collaboration |
