Guy Wilkinson

Abstract:

A study of B meson decays into DlX final states is presented. In these events, neutral and charged D mesons originate predominantly from B+ and B0 decays, respectively. The dilution of this correlation due to D** production has been taken into account. From 263 700 hadronic Z0 decays collected in 1991 with the DELPHI detector at the LEP collider, 92 D0→K-π+, 35 D+→K-π+π+ and 61 D*0→D0π+ followed by D0→K-π+ or D0→K-π+π+π -, are found with an associated lepton of the same charge as the kaon. From the D0l- and D*+l-, the probability fd that a b quark hadronizes into a B- (or {Mathematical expression}) meson is found to be 0.44 ±0.08±0.09, corresponding to a total (Bs+Λb) hadronization fraction of 0.12-0.12+0.24. By reconstructing the energy of each B meson, the b quark fragmentation is directly measured for the first time. The mean value of the B meson energy fraction is: {Mathematical expression} Reconstructing D-lepton vertices, the following B lifetimes are measured: {Mathematical expression} and an average τ(B)=1.23-0.13+0.14(stat.)±0.15(syst.) ps is found. Allowing for decays into {Mathematical expression}, the B+ and B0 lifetimes are: {Mathematical expression} © 1993 Springer-Verlag.

Abstract:

A new measurement of αs is obtained from the distributions in thrust, heavy jet mass, energy-energy correlation and two recently introduced jet broadening variables following a method proposed by Catani, Trentadue, Turnock and Webber. This method includes the full calculation of O(s2) terms and leading and next-to-leading logarithms resummed to all orders of αs. The analysis is based on data taken with the DELPHI detector at LEP during 1991. I its found that the inclusion of the resummed leading and next-to-leading logarithms reduces the scale dependence of αs and allows an extension of the fit range towards the infrared limit of the kinematical range. The combined value for αs obtained at the scale μ2=MZ2 is: {Mathematical expression} © 1993 Springer-Verlag.

Abstract:

A search for lepton flavour violation through the decays Z0 → eμ, eτ and μτ was made with the DELPHI detector at LEP, using a sample corresponding to an integrated luminosity of 11.2 pb-1. The number of candidates was consistent with the estimated background. The upper limit on the branching ratio (at 95% confidence level) for Z0 → eμ was 3.2 × 10-5, for Z0 → eτ was 10.8 × 10-5 and for Z0 → μτ was 13.5 × 10-5. © 1993.

Abstract:

A study of inclusive production of the meson resonances ρ0, K*0 (892), f{hook}0 (975) and f{hook}2 (1270) in hadronic decays of the Z0 is presented. The measured mean meson multiplicity per hadronic event is 0.83 ± 0.14 for the ρ0 0.64 ± 0.24 for the K*0 (892), 0.10 ± 0.04 for the f{hook}0 (975) in the momentum range p > 0.05pbeam (xp > 0.05) and 0.11 ± 0.05 for the f{hook}2 (1270) for xp > 0.1. These values and the corresponding differential cross sections ( 1 σhadr) dσ dxp for the vector mesons are in good agreement with the predictions of the JETSET 7.3 PS and HERWIG 5.4 models. The f{hook}2 (1270) production is overestimated by HERWIG but its xp-shape is correctly reproduced. The measured ratios of the production cross sections σ(f{hook}2(1270)) σ(ρ0) = 0.22 ± 0.08 and σ(f{hook}2(1270)) σ(f{hook}0(975)) = 3-1+7 for xp > 0.1 are consistent with the results obtained in hadronic reactions. © 1993.