Lambda(b) -> Lambda l(+)l(-) form factors and differential branching fraction from lattice QCD

Abstract

We present the first lattice QCD determination of the Lambda(b) -> Lambda transition form factors that govern the rare baryonic decays Lambda(b) -> Lambda l(+)l(-) at leading order in heavy-quark effective theory. Our calculations are performed with 2 + 1 flavors of domain-wall fermions, at two lattice spacings and with pion masses down to 227 MeV. Three-point functions with a wide range of source-sink separations are used to extract the ground-state contributions. The form factors are extrapolated to the physical values of the light-quark masses and to the continuum limit. We use our results to calculate the differential branching fractions for Lambda(b) -> Lambda l(+)l(-) with l = e, mu, tau within the standard model. We find agreement with a recent CDF measurement of the Lambda(b) -> Lambda mu(+)mu(-) differential branching fraction. DOI: 10.1103/PhysRevD.87.074502