The hadronic transitions from Υ(2S) to Υ(1S)

Abstract

Using the ARGUS detector at DORIS, we have investigated the hadronic transitions of the Υ(2S) to the Υ(1S). The decays to Υ(1S)π⁺π⁻, Υ(1S)π⁰π⁰ and Υ(1S)η where the Υ(1S) subsequently decays intoe ⁺ e ⁻ and Υ(1S)η have been investigated. The transition via two charged pions has also been studied inclusively. We obtain branching ratios of the Υ(2S) into Υ(1S)π⁺π⁻ of (18.1±0.5±1.0)%, into Υ(1S)π⁰π⁰ of (9.5±1.9±1.9)% and into Υ(1S)η of less than 0.5% with 90% confidence. From the exclusive events we find the leptonic branching ratios of the Υ(1S) to beB _ee=(2.42±0.14±0.14)% andB _μμ=(2.30±0.25±0.13)%. Kinematical parameters of the two pion transitions have been investigated in detail and found to be consistent with current algebra and colour-field multipole expansion.