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Sökning: WFRF:(Vorobyov A)

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1.
  • Schael, S, et al. (författare)
  • Precision electroweak measurements on the Z resonance
  • 2006
  • Ingår i: Physics Reports. - : Elsevier. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
  • Forskningsöversikt (refereegranskat)abstract
    • We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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2.
  • Schael, S., et al. (författare)
  • Electroweak measurements in electron positron collisions at W-boson-pair energies at LEP
  • 2013
  • Ingår i: Physics Reports. - : Elsevier. - 0370-1573 .- 1873-6270. ; 532:4, s. 119-244
  • Forskningsöversikt (refereegranskat)abstract
    • Electroweak measurements performed with data taken at the electron positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb(-1) collected by the four LEP experiments ALEPH, DELPHI, 13 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, m(w) and Gamma(w), the branching fraction of W decays to hadrons, B(W -> had), and the trilinear gauge-boson self-couplings g(1)(Z), K-gamma and lambda(gamma), are determined to be: m(w) = 80.376 +/- 0.033 GeV Gamma(w) = 2.195 +/- 0.083 GeV B(W -> had) = 67.41 +/- 0.27% g(1)(Z) = 0.984(-0.020)(+0.018) K-gamma - 0.982 +/- 0.042 lambda(gamma) = 0.022 +/- 0.019. (C) 2013 Elsevier B.V. All rights reserved.
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3.
  • Abazov, V. M., et al. (författare)
  • The upgraded DO detector
  • 2006
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 565:2, s. 463-537
  • Tidskriftsartikel (refereegranskat)abstract
    • The DO experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid -argon calorimeters and central muon detector, remaining from Run 1, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to DO.
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4.
  • Adcox, K, et al. (författare)
  • Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX Collaboration
  • 2005
  • Ingår i: Nuclear Physics, Section A. - : Elsevier. - 0375-9474. ; 757:1-2, s. 184-283
  • Forskningsöversikt (refereegranskat)abstract
    • Extensive experimental data from high-energy nucleus-nucleus collisions were recorded using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The comprehensive set of measurements from the first three years of RHIC operation includes charged particle multiplicities, transverse energy, yield ratios and spectra of identified hadrons in a wide range of transverse momenta (PT), elliptic flow, two-particle correlations, nonstatistical fluctuations, and suppression of particle production at high PT. The results are examined with an emphasis on implications for the formation of a new state of dense matter. We find that the state of matter created at RHIC cannot be described in terms of ordinary color neutral hadrons.
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5.
  • Adcox, K, et al. (författare)
  • PHENIX detector overview
  • 2003
  • Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier. - 0167-5087. ; 499:2-3, s. 469-479
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX detector is designed to perform a broad study of A-A, p-A, and p-p collisions to investigate nuclear matter under extreme conditions. A wide variety of probes, sensitive to all timescales, are used to study systematic variations with species and energy as well as to measure the spin structure of the nucleon. Designing for the needs of the heavy-ion and polarized-proton programs has produced a detector with unparalleled capabilities. PHENIX measures electron and muon pairs, photons, and hadrons with excellent energy and momentum resolution. The detector consists of a large number of subsystems that are discussed in other papers in this volume. The overall design parameters of the detector are presented. (C) 2002 Elsevier Science B.V. All rights reserved.
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6.
  • Adcox, K, et al. (författare)
  • Flow Measurements via Two-Particle Azimuthal Correlations in Au+Au Collisions at sqrt[sNN]=130 GeV
  • 2002
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114. ; 89
  • Tidskriftsartikel (refereegranskat)abstract
    • Two-particle azimuthal correlation functions are presented for charged hadrons produced in Au+Au collisions at the Relativistic Heavy Ion Collider (sqrt[sNN]=130 GeV). The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values (v2) show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone ε, the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low pT. A breakdown of this ε scaling is observed for charged hadrons with pT >1.0 GeV/c.
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7.
  • Adcox, K, et al. (författare)
  • Transverse-mass dependence of two-pion correlations in Au+Au collisions at root(NN)-N-S=130 GeV
  • 2002
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114. ; 88:19
  • Tidskriftsartikel (refereegranskat)abstract
    • Two-pion correlations in roots(NN) = 130 GeV Au+Au collisions at RHIC have been measured over a broad range of pair transverse momentum k(T) by the PHENIX experiment at RHIC. The k(T) dependent transverse radii are similar to results from heavy-ion collisions at roots(NN) = 4.1 , 4.9, and 17.3 GeV, whereas the longitudinal radius increases monotonically with beam energy. The ratio of the outwards to sidewards transverse radii (R-out/R-side) is consistent with unity and independent of k(T) .
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8.
  • Adcox, K, et al. (författare)
  • Centrality dependence of the high (PT) charged hadron suppression in Au+Au collisions at root s(NN)=130 GeV
  • 2003
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier. - 0370-2693. ; 561:1-2, s. 82-92
  • Tidskriftsartikel (refereegranskat)abstract
    • PHENIX has measured the centrality dependence of charged hadron p(T) spectra from Au +An collisions at root(s)NN = 130 GeV The truncated mean p(T) decreases with centrality for p(T) > 2 GeV/c, indicating an apparent reduction of the contribution from hard scattering to high p(T) hadrdn production. For central collisions the yield at high p(T) is shown to be suppressed compared to binary nucleon-nucleon collision scaling of p + p, data. This suppression is monotonically increasing with centrality, but most of the change occurs below 30% centrality, i.e., for collisions with less than similar to140 participating nucleons. The observed p(T) and centrality dependence is consistent with the particle production predicted by models including hard scattering and subsequent energy loss of the scattered partons in the dense matter created in the collisions. (C) 2003 Published by Elsevier Science B.V.
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9.
  • Adcox, K, et al. (författare)
  • Event-by-event fluctuations in mean p(T) and mean E(T) in root s(NN)=130 GeVAu+Au collisions
  • 2002
  • Ingår i: Physical Review C (Nuclear Physics). - : American Physical Society. - 0556-2813. ; 66:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Distributions of event-by-event fluctuations of the mean transverse momentum and mean transverse energy near mid-rapidity have been measured in Au+Au collisions at roots(NN)=130 GeV at the Relativistic Heavy-Ion Collider. By comparing the distributions to what is expected for statistically independent particle emission, the magnitude of nonstatistical fluctuations in mean transverse momentum is determined to be consistent with zero. Also, no significant nonrandom fluctuations in mean transverse energy are observed. By constructing a fluctuation model with two event classes that preserve the mean and variance of the semi-inclusive p(T) or e(T) spectra, we exclude a region of fluctuations in roots(NN)=130 GeV Au+Au collisions.
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10.
  • Adcox, K, et al. (författare)
  • Measurement of Lambda and (Lambda)over-bar particles in Au plus Au collisions at root s(NN)=130 GeV
  • 2002
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114. ; 89:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We present results on the measurement of Lambda and (&ULambda;) over bar production in Au+Au collisions at roots(NN)=130 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The (&ULambda;) over bar/Lambda ratios are constant as a function of p(T) and the number of participants. The measured net Lambda density is significantly larger than predicted by models based on hadronic strings (e.g., HIJING) but in approximate agreement with models which include the gluon-junction mechanism.
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