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Abstract:

The data collected with the DELPHI detector at centre-of-mass energies between 130 and 172 GeV, during LEP operation in 1995 and 1996, have been used to determine the hadronic and leptonic cross-sections and leptonic forward-backward asymmetries. In addition, the cross-section ratios and forward-backward asymmetries for flavour-tagged samples of light (uds), c and b quarks have been measured. No significant deviations from the Standard Model expectations are found. The results are interpreted by performing S-matrix fits to these data and to the data collected previously at the energies near the Z° resonance peak (88-93 GeV). The results are also interpreted in terms of physics beyond the Standard Model: contact interactions, R-parity violating SUSY particle exchange and of possible Z′ bosons.

Abstract:

The ����̄ forward-backward asymmetry has been determined from the average charge flow measured in a sample of 3,500,000 hadronic Z decays collected with the DELPHI detector in 1992 - 1995. The measurement is performed in an enriched ����̄ sample selected using an impact parameter tag and results in the following values for the ����̄ forward-backward asymmetry: A����̄FB (89.55 GeV) = 0.068 ± 0.018 (stat.) ± 0.0013(syst.) A����̄FB (91.26 GeV) = 0.0982 ± 0.0047(stat.) ± 0.0016(syst.) A����̄FB (92.94 GeV) = 0.123 ± 0.016 (stat.) ± 0.0027(syst.) The ����̄ charge separation required for this analysis is directly measured in the b tagged sample, while the other charge separations are obtained from a fragmentation model precisely calibrated to data. The effective weak mixing angle is deduced from the measurement to be: sin2θ1eff = 0.23186 ± 0.00083.

Abstract:

We report measurements of the D⁰, D⁺, and D⁺ s meson lifetimes using 3.7fb^-1 of e⁺e^- annihilation data collected near the ϒ(4S) resonance with the CLEO detector. The measured lifetimes of the D⁰, D⁺, and D⁺ s mesons are 408.5 ± 4.1^+3.5 -3.4 fs, 1033.6 ± 22.1^+9.9 -12.7 fs, and 486.3 ± 15.0^+4.9 -5.1 fs. The precisions of these lifetimes are comparable to those of the best previous measurements, and the systematic errors are very different. In a single experiment we find that the ratio of the D⁺ s and D⁰ lifetimes is 1.19 ± 0.04. © 1999 The American Physical Society.

Abstract:

DELPHI results are presented on the inclusive production of the neutral mesons ρ⁰, f0(980), f2(1270), K2*⁰(1430) and f2′(1525) in hadronic Z⁰ decays. They are based on about 2 million multihadronic events collected in 1994 and 1995, using the particle identification capabilities of the DELPHI Ring Imaging Cherenkov detectors and measured ionization losses in the Time Projection Chamber. The total production rates per hadronic Z⁰ decay have been determined to be: 1.19 ± 0.10 for ρ⁰; 0.164 ± 0.021 for f0(980); 0.214 ± 0.038 for f2(1270); 0.073 ± 0.023 for K2*⁰(1430); and 0.012 ± 0.006 for f2′(1525). The total production rates for all mesons and differential cross-sections for the ρ⁰, f0(980) and f2(1270) are compared with the results of other LEP experiments and with models. © 1999 Elsevier Science B.V. All rights reserved.

Abstract:

A measurement of the forward-backward asymmetry of e+e- → cc̄ and e+e- → ����̄ on the Z resonance is performed using about 3.5 million hadronic Z decays collected by the DELPHI detector at LEP in the years 1992 to 1995. The heavy quark is tagged by the exclusive reconstruction of several D meson decay modes. The forward-backward asymmetries for c and b quarks at the Z resonance are determined to be: AcFB(√s = 91.235GeV) = 0.0659 ± 0.0094 (stat) ± 0.0035 (syst) AbFB(√s = 91.235 GeV) = 0.0762 ± 0.0194 (stat) ± 0.0085 (syst) AcFB(√s = 89.434 GeV) = -0.0496 ± 0.0368 (stat) ± 0.0053 (syst) AbFB(√s = 89.434 GeV) = 0.0567 ± 0.0756 (stat) ± 0.0117 (syst) AcFB(√s = 92.990 GeV) = 0.1180 ± 0.0318 (stat) ± 0.0062 (syst) AbFB(√s = 92.990 GeV) = 0.0882 ± 0.0633 (stat) ± 0.0122 (syst) The combination of these results leads to an effective electroweak mixing angle of: sin2 θlepteff = 0.2332 ± 0.0016.