Exclusion bounds for neutral gauge bosons

We present a novel representation of the parameter space of $U(1)$ extensions of the standard model. The free parameters are the mass $M_{Z'}$ of the new neutral gauge boson $Z'$, the new gauge coupling or equivalently the mixing angle between the standard model $Z$ and the new $Z'$ boson and finally an appropriately chosen ration of the new $U(1)$ gauge charges. We use recent experimental data to constrain these parameters in the approximate range $(10^{-2},10^4)$ GeV/$c^2$ of $Z'$ masses. The role of the tree-level $\rho$ parameter as an indirect bound is investigated. Finally, we discuss the prospects of $Z'$ searches at future colliders.