Evidence of $h_{b}(\text{2P}) \to \Upsilon(\text{1S})\eta$ decay and search for $h_{b}(\text{1P,2P}) \to \Upsilon(\text{1S})\pi^0$ with the Belle detector

TL;DR

This paper presents the first evidence for the decay $h_{b}(2P) o  ext{S}) ext{eta}$, measures its branching fraction, and sets upper limits on related $ ext{pi}^0$ transitions using Belle detector data.

Contribution

It provides the first evidence for a specific bottomonium transition and measures its branching fraction, offering new insights into bottomonium decay mechanisms.

Findings

Evidence for $h_{b}(2P) o  ext{S}) ext{eta}$ with 3.5 sigma significance.

Measured branching fraction of $(7.1^{+3.7}_{-3.2} ext{(stat)} \\pm 0.8) imes 10^{-3}$.

Set upper limits on $ ext{pi}^0$ transitions at $90\\%$ confidence level.

Abstract

We report the first evidence for the $h_{b}(\text{2P}) \to \Upsilon(\text{1S})\eta$ transition with a significance of $3.5$ standard deviations. The decay branching fraction is measured to be $\mathcal{B}[h_{b}(\text{2P}) \to \Upsilon(\text{1S})\eta]=(7.1 ~^{+3.7} _{-3.2}\pm 0.8)\times10^{-3}$, which is noticeably smaller than expected. We also set upper limits on $\pi^0$ transitions of $\mathcal{B}[h_{b}(\text{2P}) \to \Upsilon(\text{1S})\pi^0] < 1.8\times10^{-3}$, and $\mathcal{B}[h_{b}(\text{1P})\to \Upsilon(\text{1S})\pi^0] < 1.8\times10^{-3}$, at the $90\%$ confidence level. These results are obtained with a $131.4$~fb$^{-1}$ data sample collected near the $\Upsilon(\text{5S})$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.