Measurement of the branching fractions and forward-backward asymmetries of the Z0 into light quarks

The OPAL Collaboration

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23 Scopus citations


Using approximately 4.3 million hadronic Z0 decays collected with the OPAL detector at LEP between 1990 and 1995, we measure the branching fractions of the Z0 into up-type and down-type light quarks, Rq, and the forward-backward asymmetries, AFB(q), using high-momentum stable particles as a tag. Adopting a method that employs double tagged events to determine the flavour tagging efficiencies, and assuming the flavour independence of strong interactions and SU(2) isospin symmetry, we measure: Rd,s/(Rd + Ru + Rs) = 0.371 ±0.016 (stat.) ±0.016 (syst.) and AFB(d, s) = 0.068 ±0.035 (stat.) ±0.011 (syst.) , assuming the branching fractions and forward-backward asymmetries of down and strange quarks to be equal. The results are essentially free of assumptions based on hadronisation models. These results are in agreement with the Standard Model expectations and are used to infer the left and right handed couplings of strange/down quarks to the Z0, yielding gLd,s = -0.44-0.09+0.13 and gRd,s = +0.13-0.17+0.15. The results for the up quark, Ru/(Rd + Ru + Rs) = 0.258 ± 0.031 (stat.) ± 0.032 (syst.) and AFB(u) = 0.040 ±0.067 (stat.) ±0.028 (syst.), are fully negatively correlated and almost completely positively correlated, respectively, with the corresponding down-type results.

Original languageEnglish
Pages (from-to)387-400
Number of pages14
JournalZeitschrift fur Physik C-Particles and Fields
Issue number3
StatePublished - 1 Jan 1997
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


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