QCD Jet Simulation with Cms at Lhc and Background Studies to H→ γγ Process

We have simulated and reconstructed one million of QCD jet events. This study was done with CMS full detector simulation, based on GEANT3 package, and object-oriented CMS C++ reconstruction program. The understanding of QCD jet background is important for the Higgs search in two-photon decay mode. The comparison with other types of backgrounds was also done. It was shown that the isolation tools were important ones to isolate the signal process from the huge background one. Using the isolation criteria based on the information from PbWO₄ electromagnetic calorimeter and the tracker we were able to reduce the QCD jet background to 15% of the total one.