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

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.

Bottomoniumlike tetraquarks in a chiral quark model

“…From the theoretical side, an enormous effort devoted to reveal the nature of the unexpected exotic hadrons has been deployed using a wide variety of approaches. In fact, one can already find in the literature many extensive reviews [17][18][19][20][21][22][23][24][25][26][27][28][29][30], which explain in detail a particular theoretical method and thus capture a certain interpretation of the XY Z states. One can find either compact or molecular tetraquark interpretaions, or even relate the signals with simple kinematical effects such as cusps.…”