Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 130–172 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.