Measurement of $e^+e^-\to\eta\Upsilon(1S,2S)$ and search for $\gamma X_b$ with $\Upsilon(10753)$ scan data

Abstract We present an analysis of the processes $e^{+}e^{-}\toηΥ(1S)$, $ηΥ(2S)$, and $γX_b$ with $X_b\toπ^+π^-χ_{bJ},~χ_{bJ}\toγΥ(1S)$$(J=1,~2)$ reconstructed from $γγπ^+π^-\ell^+\ell^-~(\ell=e,~μ)$ final states in $19.6\rm~\rm fb^{-1}$ of Belle II data collected at four energy points near the peak of the $Υ(10753)$ resonance. Here, $X_b$ is a hypothetical bottomonium-sector partner of the $X(3872)$. In the process $e^{+}e^{-} \to ηΥ(2S)$, we observe a signal with a significance that exceeds $6.0σ$. Based on an analysis of the Born cross-section, the hypothesis that these events are associated solely with the production of the $Υ(5S)$ or $Υ(10753)$ resonances is rejected at the level of 3.6$σ$. This suggests that the observed events are more likely to arise from a new state near the $B^{*}\bar{B}^{*}$ threshold or from a substantial continuum production. No significant signal is observed for $e^{+}e^{-}\toηΥ(1S)$ or $γX_b$. Upper limits on the Born cross sections for the processes $e^{+}e^{-}\toηΥ(1S)$ and $e^{+}e^{-}\toγX_b$ with $X_b\toπ^+π^-χ_{bJ}$ are determined.
Tags Run 1
Working group Quarkonium
Principal authors @  Yang Li, Eunil Won, Youwen Xue, Junhao Yin
Reference submitted to PRL
Links arXiv:2509.01917, Inspire,
Bibtex 
@article{Belle-II:2025ubm,
    author = "Adachi, I. and others",
    collaboration = "Belle-II",
    title = "{Observation of $e^+e^-\toηΥ(2S)$ and search for $e^+e^-\toηΥ(1S),~γX_b$ at $\sqrt{s}$ near 10.75 GeV}",
    eprint = "2509.01917",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II Preprint 2025-023, KEK Preprint 2025-24",
    month = "9",
    year = "2025"
}