Beyond Form Factors: Precise Angular Tests in Hadronic $\tau$ Decays

TL;DR

This paper proposes symmetry-based angular observables in semileptonic tau decays that are independent of form factors and can test the Standard Model or reveal new physics.

Contribution

It introduces a novel method to construct form-factor independent angular observables using symmetry arguments in tau decays.

Findings

Predicted angular observables are independent of hadronic form factors.

Deviations from predictions could indicate new physics or electromagnetic effects.

First estimate of new physics impact within an EFT framework.

Abstract

Semileptonic $\tau$ decays mainly proceed via interactions between charged lepton and quark currents. The hadronization of the quark current is intrinsically nonperturbative and generally cannot be addressed analytically. In these proceedings, we propose using symmetry arguments alone to construct clean angular observables, which, within the Standard Model and in the absence of long-distance electromagnetic corrections, remain form-factor independent. These predictions can be experimentally tested, and any observed deviation could signal either effects of physics beyond the Standard Model or provide a clean benchmark for long-distance electromagnetic corrections. We also perform a first estimate of the expected impact of new physics in an EFT framework.