Multiquark Hadrons - A New Facet of QCD

TL;DR

This paper reviews the discovery and phenomenology of multiquark hadrons, such as tetraquarks and pentaquarks, highlighting their significance as a new aspect of QCD and discussing various theoretical models including the diquark approach.

Contribution

It provides a comprehensive overview of multiquark states, emphasizing their experimental discovery, phenomenology, and the theoretical frameworks used to understand their dynamics, especially the diquark model.

Findings

Multiquark states extend the conventional hadron spectrum.

Some multiquark states have been experimentally observed.

The diquark model offers a promising approach to understanding multiquark dynamics.

Abstract

I review some selected aspects of the phenomenology of multiquark states discovered in high energy experiments. They have four valence quarks (called tetraquarks) and two of them are found to have five valence quarks (called pentaquarks), extending the conventional hadron spectrum which consists of quark-antiquark $(q\bar{q})$ mesons and $qqq$ baryons. Multiquark states represent a new facet of QCD and their dynamics is both challenging and currently poorly understood. I discuss various approaches put forward to accommodate them, with emphasis on the diquark model.