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 ^ 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.