From Neutrino Physics to Beam Polarisation - a High Precision Story at the ILC

In this thesis, we investigate the experimental prospects of studying a supersymmetric model with bilinearly broken R parity at the International Linear Collider.In this model, neutrinos mix with the supersymmetric neutralinos such that neutrino properties can be probed by examining neutralino decays, which incorporate usually a lepton and a W /Z boson.As a study case, we focus on the determination of the atmospheric neutrino mixing angle θ 23 , which is accessible via the ratio of the neutralino branching ratios BRpr χ 0 1 Ñ W µq{ BRpr χ 0 1 Ñ W τ q.A detailed simulation of the International Large Detector has been performed for all Standard Model backgrounds and for r χ 0 1 -pair production within a simplified model.The study is based on ILC beam parameters according to the Technical Design Report for a centerof-mass energy of ?s " 500 GeV.From muonic r χ 0 1 decays, we find that the r χ 0 1 mass can be reconstructed with an uncertainty of δpm r χ 0 1 q " p40pstat.q' 35psyst.qqMeV for an integrated luminosity of şLdt " 500 fb ´1.The ratio of branching ratios can be determined to a precision of δpBRpr χ 0 1 Ñ W µq{ BRpr χ 0 1 Ñ W τ qq " 2.9%.Due to this, the atmospheric neutrino mixing angle can be deduced with a precision comparable to modern neutrino experiments.Thus, the ILC is capable to test whether bRPV SUSY is the mechanism of neutrino mass generation.As also shown in the bRPV SUSY study of this thesis, beam polarisation is an important parameter in physics analyses at the ILC.The beam polarisation is measured with two Compton polarimeters per electron/positron beam.In order to achieve the design goal of an envisaged precision of 0.25%, the detector nonlinearity of the used Cherenkov detectors has to be determined very precisely.Herein, the main source of nonlinearity is expected to originate from the involved photomultipliers.For this reason, a differential nonlinearity measurement as well as a linearisation method is developed.The working principle is demonstrated in a Monte-Carlo simulation, which is also utilised in order to deduce design parameters for the development of a calibration light source and an appropriate measurement setup.After extensive test measurements, the nonlinearity is determined using the proposed differential method.We find nonlinearities of the photomultiplier and its read-out chain of 1.0%˘0.1% and 0.4%˘0.1%,respectively, depending on the light intensity range.We show that the measured nonlinearity can be used in order to linearise an independent dataset.Finally, a possible application of the developed method in a sliding nonlinearity monitoring and correction scheme during the ILC data taking is outlined.xii