Supersymmetric Particle Production at HERA

In the framework of the minimal supersymmetric standard model and the $R$-parity breaking model, we investigate various production processes of the supersymmetric partner at HERA energies. Our emphasis is paid upon the scalar top quark, the partner of top quark, characterized by its lighter mass than the top quark and other scalar quarks in a model. We propose experimentally feasible approaches to search for clean signals of the stop from either its production or decay processes.