Z-Z' mixing in extended gauge models from LEP 1990 data

We have studied Z-Z' mixing in the extended gauge models of left-right and extra U(1) types. This has been carried out by performing simultaneous fits to the combined data of cross sections and asymmetries from the four LEP experiments which have collected over 550,000 Z0 decays in 1990. Two methods have been adopted to determine the mixing angle ξ0 by carrying out: (a) Standard Model dependent fits, where we calculate ρ f and sin2θ f from the Standard Model, and (b) Standard Model independent fit, where we keep ρ= and sin2θ=f as free parameters. Fitted values of the mixing angle ξ0, and deviation of the ρ parameter due to Z-Z' mixing are discussed