137 research outputs found

    First Measurement of the Strange Quark Asymmetry at the Z0Z^{0} Peak

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    Limits on the production of scalar leptoquarks from Z (0) decays at LEP

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    A search has been made for pairs and for single production of scalar leptoquarks of the first and second generations using a data sample of 392000 Z0 decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95% confidence level of 45.5 GeV/c2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit and its results exclude first and second generation leptoquarks D0 with masses below 65 GeV/c2 and 73 GeV/c2 respectively, at 95% confidence level, assuming that the D0lq Yukawa coupling alpha(lambda) is equal to the electromagnetic one. An upper limit is also given on the coupling alpha(lambda) as a function of the leptoquark mass m(D0)

    Invariant mass dependence of particle correlations in hadronic final states from the decay of the Z0^0

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    Etude des hadrons beaux dans les canaux de desintegration exclusifs contenant un Ψ\Psi

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    Measurement of the Mass of the Z-Boson and the Energy Calibration of Lep

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    Contains fulltext : 26847___.PDF (publisher's version ) (Open Access

    Search for heavy neutral Higgs bosons in two doublet models

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    A search for pair production of neutral heavy Higgs bosons decaying into {Mathematical expression} has been carried out in a study of hadronic decays of the Z boson into four jet final states using data taken by DELPHI in 1991 and 1992. The two production mechanisms present in the two Higgs doublets scheme, bremsstrahlung production of hZ* and associated production of hA, may lead to four beauty jets well recognizable using the precise microvertex detector measurements. No evidence for a signal was found, leading to limits on BR(Z→hA→4b) from 3.5 to 5.5×10-4 at 95% contidence level, depending on the mass of the ligthest Higgs. When combined with the results of the recent DELPHI standard Higgs search, this result allows the kinematical limit to be reached for the masses of h and A in the minimal supersymmetric extension of the Standard Model (MSSM) scheme. It also allows the tanβ≤1 domain to be explored, and a region above the kinematic limit for direct hA production is constrained by considering virtual hA production. Results are also given in the general two-doublet scheme. © 1995 Springer-Verlag.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    Determination of alpha-s for b quarks at the Z0 resonance

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    The strong coupling constant for b quarks has been determined, and its flavour independence, as predicted by QCD, investigated. The analysis involved events with lepton candidates selected from approximately 356 000 hadronic decays of the Z0, collected by the DELPHI detector at LEP in 1990 and 1991. A method based on a direct comparison of the three-jet fraction in a b enriched sample, selected by requiring leptons with large momenta, to that of the entire hadronic sample, illustrated the significant effect of the b quark mass on the multi-jet cross section, and verified the flavour independence of the strong coupling constant to an accuracy of ±6%. A second procedure based on a fit to the momentum and transverse momentum spectra of the lepton candidates in both two-jet and three (or more)-jet event samples simultaneously determined the b content in each, and, using second order QCD calculations, gave an absolute measurement of αs for b quarks of 0.118±0.004 (stat.)±0.003 (syst.)±0.008 (scale). A comparison with αs for all quark flavours, as measured from the three-jet fraction in all hadronic events, further allowed the coupling strength for b quarks to be expressed in terms relative to that for udsc quarks, thereby cancelling certain common systematic uncertainties, and yielded View the MathML source

    First evidence of hard scattering processes in single tagged γγ\gamma\gamma collisions

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