Hidden-charm pentaquark state in Λb0 →j /ψpπ- decay

We study here the Λb0→J/ψpπ- reaction in analogy to the Λb0→J/ψpK- one, and we note that in both decays there is a sharp structure (dip or peak) in the J/ψp mass distribution around 4450 MeV, which is associated in the Λb0→J/ψpK- experiment to an exotic pentaquark baryonic state, although in Λb0→J/ψpπ- it shows up with relatively low statistics. We analyze the Λb0→J/ψpπ- interaction along the same lines as the Λb0→J/ψpK- one, with the main difference stemming from the reduced Cabibbo strength in the former and the consideration of the π-p final state interaction instead of the K-p one. We find that with a minimal input, introducing the π-p and J/ψp interaction in S-wave with realistic interactions, and the empirical P-wave and D-wave contributions, one can accomplish a qualitative description of the π-p and J/ψp mass distributions. More importantly, the peak structure followed by a dip of the experimental J/ψp mass distribution is reproduced with the same input as used to describe the data of Λb0→J/ψpK- reaction. The repercussion for the triangular singularity mechanism, invoked in some works to explain the pentaquark peak, is discussed.