514 research outputs found

    Muon-pair and tau-pair production in two-photon collisions at LEP

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    The QED processes e^+e^−→e^+e^−μ^+μ^− and e^+e^−→e^+e^−τ^+τ^− are studied with the L3 detector at LEP using an untagged data sample collected at centre-of-mass energies 161 GeV⩽√s⩽209 GeV. The τ-pairs are observed through the associated decay of one τ into eνν and the other into ππν. The cross sections are measured as a function of √s. For muon pairs, the cross section of the γγ→μ^+μ^− process is also measured as a function of the two-photon centre-of-mass energy for 3 GeV⩽W_(γγ)⩽40 GeV. Good agreement is found between these measurements and th

    Effect of solid waste landfill organic pollutants on groundwater in three areas of Sicily (Italy) characterized by different vulnerability

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    The aim of this study was to obtain information on the presence and levels of hazardous organic pollutants in groundwater located close to solid waste landfills. Eighty-two environmental contaminants, including 16 polycyclic aromatic hydrocarbons (PAHs), 20 volatile organic compounds (VOCs), 29 polychlorinated biphenyls (PCBs), 7 dioxins (polychlorinated dibenzo-p-dioxins, PCDDs) and 10 furans (polychlorinated dibenzofurans, PCDFs) were monitored in areas characterised by different geological environments surrounding three municipal solid waste landfills (Palermo, Siculiana and Ragusa) in Sicily (Italy) in three sampling campaigns. The total concentrations of the 16 PAHs were always below the legal threshold. Overall, the Fl/Fl + Py diagnostic ratio revealed that PAHs had a petrogenic origin. VOC levels, except for two notable exceptions near Palermo landfill, were always below the legal limit. As concerns PCB levels, several samples were found positive with levels exceeding the legal limits. It is worth noting that the % PCB distribution differs from that of commercial compositions. In parallel, some samples of groundwater containing PCDDs and PCDFs exceeding the legal threshold were also found. Among the 17 congeners monitored, the most abundant were the highest molecular weight ones

    Electroweak measurements in electron–positron collisions at W-boson-pair energies at LEP

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    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, L3 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 Γ_W, the branching fraction of W decays to hadrons, B(W → had), and the trilinear gauge-boson self-couplings g^z_1, κ_γ and λ_γ are determined to be: M_W = 80.376 ± 0.0333 GeV Γ_W = 2.195 ± 0.083 GeV B(W → had) = 67.41 ± 0.27% g^z_1 = 0.984^(+0.018)_(-0.020) κ_γ = 0.982 ± 0.042 λ_γ = -0.022 ± 0.01

    Muon-pair and tau-pair production in two-photon collisions at LEP

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    The QED processes e^+e^−→e^+e^−μ^+μ^− and e^+e^−→e^+e^−τ^+τ^− are studied with the L3 detector at LEP using an untagged data sample collected at centre-of-mass energies 161 GeV⩽√s⩽209 GeV. The τ-pairs are observed through the associated decay of one τ into eνν and the other into ππν. The cross sections are measured as a function of √s. For muon pairs, the cross section of the γγ→μ^+μ^− process is also measured as a function of the two-photon centre-of-mass energy for 3 GeV⩽W_(γγ)⩽40 GeV. Good agreement is found between these measurements and th

    Results of L3 BGO calorimeter calibration using an RFQ accelerator

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    A novel calibration system based on a radio-frequency-quadrupole (RFQ) accelerator has been installed in the L3 experiment. Radiative capture of 1.85 MeV protons from the RFQ accelerator in a lithium target produces a high-intensity flux of 17.6 MeV photons which are used to calibrate 11,000 crystals of the L3 BGO calorimeter. In this paper, we present results of the first fully successful RFQ run, taken in November 1997. We achieved a calibration precision of 0.6% in the barrel and 0.7% in the endcaps of the L3 BGO calorimeter. The RFQ-97 calibration proved to be the best one of all calibration techniques used in the L3 experiment
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