Form factors for Lambda_b -> Lambda transitions from lattice QCD

TL;DR

This paper calculates the Lambda_b to Lambda transition form factors using lattice QCD, providing essential inputs for studying rare baryonic decays and probing new physics beyond the Standard Model.

Contribution

It presents the first lattice QCD calculation of Lambda_b to Lambda form factors at leading order in heavy-quark effective theory, including continuum and physical quark mass extrapolations.

Findings

Form factors computed at multiple lattice spacings and quark masses.

Extrapolation to continuum limit and physical quark masses performed.

Results enable improved theoretical predictions for rare baryonic decays.

Abstract

The rare baryonic decays $\Lambda_b \to \Lambda \mu^+ \mu^-$ and $\Lambda_b \to \Lambda \gamma$ can complement rare $B$ meson decays in constraining models of new physics. In this work, we calculate the relevant $\Lambda_b \to \Lambda$ transition form factors at leading order in heavy-quark effective theory using lattice QCD. Our analysis is based on RBC/UKQCD gauge field ensembles with 2+1 flavors of domain-wall fermions, and with lattice spacings of $a\approx 0.11$ fm and $a\approx 0.08$ fm. We compute appropriate ratios of three-point and two-point correlation functions for a wide range of source-sink separations, and extrapolate to infinite separation in order to eliminate excited-state contamination. We then extrapolate the form factors to the continuum limit and to the physical values of the light-quark masses.