The hidden-charm pentaquark and tetraquark states

TL;DR

This paper reviews recent experimental discoveries of hidden-charm pentaquark and tetraquark states, discussing their implications for multiquark models and outlining future experimental directions.

Contribution

It provides a comprehensive review of experimental progress and theoretical interpretations of hidden-charm multiquark states, highlighting challenges and future research avenues.

Findings

Discovery of hidden-charm pentaquark states by LHCb

Charged $Z_c$ states as tetraquark or molecular candidates

Discussion of theoretical challenges and future measurements

Abstract

In the past decade many charmonium-like states were observed experimentally. Especially those charged charmonium-like $Z_c$ states and bottomonium-like $Z_b$ states can not be accommodated within the naive quark model. These charged $Z_c$ states are good candidates of either the hidden-charm tetraquark states or molecules composed of a pair of charmed mesons. Recently, the LHCb Collaboration discovered two hidden-charm pentaquark states, which are also beyond the quark model. In this work, we review the current experimental progress and investigate various theoretical interpretations of these candidates of the multiquark states. We list the puzzles and theoretical challenges of these models when confronted with the experimental data. We also discuss possible future measurements which may distinguish the theoretical schemes on the underlying structures of the hidden-charm multiquark states.