Compositeness and decay properties of the flavor partner of $D_{s0}^{\ast }(2317)$

In view of the recent experimental finding of the heavy quark flavor partner of the $D_{s0}(2317)$ in the bottom sector, the $B_{s0}(5700)$, we perform the $B^{(\ast )}{\bar{K}}^{(\ast )}$ coupled-channel calculation in the hidden-gauge formalism. By fixing the mass of the bound state generated by the $B\bar{K}$ interaction with $J^P=0^{+}$ to the observed state, we also predict five new states with $J^P=\{0,1,2{\}}^{+}$ in this sector. In particular, three of them have $J^P=1^{+}$ and masses $5740$, $6005$ and $6065$ MeV, respectively. In addition, we evaluate the decay width of the $B_{s0}$ and $B_{s1}$ states through the isospin breaking decay mode $B_s^0{\pi }^0$ and $B_s^{\ast 0}{\pi }^0$, respectively. We find that, because these states have large binding energies with respect to the $B^{(\ast )}\bar{K}$ threshold, the coupling to the bare component can reduce this decay width by more than half of the decay width, from $50$ keV in the purely molecular model to $10-20$ keV, when the $B_{s0}$ is coupled to the bare component. We also observe that, after considering heavy-quark-spin violating contributions, the decay width for the $B_{s1}$ becomes smaller than for the $B_{s0}$.