Measurement of the energy dependence of the $e^{+}{e}^{-}\to B\bar{B}$, $B\bar{B}{}^{\ast }$, and $B^{\ast }\bar{B}{}^{\ast }$ cross sections at Belle~II

We report measurements of the $e^{+}{e}^{-}\to B\bar{B}$, $B\bar{B}{}^{\ast }$, and $B^{\ast }\bar{B}{}^{\ast }$ cross sections at four energies, 10653, 10701, 10746 and 10805 MeV, using data collected by the Belle~II experiment. We reconstruct one $B$ meson in a large number of hadronic final states and use its momentum to identify the production process. In the first $2-5$ MeV above $B^{\ast }\bar{B}{}^{\ast }$ threshold, the $e^{+}{e}^{-}\to B^{\ast }\bar{B}{}^{\ast }$ cross section increases rapidly. This may indicate the presence of a pole close to the threshold.