Lambda(c) -> Lambda l(+)nu(l) Form Factors and Decay Rates from Lattice QCD with Physical Quark Masses

Abstract

The first lattice QCD calculation of the form factors governing Lambda(c) -> Lambda l(+)nu(l) decays is reported. The calculation was performed with two different lattice spacings and includes one ensemble with a pion mass of 139(2) MeV. The resulting predictions for the Lambda(c) -> Lambda e(+)nu(e) and Lambda(c) -> Lambda mu(+)nu(mu) decay rates divided by vertical bar V-cs vertical bar(2) are 0.2007(71)(74) and 0.1945(69)(72) p(s-1), respectively, where the two uncertainties are statistical and systematic. Taking the Cabibbo-Kobayashi-Maskawa (CKM) matrix element vertical bar V-cs vertical bar from a global fit and the Lambda(c) lifetime from experiments, this translates to branching fractions of B(Lambda(c) -> Lambda e(e)(+nu)) = 0.0380(19)(LQCD)(11)(tau Lambda c) and B(Lambda(c) -> Lambda mu(+)nu(mu)) 0.0369(19)(LQCD)(11)(tau Lambda c). These results are consistent with, and two times more precise than, the measurements performed recently by the BESIII Collaboration. Using instead the measured branching fractions together with the lattice calculation to determine the CKM matrix element gives vertical bar V-cs vertical bar = 0.949(24)(LQCD)(14)(tau)Lambda c (49)(B).