Neutral-current four-fermion production in e⁺e^- interactions at LEP

Abstract

Neutral-current four-fermion production, e⁺ e^-→ƒƒ̅ƒ'ƒ̅', is studied in 0.7 fb^-1 of data collected with the L3 detector at LEP at centre-of-mass energies √s=183-209 GeV. Four final states are considered: qq̅νν̅qq̅ℓ⁺ℓ^-, ℓ⁺ℓ^-ℓ⁺'ℓ^-', and ℓ⁺ℓ^-ν⁺ν^-, where ℓ denotes either an electron or a muon. Their cross sections are measured and found to agree with the Standard Model predictions. In addition, the e⁺ e^-→Zγ*→ ƒƒ̅ƒ'ƒ̅'process is studied and its total cross section at the average centre-of-mass energy √s=196.6 GeV is found to be 0.29± 0.05±0.03 pb, where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model prediction of 0.22 pb. Finally, the mass spectra of the qq̅ℓ⁺ℓ^-final states are analysed to search for the possible production of a new neutral heavy particle, for which no evidence is found.