Measurement of the Z resonance parameters at LEP

• Main Authors: BARATE, R., THULASIDAS, M.
• Format: text
• Language: English
• Published: Institutional Knowledge at Singapore Management University 2000
• Subjects: Computer Sciences; Databases and Information Systems
• Online Access: https://ink.library.smu.edu.sg/sis_research/5848; https://ink.library.smu.edu.sg/context/sis_research/article/6851/viewcontent/ep_99_014.pdf
• Institution: Singapore Management University

The properties of the Z resonance are measured from the analysis of 4.5 million Z decays into fermion pairs collected with the ALEPH detector at LEP. The data are consistent with lepton universality. The resonance parameters are measured to be MZ=(91.1885±0.0031)GeV/c2MZ=(91.1885±0.0031)GeV/c2, ΓZ=(2.4951±0.0043)ΓZ=(2.4951±0.0043) GeV, σ0had=(41.559±0.058)σhad0=(41.559±0.058) nb and, combining the three lepton flavours, Rℓ=20.725±0.039Rℓ=20.725±0.039. The corresponding number of light neutrino species is Nν=2.983±0.013Nν=2.983±0.013 and the strong coupling constant is αs(MZ)=0.114±0.004±0.002QCD+0.005log10[MH150GeV/c2]αs(MZ)=0.114±0.004±0.002QCD+0.005log10⁡[MH150GeV/c2]. The lepton pair forward-backward asymmetry is measured to be A0,ℓFB=0.0173±0.0016AFB0,ℓ=0.0173±0.0016 from which the effective weak mixing angle is derived: sin2θlepteff=0.23089±0.00089sin2⁡θefflept=0.23089±0.00089. The measurement of the leptonic width Γℓℓ=84.02±0.15Γℓℓ=84.02±0.15 MeV leads to a determination of the effective ρρ parameter ρlepteff=1.0064±0.0018ρefflept=1.0064±0.0018. The data support the Standard Model and favour a light Higgs.