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A Measurement of R(b) using a double tagging method

Collaboration
Aug, 1998
40 pages
Published in:
  • Eur.Phys.J.C 8 (1999) 217-239
e-Print:
DOI:
Report number:
  • CERN-EP-98-137
Experiments:
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Abstract:
The fraction of Z to bbbar events in hadronic Z decays has been measured by the OPAL experiment using the data collected at LEP between 1992 and 1995. The Z to bbbar decays were tagged using displaced secondary vertices, and high momentum electrons and muons. Systematic uncertainties were reduced by measuring the b-tagging efficiency using a double tagging technique. Efficiency correlations between opposite hemispheres of an event are small, and are well understood through comparisons between real and simulated data samples. A value of Rb = 0.2178 +- 0.0011 +- 0.0013 was obtained, where the first error is statistical and the second systematic. The uncertainty on Rc, the fraction of Z to ccbar events in hadronic Z decays, is not included in the errors. The dependence on Rc is Delta(Rb)/Rb = -0.056*Delta(Rc)/Rc where Delta(Rc) is the deviation of Rc from the value 0.172 predicted by the Standard Model. The result for Rb agrees with the value of 0.2155 +- 0.0003 predicted by the Standard Model.
Note:
  • 42 pages, LaTeX, 14 eps figures included, submitted to European Physical Journal C Report-no: CERN-EP/98-137
  • electron positron: colliding beams
  • electron positron: annihilation
  • Z0: electroproduction
  • Z0: hadronic decay
  • bottom: pair production
  • Z0: branching ratio
  • bottom: semileptonic decay
  • particle identification: bottom
  • particle identification: (muon electron)
  • track data analysis: vertex
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