Z′ search in e+e− annihilation

Expectations for constraints on extra Z bosons are derived for LEP2 and future linear e⁺e^? colliders. For typical GUTs, a Z′ with M_Z′ ≤ 3 to $6sqrt {s}$ may cause observable effects. The Z′ discovery limits are dominated by statistical errors. However, if a Z′ signal is observed, the discrimination between different models becomes much worse if systematic errors are taken into account. Discrimination between models is possible for $M_{Z^{?ime}} < 3sqrt {s}$. A determination of Z′ff couplings independently of models becomes attractive with future colliders. Anticipated bounds are determined.