Spin correlations and new physics in $\tau$-lepton decays at the LHC

TL;DR

This paper investigates how spin correlations in tau-lepton decays at the LHC can be used to constrain new physics, such as anomalous magnetic and electric dipole moments, providing a novel approach to probe beyond Standard Model effects.

Contribution

It introduces the use of single and double spin correlations in tau decays to effectively probe anomalous couplings and CP violation, enhancing sensitivity compared to previous methods.

Findings

Constraints on tau anomalous magnetic and electric dipole moments.

Identification of spin correlation observables sensitive to new physics.

Comparison showing improved sensitivity over Drell-Yan deviation methods.

Abstract

We use spin correlations to constrain anomalous $\tau$-lepton couplings at the LHC including its anomalous magnetic moment, electric dipole moment and weak dipole moments. Single spin correlations are ideal to probe interference terms between the SM and new dipole-type couplings as they are not suppressed by the $\tau$-lepton mass. Double spin asymmetries give rise to $T$-odd correlations useful to probe $CP$ violation purely within the new physics amplitudes, as their appearance from interference with the SM is suppressed by $m_\tau$. We compare our constraints to those obtained earlier on the basis of deviations from the Drell-Yan cross-section.