Double-charm tetraquark under the complex scaling method

The LHCb Collaboration discovered a double-charm tetraquark T-cc(+) with a very small width. We investigate the T-cc(+) as a DD* molecule with JP = 1(+) in the framework of the one-boson-exchange potential model. The isospin breaking effect and S - D wave coupling are taken into account carefully. We adopt the complex scaling method to study the DD* system and obtain a quasibound state corresponding to the Tthorncc. Its binding energy relative to the (DD)-D-0*(+) and width are - 354 keV and 61 keV respectively. The isospin breaking effect is found to be enormous, and the S-wave (DD)-D-0*(+) and D+D*(0) components give dominant contributions with the probabilities of 72.1% and 27.1% respectively. In addition, we do not find any resonances in the DD* system. As a by-product, we study the X(3872) as a (D (D) over bar* - D*(D) over bar) / root 2p molecule with JPC = 1(++). We also find a quasibound state corresponding to the X(3872). Its binding energy relative to the D-0(D) over bar*(0) threshold and width are -111 keV and 26 keV, respectively. The S-wave (D-0(D) over bar*(0) - D*(0)(D) over bar (0)) / root 2p component dominates this state with the probability of 92.7%.

Automated summary

The LHCb Collaboration discovered a double-charm tetraquark T-cc(+) with a very small width. It is investigated as a DD* molecule and found that isospin breaking effect and S - D wave coupling are significant. The study also identifies the X(3872) as a (D (D) over bar* - D*(D) over bar) / root 2p molecule and reveals a dominant S-wave component.