On the electroweak and gluonic corrections to the hadronic width of the Z boson

Abstract

The electroweak corrections to the Z-boson hadronic width are presented in a simple analytical form for the width itself, Λ h , for its ratio to the leptonic width, R l = Λ h Λ l , for the Λ b Λ h ratio, and for the total width Λ Z . The rational parametrization, advocated in our recent papers on leptonic decays, simplifies the analysis of the hadronic decays too. There are two main results of this analysis: (1) All electroweak precision measurements agree within 1 σ with the electroweak Born approximation if the gluon coupling constant α s = 0.12 . Thus the electroweak radiative corrections have not been observed experimentally. The unexpected smallness of electroweak radiative corrections is caused by the mutual cancellation of the large positive contribution of a heavy top quark and the large negative contribution of all other virtual particles. (2) With electroweak radiative corrections being taken into account, the value of α s extracted from the experimental value of Λ Z differs by ⩾ 3σ from that obtained from R l , if m t ⩾ 200 GeV; they agree within 1σ if m t ⩾ 150 GeV. Thus a low upper limit on m t can be obtained from hadronic decays of the Z-boson alone, even without data on its leptonic decays.