A study of the decays of tau leptons produced on the Z resonance at LEP
Zeitschrift für Physik C Particles and Fields 55:4 (1992) 555-567
Abstract:
From the analysis of a data sample corresponding to an integrated luminosity of 4.63 pb-1 taken during the 1990 run of LEP at centre of mass energies between 88.2 GeV an 94.2 GeV, the tau decays {Mathematical expression} and their charge conjugates have been studied. The following branching ratios have been measured; {Mathematical expression}, {Mathematical expression}, Br(τ- → π- (K-)vτ)=11.9±0.7±0.7%, BR (τ- → ρ- vτ)= 22.4±0.8±1.3%, in good agreement with world averages. The measured electronic and muonic branching ratios lead to a measurement of the strong coupling constant, αs (mτ) = 0.26-0.12+0.09. Extrapolating the αs value from mτ to mZ yields αs (mZ) = 0.109-0.028+0.012. The average polarization Pτ of taus produced in Z → τs τs decays has also been measured using the above decay modes. The weighted mean of the polarizations obtained from the four decay modes is Pτ=-0.24±0.07. This value of Pτ gives, in the improved Born approximation, a ratio between the axial and vector coupling constants of the tau of υτ/aτ = 0.12 ± 0.04, and hence a value of the effective electroweak mixing parameter sin2 θW(mZ2). © 1992 Springer-Verlag.Measurement of the average lifetime of B hadrons
Zeitschrift für Physik C Particles and Fields 53:4 (1992) 567-580
Abstract:
The average lifetime of B hadrons produced in hadronic Z0 decays has been measured with the DELPHI detector at LEP. The measurement is based on the analysis of the impact parameter distributions of high pt muons and hadrons. The resulting mean B lifetimes are τB=(1.30±0.10±0.08)ps and τB=(1.27±0.04±0.12)ps respectively, giving a combined value of τB=(1.28±0.10)ps. The hadronic sample was also used to measure the partial Z0 width {Mathematical expression} and gave a value of 0.222-0.031+0.033±0.017. © 1992 Springer-Verlag.Study of final state photons in hadronic Z0 decay and limits on new phenomena
Zeitschrift für Physik C Particles and Fields 53:4 (1992) 555-565
Abstract:
The differential cross section for final state radiation from primary quarks is obtained from a study of isolated energetic photons produced in the reaction e+e-→Z0→hadrons+γ, as measured in the DELPHI detector at the CERN LEP collider. When combined with the measurement of the total hadronic width of the Z0, the observed rate determines the electroweak coupling constants of up and down type quarks, i.e., {Mathematical expression} No evidence is seen for additional photon production from anomalous decays of the Z0 or from decays of new particles. This measurement leads to upper limits on the production cross section times branching fraction of (a) the Higgs boson in the reaction e+e-→Z0→H +γ, H→hadrons, (b) an excited quark, q*→q+γ, and (c) the contribution of an anomalous decay of the Z0 into a photon and hadrons. These limits, all at the 95% confidence level, vary from 3 to 10pb as the mass of the intermediate state (H, q* or Z*) varies from 10 GeV/c2 to 80 GeV/c2. © 1992 Springer-Verlag.Measurement of the Z0 branching fraction to b quark pairs using the boosted sphericity product
Physics Letters B 281:3-4 (1992) 383-393
Abstract:
From a sample of about 120 000 hadronic Z0 decays, using a technique based on a separation of the different event categories in the boosted sphericity product, the fraction of bb decays has been measured to be 0.219 ± 0.014 (stat)± 0.019 (syst). Using the DELPHI determination of the hadronic Z0 width, this corresponds to a partial width τbb = 378 ± 42 MeV (in good agreement with the standard model prediction of ∼-380 MeV). Combining this measurement with the determinations based on events with high pt leptons gives an estimate for the branching ratio of b into leptons at LEP of (11.2 ± 1.2)%, consistent with previous determinations. © 1992.Charged particle multiplicity distributions for fixed number of jets in Z0 hadronic decays
Zeitschrift für Physik C Particles and Fields 56:1 (1992) 63-75