# Emergence of a complete heavy-quark spin symmetry multiplet: seven molecular pentaquarks in light of the latest LHCb analysis

## TL;DR

This paper predicts a complete multiplet of seven heavy-quark spin symmetry molecular pentaquarks based on recent LHCb findings, using an effective field theory approach that aligns with heavy-quark symmetry principles.

## Contribution

It introduces a contact-range effective field theory model that explains observed pentaquarks and predicts four additional molecular states, forming a complete heavy-quark spin symmetry multiplet.

## Key findings

- Three observed pentaquarks fit the molecular interpretation.
- The model predicts four more molecular pentaquarks.
- The multiplet structure reflects a symmetry pattern similar to SU(3).

## Abstract

A recent analysis by the LHCb collaboration suggests the existence of three narrow pentaquark-like states --- the $P_c(4312)$,$P_c(4440)$ and $P_c(4457)$ --- instead of just one in the previous analysis (the $P_c(4450)$). The closeness of the $P_c(4312)$ to the $\bar{D} \Sigma_c$ threshold and the $P_c(4440)$/$P_c(4457)$ to the $\bar{D}^* \Sigma_c$ one suggests a molecular interpretation of these resonances. We show that these three pentaquark-like resonances can be naturally accommodated in a contact-range effective field theory description that incorporates heavy-quark spin symmetry. This description leads to the prediction of all the seven possible S-wave heavy antimeson-baryon molecules (that is, there should be four additional molecular pentaquarks in addition to the $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$), providing the first example of a heavy-quark spin symmetry molecular multiplet that is complete. If this is confirmed, it will not only give us an impressive example of the application of heavy-quark symmetries and effective field theories in hadron physics: it will also uncover a clear and powerful ordering principle for the molecular spectrum, reminiscent of the SU(3)-flavor multiplets to which the light hadron spectrum conforms.