Photon helicity in Lambda_b --> p K gamma decays

Abstract

Radiative decays of polarized Lambda_b baryons represent an attractive possibility to measure the helicity of the photon emitted in the b --> s gamma quark transition and thus to subject the Standard Model to a stringent test at existing and future hadron colliders. The most abundant mode, Lambda(1116) gamma, is experimentally very challenging because of the long decay length of the Lambda(1116). We show that the experimentally more accessible Lambda_b --> p K gamma decays proceeding via Lambda resonances may be used to extract the photon helicity for sufficient Lambda_b polarization, if the resonance spin does not exceed 3/2. A direct comparison of the potential of such resonance decays to assess the photon polarization at a hadron collider with respect to the decay to Lambda(1116) is given.