Abstract : This thesis is based on baryon number and then R-Parity (Rp) violation, both allowed
in the Minimal Supersymmetric Standard Model (MSSM) framework.
This hypothesis leads to supersymmetric particles' decay topologies significantly different
from those ever studied and opens new possibilities on searches for supersymmetry.
We will detail throughout this work the phenomenological consequences of the baryon
number violation hypothesis, the resulting decay signatures in an e+e- collider and
the analysis setup developped to isolate these decays in the data collected by the L3
experiment at LEP between 1997 and 2000.
In order to validate the search methods developped, we also measured the cross-section
of the process e+e- -> ZZ -> q qbar q' q'bar.