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Measurement of the direct photon momentum spectrum in $Υ (1 S)$ , $Υ (2 S)$ , and $Υ (3 S)$ decays

D. Besson¹, S. Henderson¹, T. K. Pedlar², D. Cronin-Hennessy³, K. Y. Gao³, D. T. Gong³, J. Hietala³, Y. Kubota³, T. Klein³ et al. (CLEO Collaboration)

T. Klein³, B. W. Lang³, S. Z. Li³, R. Poling³, A. W. Scott³, A. Smith³, S. Dobbs⁴, Z. Metreveli⁴, K. K. Seth⁴, A. Tomaradze⁴, P. Zweber⁴, J. Ernst⁵, K. Arms⁶, H. Severini⁷, D. M. Asner⁸, S. A. Dytman⁸, W. Love⁸, S. Mehrabyan⁸, J. A. Mueller⁸, V. Savinov⁸, Z. Li⁹, A. Lopez⁹, H. Mendez⁹, J. Ramirez⁹, G. S. Huang¹⁰, D. H. Miller¹⁰, V. Pavlunin¹⁰, B. Sanghi¹⁰, I. P. J. Shipsey¹⁰, G. S. Adams¹¹, M. Cravey¹¹, J. P. Cummings¹¹, I. Danko¹¹, J. Napolitano¹¹, Q. He¹², H. Muramatsu¹², C. S. Park¹², E. H. Thorndike¹², T. E. Coan¹³, Y. S. Gao¹³, F. Liu¹³, R. Stroynowski¹³, M. Artuso¹⁴, C. Boulahouache¹⁴, S. Blusk¹⁴, J. Butt¹⁴, O. Dorjkhaidav¹⁴, J. Li¹⁴, N. Menaa¹⁴, G. Moneti¹⁴, R. Mountain¹⁴, R. Nandakumar¹⁴, K. Randrianarivony¹⁴, R. Redjimi¹⁴, R. Sia¹⁴, T. Skwarnicki¹⁴, S. Stone¹⁴, J. C. Wang¹⁴, K. Zhang¹⁴, S. E. Csorna¹⁵, G. Bonvicini¹⁶, D. Cinabro¹⁶, M. Dubrovin¹⁶, A. Bornheim¹⁷, S. P. Pappas¹⁷, A. J. Weinstein¹⁷, R. A. Briere¹⁸, G. P. Chen¹⁸, J. Chen¹⁸, T. Ferguson¹⁸, G. Tatishvili¹⁸, H. Vogel¹⁸, M. E. Watkins¹⁸, J. L. Rosner¹⁹, N. E. Adam²⁰, J. P. Alexander²⁰, K. Berkelman²⁰, D. G. Cassel²⁰, V. Crede²⁰, J. E. Duboscq²⁰, K. M. Ecklund²⁰, R. Ehrlich²⁰, L. Fields²⁰, R. S. Galik²⁰, L. Gibbons²⁰, B. Gittelman²⁰, R. Gray²⁰, S. W. Gray²⁰, D. L. Hartill²⁰, B. K. Heltsley²⁰, D. Hertz²⁰, C. D. Jones²⁰, J. Kandaswamy²⁰, D. L. Kreinick²⁰, V. E. Kuznetsov²⁰, H. Mahlke-Krüger²⁰, T. O. Meyer²⁰, P. U. E. Onyisi²⁰, J. R. Patterson²⁰, D. Peterson²⁰, E. A. Phillips²⁰, J. Pivarski²⁰, D. Riley²⁰, A. Ryd²⁰, A. J. Sadoff²⁰, H. Schwarthoff²⁰, X. Shi²⁰, M. R. Shepherd²⁰, S. Stroiney²⁰, W. M. Sun²⁰, D. Urner²⁰, T. Wilksen²⁰, K. M. Weaver²⁰, M. Weinberger²⁰, S. B. Athar²¹, P. Avery²¹, L. Breva-Newell²¹, R. Patel²¹, V. Potlia²¹, H. Stoeck²¹, J. Yelton²¹, P. Rubin²², C. Cawlfield²³, B. I. Eisenstein²³, G. D. Gollin²³, I. Karliner²³, D. Kim²³, N. Lowrey²³, P. Naik²³, C. Sedlack²³, M. Selen²³, E. J. White²³, J. Williams²³, J. Wiss²³, and K. W. Edwards²⁴ (CLEO Collaboration)

