Abstract
We have performed a search for the ηb(1S) meson in the radiative decay of the Υ(2S) resonance using a sample of 91.6×106 Υ(2S) events recorded with the BABAR detector at the PEP-II B factory at the SLAC National Accelerator Laboratory. We observe a peak in the photon energy spectrum at Eγ=609.3−4.5+4.6(stat)±1.9(syst) MeV, corresponding to an ηb(1S) mass of 9394.2−4.9+4.8(stat)±2.0(syst) MeV/c2. The branching fraction for the decay Υ(2S)→γηb(1S) is determined to be [3.9±1.1(stat)−0.9+1.1(syst)]×10−4. We find the ratio of branching fractions B[Υ(2S)→γηb(1S)]/B[Υ(3S)→γηb(1S)]=0.82±0.24(stat)−0.19+0.20(syst).Received 6 March 2009DOI:https://doi.org/10.1103/PhysRevLett.103.161801©2009 American Physical Society
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