Measurement of the t distribution in diffractive photoproduction at HERA
European Physical Journal C 2:2 (1998) 237-246
Abstract:
Photon diffractive dissociation, γp → Xp, has been studied at HERA with the ZEUS detector using ep interactions where the virtuality Q2 of the exchanged photon is smaller than 0.02 GeV2. The squared four-momentum t exchanged at the proton vertex was determined in the range 0.073 < \t\ < 0.40 GeV2 by measuring the scattered proton in the ZEUS Leading Proton Spectrometer. In the photonproton centre-of-mass energy interval 176 < W < 225 GeV and for masses of the dissociated photon system 4 < Mx < 32 GeV, the t distribution has an exponential shape, dN/d\t\ ∝ exp (-b\t\), with a slope parameter b = 6.8 ± 0.9 (stat.) +1.2-1.1 (syst.) GeV-2.Rapidity correlations in Λ baryon and proton production in hadronic Z° decays
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 416:1-2 (1998) 247-256
Abstract:
In an analysis of multihadronic events recorded at LEP by DELPHI in the years 1992 through 1994, rapidity correlations of A-A, proton-proton, and A-proton pairs are compared with each other and with the predictions of the string fragmentation model. For Ap̄ pairs, the additional correlation with respect to charged kaons is also analysed. © 1998 Elsevier Science B.V.Search for charginos, neutralinos and gravitinos at LEP
European Physical Journal C 1:1-2 (1998) 1-20
Abstract:
An update of the searches for charginos and neutralinos in DELPHI is presented, based mainly on recent data collected at centre-of-mass energies of 161 GeV and 172 GeV. No signal is found. For a sneutrino with mass above 300 GeV/c2 and a mass difference between the chargino and the lightest neutralino above 10 GeV/c2, the lower limit at 95% confidence level on the chargino mass ranges from 84.3 GeV/c2 to the kinematical limit (86.0 GeV/c2), depending on the mixing parameters. The limit decreases for lower chargino-neutralino mass differences. The limit in the case of a light sneutrino is 67.6 GeV/c2, provided that that there is no light sneutrino with a mass within 10 GeV/c2 below the chargino mass. Upper limits on neutralino pair production cross-sections of about a picobarn are derived. The (μ, M2) domain excluded in the MSSM-GUT scenario is determined by combining the neutralino and chargino searches. These results imply a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 24.9 GeV/c2 for tanβ ≥ 1. The search has also been extended to the case where the lightest neutralino is unstable and decays into a photon and a gravitino.Search for neutral and charged Higgs bosons in e+e- collisions at √s = 161 GeV and 172 GeV
European Physical Journal C 2:1 (1998) 1-37
Abstract:
A search for neutral and charged Higgs bosons has been performed in the data collected by the DELPHI detector at centre-of-mass energies of 161 GeV and 172 GeV. The analysis assumes either the pair-production of charged Higgs bosons, H±, or the production of the lightest neutral Higgs boson, h, with either a Z or a neutral pseudoscalar Higgs boson, A. All final state topologies expected from the decay of h and A into hadrons or a pair of τ leptons, and from the decay of H± into a pair of quarks or a τντ pair have been considered. Lower limits at the 95% confidence level have been obtained on the Higgs boson masses. The limits are 66.2 GeV/c2 for h in the Standard Model, 59.5 GeV/c2 for h and 51.0 GeV/c2 for A in the minimal supersymmetric extension of the Standard Model with sensible assumptions on the model parameters and, using the 161 GeV data only, 51.5 GeV/c2 for H± in the general two-doublet scheme for H± branching fractions into hadrons below 0.8.π±, K±, p and p̄ production in Z0 → qq̄, Z0 bb̄, Z0 → uū, dd̄, ss̄
European Physical Journal C 5:4 (1998) 585-620