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A hidden-charm $S=-1$ pentaquark from the decay of $Λ_b$ into $J/ψηΛ$

The hidden charm pentaquark state $P_c(4450)$ observed recently by the LHCb collaboration may be of molecular nature, as advocated by some unitary approaches that also predict pentaquark partners in the strangeness $S=-1$ sector. In this work we argue that a hidden-charm strange pentaquark could be seen from the decay of the $Λ_b$, just as in the case of the non-strange $P_c(4450)$, but looking into the $J/ψηΛ$ decay mode and forming the invariant mass spectrum of $J/ψΛ$ pairs. In the model presented here, which assumes a standard weak decay topology and incorporates the hadronization process and final state interaction effects, we find the $J/ψηΛ$ final states to be populated with similar strength as the $J/ψK^- p$ states employed for the observation of the non-strange pentaquark. This makes the $Λ_ b \to J/ψηΛ$ decay to be an interesting process to observe a possible strange partner of the $P_c(4450)$ . We study the dependence of the $J/ψΛ$ mass spectra on various model ingredients and on the unknown properties of the strange pentaquark.