Λb → Λ*c (2595,2625)l-ν-. form factors from lattice QCD

We present the first lattice-QCD determination of the form factors describing the semileptonic decays Lambda(b) -> Lambda*(c) (2595)l(-)nu(-) and Lambda(b) -> Lambda*c(2625)l(-)nu(-), where the Lambda*(c) (2595) and Lambda*c(2625) are the lightest charm baryons with J(P) = 1/2(-) and J(P) = 3/2-, respectively. These decay modes provide new opportunities to test lepton flavor universality and also play an important role in global analyses of the strong interactions in b -> c semileptonic decays. We determine the full set of vector, axial vector, and tensor form factors for both decays but only in a small kinematic region near the zero-recoil point. The lattice calculation uses three different ensembles of gauge-field configurations with 2 + 1 flavors of domain-wall fermions, and we perform extrapolations of the form factors to the continuum limit and physical pion mass. We present Standard Model predictions for the differential decay rates and angular observables. In the kinematic region considered, the differential decay rate for the 1/2- final state is found to be approximately 2.5 times larger than the rate for the 3/2- final state. We also test the compatibility of our form-factor results with zero-recoil sum rules.

Automated summary

This study presents the first lattice-QCD determination of form factors for Lambda(b) -> Lambda*(c)(2595) l(-)nu(-) and Lambda(b) -> Lambda*c(2625) l(-)nu(-) decays, offering new opportunities to test lepton flavor universality and playing a key role in global analyses of strong interactions. The full set of form factors for vector, axial vector, and tensor terms are determined with extrapolations to the continuum limit and physical pion mass. Standard Model predictions for differential decay rates and angular observables are provided, with the study showing a 2.5 times larger rate for the 1/2- final state compared to the 3/2- final state. Compatibility with zero-recoil sum rules is also tested.