Peter Renton

Abstract:

Measurements of on-shell ZZ production are described, using data collected by DELPHI in 1997 and 1998, at centre-of-mass energies √s = 182.6 GeV and 188.6 GeV, respectively. Results obtained in each of the final states qq̄qq̄, μ⁺μ^-qq̄, e⁺e^-qq̄, vv̄qq̄ l⁺l^-l⁺l^-, and vv̄l⁺l^- are presented. The measured cross-sections for on-shell ZZ production via the tree-level doubly-resonant graphs (NC02) are: σNC02 (182.6 GeV) = 0.38 ± 0.18 (stat) ± 0.04 (syst) pb, σNC02 (188.6 GeV) = 0.60±0.13 (stat) ±0.07 (syst) pb. They are consistent with the Standard Model expectations of 0.25 and 0.65 pb at each energy. © 2001 Elsevier Science B.V.

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.