First evidence of ψ(2S) → Ω−+

The decay ψ(2S) → Ω−+ is analyzed using 14 × 106 ψ(2S) events recorded by the Beijing Spectrometer II (BES II) at the Beijing Electron Positron Collider (BEPC). Based upon events with no missing charged tracks and a satisfactory four-constraint kinematic fit, we determine the upper limit for the branching fraction of ψ(2S) → Ω−+ to be 1.5 × 10−4 at a 90% confidence level. By including events with one missing charged track, we are able to report the first evidence of an Ω−+ signal with a statistical significance of 3.1σ. The branching fraction of ψ(2S) → Ω−+ is determined to be (4.80±1.56(stat)±1.30(sys)) × 10−5.