Using the Crystal Ball detector at the e+e- storage ring DORIS II, we have measured the energy spectrum of direct photons from Υ(1S) decays. According to QCD, these photons result from the decays of the Υ(1S) resonance into one photon and two gluons, Υ(1S) -> gamma g g -> gamma + hadrons. The shape of our spectrum does not agree with that calculated in lowest order QCD, but can be described well by a prediction incorporating gluon self-interaction. Using this fit, the ratio R-gamma = Gamma(Y -> gamma g g) / Gamma(Y -> ggg) is determined to be (2.7+-0.2+-0.4)%. From this ratio we deduce the strong coupling constant in the MS scheme at Q2 = 2.2 GeV^2 and find alpha-s = 0.25+-0.02+-0.04.
Measurement of the direct photon spectrum from Υ(1S) decays / Bizzeti, Andrea; Schütte, J.; Antreasyan, D.; Bieler, C. h.; Bienlein, J. K.; Bloom, E. D.; Brock, I.; Brockmüller, K.; Cartacci, A.; Cavalli Sforza, M.; Compagnucci, A.; Conforto, G.; Cooper S., L; Coyne, D.; Fairfield, K. H.; Folger, G.; Fridman, A.; Glaser, G.; Godfrey, G.; Graaf, K.; Heimlich, F. H.; Heinsius, F. H.; Hofstadter, R.; Irion, J.; Jakubowski, Z.; Janssen, H.; Karch, K.; Keh, S.; Kiel, T.; Kilian, H.; Kirkbride, I.; Kobel, M.; Koch, W.; König, A. C.; Königsmann, K.; Krüger, S.; Landi, G.; Lekebusch, R.; Lowe, S.; Lurz, B.; Marsiske, H.; Maschmann, W.; Mcbride, P.; Metzger, W. J.; Monteleoni, B.; Muryn, B.; Niczyporuk, B.; Nowak, G.; Pelfer, P. G.; Reidenbach, M.; Scheer, M.; Schmitt, P.; Schotanus, J.; Sievers, D.; Skwarnicki, T.; Stock, V.; Strauch, K.; Strohbusch, U.; Tompkins, J.; Van Uitert, B.; Van De Walle, R. T.; Voigt, A.; Volland, U.; Wachs, K.; Wegener, H.; Williams, D. A.. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - STAMPA. - 267:(1991), pp. 286-292. [10.1016/0370-2693(91)91262-T]
Measurement of the direct photon spectrum from Υ(1S) decays
BIZZETI, Andrea;
1991
Abstract
Using the Crystal Ball detector at the e+e- storage ring DORIS II, we have measured the energy spectrum of direct photons from Υ(1S) decays. According to QCD, these photons result from the decays of the Υ(1S) resonance into one photon and two gluons, Υ(1S) -> gamma g g -> gamma + hadrons. The shape of our spectrum does not agree with that calculated in lowest order QCD, but can be described well by a prediction incorporating gluon self-interaction. Using this fit, the ratio R-gamma = Gamma(Y -> gamma g g) / Gamma(Y -> ggg) is determined to be (2.7+-0.2+-0.4)%. From this ratio we deduce the strong coupling constant in the MS scheme at Q2 = 2.2 GeV^2 and find alpha-s = 0.25+-0.02+-0.04.
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