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Search for radiative decays of $Υ (1 S)$ into $η$ and $η'$

S. B. Athar¹, R. Patel¹, V. Potlia¹, H. Stoeck¹, J. Yelton¹, P. Rubin², C. Cawlfield³, B. I. Eisenstein³, I. Karliner³ et al. (CLEO Collaboration)

I. Karliner³, D. Kim³, N. Lowrey³, P. Naik³, C. Sedlack³, M. Selen³, E. J. White³, J. Wiss³, M. R. Shepherd⁴, D. Besson⁵, T. K. Pedlar⁶, D. Cronin-Hennessy⁷, K. Y. Gao⁷, D. T. Gong⁷, J. Hietala⁷, Y. Kubota⁷, T. Klein⁷, B. W. Lang⁷, R. Poling⁷, A. W. Scott⁷, A. Smith⁷, S. Dobbs⁸, Z. Metreveli⁸, K. K. Seth⁸, A. Tomaradze⁸, P. Zweber⁸, J. Ernst⁹, H. Severini¹⁰, S. A. Dytman¹¹, W. Love¹¹, V. Savinov¹¹, O. Aquines¹², Z. Li¹², A. Lopez¹², S. Mehrabyan¹², H. Mendez¹², J. Ramirez¹², G. S. Huang¹³, D. H. Miller¹³, V. Pavlunin¹³, B. Sanghi¹³, I. P. J. Shipsey¹³, B. Xin¹³, G. S. Adams¹⁴, M. Anderson¹⁴, J. P. Cummings¹⁴, I. Danko¹⁴, J. Napolitano¹⁴, Q. He¹⁵, J. Insler¹⁵, H. Muramatsu¹⁵, C. S. Park¹⁵, E. H. Thorndike¹⁵, T. E. Coan¹⁶, Y. S. Gao¹⁶, F. Liu¹⁶, M. Artuso¹⁷, S. Blusk¹⁷, J. Butt¹⁷, J. Li¹⁷, N. Menaa¹⁷, R. Mountain¹⁷, S. Nisar¹⁷, K. Randrianarivony¹⁷, R. Redjimi¹⁷, R. Sia¹⁷, T. Skwarnicki¹⁷, S. Stone¹⁷, J. C. Wang¹⁷, K. Zhang¹⁷, S. E. Csorna¹⁸, G. Bonvicini¹⁹, D. Cinabro¹⁹, M. Dubrovin¹⁹, A. Lincoln¹⁹, D. M. Asner²⁰, K. W. Edwards²⁰, R. A. Briere²¹, I. Brock²¹, J. Chen²¹, T. Ferguson²¹, G. Tatishvili²¹, H. Vogel²¹, M. E. Watkins²¹, J. L. Rosner²², N. E. Adam²³, J. P. Alexander²³, K. Berkelman²³, D. G. Cassel²³, J. E. Duboscq²³, K. M. Ecklund²³, R. Ehrlich²³, L. Fields²³, R. S. Galik²³, L. Gibbons²³, R. Gray²³, S. W. Gray²³, D. L. Hartill²³, B. K. Heltsley²³, D. Hertz²³, C. D. Jones²³, J. Kandaswamy²³, D. L. Kreinick²³, V. E. Kuznetsov²³, H. Mahlke-Krüger²³, T. O. Meyer²³, P. U. E. Onyisi²³, J. R. Patterson²³, D. Peterson²³, J. Pivarski²³, D. Riley²³, A. Ryd²³, A. J. Sadoff²³, H. Schwarthoff²³, X. Shi²³, S. Stroiney²³, W. M. Sun²³, T. Wilksen²³, and M. Weinberger²³ (CLEO Collaboration)

¹University of Florida, Gainesville, Florida 32611, USA
²George Mason University, Fairfax, Virginia 22030, USA
³University of Illinois, Urbana-Champaign, Illinois 61801, USA
⁴Indiana University, Bloomington, Indiana 47405, USA
⁵University of Kansas, Lawrence, Kansas 66045, USA
⁶Luther College, Decorah, Iowa 52101, USA
⁷University of Minnesota, Minneapolis, Minnesota 55455, USA
⁸Northwestern University, Evanston, Illinois 60208, USA
⁹State University of New York at Albany, Albany, New York 12222, USA
¹⁰University of Oklahoma, Norman, Oklahoma 73019, USA
¹¹University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
¹²University of Puerto Rico, Mayaguez, Puerto Rico 00681
¹³Purdue University, West Lafayette, Indiana 47907, USA
¹⁴Rensselaer Polytechnic Institute, Troy, New York 12180, USA
¹⁵University of Rochester, Rochester, New York 14627, USA
¹⁶Southern Methodist University, Dallas, Texas 75275, USA
¹⁷Syracuse University, Syracuse, New York 13244, USA
¹⁸Vanderbilt University, Nashville, Tennessee 37235, USA
¹⁹Wayne State University, Detroit, Michigan 48202, USA
²⁰Carleton University, Ottawa, Ontario, Canada K1S 5B6
²¹Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
²²Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA
²³Cornell University, Ithaca, New York 14853

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Phys. Rev. D 76, 072003 – Published 11 October, 2007

DOI: https://doi.org/10.1103/PhysRevD.76.072003

Abstract

We report on a search for the radiative decay of $Υ (1 S)$ to the pseudoscalar mesons $η$ and $η^{'}$ in $(21.2 \pm 0.2) \times 10^{6}$ $Υ (1 S)$ decays collected with the CLEO III detector at the Cornell Electron Storage Ring. The $η$ meson was reconstructed in the three modes $η \to γ γ$ , $η \to π^{+} π^{-} π^{0}$ , or $η \to π^{0} π^{0} π^{0}$ . The $η^{'}$ meson was reconstructed in the mode $η^{'} \to π^{+} π^{-} η$ with $η$ decaying through any of the above three modes, and also $η^{'} \to γ ρ^{0}$ , where $ρ^{0} \to π^{+} π^{-}$ . Five out of the seven submodes are found to have very low backgrounds. In four of them we find no signal candidates and in one [ $Υ (1 S) \to γ η^{'}$ , $η^{'} \to π^{+} π^{-} η$ , $η \to π^{+} π^{-} π^{0}$ ] there are two good signal candidates, which is insufficient evidence to claim a signal. The other two submodes ( $η \to γ γ$ and $η^{'} \to γ ρ$ ) are background limited, and show no excess of events in their signal regions. We combine the results from different channels and obtain upper limits at the 90% C.L. which are $B (Υ (1 S) \to γ η) < 1.0 \times 10^{- 6}$ and $B (Υ (1 S) \to γ η^{'}) < 1.9 \times 10^{- 6}$ . Our limits are an order of magnitude tighter than the previous ones and below the predictions made by some theoretical models.