Dark matter at the International Linear Collider

The International Linear Collider (ILC) is a planned electron-positron collider with polarised beams and centre-of-mass energies of up to 500 GeV. By performing high-precision measurements of Standard Model observables and searches for new particles it can complement the potential of the Large Hadron Collider (LHC). One of the most prominent open questions in physics is the nature of dark matter. Weakly Interacting Massive Particles (WIMPs) are possible candidates for dark matter, which can be searched for at colliders. In this thesis, the expected sensitivity to a WIMP signal at the ILC is explored in a Monte Carlo study. The WIMPs are assumed to be produced in pairs together with a photon from initial state radiation, through which the process can be identified. A detector simulation at √(s)=500 GeV is performed for the International Large Detector (ILD) concept, including beam-induced backgrounds and the luminosity spectrum. In comparison to previous studies many aspects of the analysis are treated in a more realistic way: e.g. the cuts in the event generation have been updated, a complete description of the reconstruction in the crucial forward region has been added and the systematic uncertainties of the luminosity spectrum have been fully treated for the first time. In order to provide a model-independent WIMP search, the approach of effective operators is chosen to describe the new interaction. The photon energy spectra for different signal hypotheses and the distribution of the Standard Model background are used to calculate the expected 5σ discovery reach as well as the 2σ exclusion limits. For the example of a vector operator, energy scales of up to 3 TeV can be tested for WIMP masses <or similar 250 GeV assuming 20 years of operation. With beam polarisation the sensitivity can be increased and with the help of data sets taken with different polarisation configurations the effect of the systematic uncertainties can be significantly reduced. The role of the forward acceptance for the suppression of the Bhabha scattering background is quantified. With two different approaches, estimates for the sensitivity at other centre-of-mass energies than the 500 GeV of the full simulation can be calculated. This allows to provide results for the full ILC programme, e.g. energy scales of up to 1.4 TeV can be probed with an initial stage of the ILC at a centre-of-mass energy of 250 GeV, while energy scales of up to 4.5 TeV could be probed at √(s)=1 TeV.