A measurement of the strong coupling constant α S is presented using hadronic events produced in e + e − annihilations at s =58.0 GeV from the AMY detector at TRISTAN. The measurement is based on comparisons of the distributions of thrust, heavy jet mass, total jet broadening, wide jet broadening, and energy-energy correlations with QCD calculations resummed up to next-to-leading-logarithms matched with the O ( α S 2 ) perturbative calculation. Combining the results of the individual evaluations, we find α S (58 GeV )=0.132±0.006 .
No description provided.
The photon structure function F 2 γ has been measured at an average Q 2 value of 6.8 GeV 2 using data collected by the AMY detector at the TRISTAN e + e − collider. The measured F 2 γ is compared with several QCD-based parton density models.
No description provided.
The inclusive cross section for the production of charmed D∗± mesons in two-photon processes is measured with the AMY detector at the TRISTAN e+e− collider. D∗± mesons are identified from the distribution of charged-particle transverse momenta relative to the jet axis. A data sample corresponding to an integrated luminosity of 176 pb−1 at a center-of-mass energy of 58 GeV is used to determine a cross section σ(e+e− → e+e−D∗±X) = 270 ± 49(stat) ± 38(syst) pb. The results are compared with theoretical expectations based on the Vector Meson Dominance, direct quark-parton model, and resolved photon processes.
No description provided.
Reduced acceptance region to compare with the TOPAZ results.
The forward-backward asymmetry in e + e − → b b at s = 57.9 GeV and the b-quark branching ratio to muons have been measured using neural networks. Unlike previous methods for measuring the b b forward-backward asymmetry where the estimated background from c -quark decays and other sources are subtracted, here events are categorized as either b b or non- b b events by neural networks based on event-by-event characteristics. The determined asymmetry is −0.429 ± 0.044 (stat) ± 0.047 (sys) and is consistent with the prediction of the standard model. The measured B B mixing parameter is 0.136 ± 0.037 (stat) ± 0.040 (sys) ± 0.002 (model) and the measured b-quark branching ratio to muons is 0.122 ± 0.006 (stat) ± 0.007 (sys).
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A study of e + e − annihilations into final states containing a single energetic photon with no accompanying particles is made at a center of mass energy of 57.8 GeV. The measured cross section is consistent with expectations from standard model processes and is used to set limits on the masses of the scalar electron and photino particles predicted by supersymmetry theories. If the photino is assumed to be massless, the 90% confidence level lower limit on the mass of the degenerate scalar electron is 65.5 GeV. If the results of all the single photon experiments are combined, this lower limit increases to 79.3 GeV.
No description provided.
Measurements of open charm production in photon-photon collisions made with the AMY detector at TRISTAN are reported. Charmed hadrons were identified by detecting the high momentum muons or electrons from their semileptonic decays. The data sample corresponds to an integrated luminosity of 275 pb −1 at an average center of mass energy of 58 GeV. Results are presented in the form of cross sections of inclusive leptons from charm for both muons and electrons. The measured cross section is 1.8 standard deviations higher than theoretical predictions based on the direct and photon-gluon fusion process, where the mass of charm quark is assumed to be 1.6 GeV.
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