Phys. Rev. D
74,
012003
(2006)
[17 pages]
Measurement of the direct photon momentum spectrum in Υ(1S), Υ(2S), and Υ(3S) decays
D. Besson et al. CLEO Collaboration
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D. Besson1, S. Henderson1, T. K. Pedlar2, D. Cronin-Hennessy3, K. Y. Gao3, D. T. Gong3, J. Hietala3, Y. Kubota3, 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
Received 25 December 2005; published 14 July 2006
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(1S)→γgg, Υ(2S)→γgg, Υ(3S)→γgg. The latter two of these are first measurements. Our analysis procedures differ from previous ones in the following ways: (a) background estimates (primarily from π0 decays) are based on isospin symmetry rather than a determination of the π0 spectrum, which permits measurement of the Υ(2S) and Υ(3S) direct photon spectra without explicit corrections for π0 backgrounds from, e.g., χbJ 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(2S)→ππΥ(1S) to obtain a tagged sample of Υ(1S)→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→ggg (Rγ=B(ggγ)/B(ggg)) to be Rγ(1S)=(2.70±0.01±0.13±0.24)%, Rγ(2S)=(3.18±0.04±0.22±0.41)%, and Rγ(3S)=(2.72±0.06±0.32±0.37)%, where the errors shown are statistical, systematic, and theoretical model dependent, respectively. Given a value of Q2, one can estimate a value for the strong coupling constant αs(Q2) from Rγ.
© 2006 The American Physical Society
URL:
http://link.aps.org/doi/10.1103/PhysRevD.74.012003
DOI:
10.1103/PhysRevD.74.012003
PACS:
13.20.−v, 13.40.Hq, 14.40.Gx
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