  A study of Z boson pair production in e+e- annihilation at center-of-mass
energies near 183 GeV and 189 GeV is reported. Final states containing only
leptons, (l+l-l+l- and l+l-nu nubar), quark and lepton pairs, (q qbar l+l-, q
qbar nu nubar) and the all-hadronic final state (q qbar q qbar) are considered.
In all states with at least one Z boson decaying hadronically, q qbar and b
bbar final states are considered separately using lifetime and event-shape
tags, thereby improving the cross-section measurement. At sqrt(s) = 189 GeV the
Z-pair cross section was measured to be 0.80 (+0.14-0.13, stat.) (+0.06-0.05,
syst.) pb, consistent with the Standard Model prediction. At sqrt(s) = 183 GeV
the 95% C.L. upper limit is 0.55 pb. Limits on anomalous ZZgamma and ZZZ
couplings are derived.
