$Υ(5S)$ in the unquenched quark model

Abstract: The observation of the $\Upsilon(10753)$ state by Belle II Collaboration has sparked significant interest in the theoretical understanding of such states within the context of hadron physics. Considering the similar mass and the decay with, as well as the same quantum numbers $J^{PC}=1^{--}$ with the $\Upsilon(10860)$ state, which is referred to be the $\Upsilon(5S)$ in PDG, in this work, we try to calculate the mass of the $\Upsilon(5S)$ state. The model used to predict the high-energy spectrum of these states generally involves a constituent quark model, which can describe a variety of properties of hadrons containing heavy quarks. In the framework of the unquenched quark model, a coupled-channel calculation is employed to explore the effect of open-bottom meson-meson thresholds on the $\Upsilon(10860)$ state. The hypothesis is that coupled-channel effects could be large enough to create new dynamically generated states, thus potentially explaining the nature of the $\Upsilon(10860)$ state, as well as whether the $\Upsilon(10860)$ and $\Upsilon(10753)$ is the same state. The results indicate that unquenched effects play a crucial role in explaining the $\Upsilon(10860)$ state, providing a plausible mechanism for its formation. Besides in our calculations, the $\Upsilon(10860)$ and $\Upsilon(10753)$ may be two different states.