Amplitude analysis of the Ξ _c ⁺ → pK ⁻π ⁺ decay and Ξ _c ⁺ baryon polarization measurement in semileptonic beauty-hadron decays

An amplitude analysis of the Ξ ⁺ _c → pK ⁻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 → pK ⁻π ⁺ decay to the polarization is seen, making the amplitude model suitable for Ξ ⁺ _c polarization measurements in other systems.