Study of Υ(10753) decays to π+π−Υ(nS) final states at Belle II

A bstract We present an analysis of the process e + e − → π + π − Υ( nS ) (where n = 1, 2, or 3) reconstructed in 19 . 6 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 − → π + π − Υ( nS ) process, we report the first observation of Υ(10753) decays to the π + π − Υ(1 S ) and π + π − Υ(2 S ) final states, and find no evidence for decays to π + π − Υ(3 S ). Possible intermediate states in the π + π − Υ(1 S, 2 S ) transitions are also investigated, and no evidence for decays proceeding via the π∓Zb± π ∓ Z b ± or f 0 (980)Υ( nS ) intermediate states is found. We measure Born cross sections for the e + e − → π + π − Υ( nS ) process that, combined with results from Belle, obtain the mass and width of Υ(10753) to be (10756 . 6 ± 2 . 7 ± 0 . 9) MeV/ c 2 and (29 . 0 ± 8 . 8 ± 1 . 2) MeV, respectively. The relative ratios of the Born cross sections at the Υ(10753) resonance peak are also reported for the first time.