¹University of Kansas, Lawrence, Kansas 66045, USA
²Luther College, Decorah, Iowa 52101, USA
³University of Minnesota, Minneapolis, Minnesota 55455, USA
⁴Northwestern University, Evanston, Illinois 60208, USA
⁵State University of New York at Albany, Albany, New York 12222, USA
⁶Ohio State University, Columbus, Ohio 43210, USA
⁷University of Oklahoma, Norman, Oklahoma 73019, USA
⁸University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
⁹University of Puerto Rico, Mayaguez, Puerto Rico 00681
¹⁰Purdue University, West Lafayette, Indiana 47907, USA
¹¹Rensselaer Polytechnic Institute, Troy, New York 12180, USA
¹²University of Rochester, Rochester, New York 14627, USA
¹³Southern Methodist University, Dallas, Texas 75275, USA
¹⁴Syracuse University, Syracuse, New York 13244, USA
¹⁵Vanderbilt University, Nashville, Tennessee 37235, USA
¹⁶Wayne State University, Detroit, Michigan 48202, USA
¹⁷California Institute of Technology, Pasadena, California 91125, USA
¹⁸Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
¹⁹Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA
²⁰Cornell University, Ithaca, New York 14853
²¹University of Florida, Gainesville, Florida 32611, USA
²²George Mason University, Fairfax, Virginia 22030, USA
²³University of Illinois, Urbana-Champaign, Illinois 61801, USA
²⁴Carleton University, Ottawa, Ontario, Canada K1S 5B6, and the Institute of Particle Physics, Montreal, Canada

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Phys. Rev. D 74, 012003 – Published 14 July, 2006

DOI: https://doi.org/10.1103/PhysRevD.74.012003

Abstract

Using data taken with the CLEO III detector at the Cornell Electron Storage Ring, we have investigated the direct photon spectrum in the decays $Υ (1 S) \to γ g g$ , $Υ (2 S) \to γ g g$ , $Υ (3 S) \to γ g g$ . The latter two of these are first measurements. Our analysis procedures differ from previous ones in the following ways: (a) background estimates (primarily from $π^{0}$ decays) are based on isospin symmetry rather than a determination of the $π^{0}$ spectrum, which permits measurement of the $Υ (2 S)$ and $Υ (3 S)$ direct photon spectra without explicit corrections for $π^{0}$ backgrounds from, e.g., $χ_{b J}$ states, (b) we estimate the branching fractions with a parametrized functional form (exponential) used for the background, and c) we use the high-statistics sample of $Υ (2 S) \to π π Υ (1 S)$ to obtain a tagged sample of $Υ (1 S) \to γ + X$ events, for which there are no QED backgrounds. We determine values for the ratio of the inclusive direct photon decay rate to that of the dominant three-gluon decay $Υ \to g g g (R_{γ} = B (g g γ) / B (g g g))$ to be $R_{γ} (1 S) = (2.70 \pm 0.01 \pm 0.13 \pm 0.24) %$ , $R_{γ} (2 S) = (3.18 \pm 0.04 \pm 0.22 \pm 0.41) %$ , and $R_{γ} (3 S) = (2.72 \pm 0.06 \pm 0.32 \pm 0.37) %$ , where the errors shown are statistical, systematic, and theoretical model dependent, respectively. Given a value of $Q^{2}$ , one can estimate a value for the strong coupling constant $α_{s} (Q^{2})$ from $R_{γ}$ .