${\Lambda }_b\to \Lambda {\ell }^{+}{\ell }^{-}$ 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 ${\Lambda }_b\to \Lambda$ matrix elements of the $b\to s$ 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 ${\Lambda }_b\to \Lambda (\to p^{+}{\pi }^{-}){\mu }^{+}{\mu }^{-}$ differential branching fraction and angular observables in the Standard Model.

Comments: 33 pages, 9 figures, form factor parameters included as ancillary files. This version: corrected lepton-mass contributions to F_L