Measurement of the eta_b(1S) mass and the branching fraction for Upsilon(3S) --> gamma eta_b(1S)

The CLEO Collaboration: G. Bonvicini , D. Cinabro , A. Lincoln , M. J. Smith , P. Zhou , J. Zhu , P. Naik , J. Rademacker

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D. M. Asner K. W. Edwards J. Reed A. N. Robichaud G. Tatishvili E. J. White R. A. Briere H. Vogel P. U. E. Onyisi J. L. Rosner J. P. Alexander D. G. Cassel R. Ehrlich L. Fields R. S. Galik L. Gibbons S. W. Gray D. L. Hartill B. K. Heltsley J. M. Hunt D. L. Kreinick V. E. Kuznetsov J. Ledoux H. Mahlke-Kr\"uger J. R. Patterson D. Peterson D. Riley A. Ryd A. J. Sadoff X. Shi S. Stroiney W. M. Sun J. Yelton P. Rubin N. Lowrey S. Mehrabyan M. Selen J. Wiss M. Kornicer R. E. Mitchell M. R. Shepherd C. M. Tarbert D. Besson T. K. Pedlar J. Xavier D. Cronin-Hennessy K. Y. Gao J. Hietala R. Poling P. Zweber S. Dobbs Z. Metreveli K. K. Seth B. J. Y. Tan A. Tomaradze S. Brisbane J. Libby L. Martin A. Powell P. Spradlin C. Thomas G. Wilkinson H. Mendez J. Y. Ge D. H. Miller I. P. J. Shipsey B. Xin G. S. Adams D. Hu B. Moziak J. Napolitano K. M. Ecklund J. Insler H. Muramatsu C. S. Park E. H. Thorndike F. Yang M. Artuso S. Blusk S. Khalil R. Mountain K. Randrianarivony T. Skwarnicki J. C. Wang L. M. Zhang

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classification ✦ hep-ex

keywords gammaupsilondecaydecaysmassmillionstatisticalannihilation

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We report evidence for the ground state of bottomonium, eta_b(1S), in the radiative decay Upsilon(3S) --> gamma eta_b in e^+e^- annihilation data taken with the CLEO III detector. Using 6 million Upsilon(3S) decays, and assuming Gamma(eta_b) = 10 MeV/c^2, we obtain B(Upsilon(3S) --> gamma eta_b) = (7.1 +- 1.8 +- 1.1) X 10^{-4}, where the first error is statistical and the second is systematic. The statistical significance is about 4 sigma. The mass is determined to be M(eta_b) = 9391.8 +- 6.6 +- 2.0 MeV/c^2, which corresponds to the hyperfine splitting Delta M_{hf}(1S)_b = 68.5 +- 6.6 +- 2.0 MeV/c^2. Using 9 million Upsilon(2S) decays, we place an upper limit on the corresponding Y(2S) decay, B(Y(2S) --> gamma eta_b) < 8.4 X 10^{-4} at 90 % confidence level.

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Measurement of the eta_b(1S) mass and the branching fraction for Upsilon(3S) --> gamma eta_b(1S)

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