Results 1 - 10 of 10968
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[en] New results of the W mass and width measurements at LEP are presented, which yield Mw = 80.401 ± 0.048 GeV and ΓW = 2.19 ± 0.15 GeV. A comparison of this direct and the indirect W mass, obtained in an analysis of electroweak measurements, is made and good agreement is observed. All electroweak data are very consistent with the Standard Model predictions. In a combined fit an upper limit on the mass of Higgs boson is put to MH < 188 GeV, while direct searches at LEP exclude Higgs masses below 107.9 GeV at 95% confidence level. (author)
[en] Details of the recent calculation of the two-loop bosonic corrections to the effective leptonic weak mixing angle are presented. In particular, the expansion in the difference of the W and Z boson masses is studied and some of the master integrals needed are given in analytic form
[en] We present a new measurement of the W mass using the W → eν data from the D0 forward detectors at the Fermilab Tevatron p anti p Collider. This is the first measurement of the W mass with electron candidates in the range 1.5 <| η |< 2.5. We present measurements of the W mass using the transverse mass, the electron transverse momentum and the neutrino transverse momentum, and the combined result using all three techniques. The combination of the forward detector measurement with the previous measurements using the central detector gives a new precise measurement of the W mass from D0
[en] The authors have measured the bottom hadron lifetime from b bar b events produced at the Z0 resonance. Using the precision vertex detectors of the Mark II detector at the Stanford Linear Collider, they developed an impact parameter tag to identify bottom hadrons. The vertex tracking system resolved impact parameters to 30 μm for high momentum tracks, and 70 μm for tracks with a momentum of 1 GeV. They selected B hadrons with an efficiency of 40% and a sample purity of 80% by requiring there be at least two tracks in a single jet that significantly miss the Z0 decay vortex. From a total of 208 hadronic Z0 events collected by the Mark II detector in 1990, they tagged 53 jets, of which 22 came from 11 double-tagged events. The jets opposite the tagged ones, referred as the 'untagged' sample, are rich in B hadrons and unbiased in B decay times. The variable Σδ is the sum of impact parameters from tracks in the jet, and contains vital information on the B decay time. They measured the B lifetime from a one-parameter likelihood fit to the untagged Σδ distribution, obtaining τb = 1.54+0.55-0.45±0.16 ps which agrees with the current world average. The first error is statistical and the second is systematic. The systematic error was dominated by uncertainties in the track resolution function. As a check, they also obtained consistent results using the Σδ distribution from the tagged jets and from the entire hadronic sample without any bottom enrichment
[en] The observation that Baryon number and Lepton number are conserved in nature provides strong motivation for associating gauge symmetries to these conserved numbers. This endeavor requires that the gauge group of electroweak interactions be extended from SU(2)L X U(1)Y to SU(2)L X U(1)R X U(1)Lepton where U(1)R couples only to the right-handed quarks and leptons. If it furthur postulated that right-handed currents exist on par with the left-handed ones, then the full electroweak symmetry is SU(2)L X SU(2)R X U(1)Baryon X U(1)Lepton. The SU(2)L X SU(2)R X U(1)Baryon X U(1)Lepton model is described in some detail. The triangle anomalies of the three families of quarks and leptons in the model are cancelled invoking leptoquark matter which is new fermionic matter that carries baryon as well as lepton numbers. In addition to the standard neutral boson (Z degree), the theory predicts two neutral gauge bosons with mass lower bounds of 120 GeV and 210 GeV which makes these particles prospective candidates for production at LEP, the TEVATRON and the SSC
[en] We study vector portal dark matter models where the mediator couples only to leptons. In spite of the lack of tree-level couplings to colored states, radiative effects generate interactions with quark fields that could give rise to a signal in current and future experiments. We identify such experimental signatures: scattering of nuclei in dark matter direct detection; resonant production of lepton–antilepton pairs at the Large Hadron Collider; and hadronic final states in dark matter indirect searches. Furthermore, radiative effects also generate an irreducible mass mixing between the vector mediator and the Z boson, severely bounded by ElectroWeak Precision Tests. We use current experimental results to put bounds on this class of models, accounting for both radiatively induced and tree-level processes. Remarkably, the former often overwhelm the latter.
[en] This report presents the Z-boson cross section decay measurement in the electron channel in pp collisions at √s = 7TeV. The measurement has been performed with data taken in 2010 by the ATLAS experiment at LHC, corresponding to an integrated luminosity of about 36 pb-1.
[en] Classical solutions describing strings endowed with an electric charge and carrying a constant electromagnetic current are constructed within the bosonic sector of the electroweak theory. For any given ratio of the Higgs boson mass to W boson mass and for any Weinberg's angle, these strings comprise a family that can be parameterized by values of the current through their cross section, I3, by their electric charge per unit string length, I0, and by two integers. These parameters determine the electromagnetic and Z fluxes, as well as the angular momentum and momentum densities of the string. For I0->0 and I3->0 the solutions reduce to Z strings, or, for solutions with I0=+/-I3, to the W-dressed Z strings whose existence was discussed some time ago
[en] I study the phenomenology of new heavy neutral gauge bosons Z', predicted by Grand Unification Theories-driven U(1)' gauge groups and by the sequential standard model. BSM (Beyond Standard Model) decays into supersymmetric final states are accounted for, besides the SM (Standard Model) modes usually investigated. I give an estimate of the number of supersymmetric events in Z' decays possibly expected at LHC, as well as of the product of the Z' cross section times the branching fraction into electron and muon pairs. (author)
[en] The Tevatron and LEP2 experiments presently provide the most precise direct determinations of the mass and width of the W boson. The combined results are: Mw = 80.394 ± 0.042 GeV and Γw = 2.095 ± 0.106 GeV. The results are in excellent agreement with the predictions of the Standard Model. In this article the latest results are described and the systematic errors which could limit further significant improvements in the precision of these measurements are reviewed