Abstract
Stimulated by the recent observation of the exotic $X(5568)$ state by D0 Collaboration, we study the four-quark system $us\bar{b}\bar{d}$ with quantum numbers $J^P=0^+$ in the framework of chiral quark model. Two structures, diquark-antidiquark and meson-meson, with all possible color configurations are investigated by using Gaussian expansion method. The results show that energies of the tetraquark states with diquark-antiquark structure are too high to the candidate of $X(5568)$, and no molecular structure can be formed in our calculations. The calculation is also extended to the four-quark system $us\bar{c}\bar{d}$ and the same results as that of $us\bar{b}\bar{d}$ are obtained.
Highlights
Since the charmonium-like resonance X (3872) is observed by the Bell Collaboration [1] in 2003, a lot of experiments have emerged to study the exotic states-X Y Z particles from the Belle, BaBar, BESIII, LHCb, CDF, D0, and other Collaborations
The exotic states were observed in B meson decays, in e+e− and pp annihilations
X (5568) may be J P = 0+ because Bs0π ± is produced in S-wave
Summary
Since the charmonium-like resonance X (3872) is observed by the Bell Collaboration [1] in 2003, a lot of experiments have emerged to study the exotic states-X Y Z particles from the Belle, BaBar, BESIII, LHCb, CDF, D0, and other Collaborations. Agaev et al studied the state X (5568) within the two-point sum rule method using the diquark–antidiquark interpolating current [4,15] and meson molecule structure [16], their results preferred diquark–antidiquark picture rather than molecule and a nice agreement with experimental data is obtained. [10], a tetraquark interpretation of the X (5568) was proposed based on the diquark–antidiquark scheme, the identification is possible when the systematic errors of the model is taken into account. This result is supported by simple quark model estimations [12,13].
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