Observability of “invisible” or “nearly invisible” charginos

Abstract

It is shown that if the charginos decay into very soft leptons or hadrons + $E/$ due to degeneracy or near degeneracy with the lightest supersymmetric particle or the sneutrino, the observability of the recently proposed signal via the single photon (+ soft particles) + $E/$ channel crucially depends on the magnitude of the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}$ mass due to destructive interferences in the matrix element squared. If the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}$'s and, consequently, left sleptons are relatively light, the size of the signal, previously computed in the limit ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}}\ensuremath{\rightarrow}\ensuremath{\infty}$ only, is drastically reduced. We present the formula for the signal cross section in a model independent way and discuss the observability of the signal at CERN LEP 192 and NLC energies.