Measurement of the e + e ! ZZ Production Cross Section at Centre-of-Mass Energies of 183 and 189 GeV

Abstract The e + e − →ZZ cross section at s =182.7 and 188.6 GeV has been measured using the ALEPH detector. A cut-based analysis yields cross section measurements of σ ZZ (182.7 GeV )=0.11± 0.16 0.11 ( stat. )±0.04 ( syst. ) pb and σ ZZ (188.6 GeV )=0.69± 0.13 0.12 ( stat. )±0.03 ( syst. ) pb . A neural network-based analysis yields σ ZZ (188.6 GeV )=0.64± 0.12 0.11 ( stat. )±0.04 ( syst. ) pb . These measurements are consistent with the Standard Model expectations.