Invisible Events with Radiative Photons at LEP

A study of the radiative neutrino counting reaction e + e − → ν ¯ νγ at LEP1 and LEP2 energies is presented. An approximate expression for the spectrum of the observed photon is derived within the framework of the p t -dependent structure function approach. This is compared with an exact expression and found in agreement within the foreseen experimental accuracy. This model describing single-photon radiation can be applied to the more general case of initial-state single-photon emission accompanying invisible final-state events. Higher-order QED corrections due to undetected initial-state radiation are also included. The implementation in a Monte Carlo event generator is briefly described.