292 research outputs found
Measurement of the Mass of the
No full textThe mass of the Z boson has been determined by combining the data from the four LEP experiments ALEPH, DELPHI, L3 and OPAL. The dominant error arises from uncertainties in the calibration of the energy of the beams in LEP. A programme of investigations including energy calibration by resonant depolarization of transversely polarized beams has led to a significant reduction of the uncertainty on the Z mass compared with the precision achieved with the 1990 data. The mass of the Z is measured to be M Z = (91:187 \Sigma 0:007) GeV. (subm. to Phys. Lett. B) 1) Author list see [1] 2) Lists of authors can be found in the references listed under [2] 1 Introduction The mass, M Z , of the neutral weak boson is a fundamental parameter of nature and the large electron-positron collider, LEP, at CERN is the ideal place to measure it precisely. Although the precision of present tests of the standard model requires a knowledge of M Z to only a few tens of MeV, a direct measurement of the mass ..
Search for Neutral MSSM Higgs Bosons at LEP
No full textThe four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted within the framework of the Minimal Supersymmetric Standard Model (MSSM). the data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and for a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are thus used to set upper bounds on the cross sections of various Higgs-like event topologies. The results are interpreted within the MSSM for a number of "benchmark" models, including CP-conserving and CP-violating scenarios. In all cases these interpretations lead to large exclusions in the MSSM parameter space. In some scenarios absolute limits are set on the masses of neutral Higgs bosons
A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model
No full textThis note presents a combination of published and preliminary electroweak results from the four LEP collaborations and the SLD collaboration which were prepared for the 2004 summer conferences. [...] The main changes with respect to the experimental results presented in summer 2003 are updates to the W branching fractions and four-fermion cross sections measured at LEP-2, and the SLD/LEP heavy-flavour results measured at the Z pole. The results are compared with precise electroweak measurements from other experiments, notably the final result on the electroweak mixing angle determined in neutrino-nucleon scattering by the NuTeV collaboration, the latest result in atomic parity violation in Caesium, and the measurement of the electroweak mixing angle in Moller scattering. The parameters of the Standard Model are evaluated, first using the combined LEP electroweak measurements, and then using the full set of high- electroweak results
Representing the LEP Collaborations
No full textThe status of the LEP precision measurements is reviewed, covering the electroweak measurements at the Z0, the studies of fermion pair production, and the totally new subject of W physics at LEP-2. The results presented here include both published and preliminary ones. These precision results are used to check the overall consistency of the Standard Model, and in its framework, constraints on its parameters are derived. For some of the topics, some details of the experimental procedure are also discussed. A major subject of the LEP e + e collider at CERN is to explore the Standard Model in a precise and systematic manner. An e + e collider with the center-ofmass energy su cient tocover all known gauge bosons,,Z0,W, and the gluon, allows precision studies of the interaction of these particles with fermions, as wel
Search for the standard model Higgs boson at LEP
No full textThe four LEP Collaborations, ALEPH, DELPHI, L3 and OPAL, have collected a total of 2461 pb(-1) of e(+)e(-) collision data at centre-of-mass energies between 189 and 209 GeV. The data are used to search for the Standard Model Higgs boson. The search results of the four Collaborations are combined and examined in a likelihood test for their consistency with two hypotheses: the background hypothesis and the signal plus background hypothesis. The corresponding confidences have been computed as functions of the hypothetical Higgs boson mass. A lower bound of 114.4 GeV/c(2) is established, at the 95% confidence level, on the mass of the Standard Model Higgs boson. The LEP data are also used to set upper bounds on the HZZ coupling for various assumptions concerning the decay of the Higgs boson
Search for the Standard Model Higgs boson at LEP
No full textThe four LEP Collaborations, ALEPH, DELPHI, L3 and OPAL, have collected a total of 2461 pb^(−1) of e^+e^− collision data at centre-of-mass energies between 189 and 209 GeV. The data are used to search for the Standard Model Higgs boson. The search results of the four Collaborations are combined and examined in a likelihood test for their consistency with two hypotheses: the background hypothesis and the signal plus background hypothesis. The corresponding confidences have been computed as functions of the hypothetical Higgs boson mass. A lower bound of 114.4 GeV/c^2 is established, at the 95% confidence level, on the mass of the Standard Model Higgs boson. The LEP data are also used to set upper bounds on the HZZ coupling for various assumptions concerning the decay of the Higgs boson
