Search for anomalous production of single photons at root s=130 and 136 GeV

This letter reports the results of the measurement of single photon production in the reaction e(+)e(-) --> gamma+ invisible particles at centre-of-mass energies root s = 130 and 136 GeV and an integrated luminosity of 5.83 pb(-1), collected with the DELPHI detector at LEP. The signal is compatible with the prediction of the Standard Model for the process e(+)e(-) --> nu<(nu)over bar>gamma, and the number of neutrino families has been determined to be N-nu = 3.1 +/- 0.6. Limits have been derived on anomalous neutral gauge boson couplings and on compositeness in the framework of a specific model.