Guy Wilkinson

Abstract:

Data taken by DELPHI during the 1995 and 1996 LEP runs have been used to search for the supersymmetric partners of electron, muon and tau leptons and of top and bottom quarks. The observations are in agreement with standard model predictions. Limits are set on sfermion masses. Searches for long lived scalar leptons from low scale supersymmetry breaking models exclude stau masses below 55 GeV/c2 at the 95% confidence level irrespective of the gravitino mass.

Abstract:

A search for the Higgs boson in final states with one, two or three isolated photons has been performed based on data taken at LEP 2 by the DELPHI detector. The data analysed correspond to a total integrated luminosity of 67.5 pb-1 at centre-of-mass energies of 161 GeV (9.7 pb-1), 172 GeV (10.1 pb-1) and 183 GeV (47.7 pb-1). No evidence for the processes e+e- → Hγ with H → bb̄ or γγ and e+e- → Hqq̄ with H → γγ was observed. Model-independent limits on σ(e+e- → Hγ) × BR(H → bb̄), σ(e+e- → Hqq̄) × BR(H γγ) and σ(e+e- → Hγ) × BR(H → γγ) are set, as well as model-dependent limits on Higgs boson anomalous couplings to vector bosons. © 1999 Published by Elsevier Science B.V. All rights reserved.

Abstract:

The four-jet events collected by DELPHI during the special LEP run at centre-of-mass energies of 130 and 136 GeV in 1997 with an integrated luminosity of 5.9pb-1 are analysed. Their rate and the distributions of their di-jet masses, their smallest jet charges, and their di-jet charge separations all agree well with Standard Model predictions. Thus the hypothesis of pair production of a new particle with a sum of di-jet masses around 105 GeV/c2 is not supported. The combined result of the four LEP collaborations refuting this hypothesis at over 99% confidence level is also given. © 1999 Published by Elsevier Science B.V. All rights reserved.

Abstract:

Data collected at the Z resonance using the DELPHI detector at LEP are used to determine the charged hadron multiplicity in gluon and quark jets as a function of a transverse momentum-like scale. The colour factor ratio, CA/CF, is directly observed in the increase of multiplicities with that scale. The smaller than expected multiplicity ratio in gluon to quark jets is understood by differences in the hadronization of the leading quark or gluon. From the dependence of the charged hadron multiplicity on the opening angle in symmetric three-jet events the colour factor ratio is measured to be: CA/CF = 2.246 ± 0.062(stat.) ± 0.080 (syst.) ± 0.095 (theo.) © 1999 Elsevier Science B.V. All rights reserved.

Abstract:

The cross-section for the process e+e-→W+W- has been measured with the data sample collected by DELPHI at an average centre-of-mass energy of 182.65 GeV and corresponding to an integrated luminosity of 53 pb-1. Based on the 770 events selected as WW candidates, the cross-section for the doubly resonant process δ(e+e-→W+W-) = 15.86 ± 0.69 (stat) ± 0.26 (syst)pb has been measured and found to be in good agreement with the Standard Model expectation. The branching fractions of the W decay were also measured. From these a value of the CKM mixing matrix element \Vcs\ = 0.985 ± 0.073 (stat) ± 0.025 (syst) was derived. Our previously published WW cross-section measurements and the derived measurement of mW have been revised and updated with the present cross-section measurement to yield mW = 80.49 ± 0.43(stat) ± 0.09(syst) ± 0.03(LEP)GeV/c2. © 1999 Published by Elsevier Science B.V. All rights reserved.