Photo- and electro-production of narrow exotic states: from light quarks to charm and up to bottom

TL;DR

This paper reviews the search for exotic narrow hadronic states across light, charm, and bottom quark sectors, highlighting recent progress in photoproduction experiments and future prospects at electron-ion colliders.

Contribution

It provides a concise overview of recent experimental efforts and theoretical implications in the search for exotic narrow states involving different quark flavors.

Findings

Progress in detecting $P_c$ and $Z_c$ states via photoproduction.

Implications for $P_b$ and $Z_b$ states in bottom quark sector.

Future potential of electron-ion colliders for understanding exotic states.

Abstract

Accessing a full image of the inner content of hadrons represents a central endeavour of modern particle physics, with the main scientific motivation to investigate the strong interaction binding the visible matter. On the one hand, the structure of known exotic candidates is a fundamental open issue addressed widely by scientists. On the other hand, looking for new states of exotic nature is a central component for theoretical and experimental efforts from electron-positron machine and electron accelerator with fixed target to heavy ion and electron-ion colliders. In this article we present a succinct short overview of the attempt to search for exotic narrow $N^*$ and $Z$ states containing light quarks only or also charm, and its connotation for bottom regions (the latter two are also known as $P_c$ ($Z_c$) and $P_b$ ($Z_b$) states, respectively in {the literature}). We address the effort of searching for exotic narrow $N^*$ and $Z$ states in light quark sector. We focus on recent progress in searching for signal of $P_c$ and $Z_c$ states photoproduction and its implication into the $P_b$ and $Z_b$ photoproduction and their decay properties. We also discuss future perspectives for the field in electron-ion colliders, a good place to disentangle the nature of some of these states and investigate some other enlightening topics including QCD trace anomaly and quarkonium-nucleon scattering length.