Improving the pair separation of WW/ZZ at the ILC by consideration of photon radiation in kinematic fits

The International Linear Collider (ILC) is intended for high precision measurements. This places enormous demands on detector precision in the ongoing detector development program. Precision can be further improved by application of a kinematic fit to the data, forcing energy and momentum conservation. However, this requires all energies and momenta to be considered. Initial state radiation and beamstrahlung are two processes which emit photons predominantly in the beam direction and which escape detection. Due to higher center-of-mass energy and stronger focussing of the beam, these processes will have more impact at the ILC than at earlier colliders. This thesis investigates the effects of these processes on kinematic fits at the example of the separation of events with WW/ZZ pair production events. Different approaches in consideration of these processes are pointed out. A kinematic fit was performed on a sample of simulated e+e- → u anti dd anti u events, forcing energy and momentum conservation and equal boson masses. It is shown that 25% more events can be covered in this fit, if photon radiation is taken into consideration using a basic approximation of the momentum spectrum of the photons. This method obtains even a further increase in resolution. Thus, a mass resolution of 1.9 GeV (without decay width) can be obtained. (orig.)