BUSKULIC, D (reprint author), CNRS, IN2P3, PHYS PARTICULES LAB, F-74019 ANNECY LE VIEUX, FRANCE.
The ALEPH detector at LEP is used to study single photon events in e+e- collisions at the Z resonance. In a total data sample of 15.7 pb-1 taken in 1990 and 1991 scanning the resonance, 400 events were recorded where each has a single deposition of more than 1.5 GeV measured in the polar angular region \costheta(gamma)\ < 0.74 of the electromagnetic calorimeter. It is shown that this number of events can be accounted for by known processes. After subtraction of background events, the invisible width of the Z is determined to be 450 +/- 34(stat.) +/- 34(syst.) MeV. Using Z resonance parameters derived by ALEPH, the corresponding number of light neutrino generations is found to be 2.68 +/- 0.20(stat.) +/- 0.20(syst.).