Guy Wilkinson

Abstract:

Kaon production in one prong tau decays has been studied using data collected with the DELPHI detector at the LEP collider. Charged kaons were identified over a large momentum range by the DELPHI barrel Ring Imaging Cherenkov detector. The following branching ratios have been determined: BR(τ→Kντ)=(0.85±0.18)%, BR(τ→Kντ≥0 neutrals)=(1.54±0.24)%, BR(τ→Kντ≥1 neutrals)=(0.69±0.25)%. The result for the exclusive branching ratio is consistent with the Standard Model prediction based on τ-μ-e universality. In addition, tau decay into K*- was studied in the channel K*-→K-π0. The result BR(τ→K*-ντ)×BR(K *-→K-π0)=(0.57±0.23)% was obtained. © 1994.

Abstract:

A total of about 900 000 Z0 → qq decays have been analyzed to measure the B0B0 mixing probability. Two different b tagging techniques have been used: events with two leptons and events with one lepton and one Λ. From a combination of the two methods the average mixing parameter, χ, was determined to be (12.1±1.6(stat.)±0.4(syst.)±0.4(model)%. © 1994.

Abstract:

A search for the Standard Model Higgs boson was performed in the data sample of around 1 million hadronic Z0 decays recorded in 1991 and 1992 with the DELPHI detector at LEP. The Higgs boson was searched for through its production in association with either neutrinos, electrons or muons. Four low mass events remain after the selections in the charged leptonic channels, that are likely to be due to background, especially four fermion processes. These results restrict the mass of the Standard Model Higgs boson to be larger than 55.7 GeV/c2 at the 95% confidence level. © 1994.

Abstract:

A search for charged Higgs bosons decaying into quarks is described, based on statistics of around 1.7 million hadronic Zo decays detected in DELPHI. Despite the very high background from standard hadronic decays of the Zo, masses in the range up to 43.5 GeV/c2 are excluded at the 95% confidence level. After combination with a search for leptonic decays, this mass limit is extended to cover all branching ratios. A similar analysis sets new limits on the possible production of any pair-produced heavy scalar decaying into a pair of jets, such as neutral Higgs bosons in a two doublet scheme and diquarks. © 1994 Springer-Verlag.

Abstract:

The total and the differential cross sections for the reaction e⁺e^- → γγ(γ) have been measured with the DELPHI detector at LEP using an integrated luminosity of 36.9 pb^-1. The results agree with the QED predictions and consequently there is no evidence for non-standard channels with the same experimental signature. The lower limits obtained on the QED cutoff parameters are Λ+ > 143 GeV and Λ- > 120 GeV, and the lower bound on the mass of an excited electron with an effective coupling constant λγ = 1 is 132 GeV/c². Upper limits on the branching ratios for the decays Z⁰ → γγ, Z⁰ → π⁰γ, Z⁰ → ηγ and Z⁰ → γγγ have been determined to be 5.5 × 10^-5, 5.5 × 10^-5, 8.0 × 10^-5, and 1.7 × 10^-5 respectively. All the limits are at the 95% confidence level. © 1994.