Test-beam measurements and simulation studies of thin pixel sensors for the CLIC vertex detector

Abstract

The multi- TeV e+e− Compact Linear Collider (CLIC) is one of the options for a future high-energy collider for the post-LHC era. It would allow for searches of new physics and simultaneously offer the possibility for precision measurements of standard model processes. The physics goals and experimental conditions at CLIC set high precision requirements on the vertex detector made of pixel detectors: a high pointing resolution of 3 μm, very low mass of 0.2% X0 per layer, 10 ns time stamping capability and low power dissipation of 50 mW/cm2 compatible with air-flow cooling. In this thesis, hybrid assemblies with thin active-edge planar sensors are characterised through calibrations, laboratory and test-beam measurements. Prototypes containing 50 μm to 150 μm thin planar silicon sensors bump-bonded to Timepix3 readout ASICs with 55 μm pitch are characterised in test beams at the CERN SPS in view of their detection efficiency and single-point resolution. A digitiser for AllPix, a Geant4-based simulation framework, has been developed in order to gain a deeper understanding of the charge deposition spectrum and the charge sharing in such thin sensors. The AllPix framework is also used to simulate the beam telescope and extract its tracking resolution. It is also employed to predict the resolution that can be achieved with future assemblies with thin sensors and smaller pitch. For CLIC, a full coverage of the vertex detector is essential while keeping the material content as low as possible. Seamless tiling of sensors, without the need for overlaps, by the active-edge technology allows for extending the detection capability to the physical edge of the sensor and thereby minimising the inactive regions. Thin-sensor prototypes containing active edges with different configurations are characterised in test-beams in view of the detection performance at the sensor edge. Technology Computer-Aided Design (TCAD) finite- element simulations are implemented to reproduce the fabrication and the operation of such devices. The simulation results are compared to data for different edge terminations.