Z boson pair production in e+e- collisions at √s = 183 and 189 Gev

Abstract 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 − ν ν ), quark and lepton pairs, ( q q l + l − , q q ν ν ) and the all-hadronic final state ( q q q q ) are considered. In all states with at least one Z boson decaying hadronically, q q and b b final states are considered separately using lifetime and event-shape tags, thereby improving the cross-section measurement. At 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 s =183  GeV the 95% C.L. upper limit is 0.55 pb . Limits on anomalous ZZ γ and ZZZ couplings are derived.