Recherche de supersymetrie dans les canaux avec un ou deux leptons avec le detecteur L3 a LEP

摘要

The present thesis presents two different acpects of my work in the L3 experiment, which areon one side the search for supersymmetric particles, the scalar leptons, in two different topologies :" electron + X + Ebar " and " 2 leptons + 2 photons + Ebar ", each of them being related to two theoretical SUSY models, m-SUGRA and GMSB. On the other side my work has been completed bythe study of the BGO cristal electromagnetic calorimeter of L3, and the calibration of the electromagnetic calorimeter EGAP. After the essential motivations being reviewed, the production anddesintegration modes are detailled concerning the scalar lepton sector at LEP. Then one presentsthe analysis techniques which I used to perform my selection, and also the results obtained from thedata collected by L3 for center of mass energies between 183 GeV and 202 GeV. The selectioncriteria that allow to isolate the events I looked for, including efficiencies but also the backgroundrate coming from Standard Model that one can expect are presented. The final interpretations ofthose results in both frameworks of m-SUGRA and GMSB are detailled at the end of this thesis.I took benefit of those results to derive some limits on the masses of the scalar leptons that donot depend on the free parameters of the SUSY models, especially on the selectron mass in theframework of m-SUGRA: M > 71:2 GeV