Understanding $P_{cs}(4459)$ as a hadronic molecule in the ${\Xi }_b^{-}\to J/\psi \Lambda K^{-}$ decay

Abstract

Recently, the LHCb Collaboration reported on the evidence for a hidden charm pentaquark state with strangeness, i.e., $P_{cs}(4459)$, in the $J/\psi \Lambda$ invariant mass distribution of the ${\Xi }_b^{-}\to J/\psi \Lambda K^{-}$ decay. In this work, assuming that $P_{cs}(4459)$ is a ${\bar{D}}^{\ast }{\Xi }_c$ molecular state, we study this decay via triangle diagrams ${\Xi }_b\to {\bar{D}}_s^{(\ast )}{\Xi }_c\to ({\bar{D}}^{(\ast )}\bar{K}){\Xi }_c\to P_{cs}\bar{K}\to (J/\psi \Lambda )\bar{K}$. Our study shows that the production yield of a spin 3/2 ${\bar{D}}^{\ast }{\Xi }_c$ state is approximately one order of magnitude larger than that of a spin $1/2$ state due to the interference of ${\bar{D}}_s{\Xi }_c$ and ${\bar{D}}_s^{\ast }{\Xi }_c$ intermediate states. We obtain a model independent constraint on the product of couplings $g_{P_{cs}{\bar{D}}^{\ast }{\Xi }_c}$ and $g_{P_{cs}J/\psi \Lambda }$. With the predictions of two particular molecular models as inputs, we calculate the branching ratio of ${\Xi }_b^{-}\to (P_{cs}\to )J/\psi \Lambda K^{-}$ and compare it with the experimental measurement. We further predict the lineshape of this decay which could be useful to future experimental studies.

Comments: 19 pages,7 figures