Search for pair-produced neutralinos in events with photons and missing energy from e+e- collisions at √s=130-183 GeV
European Physical Journal C 6:3 (1999) 371-384
Abstract:
The events with two photons and missing (transverse) energy collected by the DELPHI detector at centre-of-mass energies between 130 GeV and 183 GeV have been studied to search for processes of the type e+e- → YY with the subsequent decay Y → Xγ, where X is an undetectable neutral particle. Reactions of this kind are expected in supersymmetric models, where the Y particle can be either the lightest neutralino, decaying to a photon and a gravitino, or the next-to-lightest neutralino, decaying to a photon and the lightest neutralino. To study the case of long-lived Y particles, a search for single-photon events with the reconstructed photon axis pointing far from the beam interaction region has also been performed. No evidence for a deviation from Standard Model expectations has been observed in the data and upper limits have been derived on the signal cross-section as a function of the the X and Y masses and of the Y mean decay path.Search for scalar fermions and long-lived scalar leptons at centre-of-mass energies of 130 GeV to 172 GeV
European Physical Journal C 6:3 (1999) 385-401
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.Search for the Higgs boson in events with isolated photons at LEP 2
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 458:2-3 (1999) 431-446
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.The scale dependence of the hadron multiplicity in quark and gluon jets and a precise determination of CA /CF
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 449:3-4 (1999) 383-400
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.W pair production cross-section and W branching fractions in e+e- interactions at 183 GeV
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 456:2-4 (1999) 310-321