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The Large Hadron Collider (LHC) currently in operation intends to explore particle physics on the TeV scale. The International Linear Collider (ILC) and the Compact Linear Collider (CLIC) are being designed to measure the properties of particles possibly discovered at the LHC with high precision. Very forward detector systems at these machines are needed for the precise measurement of the luminosity and to approach full polar angle coverage. In the current detector concepts for linear collider detectors two electromagnetic calorimeters, Beam Calorimeter (BeamCal) and Luminosity Calorimeter (LumiCal), are foreseen. Both calorimeters are designed as sandwich calorimeters with tungsten absorber layers instrumented with finely segmented sensors. Due to a large amount of beamstrahlung remnants hitting BeamCal at the innermost radii, the sensors must withstand up to 1 MGy radiation dose per year. In this thesis two types of sensor materials were investigated: single crystal chemical vapour deposition diamonds (scCVDD) and gallium arsenide doped by chromium (GaAs:Cr). The very forward calorimeters ensure coverage for high energy electrons, positrons and photons down to very low polar angles. Within this thesis, simulation studies are presented for different beam parameters of the ILC. A new sensor segmentation was proposed to achieve better reconstruction efficiency of single high-energy electrons, positrons and photons on top of the beamstrahlung background. Only for a few years ago polycrystalline diamond sensors have been used for beam diagnostics in high-energy physics experiments. The Compact Muon Solenoid experiment, CMS, at the LHC is instrumented with several detectors for the Beam Conditions and Radiation Monitoring. The Fast Beam Conditions Monitor (BCM1F) is part of these systems. Here for the first time single crystal diamond sensors have been used. Eight detectors, comprising each a single crystal sensor and front-end electronics, are positioned around the beam pipe on both sides of the interaction region. They monitor the beam halo to protect the inner CMS detectors from adverse beam conditions and ensure high quality data for CMS. In this thesis, BCM1F data is evaluated for intrinsic time resolution and performance under harsh radiation conditions. Furthermore, it is investigated if it can be used for a bunch by bunch on-line luminosity measurement. The second type of sensor, made of GaAs:Cr, was produced in Tomsk State University and tested as a candidate for the BeamCal for future ILC and CLIC detectors. Several GaAs:Cr sensors were characterized in the laboratory for leakage current and capacitances and used for test beam investigations. Two sensors were assembled with a fan-out, front-end and ADC ASICs to build a fully functional prototype of a sensor plane. Several test beam campaigns were done to measure the performance of the system.
The International Linear Collider offers a lot of different interesting challenges concerning the physics of elementary particles as well as the development of accelerator and detector technologies. In this thesis, we investigate two rather separate topics - the precision measurement of the Higgs boson mass and of its coupling to the neutral gauge boson Z and the research and development of sensors for BeamCal, which is a sub-detector system of the ILC detector. After the Higgs boson has been found, it is important to determine its properties with high precision. We employ the Higgs-strahlung process for this purpose. A virtual Z boson is created in the electron-positron collisions, which emits a Higgs-boson while becoming on-shell. Using the so-called recoil technique, we determine the Higgs boson mass by reconstructing the Z boson momentum and using the center-of-mass energy of the colliding leptons. This technique allows to measure the Higgs boson mass without considering the Higgs boson decay, i.e. it can be applied even to a Higgs boson invisibly decaying. Monte-Carlo studies including a full detector simulation and a full event reconstruction were performed to simulate the impact of a realistic detector model on the precision of the Higgs boson mass and production cross-section measurement. Also, an analytical estimate of the influence of a given detector performance on the Higgs boson mass measurement uncertainty is given. We included a complete sample of background events predicted by the Standard Model, which may have a detector response similar to the signal events. A probabilistic method is used for the signal-background separation. Several other probabilistic methods were used to investigate and improve the measurement of the Higgs-strahlung cross-section and the Higgs boson mass from the recoil mass spectrum obtained after the signal-background separation. For a Higgs boson mass of 120 GeV, a center-of-mass energy of 250 GeV and an integrated luminosity of 50/fb, a relative uncertainty of 10% is obtained for the cross-section measurement, and a precision of 118 MeV for the Higgs boson mass. The original motivation to use the recoil technique for a Higgs boson mass measurement independent on its decay modes could not be completely confirmed. For a Higgs boson mass of 180 GeV and 350 GeV, a statistics corresponding to 50/fb is not sufficient to achieve the necessary significance of the recoil mass peak above the background. The BeamCal is a calorimeter in the very forward region, about 3 m away from the nominal interaction point and surrounding the beam pipe. Due to its location, a lot of beamstrahlung pair particles will hit this calorimeter, representing a challenge for the operational reliability of the sensors under such harsh radiation conditions. We investigated single-crystal and polycrystalline CVD diamond, gallium arsenide and radiation-hard silicon as sensor candidates for their radiation hardness and found that diamond and gallium arsenide are promising. We used a 10 MeV electron beam of few nA to irradiate the samples under investigation up to doses of 5 MGy for diamond, up to about 1.5 MGy for gallium arsenide and up to about 90 kGy for silicon. We measured in regular periods the CCD to characterize the impact of the absorbed dose on the size of the signal, which is generated by electrons of a Sr-90 source crossing the sensor. Additional measurements such as the dark current and the CCD as functions of the voltage completed the characterization of the sensor candidates. For the single-crystal CVD diamond, also the thermally stimulated current was measured to determine amongst others the defect density created by irradiation. In the diamond samples, evidence for strong polarization effects inside the material was found and investigated in more detail. A phenomenological model based on semi-conductor physics was developed to describe the sensor properties as a function of the applied electric field, the dose and the dose rate. Its predictions were compared with the results of the measurements. Several parameters such as time scales and cross-sections were determined using this model, which led to ongoing investigations.