Scalar and Tensor Form Factors for $\Lambda \rightarrow p\ell \bar{\nu}_\ell$ from Lattice QCD

TL;DR

This paper calculates scalar and tensor form factors for the Lambda to proton transition using lattice QCD, aiding searches for physics beyond the Standard Model in hyperon decays.

Contribution

It provides the first lattice QCD determination of these form factors and assesses their impact on constraining non-standard charged-current interactions.

Findings

Form factors are provided as functions of q^2 using a model-independent parametrization.

The results enable improved constraints on non-standard scalar and tensor interactions in hyperon decays.

Comparison with experimental data helps refine limits on physics beyond the Standard Model.

Abstract

We present a determination of the scalar and tensor $\Lambda\to p$ transition form factors using lattice QCD. These form factors are relevant for semileptonic hyperon decays in the presence of extensions of the Standard Model that include scalar and tensor interactions. The calculation is carried out using a gauge ensemble of twisted mass fermions at the physical pion mass, following the same strategy as our recent study on vector and axial form factors for the same transition. We provide the complete set of form factors as functions of $q^2$ employing a model-independent parametrization. We examine their impact on searches for non-standard charged-current interactions via the muon-to-electron decay-rate ratio $R^{\mu e}=\Gamma(\Lambda\to p\mu\bar\nu_\mu)/\Gamma(\Lambda\to pe\bar\nu_e)$, where scalar and tensor contributions enter linearly and are helicity-enhanced relative to the electron channel. We compare this first-principles prediction for the decay-rate ratio with recent experimental measurements, thereby enabling improved constraints on non-standard charged-current interactions.