1,722,468 research outputs found
Multiplicity fluctuations in one- and two-dimensional angular intervals compared with analytic QCD calculations
No full textMultiplicity fluctuations in rings around the jet axis and in off-axis canes 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. (C) 1999 Published by Elsevier Science B.V. All rights reserved
Update of the search for supersymmetric particles in scenario with gravitino LSP ans sleptons NLSP
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A precise measurement of the <tex>B^{+}</tex> and mean b-hadron lifetime with the DELPHI detector at LEP
No full textAbstract: Final results from the DELPHI Collaboration on the lifetime of B + and B0 mesons and the mean b-hadron lifetime, are presented using the data collected at the Z0 peak in 1994 and 1995. Elaborate, inclusive, secondary vertexing methods have been employed to ensure a b-hadron reconstruction with good efficiency. To separate samples of B + and B0 mesons, high performance neural network techniques are used that achieve very high purity signals. The results obtained are: \tau_{\mathrm B
13th DELPHI Collaboration meeting on 14 and 15 April, 1983 Copies of transparencies-second part
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Search for stable heavy charged particles in e(+)e(-) collisions at root s=130-136, 161 and 172 GeV
No full textA search for stable or long-lived heavy charged particles in e(+)e(-) interactions at energies of 130-136, 161 and 172 CeV has been performed using the data taken by the DELPHI experiment at LEP. The search is based on particle identification provided by the Time Projection Chamber and the Ring Imaging Cherenkov detector. Upper limits at 95% confidence level are derived on the cross-section for heavy long-lived pair-produced charge +/-e and +/-2/3e particles in the range of 0.4-2.3 pb for masses from 45 to 84 GeV/c(2). Within supersymmetric extensions of the Standard Model, long-lived charginos with masses from 45 to 84 (80) GeV/c(2) for high (low) sneutrino masses can be excluded at 95% confidence level. Left-handed (right-handed) long-lived or stable smuons and staus with masses between 45 and 68 (65) GeV/c(2) can be excluded at 95% confidence level. (C) 1997 Elsevier Science B.V
Cross-sections and leptonic forward-backward asymmetries from the Z(0) running of LEP
No full textDuring 1993 and 1995 LEP was run at 3 energies near the Z(0) peak in order to give improved measurements of the mass and width of the resonance. During 1994, LEP operated only at the Z(0) peak. In total DELPHI accumulated data corresponding to an integrated luminosity of approximately 116 pb(-1). Analyses of the hadronic cross-sections and of the cross-sections and forward-backward asymmetries in the leptonic channels used the most precise evaluations of the LEP energies. In the dimuon channel, events with a photon radiated horn the initial state have been used to probe the cross-sections and asymmetries down to PETRA energies. Model independent fits to all DELPHI lineshape and asymmetry data horn 1990 to 1995 have been carried out giving values of the resonance parameters: M-Z = 91.1863 +/- 0.0028 GeV Gamma(Z) = 2.4876 +/- 0.0041 GeV sigma(0) = 41.578 +/- 0.069 nb R-iota = 20.730 +/- 0.060 A(FB)(0) = 0.0187 +/- 0.0019. These values are significantly more precise than those previously published. The results are interpreted in terms of the Standard Model
Measurement of the semileptonic b branching fractions and average b mixing parameter in Z decays
No full textThe semileptonic branching fractions for primary and cascade b decays BR(b --> l(-)), BR(b --> c --> l(+)) and BR(b --> (c) over bar --> l(-) were measured in hadronic Z decays collected by the DELPHI experiment at LEP. The sample was enriched in b decays using the lifetime information and various techniques were used to separate leptons from direct or cascade b decays. By fitting the momentum spectra of di-leptons in opposite jets, the average b mixing parameter )over bar> was also extracted. The following results have been obtained: BR(b --> l(-)l(-)) = (10.70 +/- 0.08(stat) +/- 0.21(syst)(+0.44)(-0.30)(model))% BR(b --> c --> l(+)) = (7.98 +/- 0.22(stat) +/- 0.21(syst)(-0.20)(+0.14)(model))% BR(b --> (c) over bar --> l(-)) = (1.61 +/- 0.20(stat) +/- 0.17(syst)(-0.44)(+0.30)(model))% )over bar> = 0.127 +/- 0.013(stat) +/- 0.005(syst) +/- 0.004(model)
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