Guy Wilkinson

Abstract:

The average lifetime of weakly decaying b-baryons was studied using 3.6 million Z0 hadronic decays collected by the DELPHI detector at LEP. The measurement of the proper decay time distribution of secondary vertices was used on three complementary samples. The first sample consisted of events with a fully reconstructed Λ+c and an opposite charge lepton, or an oppositely charged lepton pair accompanied by a Λ0. The other two samples were more inclusive, where b-baryon semileptonic decays were recognized by the presence of either a proton identified by the RICH detector or a Λ0 and a lepton of charge opposite to that of the proton. The combined result was: τ(b-baryon) = 1.14 ± 0.08 (stat) ± 0.04 (syst) ps.

Abstract:

From data corresponding to an integrated luminosity of 53.5 pb-1 taken during the 183 GeV run in 1997, DELPHI has measured the W mass from direct reconstruction of WW → ℓv̄qq̄ and WW → qq̄qq̄ events. Combining these channels, a value of mw = 80.238 ± 0.154(stat) ± 0.035(syst) ± 0.035(fsi) + 0.021(LEP)GeV/c2 is obtained, where fsi denotes final state interaction. Combined with the W mass obtained by DELPHI from the WW production cross-section and with the direct measurement at 172 GeV this leads to a measured value of mw = 80.270 ± 0.137(stat) ± 0.031(syst) ± 0.030(fsi) ± 0.021(LEP)GeV/c2, in good agreement with the Standard Model expectation. The width of the W boson is also measured, giving the value Γw= 2.48 ± 0.40(stat) ± 0.10(syst)GeV/c2. © 1999 Elsevier Science B.V. All rights reserved.

Abstract:

The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in e+e- collisions at LEP. As in deep inelastic scattering, these data are important for tests of QCD. The transverse σΤ and longitudinal σL components of the total hadronic cross section σtot are evaluated from the measured fragmentation functions. They are found to be σΤ/σtot = 0.949 ± 0.001(stat.) ± 0.007(syst.) and σL/σtot = 0.051 ± 0.001(stat) ± 0.007(syst.) respectively. The strong coupling constant is calculated from σL/σtot in next-to-leading order of perturbative QCD, giving αs(Mz) = 0.120 ± 0.002(stat.) ± 0.013(syst.) ± 0.007(scale) . Including non-perturbative power corrections leads to αs(Mz) = 0.101 ± 0.002(stat.) ± 0.013(syst.) ± 0.007(scale) . The measured transverse and longitudinal components of the fragmentation function are used to estimate the mean charged multiplicity, 〈nch〉 = 21.21 ± 0.01(stat.) ± 0.20(syst.) The fragmentation functions and multiplicities in bb̄ and light quark events are compared. The measured transverse and longitudinal components of the fragmentation function allow the gluon fragmentation function to be evaluated.

Abstract:

The rate Z → bb̄bb̄ was measured using about 2×106 hadronic decays collected by the DELPHI experiment in 1994 and 1995. Events were forced into 3-jets with ymin > 0.06 and a b-tag was required for every jet. The rate was measured to be: R4b = BR(Z → bb̄bb̄)/BR(Z → hadrons), = (6.0 ± 1.9(stst.)) ± 1.4(Syst.)) × 10-4 where the invariant mass of every bb̄ system is above twice the b quark mass. Using the value of R4b the probability of secondary production of a bb̄ pair from a gluon per hadronic Z decay, gbb, was extracted and found to be: gbb = (3.3 ± 1.0(stat) ± 0.8(syst.)) × 10-3. © 1999 Published by Elsevier Science B.V. All rights reserved.

Abstract:

Data collected with the DELPHI detector from 1993 to 1995 combined with previous DELPHI results for data from 1991 and 1992 yield the branching fractions B(τ → evv̄) = (17.877 ± 0.109stat ± 0.110sys)% and B(τ → μvv̄) = (17.325 ± 0.095stat ± 0.077sys)%.