Production of fermion-pair events in e+e− collisions at 161 GeV centre-of-mass energy

Cross-sections for hadronic and leptonic two-fermion events, and leptonic forward-backward asymmetries, have been measured in e+e− collisions at a centre-of-mass energy of 161 GeV, using the OPAL detector at LEP. Results are presented both including and excluding the dominant production of radiative γZ0 events. We have measured Rb, the ratio of the number of bb to all multihadronic events at 161 GeV, and compared it to the result obtained at 130–136 GeV. All results agree well with the Standard Model expectations. In a model-independent fit to the Z0 lineshape, the data presented here give an improved precision on the γZ0-interference term. The data have also been used to obtain new limits on extensions of the Standard Model described by effective four-fermion contact interactions.