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

TL;DR

This paper presents precise measurements of specific B meson pair production cross sections at Belle II across four energies, revealing a rapid increase near the $B^*\bar{B}^*$ threshold that suggests a possible nearby pole.

Contribution

First measurements of $e^+e^- \to B\bar{B}$, $B\bar{B}^*$, and $B^*\bar{B}^*$ cross sections at these energies using Belle II data, indicating threshold effects.

Findings

Rapid cross section increase near $B^*\bar{B}^*$ threshold

Potential evidence for a nearby pole

Enhanced understanding of bottomonium-like states

Abstract

We report measurements of the $e^+e^- \to B\bar{B}$, $B\bar{B}{}^*$, and $B^*\bar{B}{}^*$ 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 $B^*\bar{B}{}^*$ threshold, the $e^+e^- \to B^*\bar{B}{}^*$ cross section increases rapidly. This may indicate the presence of a pole close to the threshold.