Doubly charmed tetraquark $T_{cc}^+$ in (2+1)-flavor QCD near physical point

TL;DR

This study uses lattice QCD to analyze the $T_{cc}^+$ tetraquark, revealing an attractive interaction that suggests a virtual state near the $D^* D$ threshold, which could become a loosely bound state at physical pion mass.

Contribution

First lattice QCD calculation of the $T_{cc}^+$ tetraquark near physical pion mass using the HAL QCD method, showing potential and pole structure insights.

Findings

Attractive potential in $D^* D$ system at all distances.

Virtual pole near $D^* D$ threshold with specific energy and scattering length.

Potential at physical pion mass suggests a loosely bound state.

Abstract

We study the doubly charmed tetraquark state $T_{cc}^+$ by the HAL QCD method applied to the $D^*D$ system in $(2+1)$ flavor lattice QCD at nearly physical pion mass, $m_\pi= 146$ MeV. We obtain the attractive potential at all distances in the $S$-wave of the isoscalar $D^* D$ system, whose long distance behavior is well described by the two-pion exchange (TPE), and it generates a virtual pole near $D^* D$ threshold with a pole position $E_{\rm pole} = -59 (^{+53}_{-99}) (^{+2}_{-67})$ keV and an inverse scattering length $1/a_0=0.05(5)(^{+2}_{-2})$ fm$^{-1}$. The virtual pole turns into a loosely bound state pole if the pion mass in the TPE potential is extrapolated to the physical value, $m_\pi =135$ MeV. The potential at the physical pion mass is shown to give a semi-quantitative description of the $D^0 D^0\pi^+$ mass spectrum at the LHCb.