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

Abstract

Neutral-current four-fermion production, e+e -→ff̄f′f̄′, 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: qq̄νν̄ , qq̄ℓ+ℓ-, ℓ+ℓ-ℓ′+ℓ′- and ℓ+ℓ-νν̄, 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 *→ff̄f′f̄′ 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 qq̄ℓ+ℓ- final states are analysed to search for the possible production of a new neutral heavy particle, for which no evidence is found.