Search for Supersymmetric Particles

The increased LEP energy opens a new window to search for physics beyond the Standard Model. The supersymmetric extension of the Standard Model is very attractive in this context, since it predicts news particles in the 100 GeV mass range which should be visible at LEP. Up to now no SUSY particles have been observed. The exclusion limits both for sleptons ( the supersymmetric partners of the leptons ) and gauginos ( the supersymmetric partners of vector bosons and the Higgs particles ) have been increased significantly. In many cases they are already close to the kinematical limit.

The Lightest Supersymmetric Particle ( LSP ) which is stable in P-conserving supersymmetric models is a candidate for the dark matter in the universe. In most models the lightest neutralino turns out to be the LSP. Since it interacts only weakly with matter, it is essentially invisible in the detector. In order to derive mass limits for the lightest neutralino the various SUSY results are combined to exclude regions in the SUSY parameter space. Fig. 2.5 shows the resulting lower limits as function of the parameters tan$\beta$ and m₀. In this way neutralinos below 32 GeV can be excluded.

Figure 2.4: Excluded slepton masses as function of the neutralino mass.

Figure 2.5: Excluded neutralino masses.