The number of neutrinos and the Z line shape

Thanks to a precise calibration and monitoring of the LEP beam energy the Z resonance line shape has been precisely measured, hence permitting accurate determinations of the Z mass and width. A large effort was spent on experiments for the measurement of the LEP luminosity, enabling the number of neutrino types to be precisely determined. The result, N/sub nu /=2.9841+or-0.0083, demonstrates the existence of only 3 neutrino species. (16 refs).