176 research outputs found

    ATLAS detector and physics performance: Technical Design Report, 1

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    Tevatron Run II combination of the effective leptonic electroweak mixing angle

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    Drell-Yan lepton pairs produced in the process pp→â.,"+â.,"-+X through an intermediate γ∗/Z boson have an asymmetry in their angular distribution related to the spontaneous symmetry breaking of the electroweak force and the associated mixing of its neutral gauge bosons. The CDF and D0 experiments have measured the effective-leptonic electroweak mixing parameter sin2θefflept using electron and muon pairs selected from the full Tevatron proton-antiproton data sets collected in 2001-2011, corresponding to 9-10 fb-1 of integrated luminosity. The combination of these measurements yields the most precise result from hadron colliders, sin2θefflept=0.23148±0.00033. This result is consistent with, and approaches in precision, the best measurements from electron-positron colliders. The standard model inference of the on-shell electroweak mixing parameter sin2θW, or equivalently the W-boson mass MW, using the zfitter software package yields sin2θW=0.22324±0.00033 or equivalently, MW=80.367±0.017 GeV/c2

    Observation of charge-ordering in particle production in hadronic Z(0) decay

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    Analysis of the rapidity structure of charge correlations in hadronic events from Z(0) decays gives evidence for chain-like charge-ordering of particle production along the thrust axis, as predicted by ‘QCD-motivated’ string-like fragmentation models. (C) 1997 Published by Elsevier Science B.V

    Search for neutral Higgs bosons in e(+)e(-) collisions at root s=183 GeV

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    Neutral Higgs bosons were searched for in the data collected by DELPHI at a centre-of-mass energy of 183 GeV, corresponding to an integrated luminosity of 54 pb(-1). The production of the lightest neutral Higgs boson with either an on-shell Z boson or a neutral pseudo-scalar Higgs boson was analysed. Lower limits at the 95% confidence level were obtained on the Higgs boson masses. The limits are 85.7 GeV/c(2) for the Standard Model Higgs boson and 74.4 GeV/c(2) for the scalar and 75.3 GeV/c(2) for the pseudo-scalar Higgs bosons as predicted by the minimal super-symmetric extension of the Standard Model with commonly used assumptions on the model parameters, plus the assumption that the mass of the pseudo-scalar boson is greater than 20 GeV/c(2). These results significantly improve the limits reached with previous data

    Search for charginos, neutralinos and gravitinos in e(+)e(-) interactions at root s = 183 GeV

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    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/c(2) higher than those obtained at a centre-of-mass energy of 172 GeV. The (mu M-2) 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/c(2) for tan beta greater than or equal to 1. (C) 1999 Elsevier Science B.V. All rights reserved

    Energy dependence of inclusive spectra in e(+)e(-) annihilation

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    Inclusive charged hadron distributions as obtained from the DELPHI measurements at 130, 136, 161, 172 and 183 GeV are presented as a function of the variables rapidity, xi(p), p and transversal momenta. Data are compared with event generators and with MLLA calculations, in order to examine the hypothesis of local parton hadron duality. The differential momentum spectra show an indication for coherence effects in the production of soft particles. The relation between the energy dependence of the charged multiplicity and the rapidity distribution is examined. (C) 1999 Elsevier Science B.V. All rights reserved

    Measurement of the spin density matrix for the rho(0), K*(0)(892) and phi produced in Z(0) decays

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    The spin density matrix elements for the rho(0), K-*0(892) and phi produced in hadronic Z(0) decays are measured in the DELPHI detector. There is no evidence for spin alignment of the K-*0(892) and phi, in the region x(p) less than or equal to 0.3 (x(p) = p/p(beam)), where rho(00) = 0.33 +/- 0.05 and rho(00) = 0.30 +/- 0.04, respectively. In the fragmentation region, x(p) greater than or equal to 0.4, there is some indication for spin alignment of the rho(0) and K-*0(892), since rho(00) = 0.43 +/- 0.05 and rho(00) = 0.46 +/- 0.08, respectively. These values are compared with those found in meson-induced hadronic reactions. For the phi, rho(00) = 0.30 +/- 0.04 for x(p) greater than or equal to 0.4 and 0.55 +/- 0.10 for x(p) greater than or equal to 0.7. The off-diagonal spin density matrix element rho(1-1) is consistent with zero in all cases. (C) 1997 Published by Elsevier Science B.V

    A search for eta `(c) production in photon-photon fusion at LEP

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    A search for the production of the eta(c)’ meson, the first radial excitation of the ground state of charmonium eta(c)(2980), in the photon-photon fusion reaction at LEP has been performed using the data collected by the DELPHI detector during 1992-1996. No evidence of eta(c)’ production is found in the mass region 3520-3800 MeV/c(2). An upper limit for the ratio of the two-photon widths of the eta(c)’ and eta(c) is obtained. (C) 1998 Published by Elsevier Science B.V. All rights reserved

    Search for lightest neutralino and stau pair production in light gravitino scenarios with stau NLSP

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    Promptly decaying lightest neutralinos and long-lived staus are searched for in the context of light gravitino scenarios. It is assumed that the stau is the next to lightest supersymmetric particle (NLSP) and that the lightest neutralino is the next to NLSP (NNLSP). Data collected with the Delphi detector at centre-of-mass energies from 161 to 183 GeV are analysed. No evidence of the production of these particles is found. Hence, lower mass limits for both kinds of particles are set at 95% C.L.. The mass of gaugino-like neutralinos is found to be greater than 71.5 GeV/c(2). In the search for long-lived stau: masses less than 70.0 to 77.5 GeV/c(2) are excluded for gravitino masses from 10 to 150 eV/c(2). Combining this search with the searches for stable heavy leptons and minimal supersymmetric standard model staus a lower limit of 68.5 GeV/c(2) may be set for the stau mass independent of the mass of the gravitino

    A precise measurement of the tau lepton lifetime

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    The tau lepton lifetime has been measured using three different methods with the DELPHI detector. Two measurements of one-prong decays are combined, accounting for correlations, giving a result of tau(tau) = 291.8 +/- 3.3 (stat.) +/- 2.0(sys.) fs while the decay length distribution of three-prong decays gives the result tau(tau) = 286.7 +/- 4.9 (stat.) +/- 3.3 (sys.) fs. Combining the results presented here with previous DELPHI measurements, we get tau(tau) = 291.4 +/- 3.0 fs and find that the ratio of the coupling constant for tau decay relative to that for muon decay is 0.990 +/- 0.009, compatible with lepton universality
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