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

Neutral-current four-fermion production, e+e−→ff¯f′f¯′, is studied in 0.7 fb−1 of data collected with the L3 detector at LEP at centre-of-mass energies s=183-209GeV. Four final states are considered: qq¯νν¯, qq¯ℓ+ℓ−, ℓ+ℓ−ℓ′+ℓ′− and ℓ+ℓ−νν¯, 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∗→ff¯f′f¯′ process is studied and its total cross section at the average centre-of-mass energy 〈s〉=196.6GeV is found to be 0.29±0.05±0.03pb, 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 qq¯ℓ+ℓ− final states are analysed to search for the possible production of a new neutral heavy particle, for which no evidence is found.