Single and multi-photon events with missing energy in e+e− collisions at =183 GeV

An analysis of single and multi-photon events with missing energy is performed using data collected with the L3 detector at LEP at centre-of-mass energies around 183GeV, for a total of 55.3 pb−1 of integrated luminosity. The results obtained are in good agreement with the Standard Model prediction and are used to derive the value for the e+e−→νν̄γ(γ) cross section as well as upper limits on cross sections of new physics processes. Several interpretations in supersymmetric models providing new limits on the masses of the lightest neutralino and of the gravitino are presented.