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

Abstract

Neutral-current four-fermion production, e⁺e^- → f ̄f f' ̄ f', is studied in 0.7 fb⁻¹ of data collected with the L3 detector at LEP at centre-of-mass energies √s = 183–209 GeV. Four final states are considered: q ̄qν ̄ν, q ̄qℓ⁺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 ^∗ → f ̄f f' ̄ f' 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 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.