Radiative Corrections to Z and W Propagators near Resonance

by M. PASSERA (University of Bern)

Thursday 21 Oct 1999, 14:00 → 14:15 Europe/Zurich

TH Auditorium (CERN)

The analysis of the Z resonant amplitude in general Rx gauges shows that, when the original on-shell definition of the Z mass is employed, a gauge dependence of the same magnitude as the current experimental error arises in the next-to-leading order (NLO) approximation. In the next order of expansion these unphysical effects are unbounded. The extension of this analysis to the W and quarks propagators in the resonance region shows new and more serious problems. The on-shell mass, when applied to photonic or gluonic diagrams, leads in fact in NLO to a non-convergent series in the resonance region. A solution to these difficulties, based on the concept of pole mass and width, is presented. The evaluation of the width in the conventional and pole formulations is also compared and shown to agree in NLO but not beyond.