Guy Wilkinson

Abstract:

The bb̄ 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 bb̄ sample selected using an impact parameter tag and results in the following values for the bb̄ forward-backward asymmetry: Abb̄FB (89.55 GeV) = 0.068 ± 0.018 (stat.) ± 0.0013(syst.) Abb̄FB (91.26 GeV) = 0.0982 ± 0.0047(stat.) ± 0.0016(syst.) Abb̄FB (92.94 GeV) = 0.123 ± 0.016 (stat.) ± 0.0027(syst.) The bb̄ 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:

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- → bb̄ 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.

Abstract:

The average lifetime of weakly decaying b-baryons was studied using 3.6 million Z0 hadronic decays collected by the DELPHI detector at LEP. The measurement of the proper decay time distribution of secondary vertices was used on three complementary samples. The first sample consisted of events with a fully reconstructed Λ+c and an opposite charge lepton, or an oppositely charged lepton pair accompanied by a Λ0. The other two samples were more inclusive, where b-baryon semileptonic decays were recognized by the presence of either a proton identified by the RICH detector or a Λ0 and a lepton of charge opposite to that of the proton. The combined result was: τ(b-baryon) = 1.14 ± 0.08 (stat) ± 0.04 (syst) ps.

Abstract:

From data corresponding to an integrated luminosity of 53.5 pb-1 taken during the 183 GeV run in 1997, DELPHI has measured the W mass from direct reconstruction of WW → ℓv̄qq̄ and WW → qq̄qq̄ events. Combining these channels, a value of mw = 80.238 ± 0.154(stat) ± 0.035(syst) ± 0.035(fsi) + 0.021(LEP)GeV/c2 is obtained, where fsi denotes final state interaction. Combined with the W mass obtained by DELPHI from the WW production cross-section and with the direct measurement at 172 GeV this leads to a measured value of mw = 80.270 ± 0.137(stat) ± 0.031(syst) ± 0.030(fsi) ± 0.021(LEP)GeV/c2, in good agreement with the Standard Model expectation. The width of the W boson is also measured, giving the value Γw= 2.48 ± 0.40(stat) ± 0.10(syst)GeV/c2. © 1999 Elsevier Science B.V. All rights reserved.