Phenomenology of $P_c(4380)^+$, $P_c(4450)^+$ and related states

TL;DR

This paper investigates the nature of the pentaquark states $P_c(4380)^+$ and $P_c(4450)^+$, proposing a meson-baryon molecular interpretation, and discusses how future experiments can distinguish between different theoretical models.

Contribution

It provides a phenomenological analysis of the pentaquark states as meson-baryon molecules and suggests experimental signatures to differentiate models.

Findings

States may be mixtures of isospins 1/2 and 3/2

Neutral partners' masses can distinguish models

Further decay channel studies can discriminate models

Abstract

The $P_c(4380)^+$ and $P_c(4450)^+$ states recently discovered at LHCb have masses close to several relevant thresholds, which suggests they can be described in terms of meson-baryon degrees of freedom. This article explores the phenomenology of these states, and their possible partners, from this point of view. Competing models can be distinguished by the masses of the neutral partners which have yet to be observed, and the existence or otherwise of further partners with different isospin, spin, and parity. Future experimental studies in different decay channels can also discriminate among models, using selection rules and algebraic relations among decays. Among the several possible meson-baryon pairs which could be important, one implies that the states are mixtures of isospins 1/2 and 3/2, with characteristic signatures in production and decay. A previous experimental study of a Cabibbo-suppressed decay showed no evidence for the states, and further analysis is required to establish the significance of this non-observation. Several intriguing similarities suggest that $P_c(4450)^+$ is related to the $X(3872)$ meson.