Hunting effective LSPs at LEP 200

Abstract

Relatively light sneutrinos, which are experimentally allowed, may significantly affect the currently popular search strategies for supersymmetric particles by decaying dominantly into an invisible channel. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy — in addition to the lightest supersymmetric particle (LSP)$\tilde Z_1$ — the effective LSPs (ELSPs). It is shown that these ELSPs are allowed in supergravity models with common scalar and gaugino masses at the unification scale for a sizable region of parameter space and are consistent with all constraints derived so far from SUSY searches. The pair production of right handed sleptons, which can very well be the lightest charged SUSY particles in this scenario, at LEP 200 and their decay signatures are discussed. The signal survives kinematical cuts required to remove the standard model background. Charginos are also pair produced copiously if kinematically accessible; they also decay dominantly into hadronically quiet di-lepton +$\not E_T$ modes leading to interesting unlike sign dilepton events which are again easily separable from the Standard Model backgrounds at LEP 200 energies.