Supersymmetric $W$ Boson Decays as a Means to Search for Charginos and Neutralinos

Abstract

If the sneutrino mass is below the chargino mass, the dominant decay mode of the lightest chargino is via a two-body decay channel $\chi^{\pm}_1 \ra \tilde{\nu} + l^{\pm}$. Sneutrinos are invisible in $R$-parity conserving supersymmetric models and, if the mass gap $m(\chi^{\pm}_1)-m(\tilde{\nu})$ is sufficiently small, the soft decay lepton may escape detection leading to invisible chargino decays. This ``blind spot'' of the supersymmetry parameter space would jeopardize the chargino search at LEP2. We point out that such a scenario can be tested by searching for single $W$ events in $e^+e^- \ra W^+W^-$, with one $W$ boson decaying to visible leptons or quark jets, and the second $W$ boson decaying to invisible charginos and neutralinos.