Speaker
Description
In ultra-relativistic heavy-ion collisions, large rates of $\gamma\gamma$ processes arise from the intense electromagnetic fields generated by the colliding nuclei. These $\gamma\gamma$ interactions provide a powerful laboratory to study reactions that may be sensitive to physics beyond the Standard Model. In ultra-peripheral collisions (UPCs), where the impact parameter between the nuclei exceeds the sum of their radii, the final-state particles are predominantly produced back-to-back in the transverse plane, enabling precise and efficient event identification. This talk presents an overview of recent ATLAS measurements potentially sensitive to physics beyond the Standard Model. Measurements of differential cross-sections for $\tau$-lepton pair production are reported, providing constraints on the $\tau$-lepton anomalous magnetic moment. Results are also presented on measurements of light-by-light scattering, which can be used to set limits on the existence of gravitons or axion-like particles (ALPs). In addition, a search for monopole-pair production in UPCs is presented for monopole masses in the 20–150 GeV range. The results are compared with predictions from a leading-order model of spin-1/2 particle production via photon–photon fusion, as well as with a recently developed semi-classical model that includes non-perturbative cross-section calculations.
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