National Centre for Physics Quaid-e-Azam University Campus Shahdra Valley Road, Islamabad. Name: Waqar Ahmad Research Topic: Top Quark Kinematics and W- Polarization at CMS Academic Status: M.Phil University/Institute: University of Karachi Supervisor Name: Prof. Tehseen Rahim, Prof. Dr. Hafeez Hoorani Abstract: The top quark is the heaviest known elementary particle, discovered at the FERMILAB TEVATRON collider in 1995. Ever since its discovery in 1995, top quark has been the best candidate for the search of new physics. It is because its mass is extremely close to the electroweak symmetry breaking scale. The top quark interacts primarily by the strong interaction but can only decay through the weak force. Owing to its unusually huge mass and consequently short lifetime, its behavior is different from all other quarks. Unlike other quarks it decays without forming hadrons and its spin information is passed to its decay products. This makes it possible to measure observables that depend on the top quark spin, providing a unique environment for tests of the Standard Model and for searches for physics beyond the Standard Model. The best way to access particle spin information is to measure the angular distribution of its decay products. Depending upon the decay modes of W, ttbar can decay in three ways, i.e. fully leptonically, fully hadronically and semi-leptonically. This research focuses on semi-leptonic one i.e. The spin one W has three possible helicities; we label these as -1 (left-handed), 0 (longitudinal) and +1 (right-handed). The corresponding probabilities are , and respectively. W spin information can be inferred from angular distribution of the daughter particles in the W rest frame. In this work, I will study how top quark decays and W boson polarization at Compact Muon Solenoid (CMS) detector located at Large Hadron Collider (LHC). Current Status of Work: During my last visit to NCP, I studied my channel i.e. at generator level. .