Q Q s ¯s ¯ tetraquarks in the chiral quark model

The low-lying S -wave Q Q s ¯s ¯ (Q =c , b ) tetraquark states with I (J^P)=0 (0⁺), 0 (1⁺) and 0 (2⁺) are systematically investigated in the framework of complex scaling range of chiral quark model. Every structure including meson-meson, diquark-antidiquark and K-type configurations, and all possible color channels in four-body sector are considered by means of a commonly extended variational approach, Gaussian expansion method. Within the studied mass region, several narrow and wide resonance states are obtained for c c s ¯s ¯ and b b s ¯s ¯ tetraquarks with I (J^P)=0 (0⁺) and 0 (2⁺). Meanwhile, narrow resonances for c b s ¯s ¯ tetraquarks are also found in I (J^P)=0 (0⁺), 0 (1⁺) and 0 (2⁺) states. The possibility of finding tetraquark structures with masses ∼0.6 GeV above the non-interacting hadron-hadron thresholds (and not close to them) is a feature related with the absence of the one-pion exchange interaction in the Q Q s ¯s ¯ sector and thus it could deserve experimental confirmation.