Strange hidden-charm pentaquark poles from $B^{-}\to J/\psi \Lambda \bar{p}$

Abstract

Recent LHCb data for $B^{-}\to J/\psi \Lambda \bar{p}$ show a clear peak structure at the ${\Xi }_c\bar{D}$ threshold in the $J/\psi \Lambda$ invariant mass ($M_{J/\psi \Lambda }$) distribution. The LHCb's amplitude analysis identified the peak with the first hidden-charm pentaquark with strangeness $P_{\psi s}^{\Lambda }(4338)$. We conduct a coupled-channel amplitude analysis of the LHCb data by simultaneously fitting the $M_{J/\psi \Lambda }$, $M_{J/\psi \bar{p}}$, $M_{\Lambda \bar{p}}$, and $\cos {\theta }_{K^{\ast }}$ distributions. Rather than the Breit-Wigner fit employed in the LHCb analysis, we consider relevant threshold effects and a unitary ${\Xi }_c\bar{D}$-${\Lambda }_c{\bar{D}}_s$ coupled-channel scattering amplitude from which $P_{\psi s}^{\Lambda }$ poles are extracted for the first time. In our default fit, the $P_{\psi s}^{\Lambda }(4338)$ pole is almost a ${\Xi }_c\bar{D}$ bound state at $(4338.2\pm 1.4)-(1.9\pm 0.5)i$ MeV. Our default model also fits a large fluctuation at the ${\Lambda }_c{\bar{D}}_s$ threshold, giving a ${\Lambda }_c{\bar{D}}_s$ virtual state, $P_{\psi s}^{\Lambda }(4255)$, at $4254.7\pm 0.4$ MeV. We also found that the $P_{\psi s}^{\Lambda }(4338)$ peak cannot solely be a kinematical effect, and a nearby pole is needed.

Comments: 4 pages, 4 figures, Contribution to the Proceedings for 16th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2023), October 15-20, 2023, Mainz, Germany