Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
1995-11-08
Phys.Rev. D54 (1996) 4566-4577
Physics
High Energy Physics
High Energy Physics - Phenomenology
23 pages, REVTEX3.0, uses epsf.tex to insert figures; with 6 figures in encapsulated postscript form
Scientific paper
10.1103/PhysRevD.54.4566
We study the perturbative QCD series for the hadronic width of the Z boson. We sum a class of large ``pi^2 terms'' and reorganize the series so as to minimize ``renormalon'' effects. We also consider the renormalization scheme-scale ambiguity of the perturbative results. We find that, with three nontrivial known terms in the perturbative expansion, the treatment of the pi^2 terms is quite important, while renormalon effects are less important. The measured hadronic width of the Z is often used to determine the value of alpha_s(M_Z^2). A standard method is to use the perturbative expansion for the width truncated at order alpha_s^3 in the MS-bar scheme with scale mu = M_Z. We estimate that the determined value of alpha_s(M_Z^2) should be increased by 0.6% compared to the value extracted with this standard method. After this adjustment for pi^2 and renormalon effects, we estimate that the uncertainty in alpha_s(M_Z^2) arising from QCD theory is about 0.4%. This is, of course, much less than the experimental uncertainty of about 5%.
Soper Davison E.
Surguladze Levan
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