Precision Tests of Perturbative QCD at the Neutral Z Boson Peak
Abstract
A QCD analysis of hadronic decays of the Z ^0 in e^+e^ annihilation is presented. Jet production rates and other infrared safe observables (C planarity, oblateness and thrust) are studied in order to test the predictions of o(alpha_sp{s}{2}) QCD calculations. To provide a complete accountability of theoretical uncertainties, different recombination schemes in the cluster jet algorithm have been used; thus the ambiguity caused by the degree of freedom provided by the theory to define jets is investigated. It is found that different schemes predict different jet rates, and the difference is reproduced by the experimental data. It is demonstrated that the scheme ambiguity can be totally removed by consistently applying the same scheme at theoretical and experimental levels and that the values of alpha_ {s} thus determined from different schemes agree with each other. A special emphasis is given on estimating the theoretical uncertainties. The uncertainties due to the hadronization, parton virtuality, renormalization scale and the experimental systematics are estimated. The alpha_{s} values determined from different observables are found to be in agreement with each other and with the theoretical predictions based on the lower energy experiments. The theoretical uncertainties are found to be dominant over the experimental ones and hence the higher order calculations are required to further improve the results. The theoretical predictions for the renormalization scale mu^2 optimized to o( alpha_sp{s}{2}) are calculated using various QCD inspired procedures, and are compared to the optimized scale deduced from the experiment. An experimental procedure to eliminate the renormalization scale ambiguity is presented. The overall conclusion is that QCD is apparently a valid theory of strong interactions, and higher order calculations are indispensable to further improve the precision of these tests.
 Publication:

Ph.D. Thesis
 Pub Date:
 1991
 Bibcode:
 1991PhDT.......344S
 Keywords:

 Z BOSON;
 Physics: Elementary Particles and High Energy