X(5568) as a $s u \bar d \bar b$ tetraquark in a simple quark model
  The $S$-wave eigenstates of tetraquarks of type $s u \bar d \bar b$ with J$^{P}$ = 0$^{+}$, 1$^{+}$ and 2$^{+}$ are studied within a simple quark model with chromomagnetic interaction and effective quark masses extracted from meson and baryon spectra. It is tempting to see if this spectrum can accommodate the new narrow structure X(5568), observed by the D\O~~Collaboration, but not confirmed by the LHCb Collaboration. If it exists, such a tetraquark is a system with four different flavors and its study can improve our understanding of multiquark systems. The presently calculated mass of X(5568) agrees quite well with the experimental value of he D\O~~Collaboration. Predictions are made for the spectrum of the charmed partner $s u \bar d \bar c$. However we are aware of the difficulty of extracting effective quark masses, from mesons and baryons, to be used in multiquark systems. 
Fl. Stancu
hep-ph