Electroweak measurements in electron–positron collisions at w-boson-pair energies at lep

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Determination of the leptonic branching ratios of the Z

The ratios of the numbers of Z bosons decaying to e+e−, μ+μ− and τ+τ− pairs to the number decaying to hadrons have been measured. The branching ratios and partial widths for each channel were determined and found to be equal, consistent with lepton universality. The mean leptonic branching ratio was found to be 0.0321 ± 0.0013 and the leptonic partial width to be 85.4 ± 5.3 MeV. The partial widths for hadronic decays and for invisible decays were deduced to be 1833 ± 116 MeV and 569 ± 92 MeV, respectively. The number of light neutrino types, assuming only the standard model value for the ratio , was found to be 3.35 ± 0.41

Search for the neutral Higgs boson from Z0 decay

A search for the neutral Higgs boson, using the processes , is performed on data collected by the ALEPH detector corresponding to about 11 550 events of Z0 → hadrons. Combining all these processes, the mass range excluded is 32 MeV−15 GeV at 95% CL and 40 MeV−12 GeV at 99% CL. The result from this experiment is unambiguous in the context of the standard model

ALEPH: A detector for electron-positron annihilations at LEP

The design, construction and performace of a large 4pi solid angle detector with soleinoidal magnet is described. The detector serves to study electron-positron annihilation processes at a centre of mass energy between 80 and 200 GeV at the Large electron positron storage ring (LEP) at CERN