THE EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS
Abstract
The production of single photons has been studied in the reaction e(+)e(-) --> gamma +invisible particles at centre-of-mass energies of 183 GeV and 189 GeV. A previously published analysis of events with multiphoton final states accompanied by missing energy has been updated with 189 GeV data. The data were collected with the DELPHI detector and correspond to integrated luminosities of about 51 pb(-1) and 158 ph(-1) at the two energies. The number of light neutrino families is measured to be 2.84 +/- 0.15(stat) +/- 0.14(syst). The absence of an excess of events beyond that expected from Standard Model processes is used to set limits on new physics as described by supersymmetric and composite models. A limit on the gravitational scale is also determined.
