Study of hadronic transitions between Υ states and observation of Υ(4S)→ηΥ(1S) decay

Abstract

We present a study of hadronic transitions between Υ ( m S ) ( m = 4 , 3, 2) and Υ ( n S ) ( n = 2 , 1) resonances based on 347.5 fb − 1 of data taken with the BABAR detector at the PEP-II storage rings. We report the first observation of Υ ( 4 S ) → η Υ ( 1 S ) decay with a branching fraction B ( Υ ( 4 S ) → η Υ ( 1 S ) ) = ( 1.96 ± 0.06 stat ± 0.09 syst ) × 10 − 4 and measure the ratio of partial widths Γ ( Υ ( 4 S ) → η Υ ( 1 S ) ) / Γ ( Υ ( 4 S ) → π + π − Υ ( 1 S ) ) = 2.41 ± 0.40 stat ± 0.12 syst . We set 90% CL upper limits on the ratios Γ ( Υ ( 2 S ) → η Υ ( 1 S ) ) / Γ ( Υ ( 2 S ) → π + π − Υ ( 1 S ) ) < 5.2 × 10 − 3 and Γ ( Υ ( 3 S ) → η Υ ( 1 S ) ) / Γ ( Υ ( 3 S ) → π + π − Υ ( 1 S ) ) < 1.9 × 10 − 2 . We also present new measurements of the ratios Γ ( Υ ( 4 S ) → π + π − Υ ( 2 S ) ) / Γ ( Υ ( 4 S ) → π + π − Υ ( 1 S ) ) = 1.16 ± 0.16 stat ± 0.14 syst and Γ ( Υ ( 3 S ) → π + π − Υ ( 2 S ) ) / Γ ( Υ ( 3 S ) → π + π − Υ ( 1 S ) ) = 0.577 ± 0.026 stat ± 0.060 syst .