A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model
No full textThis note presents a combination of published and preliminary electroweak results from the four LEP collaborations and the SLD collaboration which were prepared for the 2003 summer conferences. Averages from \Zzero resonance results are derived for hadronic and leptonic cross sections, the leptonic forward-backward asymmetries, the polarisation asymmetries, the \bb and \cc partial widths and forward-backward asymmetries and the \qq charge asymmetry. Above the \Zzero resonance, averages are derived for di-fermion cross sections and forward-backward asymmetries, photon-pair, W-pair, Z-pair, single-W and single-Z cross sections, electroweak gauge boson couplings, W mass and width and W decay branching ratios. Also, an investigation of the interference of photon and Z-boson exchange is presented, and colour reconnection and Bose-Einstein correlation analyses in W-pair production are combined. The main changes with respect to the experimental results presented in summer 2002 are updates to the mass of the W boson, four-fermion cross sections and gauge couplings, all measured at LEP-2, and the LEP heavy-flavour results measured at the Z pole. The results are compared with precise electroweak measurements from other experiments, notably the recent final result on the electroweak mixing angle determined in neutrino-nucleon scattering by the NuTeV collaboration and the new result in atomic parity violation in Caesium. The parameters of the Standard Model are evaluated, first using the combined LEP electroweak measurements, and then using the full set of electroweak results
A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model
No full textThis note presents a combination of published and preliminary electroweak results from the four LEP collaborations ALEPH, DELPHI, L3 and OPAL based on electron-positron collision data taken at centre-of-mass energies above the Z-pole, 130 \GeV to 209 \GeV (\LEPII), as prepared for the 2006 summer conferences. Averages are derived for di-fermion cross sections and forward-backward asymmetries, photon-pair, W-pair, Z-pair, single-W and single-Z cross sections, electroweak gauge boson couplings, W mass and width and W decay branching ratios. An investigation of the interference of photon and Z-boson exchange is presented, and colour reconnection and Bose-Einstein correlation analyses in W-pair production are combined. The main changes with respect to the experimental results presented in 2005 are new preliminary combinations of final {\LEPII} results on the mass and width of the W boson. Including the precision electroweak measurements performed at the Z pole published recently, the results are compared with precise electroweak measurements from other experiments, notably CDF and D{\O}at the Tevatron. Constraints on the input parameters of the Standard Model are derived from the results obtained in high- interactions, and used to predict results in low- experiments, such as atomic parity violation, M{\"o}ller scattering, and neutrino-nucleon scattering
A combination of preliminary measurements of triple gauge boson coupling parameters measured by the LEP experiments
No full textA Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model
No full textThis note presents a combination of published and preliminary electroweak results from the four LEP collaborations ALEPH, DELPHI, L3 and OPAL based on electron-positron collision data taken at centre-of-mass energies above the Z-pole, 130 \GeV to 209 \GeV (\LEPII), as prepared for the 2005 summer conferences. Averages are derived for di-fermion cross sections and forward-backward asymmetries, photon-pair, W-pair, Z-pair, single-W and single-Z cross sections, electroweak gauge boson couplings, W mass and width and W decay branching ratios. An investigation of the interference of photon and Z-boson exchange is presented, and colour reconnection and Bose-Einstein correlation analyses in W-pair production are combined. The main changes with respect to the experimental results presented in 2004 are updates to some 4-fermion cross sections, final results on BE correlations and a new preliminary combination of the mass and width of the W boson. Including the precision electroweak measurements performed at the Z pole published recently, the results are compared with precise electroweak measurements from other experiments, notably CDF and D{\O}at the Tevatron. Constraints on the input parameters of the Standard Model are derived from the results obtained in high- interactions, and used to predict results in low- experiments, such as atomic parity violation, Moller scattering, and neutrino-nucleon scattering
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