Guy Wilkinson

Abstract:

The 4-jet events collected by the DELPHI experiment at LEP1 in 1992, 1993 and 1994 are analysed to determine the contribution of the triple-gluon vertex. Two of the four jets are tagged as jets from b-or c-quarks using lifetime and lepton transverse momentum information. The 4-jet contributions from double-gluon brems Strahlung, the triple-gluon vertex, and secondary quark-antiquark pair production then yield significantly different two-dimensional distributions in the generalized Nachtmann Reiter angle versus the opening angle of the two secondary jets. These distributions are used to fit CA/CF, the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung, and NC/NA, the ratio of the number of quark colours to the number of gluons, giving CA/CF = 2.51 ± 0.28 and NC/NA = 0.38 ∓ 0.10 in agreement with the values expected from QCD: CA/CF= 9/4 = 2.25 and NC/NA = 3/8 = 0.375. © 1997 Published by Elsevier Science B.V.

Abstract:

Oscillations of B⁰s mesons were studied in events with a large transverse momentum lepton selected from 3.2 million hadronic Z⁰ decays registered by DELPHI between 1991 and 1994. A limit on the mass difference between the physical B⁰s states Δms > 6.5ps^-1 at 95% C.L. was obtained by combining the results obtained in three channels. © 1997 Published by Elsevier Science B.V.

Abstract:

Analysis of the rapidity structure of charge correlations in hadronic events from Z0 decays gives evidence for chain-like charge-ordering of particle production along the thrust axis, as predicted by 'QCD-motivated string-like fragmentation models. © 1997 Published by Elsevier Science B.V.

Abstract:

The spin density matrix elements for the ρ⁰, K*⁰(892) and φ produced in hadronic Z⁰ decays are measured in the DELPHI detector. There is no evidence for spin alignment of the K*⁰(892) and φ in the region xp ≤ 0.3 (xp = p/pbeam), where ρ00 = 0.33 ± 0.05 and ρ00 = 0.30 ± 0.04, respectively. In the fragmentation region, xp ≥ 0.4, there is some indication for spin alignment of the ρ⁰ and K*⁰(892), since ρ00 = 0.43 ± 0.05 and ρ00 = 0.46 ± 0.08, respectively. These values are compared with those found in meson-induced hadronic reactions. For the φ, ρ00 = 0.30 ± 0.04 for xp ≥ 0.4 and 0.55 ± 0.10 for xp ≥ 0.7. The off-diagonal spin density matrix element ρ1 - 1 is consistent with zero in all cases.© 1997 Published by Elsevier Science B.V.

Abstract:

An inclusive measurement of the average multiplicity of bb̄ pairs from gluons, gbb̄, in hadronic Z⁰ events collected by the DELPHI experiment at LEP, is presented. A counting technique, based on jet b-tagging in 4-jet events, has been used. Looking for secondary bottom production in events with production of any primary flavour, by requiring two b-tagged jets in well defined topological configurations, gave gbb̄ = (0.21 ± 0.11(stat) ± 0.09(syst))%. This result was checked with a different method designed to select events with four b quarks in the final state. Agreement within the errors was found.© 1997 Elsevier Science B.V.