Single-photon signal from neutralinos at LEP2

Abstract

The production of invisible pairs of lightest neutralinos accompanied by a large-angle hard photon in the reaction $e^{+}{e}^{-}\to {\chi }_1^0{\chi }_1^0\gamma$ is studied at LEP2 energies. The most general gaugino/higgsino composition of the ${\chi }_1^0$ within the Minimal Supersymmetric Standard Model is assumed. The spectrum of the observed photon is derived within the framework of the $p_t$-dependent structure-function approach, whose accuracy is assessed to be within the foreseen 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 $e^{+}{e}^{-}\to \nu \bar{\nu }\gamma$ is performed for optimized photon kinematical cuts. Quantitative conclusions on the signal/background ratio are given for a wide range of values of the SUSY parameters.

Comments: 19 pages, 6 figures, uuencoded gzipped postscript file. Revised (->shortened) version. To be published in Nuclear Physics B