Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 189-209 GeV at LEP

Abstract

Production of events with hadronic and leptonic final states has been measured in \({\rm e^+e^-}\) collisions at centre-of-mass energies of 130–172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward asymmetries are presented, both including and excluding the dominant production of radiative Z\(\gamma\) events, and compared to Standard Model expectations. The ratio \(R_{\rm b}\) of the cross-section for \({\rm b\bar b}\) production to the hadronic cross-section has been measured. In a model-independent fit to the Z lineshape, the data have been used to obtain an improved precision on the measurement of \(\gamma\)-Z interference. The energy dependence of \(\alpha_{\mathrm{em}}\) has been investigated. The measurements have also been used to obtain limits on extensions of the Standard Model described by effective four-fermion contact interactions, to search for \(t\)-channel contributions from new massive particles and to place limits on gaugino pair production with subsequent decay of the gaugino into a light gluino and a quark pair.