Form factors for Λ_b → Λ transitions from lattice QCD

The rare baryonic decays Lb Lm+m and Lb Lg can complement rare B meson decays in constraining models of new physics. In this work, we calculate the relevant Lb-L 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-0:11 fm and a-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.