ATLAS Transition Radiation Tracker and Higgs Physics Related to Extra Standard Model Families

The enhancement in the production cross-section of the Higgs boson via gluon fusion at hadron colliders due to the quarks of new SM families might be an indirect verification of the existence of extra SM families. With this motivation, we study the consequences of extra SM families on the observability of the Higgs boson. On the latter part of this thesis, we present the induced radioactivity studies of the ATLAS Inner Detector Transition Radiation Tracker (ID-TRT) and the TRT test run data analysis done to validate the performance of the detector under different conditions.