Mass spectra of doubly heavy tetraquarks in an improved chromomagnetic interaction model

Doubly heavy tetraquark $(QQ\bar q\bar q)$ states are the prime candidates of tightly bound exotic systems and weakly decaying. In the framework of the improved chromomagnetic interaction (ICMI) model, we complete a systematic study on the mass spectra of the $S$-wave doubly heavy tetraquark states $QQ\bar{q}\bar{q}$ ($q=u, d, s$ and $Q=c, b$) with different quantum numbers $J^P=0^+$, $1^+$, and $2^+$. The parameters in the ICMI model are extracted by fitting the conventional hadron spectra and used directly to predict the masses of tetraquark states. For heavy quarks, the uncertainties of the parameters are acquired by comparing the masses of doubly (triply) heavy baryons with these given by lattice QCD, QCD sum rule, and potential models. Several compact and stable bound states are found in both charm and bottom tetraquark sectors. The predicted mass of $cc\bar u\bar d$ state is compatible with the recent result of the LHCb collaboration.