Guy Wilkinson

Abstract:

Multiplicity fluctuations in rings around the jet axis and in off-axis cones have been measured by the DELPHI collaboration in e+ e- annihilations into hadrons at LEP energies. The measurements are compared with analytical perturbative QCD calculations for the corresponding multiparton system, using the concept of Local Parton Hadron Duality. Some qualitative features are confirmed by the data but substantial quantitative deviations are observed. © 1999 Published by Elsevier Science B.V. All rights reserved.

Abstract:

A search for pair produced charged Higgs bosons has been performed in the high energy data collected by DELPHI at LEP with √s = 161, 172 and 183 GeV. The analysis uses the τντν, cs̄τν and cs̄c̄s final states and a combination of event shape variables, di-jet masses and jet flavour tagging for the separation of a possible signal from the dominant W+W- and QCD backgrounds. The number of selected events has been found to be compatible with the expected background. The lower excluded value of the H± mass obtained by varying the H±→ hadrons decay branching ratio has been found to be 56.3 GeV/c2. © 1999 Published by Elsevier Science B.V. All rights reserved.

Abstract:

Promptly decaying lightest charginos were searched for in the context of scenarios with gravitino LSP. It was assumed that the stau is the next to lightest supersymmetric particle (NLSP). Data collected with the DELPHI detector at a centre-of-mass energy near 183 GeV were analysed combining the methods developed in previous searches. No evidence for the production of these partiel es was found. Hence, limits were derived at 95% confidence level. The mass of charginos was found to be greater than 85.5 GeV/c2 for mχ + ̃1+ - mτ + ̃1 ≥ 0.3 GeV/c2, independently of the mass of the gravitino. © 1999 Published by Elsevier Science B.V. All rights reserved.

Abstract:

An update of the searches for charginos and neutralinos is presented, based on a data sample corresponding to the 53.9 pb-1 recorded by the DELPHI detector in 1997, at a centre-of-mass energy of 183 GeV. No evidence for a signal was found. The lower mass limits are 4-5 GeV/c2 higher than those obtained at a centre-of-mass energy of 172 GeV. The (μ,M2) domain excluded by combining the neutralino and chargino searches implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 29.1 GeV/c2 for tan β ≥ 1. © 1999 Elsevier Science B.V. All rights reserved.

Abstract:

A search for charginos with masses close to the mass of the lightest neutralino is reported, based on the data collected with the DELPHI detector at LEP from 1995 to 1997 at centre-of-mass energies between 130 and 183 GeV. The signature of a photon at high transverse momentum radiated from the initial state reduces the two-photon background to acceptable rates, thus making the mass differences between a few hundred MeV/c2 and 3 GeV/c2 detectable. In very nearly degenerate scenarios, the lifetime of the chargino can be large enough to produce either visible secondary vertices or decays outside the detector; therefore, quasi-stable heavy charged particles and displaced decay vertices were also searched for. No excess of events with respect to the Standard Model expectations was observed, and limits in the plane of chargino-neutralino mass difference versus chargino mass are given.