The nature of $\chi_{c1}\left(3872\right)$ and $T_{cc}^+\left(3875\right)$

TL;DR

This paper uses Born--Oppenheimer Effective Field Theory (BOEFT) to analyze the nature of the exotic hadrons $ ext{chi}_{c1}(3872)$ and $T_{cc}^+(3875)$, providing insights into their composition and making predictions for related states.

Contribution

It applies BOEFT to clarify the structure of key XYZ exotic states and offers predictions for similar states in the bottomonium sector, advancing theoretical understanding.

Findings

BOEFT describes the main features of $ ext{chi}_{c1}(3872)$ and $T_{cc}^+(3875)$

QCD determines their composition

Predictions made for bottomonium sector states

Abstract

Two decades ago the $\chi_{c1}\left(3872\right)$ was discovered in the hadron spectrum with two heavy quarks. The discovery fueled a surge in experimental research, uncovering dozens of so called XYZ exotics states lying outside the conventional quark model, as well as theoretical investigations into new forms of matter, such as quark-gluon hybrids, tetraquarks, pentaquarks, with the potential of disclosing new information about the fundamental strong force. Among the XYZs, the $\chi_{c1}\left(3872\right)$ and $T_{cc}^+\left(3875\right)$ stand out for their striking characteristics and unlashed many discussions about their nature. Here, we address this question using the Born--Oppenheimer Effective Field Theory (BOEFT) and show how QCD settles the issue of their composition. Not only we describe well the main features of the $\chi_{c1}\left(3872\right)$ and $T_{cc}^+\left(3875\right)$ but obtain also predictions in the bottomonium sector. This opens the way to systematic applications of BOEFT to all XYZs.