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arXiv · 0809.1672

Observation of the bottomonium ground state, eta_b, at BaBar

Philippe Grenier
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Abstract

We present the first observation of the bottomonium ground state eta_b(1S) in the photon energy spectrum using a sample of 109+/-1 million of Upsilon(3S) events recorded at the Upsilon(3S) energy with the BaBar detector at the PEP-II B factory at SLAC. A peak at E_gamma = 921.2 {+2.1}{-2.8}(stat) +/- 2.4(syst) MeV observed with a significance of 10 standard deviations in the photon energy spectrum is interpretated as being due to the radiative transition Upsilon(3S) -> gamma eta_b(1S). This photon energy corresponds to an eta_b(1S) mass of 9388.9 {+3.1}{-2.3}(stat) +/- 2.7(syst) MeV/c2. The hyperfine Upsilon(1S)-eta_b(1S) mass splitting is 71.4 {+2.3}{-3.1}(stat) +/- 2.7(syst) MeV/c2. The branching fraction for this radiative \Upsilon(3S) decay is obtained as (4.8 +/- 0.5(stat) +/- 1.2 (syst)) x 10^(-4).

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Philippe Grenier. 2008-09-09. Observation of the bottomonium ground state, eta_b, at BaBar. https://arxiv.org/abs/0809.1672

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