Study of $Υ(10753)$ decays to $π^{+}π^{-}Υ(nS)$ final states at Belle II

Abstract: We present an analysis of the process $$e<sup>{+}e<sup>{-}\to\pi<sup>{+}\pi<sup>{-}\Upsilon(nS)$$ (where $n$ = 1, 2, or 3) reconstructed in $19.6\rm$ $\rm fb<sup>{-1}$ of Belle II data during a special run of the SuperKEKB collider at four energy points near the peak of the $\Upsilon(10753)$ resonance. By analyzing the mass distribution of the $\pi<sup>+\pi<sup>-\Upsilon(nS)$ system and the Born cross sections of the $$e<sup>{+}e<sup>{-}\to\pi<sup>{+}\pi<sup>{-}\Upsilon(nS)$$ process, we report the first observation of $\Upsilon(10753)$ decays to the $\pi<sup>{+}\pi<sup>{-}\Upsilon(1S)$ and $\pi<sup>{+}\pi<sup>{-}\Upsilon(2S)$ final states, and find no evidence for decays to $\pi<sup>{+}\pi<sup>{-}\Upsilon(3S)$. Possible intermediate states in the $\pi<sup>+\pi<sup>-\Upsilon(1S,2S)$ transitions are also investigated, and no evidence for decays proceeding via the $\pi^\mp Z_b<sup>\pm$ or $f_0(980)\Upsilon(nS)$ intermediate states is found. We measure Born cross sections for the $$e<sup>{+}e<sup>{-}\to\pi<sup>{+}\pi<sup>{-}\Upsilon(nS)$$ process that, combined with results from Belle, improve the precision of measurements of the $\Upsilon(10753)$ mass and width by nearly a factor of two to $(10756.3\pm2.7\pm0.6)$ MeV/$c<sup>2$ and $(29.7\pm8.5\pm1.1)$ MeV, respectively. The relative ratios of the Born cross sections at the $\Upsilon(10753)$ resonance peak are also reported for the first time.