Guy Wilkinson

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.

Abstract:

The measurement of the correlation between the transverse spin components of τ⁺ τ^- pairs collected during 1992 to 1994 with the DELPHI detector at LEP1 is presented. A value CTT = 0.87 ± 0.20 (stat.) +^0.10-0.12 (syst.) was obtained for the correlation parameter, in agreement with the Standard Model expectation. © 1997 Published by Elsevier Science B.V.

Abstract:

A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the first time the momentum spectra of K+, K0, p, Λ and their antiparticles in gluon and quark jets. As observed for inclusive charged particles, the production spectra of identified particles were found to be softer in gluon jets than in quark jets, with a higher total multiplicity. © 1997 Published by Elsevier Science B.V.

Abstract:

Correlations between pions from different Ws in e⁺e^- → W⁺W^- events are studied using data collected by the DELPHI detector at LEP running at a centre-of-mass energy of 172 GeV in 1996. At the present level of statistics, no enhancement of the correlation function above that expected from a pair of uncorrelated W's is observed at small values of the four- momentum difference of the pions. © 1997 Published by Elsevier Science B.V.