Using the Belle data on the decay $\mathrm{\Upsilon }(10860)\to \mathrm{\Upsilon }(1S)f_0(980)\to \mathrm{\Upsilon }(1S){\pi }^{+}{\pi }^{-}$, we estimate the fraction of the process $\mathrm{\Upsilon }(10860)\to \mathrm{\Upsilon }(1S)f_0(980)\to \mathrm{\Upsilon }(1S)\eta {\pi }^0$, 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 $8\times {10}^{35}{\mathrm{cm}}^{-2}·{\mathrm{s}}^{-1}$ at the SuperKEKB collider, one can collect with the Belle II detector about a hundred $\mathrm{\Upsilon }(10860)\to \mathrm{\Upsilon }(1S)\eta {\pi }^0$ events in the narrow region of the $\eta {\pi }^0$ invariant mass near the $K\overline{K}$ thresholds in a time roughly spent on the present Belle experiment.

• Received 7 September 2017

DOI:https://doi.org/10.1103/PhysRevD.96.091501