Evidence for exotic hadron contributions to $\Lambda_b^0 \to J/\psi p \pi^-$ decays

TL;DR

This study performs a detailed amplitude analysis of $ ext{Lambda}_b^0$ decays, providing evidence that exotic hadron states like $P_c$ and $Z_c$ contribute significantly, supporting their existence with high statistical significance.

Contribution

It is the first analysis to include multiple exotic states simultaneously in $ ext{Lambda}_b^0$ decay modeling, confirming their contributions with over three sigma significance.

Findings

Evidence supports the existence of all three exotic states in $ ext{Lambda}_b^0$ decays.

The data are consistent with previous production rate estimates of the exotic states.

Including these states improves the fit quality significantly.

Abstract

A full amplitude analysis of $\Lambda_b^0 \to J/\psi p \pi^-$ decays is performed with a data sample acquired with the LHCb detector from 7 and 8 TeV $pp$ collisions, corresponding to an integrated luminosity of 3 fb$^{-1}$. A significantly better description of the data is achieved when, in addition to the previously observed nucleon excitations $N\to p\pi^-$, either the $P_c(4380)^+$ and $P_c(4450)^+\to J/\psi p$ states, previously observed in $\Lambda_b^0 \to J/\psi p K^-$ decays, or the $Z_c(4200)^-\to J/\psi \pi^-$ state, previously reported in $B^0 \to J/\psi K^+ \pi^-$ decays, or all three, are included in the amplitude models. The data support a model containing all three exotic states, with a significance of more than three standard deviations. Within uncertainties, the data are consistent with the $P_c(4380)^+$ and $P_c(4450)^+$ production rates expected from their previous observation taking account of Cabibbo suppression.