A global determination ofα _s (M_{Z^0 } ) at LEP
Abstract
The value of the strong coupling constant,α _s (M_{Z^0 } ), is determined from a study of 15 different observables in hadronic Z 0 and τ decays. The study includes global event shape variables, jet production rates, energy correlations, the Z 0 line shape and decay asymmetries and the hadronic branching fraction of τ-leptons. Differences between the αs values from the different observables can be consistently attributed to unknown higher order contributions to the MediaObjects/10052_2005_BF01558285_f1.tif calculations. These uncertaities may be parametrized by variations of the renormalization scale and of the parton virtuality to which the data are corrected, separately for each observable, resulting in a consistent description of the event shapes, jet rates and energy correlations with the valueα _s (M_{Z^0 } ) = 0.122_{ - 0.005}^{ + 0.006} in MediaObjects/10052_2005_BF01558285_f2.tif . The error is dominated by the theoretical uncertainties. Application of recent calculations which include the resummation of leading and next-to-leading logarithms to all orders for some observables confirm this result with a reduced sensitivity to renormalization scale variations. The Z 0 line shapes and τ-lepton branching ratios yieldα _s (M_{Z^0 } ) = 0.148 ± 0.021 andα _s (M_{Z^0 } ) = 0.123_{ - 0.007}^{ + 0.006} , respectively, in<Figure ID="Fig3" Float="No" Category="Standard"> MediaObjects/10052_2005_BF01558285_f3.tif </Figure>. These measurements and their uncertainties are entirely independent of each other and from event shape and jet observables; the good agreement of the resulting αs values thus constitutes an important consistency check of the reliability of perturbative QCD.
- Publication:
-
Zeitschrift fur Physik C Particles and Fields
- Pub Date:
- March 1992
- DOI:
- 10.1007/BF01558285
- Bibcode:
- 1992ZPhyC..55....1A