Top pair production at the ILC

The top quark is unique among all other quarks. Its short lifetime does not permit the top quark to form top-flavored hadrons or other bound states and allows therefore a direct measurement of its mass. The mass of the top quark enters the electroweak fit for the Higgs boson mass via radiative corrections and helps therefore to constrain the Higgs mass. It decays almost exclusively into a W boson and a b quark via the weak interaction. The W boson can decay either leptonically into a lepton-neutrino pair or hadronically into a quark-antiquark pair. This thesis deals with the production, detector simulation and analysis of t¯t pairs at the future International Linear Collider (ILC). The ILC is a e+e- collider with a center of mass energy of vs = 500GeV and a total luminosity of 500fb-1 within the first four years of operation. A precise method to measure the invariant mass and width of the top quark from the direct reconstruction of top quark decays is presented considering the fully hadronic decay and the semi-leptonic decay of t¯t pairs as signal processes. In the fully hadronic decay both W bosons decay into q¯q pairs and in the semi-leptonic decay one W boson decays into a q¯q pair and the other W boson into a lepton and a neutrino. In addition to the signal processes, various background processes are also taken into account. The Monte Carlo production of the t¯t and background events is performed using the software PYTHIA for an integrated luminosity of L = 20fb-1 and the simulation of the detector response is carried out with the software Mokka. The ILC detector used for simulation is the LDC’ detector, an intermediate detector designed as a first attempt to merge the European detector concept LDC and the Asian detector concept GLD. The data obtained from the detector simulation is analyzed within the Marlin software reconstruction framework. All particles are reconstructed according to the particle flow paradigm and clustered into jets. A challenging task is the determination of the correct assignment of jets (or lepton) to the W± and t¯t. The number of possible assignments is reduced by performing Flavour tagging in order to identify the two jets that originated from the b quarks. The values obtained for the invariant mass and width of the top quark are mt = 175.02±0.17(stat.)GeV and Tt = 1.67 ± 0.10(stat.)GeV