Energy scan of the $e^+e^- \to h_b(nP)\pi^+\pi^-$ $(n=1,2)$ cross sections and evidence for $\Upsilon(11020)$ decays into charged bottomonium-like states

TL;DR

This study measures the energy dependence of specific bottomonium production cross sections in electron-positron collisions, revealing peaks associated with known states and evidence for decay via intermediate exotic states.

Contribution

First measurement of the energy dependence of $e^+e^- o h_b(nP)\pi^+\pi^-$ cross sections up to 11.02 GeV, with evidence for decay via $Z_b$ states.

Findings

Identification of $(10860)$ and $(11020)$ peaks

Evidence that $(11020)$ decays proceed via $Z_b(10610)$ and $Z_b(10650)$

Exclusion of only $Z_b(10610)$ production at 3.3 standard deviations

Abstract

Using data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider, we measure the energy dependence of the $e^+e^- \to h_b(nP)\pi^+\pi^-$ $(n=1,2)$ cross sections from thresholds up to $11.02\,$GeV. We find clear $\Upsilon(10860)$ and $\Upsilon(11020)$ peaks with little or no continuum contribution. We study the resonant substructure of the $\Upsilon(11020) \to h_b(nP)\pi^+\pi^-$ transitions and find evidence that they proceed entirely via the intermediate isovector states $Z_b(10610)$ and $Z_b(10650)$. The relative fraction of these states is loosely constrained by the current data: the hypothesis that only $Z_b(10610)$ is produced is excluded at the level of 3.3 standard deviations, while the hypothesis that only $Z_b(10650)$ is produced is not excluded at a significant level.