SINGLE-PHOTON SIGNAL FROM NEUTRALINOS AT LEP2

The production of invisible pairs of lightest neutralinos accompanied by a large-angle hard e(+)e(-) --> <(chi)over tilde>(0)(1)<(chi)over t ilde>(0)(1) gamma is studied at LEP2 energies. The most general gaugin o-higgsino composition of the <(chi)over tilde>(0)(1) within the Minim al Supersymmetric Standard Model is assumed. The spectrum of the obser ved photon is derived within the framework of the p(t)-dependent struc ture-function approach, whose accuracy is assessed to be within the fo reseen experimental accuracy at LEP2. Higher-order QED corrections due to undetected initial-state radiation are also included. A comparison with the Standard Model main background from e(+)e(-) --> nu<(nu)over tilde>gamma is performed for optimized photon kinematical cuts. Quant itative conclusions on the signal/background ratio are given for a wid e range of values of the SUSY parameters.