Guy Wilkinson

Abstract:

From the combined data of 1990 and 1991 of the DELPHI experiment at LEP, 13057 4-jet events are obtained and used for determining the contribution of the triple-gluon vertex. The relevant variables are the generalized Nachtmann Reiter angle θNR* and the opening angle of the two least energetic jets. A fit to their two-dimensional distribution yields {Mathematical expression} where CA/CF is the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung from quarks, and NC/NA, the ratio of the number of quark colours to the number of gluons. This constitutes a convincing model-independent proof of the existence of the triple-gluon vertex, since its contribution is directly proportional to CA/CF. The results are in agreement with the values expected from QCD:CA/CF=2.25, and NC/NA=3/8. © 1993 Springer-Verlag.

Abstract:

Based on a sample equivalent to 365 000 hadronic Z0 decays, the search in DELPHI data for pairs of leptons accompanied by a pair of charged particles is described. A total of 11 events were found in the electron channel, 9 in the muon channel and 7 in the tau channel. Results on lepton pairs with a radiated photon are also presented. The data from all channels are compatible with the expectations from standard processes. However, one event was found in the tau channel with an unusually high mass of the charged particle pair. © 1993.

Abstract:

The decays of B-hadrons have been reconstructed using the charged particles recorded in the DELPHI silicon microstrip detector. The sum of the charges of the secondaries determines the charge of the B-hadron parent. Some 232 114 multihadronic Z0 decays recorded during the 1991 run of LEP at centre-of-mass energies between 88.2 GeV and 94.2 GeV yield 253 B-hadron candidates with well-measured charge. From these the mean lifetimes of neutral and charged B-hadrons are found to be 1.44±0.21 (stat.)±0.14(syst.) ps and 1.56±0.19(stat.)±0.13(syst.) ps respectively. The ratio of their lifetimes is 1.09-0.23+0.28 (stat.) ± 0.11(syst.). Under some assumptions on the abundance and lifetime of the Λb0 and Bs0 states, the B0 and B+ lifetimes are inferred. © 1993.

Abstract:

A determination of the hadronic fragmentation functions of the Z0 boson is presented from a study of the inclusive hadron production with the DELPHI detector at LEP. These fragmentation functions were compared with the ones at lower energies, thus covering data in a large kinematic range: 196 ≤ Q2 ≤ 8312 GeV2 and x (= Ph Ebeam) > 0.08. A large scaling violation was observed, which was used to extract the strong coupling constant in second order QCD: αs(MZ) = 0.118 ± 0.005. The corresponding QCD scale for five quark flavours is: Λ (5) MS = 230 ± 60 MeV. © 1993.

Abstract:

Evidence for the production of b-flavoured baryons in Z0 decays is reported from the analysis of 365 000 hadronic events collected by the DELPHI detector. Assuming that most of the weakly decaying b flavoured baryons produced by the Z0 are Λb, the observed signal of (Λ-+Λl+) pairs, where l is a high transverse momentum lepton in the same jet as the Λ, leads to a production rate: f(b→Λb)×Br(Λb→ Λlν X) = (0.41±0.13±0.09)%. Using a sample of 18 reconstructed Λb decay vertices, the lifetime is determined to be τ(Λb) = (1.04+0.48-0.38±0.10) ps. © 1993.