Decays of W bosons to charginos and neutralinos

The region of the supersymmetry parameter space, in which charginos decay predominantly into sneutrinos and leptons: χ1+ → ν + l+, is not excluded experimentally for small mass differences between charginos and sneutrinos. The decay sneutrinos are invisible in R-parity conserving theories since they are either the lightest supersymmetric particles or they decay primarily into the channel ν → ν + χ10. If the energy of the decay leptons is so small that they escape detection, chargino events e+e− → χ1+χ1− in e+e− collisions remain invisible, eroding the excluded chargino mass range at LEP. This region of the supersymmetry parameter space can partly be covered by searching for single W events in e+e− → W+W−, with one W boson decaying to leptons or quark jets, but the second W boson decaying to (undetected) charginos and neutralinos.