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

Abstract

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