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.