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Determination of the leptonic branching ratios of the Z

Research output: Contribution to Journal/MagazineJournal articlepeer-review

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  • ALEPH Collaboration
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<mark>Journal publication date</mark>1990
<mark>Journal</mark>Physics Letters B
Issue number3
Volume234
Number of pages10
Pages (from-to)399-408
Publication StatusPublished
<mark>Original language</mark>English

Abstract

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.