# The hidden-charm multiquark states

## TL;DR

This paper reviews experimental discoveries of hidden-charm multiquark states like tetraquarks and pentaquarks, discussing their theoretical interpretations, challenges, and future experimental prospects.

## Contribution

It provides a comprehensive overview of experimental findings and evaluates various theoretical models for hidden-charm multiquark states.

## Key findings

- Observation of charged charmonium-like $Z_c$ states
- Discovery of hidden-charm pentaquark states by LHCb
- Discussion of theoretical challenges and future measurements

## Abstract

Since 2003 many charmonium-like states were observed experimentally. Especially those charged charmonium-like $Z_c$ states and bottomonium-like $Z_b$ states cannot be accommodated within the naive quark model, which are good candidates of either the hidden-charm tetraquark states or molecules composed of a pair of charmed mesons. In 2015, the LHCb Collaboration discovered two hidden-charm pentaquark states, which are also beyond the quark model. In this talk, 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.