Peter Renton

Abstract:

A sample of 25000 Z0 → τ+τ- events collected by the DELPHI experiment at LEP in 1991 and 1992 is used to measure the leptonic branching fractions of the τ lepton. The results are B(τ → eνν) = (17.51 ± 0.39)% and B(τ → μνν) = (17.02 ± 0.31) %. The ratio of the muon and electron couplings to the weak charged current is measured to be gμ ge = 1.000 ± 0.013, satisfying e-μ universality. The leptonic branching fraction corrected to the value for a massless lepton, assuming e-μ universality, is found to be B(τ → lνν) = (17.50 ± 0.25)%. © 1995.

Abstract:

The production and decay of beauty baryons (b-baryons) have been studied using 1.7×106 Z hadronic decays collected by the DELPHI detector at LEP. Three different techniques were used to identify the b-baryons. The first method used pairs of a Λ and a lepton to tag the b-baryon decay. The second method associated fully reconstructed ΛC baryons with leptons. The third analysis reconstructed the b-baryon decay points by forming secondary vertices from identified protons and muons of opposite sign. Using these methods the following production rates were measured:[Figure not available: see fulltext.] The average b-baryon lifetime was determined to be:[Figure not available: see fulltext.] © 1995 Springer-Verlag.

Abstract:

The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993. B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic Z0 decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1±0.3%, and 83% (70%) of the events measured as neutral (charged) came from neutral (charged) B's. The mean lifetimes of charged and neutral B hadrons were found to be 1.72±0.08 (stat.) ±0.06 (syst.) ps and 1.58±0.11 (stat.)±0.09 (syst.) ps respectively. The ratio of their lifertimes, τcharged/τneutral, was 1.09-0.10+0.11 (stat.)±0.08 (syst.). By making assumptions about the Bs0 and Λb0 states, the B+ and B0 meson lifetimes were determined to be τB+ = 1.72 ± 0.08 (stat.) ±0.06 (syst.) ps and τB+ = 1.63 ± 0.14 (stat.)±0.13 (syst.) ps and the ratio of their lifetimes was: τB+/τB0 = 1.06-0.11+0.13 ±0.10. The mean B lifetime was also deduced to be < τ > = 1.64 ±0.06 (stat.)±0.04 (syst.) ps. © 1995 Springer-Verlag.

Abstract:

The partial decay width of the Z to {Mathematical expression} quark pairs has been measured by the DELPHI detector at LEP. b-hadrons, containing b-quarks, were tagged by leptons with high transverse momentum relative to the hadron or by tracks with large impact parameters to the primary vertex. The ratio of the numbers of events with a single such tag to those with two tags was used to estimate the efficiency of the method and to reduce the systematic uncertainty. Combining all methods, the value: {Mathematical expression} was found, where the third error corresponds to a±8% uncertainty on the {Mathematical expression} production width. A maximum likelihood in to the single and di-lepton distributions gave the branching fraction of the decays of b-quarks to leptons as: {Mathematical expression} © 1995 Springer-Verlag.

Abstract:

Charmless hadronic decays of beauty mesons have been searched for using the data collected with the DELPHI detector at the LEP collider. Several two, three and four-body decay modes have been investigated. Particle identification was used to distinguish the final states with protons, kaons and pions. Three candidate events selected in two-body decay modes are interpreted as evidence for charmless B decays. No excess has been found in higher multiplicity modes and improved upper limits for some of the branching ratios are given. © 1995.