Amplitude analysis of the $ \Xi_c^+ \to p K^- \pi^+ $ decay and $ \Xi_c^+ $ baryon polarization measurement in semileptonic beauty-hadron decays

An amplitude analysis of the Ξ c + → p K − π + decay together with a measurement of the Ξ c + polarization vector in semileptonic beauty-hadron decays is presented. The analysis is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb − 1 . An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. A sizeable Ξ c + polarization is found. A large sensitivity of the Ξ c + → p K − π + decay to the polarization is seen, making the amplitude model suitable for Ξ c + polarization measurements in other systems.