Doubly heavy tetraquark states in a mass splitting model

Treating X(4140) as a compact JPC=1++ csc¯s¯ state and using its mass as a reference scale, we systematically estimate the masses of doubly heavy tetraquark states QQq¯q¯, where Q=c, b and q=u, d, s. Their decay properties are studied with a simple rearrangement scheme. Based on our results, the lowest I(JP)=0(1+) bbn¯n¯ state is a stable tetraquark about 20 MeV below the B¯*B¯ threshold. The mass and width of the low-mass 0(1+) ccn¯n¯ (n=u, d) tetraquark are compatible with the Tcc(3875)+ observed by the LHCb Collaboration. The locations of the lowest 0(0+) and 0(1+) bcn¯n¯ states are found to be close to the B¯D and B¯*D thresholds, respectively. We hope that the predicted ratios between partial widths of different channels may be helpful to identify compact tetraquark states from future measurements.