Kinematic Fits to Determine Masses of Supersymmetric Particles at LHC

In this thesis the method of kinematic fits is applied to determine the masses of supersymmetric particles. This is implemented by a constrained least square fit. If Supersymmetryis realized with R-parity conservation, the produced supersymmetric particles decay directly or over a cascade into the lightest supersymmetric particle (LSP) which has to bestable and escapes undetected. Each massive particle in the decay chain can be used asa constraint on the invariant mass. With such constraints the unmeasurable momentumcomponents of the LSPs can be reconstructed.The masses of the Susy particles enter the fit as hypotheses. By scanning over themasses the fit is redone with different hypotheses. The χ2 of the fit is suitable to distinguish between good and bad hypotheses. Therefore the method can be used to measure the mass parameters. The technique is presented by means of the Susy modelmSUGRA. The branches of the signal cascade are g → q → χ0 /χ± → χ0 (LSP) and˜˜211q → χ0 /χ± → χ0 (LSP).˜211The challenges are the selection of the jets belonging to the cascade, the combinatorialbackground, and the background from other Susy events. This study shows that kinematic fits are capable to exclude regions in the parameter space and to indicate wherethe true masses lie.