# Top Quark Physics with the CMS Experiment

source: CMS/CERN

The top quark is the heaviest elementary particle in the Standard Model of particle physics. Its mass is almost 180 times larger than that of a proton. The top quark was observed for the first time in 1995 at the Tevatron (Fermilab, Chicago) which provided sufficient energy in proton-antiproton collisions to produce top-antitop quark pairs. Nowadays, large numbers of top quarks are produced at the LHC (CERN, Geneva), which has brought it the title of being a top factory in analogy to the very successful B-factories KEKB and PEP-II. The large centre-of-mass energy, the high intensity and collision rate of the proton beams at the LHC, allow the study of the properties of top quarks such as its production mechanisms, mass, and charge, in far greater detail than previously possible.

The CMS group of the Universität Hamburg focusses on measuring the top quark pair production rate (inclusively and differentially) in proton-proton collisions and on measuring the top quark mass. These types of high-precision measurements provide important tests to the understanding of the top quark within the Standard Model.
These measurements also form a crucial basis for searches beyond the Standard Model, because top quark production often appears as a dominant background in scenarios extending the Standard Model, such as supersymmetry and a sequential fourth generation. Many extensions of the Standard Model also predict top quark rich final states. At the same time the top quark mass is a powerful parameter in the electro-weak theory that contrains the allowed region of possible masses for a Standard Model Higgs boson.