Determination of alpha-s for b quarks at the Z0 resonance
Collaboration
21 pages
Published in:
- Phys.Lett.B 307 (1993) 221-236
Report number:
- CERN-PPE-93-59
Experiments:
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Abstract: (Elsevier)
The strong coupling constant for b quarks has been determined, and its flavour independence, as predicted by QCD, investigated. The analysis involved events with lepton candidates selected from approximately 356 000 hadronic decays of the Z 0 , collected by the DELPHI detector at LEP in 1990 and 1991. A method based on a direct comparison of the three-jet fraction in a b enriched sample, selected by requiring leptons with large momenta, to that of the entire hadronic sample, illustrated the significant effect of the b quark mass on the multi-jet cross section, and verified the flavour independence of the strong coupling constant to an accuracy of ±6%. A second procedure based on a fit to the momentum and transverse momentum spectra of the lepton candidates in both two-jet and three (or more)-jet event samples simultaneously determined the b content in each, and, using second order QCD calculations, gave an absolute measurement of α s for b quarks of 0.118±0.004 (stat.)±0.003 (syst.)±0.008 (scale). A comparison with α s for all quark flavours, as measured from the three-jet fraction in all hadronic events, further allowed the coupling strength for b quarks to be expressed in terms relative to that for udsc quarks, thereby cancelling certain common systematic uncertainties, and yielded α s b α s udsc = 1.00 ± 0.04 ( stat. ) ± 0.03 ( syst. ) .- electron positron: colliding beams
- colliding beams: electron positron
- electron positron: annihilation
- annihilation: electron positron
- Z0: electroproduction
- electroproduction: Z0
- Z0: nonleptonic decay
- nonleptonic decay: Z0
- coupling constant: strong interaction
- strong interaction: coupling constant
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