Guy Wilkinson

Abstract:

Using data collected in the DELPHI detector at LEP-1, measurements of the inclusive τ branching ratios for decay modes containing one, three, or five charged particles have been performed, giving the following results: B1 ≡ B(τ- → (particle)-≥0π0≥0K0 vτ(v̄)) = (85.316 ± 0.093 ± 0.049)%; B3 ≡ B(τ- → 2h-h+≥0π0≥0K0vτ) = (14.569 ± 0.093 ± 0.048)%; B5 ≡ B(τ- → 3h-2h+≥0π0≥0K0vτ) = (0.115 ± 0.013 ± 0.006)%, where h is either a charged π or K meson. The first quoted uncertainties are statistical and the second systematic.

Abstract:

The semileptonic branching fractions for primary and cascade b decays BR(b → l-), BR(b → c → l+) and BR(b → c̄ → l- were measured in hadronic Z decays collected by the DELPHI experiment at LEP. The sample was enriched in b decays using the lifetime information and various techniques were used to separate leptons from direct or cascade b decays. By fitting the momentum spectra of di-leptons in opposite jets, the average b mixing parameter x̄ was also extracted. The following results have been obtained: (equation presented).

Abstract:

A search for pair-production of neutralinos at a LEP centre-of-mass energy of 189 GeV gave no evidence for a signal. This limits the neutralino production cross-section and excludes regions in the parameter space of the Minimal Supersymmetric Standard Model (MSSM).

Abstract:

Data taken by the DELPHI experiment at centre-of-mass energies of 183 GeV and 189 GeV with a total integrated luminosity of 212 pb-1 have been used to search for the supersymmetric partners of the electrons, muons, and taus in the context of the Minimal Supersymmetric Standard Model (MSSM). The decay topologies searched for were the direct decay (ℓ̃ → ℓx̃), producing acoplanar lepton pairs plus missing energy, and the cascade decay (ℓ → ℓx̃02 → ℓγx̃01), producing acoplanar lepton and photon pairs plus missing energy. The observed number of events is in agreement with Standard Model predictions. The 95% CL excluded mass limits for selectrons, smuons and staus are mẽ ≤ 87 GeV/c2, mμ̃ ≤ 80 GeV/c2 and mτ̃ 75 GeV/c2, respectively, for values of μ=-200 GeV/c2 and tanβ=1.5.

Abstract:

Muon pair production in the process e⁺e^- → e⁺e^- μ⁺μ^- is studied using the data taken at LEP1 (√s ≃ mz) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb^-1. The QED predictions have been tested over the whole Q² range accessible at LEP1 (from several GeV²/c⁴ to several hundred GeV²/c⁴) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function F^γ2. Azimuthal correlations are used to obtain information on additional structure functions, F^γA and F^γB, which originate from interference terms of the scattering amplitudes. The measured ratios F^γA/F^γ2 and FγB/F^γ2 are significantly different from zero and consistent with QED predictions.