Spin asymmetry and dipole moments in τ-pair production with ultraperipheral heavy ion collisions

The anomalous magnetic (MDM) and electric (EDM) dipole moments of the τ lepton serve as crucial indicators of new physics beyond the standard model. Leveraging azimuthal angular asymmetry as a novel tool in ultraperipheral collisions (UPCs), we attain unparalleled precision in the study of these key properties. Driven by the highly linear polarization of coherent photons, this method uniquely enables both the MDM and EDM to contribute to the cos 2ϕ angular distribution in similar magnitudes. Importantly, our approach substantially narrows the parameter space, excluding more than half of it compared to expected UPC-based measurements reliant solely on the total cross-section. This method not only provides improved constraints but also minimizes the need for additional theoretical assumptions, and offers a novel avenue to probe the EDM effects.