Some remarks on compositeness of $T_{cc}^{+}$

Abstract

Recently LHCb experimental group find an exotic state $T_{cc}^{+}$ from the process $p\bar{p}\to D^0{D}^0{\pi }^{+}+X$. A key question is if it is just a molecule or may have confined tetraquark ingredient. To investigate this, different methods are taken, including two channel ($D^{\ast +}{D}^0$ and $D^{\ast 0}{D}^{+}$) K-matrix unitarization and single channel Flatté-like parametrization method analysed by pole counting rule and spectral density function sum rule. It demonstrates that $T_{cc}^{+}$ is a molecular state, though the possibility that there may exist elementary ingredient can not be excluded, by rough analysis on its production rate.