Composite nature of the $T_{cc}$ state

TL;DR

This paper analyzes the $T_{cc}$ state using a scattering amplitude approach considering CDD poles, revealing it has a significant non-molecular component and providing a detailed line shape fit to experimental data.

Contribution

The study introduces a general method incorporating CDD poles to analyze the $T_{cc}$ state, highlighting its mixed molecular and elementary nature.

Findings

The $T_{cc}$ state has a compositeness of approximately 0.23.

The line shape fits well with experimental data.

The $T_{cc}$ state contains a substantial non-molecular component.

Abstract

In 2021, LHCb collaboration reported a very narrow state in the $D^0D^0\pi^+$ mass spectrum just below the $D^{*+}D^0$ mass threshold. We consider the influence of the Castillejo-Dalitz-Dyson (CDD) pole in the scattering amplitude to derive a general treatment for the two-body final state interaction near its threshold. The line shape (or the energy dependent event distribution) are then obtained, where the parameters can be fixed by fitting to the experimental data on the $D^0D^0\pi^+$ mass spectrum. Within our method the data are quite well reproduced. The pole structure in the complex energy plane indicates that the $T_{cc}$ state has a large portion of elementary degree of freedom (e.g., the compact tetraquark component) inside its hadron wave function. The compositeness as a measure of molecule component in its wave function is predicted to be $0.23_{-0.09}^{+0.40}$. Clearly, the non-molecular component takes a non-negligible or even dominant portion.