Guy Wilkinson

Abstract:

The interference between initial and final state radiation in the process e+e- → μ+μ- at √s ≈ MZ has been studied by measuring the forward-backward asymmetry as a function of the acoplanarity angle between the final state muons. The interference is expected to be sensitive to the space-time separation of the initial and final state radiation. The measured asymmetry distribution has been compared to theoretical predictions using the KORALZ generator, with and without script O sign(α) interference. The magnitude of the interference between initial and final state radiation was found to be of the order predicted and to follow the expected distribution. Using the theoretical predictions, a value of ΓZ = 2.50 ± 0.21 (stat.) ±0.06 (syst.) GeV . has been extracted. The interpretation of this result is discussed. There is an additional uncertainty in the estimate of ΓZ from as yet uncalculated higher order interference terms. By assuming a value of ΓZ consistent with the world average, the data were used to estimate the size of these uncalculated corrections. © Springer-Verlag 1996.

Abstract:

This paper presents an update of the measurement of the mean lifetime of the Bs0 meson. Combining Ds - ℓ, Ds - h, φ - ℓ and inclusive Ds final states from the 3.2 million hadronic Z decays collected by DELPHI between 1991 and 1994, the Bs0 mean lifetime was measured to be: τ(Bs0) = 1.67 ± 0.14ps. © Springer-Verlag 1996.

Abstract:

The inclusive production of the neutral vector mesons K*0(892) and φ(1020), and of the tensor meson K2*0(1430), in hadronic decays of the Z has been measured by the DELPHI detector at LEP. The average production rates per hadronic Z decay have been determined to be 0.77 ± 0.08 K*0(892), 0.104 ± 0.008 φ(1020) and 0.079 ± 0.040 K2*0(1430). The ratio of the tensor-to-vector meson production yields, 〈K2*0(1430)〉/〈K *0(892)〉 = 0.10± 0.05, is smaller than the 〈f2(1270)〉/〈ρ0(770)〉 and 〈f2′(1525)〉 /〈φ(1020)〉 ratios measured by DELPHI. The production rates and differential cross sections are compared with the predictions of JETSET 7.4 tuned to the DELPHI data and of HERWIG 5.8. The K*0(892) and φ(1020) data are compatible with model predictions, but a large disagreement is observed for the K2*0(1430).

Abstract:

A measurement of the mass difference, Δmd, between the two physical Bd0 states has been obtained from the analysis of the impact parameter distribution of a lepton emitted at large transverse momentum (pt) relative to the jet axis and from the analysis of the flight distance distribution of secondary vertices tagged by either a high pt lepton or an identified kaon. In the opposite hemisphere of the event, the charge of the initial quark has been evaluated using a high pt lepton, a charged kaon or the mean jet charge. With 1.7 million hadronic Z0 decays recorded by DELPHI between 1991 and 1993, Δmd is found to be: Δmd = 0.531-0.046+0.050 (stat.) ± 0.078 (syst.) ps-1. © Springer-Verlag 1996.

Abstract:

The partial decay width of the Z to bb̄ quark pairs has been measured by the DELPHI detector at LEP. B-hadrons, containing b-quarks, were tagged by several methods using tracks with large impact parameters to the primary vertex complemented sometimes by event shape variables or using leptons with high transverse momentum relative to the hadron. In order to reduce the systematic uncertainties, in all methods the b-tagging efficiency has been extracted directly from the data. Combining all methods, the value: Γbb̄/Γhad = 0.2216 ± 0.0016(stat.) ± 0.0021(syst.) was found, where the cc̄ production fraction was fixed to its Standard Model value. © Springer-Verlag 1996.