Search for New Particles and Study of Interactions between Particles with "OPAL" Detector at Electron Position Collider "LEP".

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The OPAL experiment, in which we are participating, is one of the four experiments at the large electron-positron collider at CERN (LEP) which started operation in August 1989 to study electron-positron reactions in the vicinity of the Z^0 resonance. We successfully recorded 30k Z^0 events in 1989, which led to numerous exciting findings from the beginning of the experiment. In the following years more and more Z^0 events (170k events in 1990 and 400k events in 1991) were collected to obtain yet more precise and significant results. Among the most important findings we have obtained are :1. Precise determinations of Z^0 properties (mass, total width, partial widths, etc.) which verified the validity of the standard model.2. There are only 3 generations of the elementary particles. This significantly constrained various models of the origin of the universe.3. The Higgs particle, elementary scalar particle essential in the standard model, is heavier than 51 GeV.4. The mass of the top quark, the sixth quaxk in the standard model, probably lies between 100 GeV and 180 GeV.5. No new particles, such as supersymmetric (SUSY) partners, exists up to the Zo energy region.6. Precise determination of the properties of the tau leptons and the bottom quarks, which were abundantly observed as decay products of the Z^0 particle. These data further signify the validity of the standard model.7. The coupling constant of the strong interaction was precisely determined. The theory of the Quantum Chromodynamics (QCD) was extensively examined in various ways.8. Grand Unified Theories were examined. The simplest SU (5) model proved not in accordance with our data, instead the SUSY SU (5) model looks most promising.As LEP keeps running at the Z^0 resonance, several millions of Z^0 events will be collected by the end of 1993, which will enable us to look for possible breakings of the standard model.