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

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