We report a high-precision measurement of the ratio R of the total cross section for e+e−→hadrons to that for e+e−→μ+μ−, at a center-of-mass energy of 29.0 GeV using the MAC detector. The result is R=3.96±0.09. This value of R is used to determine a value of the strong coupling constant αs of 0.23±0.06, nearly independent of fragmentation models. Two different analysis methods having quite different event-selection criteria have been used and the results are in agreement. Particular attention has been given to the study of systematic errors. New higher-order QED calculations are used for the luminosity determination and the acceptance for hadrons.
No description provided.
No description provided.
We measured the differential jet-multiplicity distribution in e+e− annihilation with the Mark II detector. This distribution is compared with the second-order QCD prediction and αs is determined to be 0.123±0.009±0.005 at √s≊MZ (at the SLAC Linear Collider) and 0.149±0.002±0.007 at √s=29 GeV (at the SLAC storage ring PEP). The running of αs between these two center-of-mass energies is consistent with the QCD prediction.
DIFFERENTIAL JET MULTIPLICITIES.
DIFFERENTIAL JET MULTIPLICITIES.