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Open Access item Evidence for the eta(b)(1S) Meson in Radiative Y(2S) Decay

Authors:Babar Collaboration
Azzolini, Virginia
López-March, Neus
Martínez-Vidal, Fernando
Milanés, Diego A.
Oyanguren, Arantza
Aubert, B.
Issue Date:15-Oct-2009
Publisher:American Physical Society
Citation:Physical Review Letters 103 (16): 161801 (2009)
Abstract:We have performed a search for the eta_b(1S) meson in the radiative decay of the Upsilon(2S) resonance using a sample of 91.6 million Upsilon(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 E_gamma = 609.3 {+4.6} {-4.5} (stat) +/- 1.9 (syst) MeV, corresponding to an eta_b(1S) mass of 9394.2 {+4.8} {-4.9} (stat) +/- 2.0 (syst) MeV/c^2. The branching fraction for the decay Upsilon(2S) --> gamma eta_b(1S) is determined to be [3.9 +/-1.1 (stat) {+1.1} {-0.9} (syst)] x 10^(-4). We find the ratio of branching fractions B[Upsilon(2S) --> gamma eta_b(1S)]/B[Upsilon(3S) --> gamma eta_b(1S)] = 0.82 +/- 0.24 (stat) {+0.20}{-0.19} (syst).
Publisher version (URL):http://dx.doi.org/ 10.1103/PhysRevLett.103.161801
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