Λ[subscript b] → Λℓ[superscript +]ℓ[superscript −] form Factors, Differential Branching Fraction, and Angular Observables from Lattice QCD with Relativistic b quarks

Abstract

Using (2 + 1)-flavor lattice QCD, we compute the 10 form factors describing the Λ[subscript b] → Λ matrix elements of the b → s vector, axial vector, and tensor currents. The calculation is based on gauge field ensembles generated by the RBC and UKQCD Collaborations with a domain-wall action for the u, d, and s quarks and the Iwasaki gauge action. The b quark is implemented using an anisotropic clover action, tuned nonperturbatively to the physical point, and the currents are renormalized with a mostly nonperturbative method. We perform simultaneous chiral, continuum, and kinematic extrapolations of the form factors through modified z expansions. Using our form factor results, we obtain precise predictions for the Λ[subscript b] → Λ(→ p[superscript +]π[superscript -])μ[superscript +]μ[superscript -] differential branching fraction and angular observables in the Standard Model.