Observation of the isospin breaking decay $\Upsilon(10860)\to\Upsilon(1S)f_0(980)\to\Upsilon(1S)\eta\pi^0$ with the Belle II detector

TL;DR

This paper reports the observation of isospin breaking decay of the $
0860$ resonance into $1S$ and $ heta ext{pi}^0$ via mixing of scalar mesons, using Belle II data to estimate the process fraction.

Contribution

The study provides the first estimate of the isospin breaking decay process involving $a_0^0(980)$ and $f_0(980)$ mixing at Belle II, highlighting the potential to observe about a hundred such events.

Findings

Estimated the fraction of the isospin breaking decay process.

Projected about a hundred events could be collected at Belle II.

Demonstrated the feasibility of observing this decay with current collider parameters.

Abstract

Using the Belle data on the decay $\Upsilon(10860)\to \Upsilon(1S)f_0(980)\to\Upsilon(1S)\pi^+\pi^-$, we estimate the fraction of the process $\Upsilon(10860)\to\Upsilon(1S)f_0(980)\to \Upsilon(1S)\eta\pi^0$, caused by the mixing of $a^0_0(980)$ and $f_0(980)$ resonances that breaks the isotopic invariance due to the $K^+$ and $K^0$ meson mass difference. With an instantaneous luminosity of $8\times10^{35}$ cm$^2\cdot$\,s$^{-1}$ at the SuperKEKB collider, one can collect with the Belle II detector about a hundred $\Upsilon(10860)\to\Upsilon(1S)\eta\pi^0$ events in the narrow region of the $\eta\pi^0$ invariant mass near the $K\bar K$ thresholds in a time roughly spent on the present Belle experiment.