Endpoint relations for baryons

Following our earlier work we establish kinematic endpoint relations for baryon decays using the Wigner-Eckart theorem and apply them to 1/2 -> 1/2 and 1/2 -> 3/2 baryon transitions. We provide angular distributions at the kinematic endpoint which hold for the generic d = 6 model-independent effective Hamiltonian and comment on the behaviour in the vicinity of the endpoint. Moreover, we verify the endpoint relations, using an explicit form factor parametrisation, and clarify constraints on helicity-based form factors to evidence endpoint relations. Our results provide guidance for phenomenological parameterisations, consistency checks for theory computations and experiment. Results are applicable to ongoing and future new physics searches at LHCb, BES III and Belle II with rare semileptonic-, dineutrino-and charged-modes, which include Lambda(b) -> Lambda(()*())ll, Lambda(b) -> Lambda(()*())nu nu, Omega(b) -> Omega ll, Lambda(c) -> pll, Sigma -> pll and Lambda(b) -> Lambda(()(c)*())l nu.

Automated summary

In this study, kinematic endpoint relations for baryon decays were established using the Wigner-Eckart theorem and applied to various baryon transitions. Angular distributions and constraints on form factors were provided, contributing to phenomenological parameterisations, consistency checks, and guidance for ongoing and future new physics searches at LHCb, BES III and Belle II.