Spin asymmetry and dipole moments in $\tau$-pair production with ultraperipheral heavy ion collisions

TL;DR

This paper introduces a novel azimuthal angular asymmetry technique in ultraperipheral heavy ion collisions to precisely measure the tau lepton's magnetic and electric dipole moments, significantly narrowing the parameter space and reducing theoretical assumptions.

Contribution

It presents a new method using azimuthal asymmetry in UPCs to simultaneously constrain tau's MDM and EDM with higher precision and fewer assumptions than previous approaches.

Findings

Enhanced constraints on tau's MDM and EDM.

Method reduces parameter space by over 50%.

Improves measurement precision in ultraperipheral collisions.

Abstract

The anomalous magnetic (MDM) and electric (EDM) dipole moments of the $\tau$ 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 $\cos2\phi$ 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.