Top quark pair production and calorimeter energy resolution studies at a future collider experiment

This thesis is focused on detector concepts and analyses
investigated at a future linear electron positron collider. For
precision measurements at such a collider, the CALICE collaboration
develops imaging calorimeters, which are characterized by a fine
granularity. CALICE has constructed prototypes of several design
options for electromagnetic and hadronic calorimeters and has
successfully operated these detectors during combined test beam
programs at DESY, CERN and Fermilab. To improve the hadronic energy
reconstruction and energy resolution of a hadron calorimeter
prototype with analog readout three software compensation
techniques are presented in this thesis, of which one is a local
and two are global software compensation approaches. One method is
based on a neural network to optimize the energy reconstruction,
while two are energy weighting techniques, depending on the energy
density. Weight factors are extracted from and applied to simulated
and test beam data and result in an average energy resolution
improvement of 15 - 25 % compared to a reconstruction without
software compensation. Whether such software compensation
techniques are also applicable to a detector concept for a future
linear electron positron collider is studied in the second part of
this thesis. Simulated data, two different hadronic detector models
and a local software compensation technique are used for this
study. The energy resolutions for single hadrons and for jets are
presented with and without software compensation. In the third part
of this thesis, a study on top quark pair production at a
center-of-mass energy of 500 GeV at the proposed electron positron
collider CLIC is presented. The analysis is based on full detector
simulations, including realistic background contributions dominated
by two photon processes. The mass and width of the top quark are
studied in fully-hadronic and semi-leptonic decays of top quark
pairs using event samples of signal and Standard Model background
processes, corresponding to an integrated luminosity of 100 fb^-1.
Statistical uncertainties of the top mass of 0.08 GeV and 0.09 GeV
are obtained for the fully-hadronic and the semi-leptonic channels,
respectively.