Strange hidden-charm pentaquark poles from B− → J / ψΛp.

Recent LHCb data for B⁻ → J/ψΛp¯ show a clear peak structure at the Ξ_cD¯ threshold in the J/ψ invariant mass (M_J/ψΛ) distribution. In their amplitude analysis, LHCb identified the peak with the first hidden-charm pentaquark with strangeness P_ψs^Λ(4338). We conduct a coupled-channel amplitude analysis of the LHCb data by simultaneously fitting the M_J/ψΛ,M_J/ψp¯,M_Λp¯, and cos_θ^K* distributions. Rather than the Breit-Wigner fit employed in the LHCb analysis, we consider relevant threshold effects and a unitary Ξ_cD¯ − Λ_cD¯_s coupled-channel scattering amplitude from which P_ψs^Λ poles are extracted for the first time. In our default fit, the P_ψs^Λ(4338) pole is almost a Ξ_cD¯ bound state at (4338:2±1:4)−(1:9±0:5) i MeV. Our default model also fits a large fluctuation at the Λ_cD¯_s threshold, giving a Λ_cD¯_s virtual state, P_ψs^Λ(4255), at 4254:7±0:4 MeV. We also found that the P_ψs^Λ(4338) peak cannot solely be a kinematical effect, and a nearby pole is needed. [ABSTRACT FROM AUTHOR]