A hidden-charm pentaquark state in $\Lambda^0_b \to J/\psi p \pi^-$ decay

TL;DR

This paper investigates the $ o J/\psi p \pi^-$ decay, revealing a pentaquark-like structure in the $J/\psi p$ mass distribution similar to previous observations, and discusses the underlying mechanisms.

Contribution

It provides a theoretical analysis showing that a minimal model can reproduce the pentaquark-like peak in the $ o J/\psi p \pi^-$ decay, extending previous work on related decays.

Findings

Reproduces the $J/\psi p$ mass peak with minimal input

Shows the peak structure is consistent with a pentaquark state

Discusses the role of triangular singularity mechanisms

Abstract

We study here the $\Lambda_b^0 \to J/\psi p \pi^-$ reaction in analogy to the $\Lambda^0_b \to J/\psi p K^-$ one, and we note that in both decays there is a sharp structure (dip or peak) in the $J/\psi p$ mass distribution around $4450$ MeV, which is associated in the $\Lambda^0_b \to J/\psi p K^-$ experiment to an exotic pentaquark baryonic state, although in $\Lambda_b^0 \to J/\psi p \pi^-$ it shows up with relatively low statistics. We analyze the $\Lambda^0_b \to J/\psi p \pi^-$ interaction along the same lines as the $\Lambda^0_b \to J/\psi p K^-$ one, with the main difference stemming from the reduced Cabibbo strength in the former and the consideration of the $\pi^-p$ final state interaction instead of the $K^-p$ one. We find that with a minimal input, introducing the $\pi^-p$ and $J/\psi p$ interaction in $S$-wave with realistic interactions, and the empirical $P$-wave and $D$-wave contributions, one can accomplish a qualitative description of the $\pi^-p$ and $J/\psi p$ mass distributions. More importantly, the peak structure followed by a dip of the experimental $J/\psi p$ mass distribution is reproduced with the same input as used to describe the data of $\Lambda^0_b\rightarrow J/\psi p K^-$ reaction. The repercussion for the triangular singularity mechanism, invoked in some works to explain the pentaquark peak, is discussed.