A study of the top quark production threshold at a future electron-positron linear collider

Abstract

One of the most important physics targets for any future electron positron linear collider will be the precision measurements of the top quark properties, and especially the top quark mass. Top-antitop production at threshold provides the ideal environment for making such measurements but is complicated by the machine’s luminosity spectrum and thus needs to be carefully studied to understand the constraints involved and the potential precision reach. This thesis presents developments in both the understanding of the luminosity spectrum and the top quark production threshold by the means of new simulation tools and simulation results of systematic and statistical uncertainties in the measurements of the luminosity spectrum and the top quark parameters by the use of a threshold scan. The luminosity spectrum is studied by employing a new parametrization method that takes into account the beam energy spread in the fit parameters, and detailed simulation studies of the measurement of the luminosity spectrum by the use of Bhabha scattering events. A detailed account is given of the possible systematic uncertainties arising due to beam-beam and detector induced effects influencing the luminosity measurement, by looking at the different luminosity spectra of the International Linear Collider (ILC) Reference Design Report (RDR) accelerator parameter plane. A new simulation tool for the top quark production threshold is presented, in the form of a new fully differential Monte Carlo event generator using a state-of-the-art next-to-next-to leading order (NNLO) QCD calculation of the top quark production threshold in order to describe the total and differential distributions that can be used in the top threshold measurements, by including a full description of the luminosity spectrum. Finally, a study of how the uncertainties of the luminosity spectrum measurement can affect the top quark threshold measurements is presented, by examining simulated threshold scan measurements for the different luminosity spectra of the ILC RDR accelerator parameter plane