The CMS Pixel Detector Upgrades and Novel Timing-Sensor Technology

This dissertation focuses on the development of silicon detectors for precision tracking of charged particles in the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC). Part I of the thesis serves as an introduction to my dissertation. Part II of the thesis comprises the research of my dissertation. My work is divided in three different chapters. Chapter three describes my contributions to the construction of the CMS phase-one pixel detector, which has been in operation since 2017. The services for the barrel pixel detector are contained in four half-cylindrical shells, two on each side of the detector. The STs provide cooling and power, while allowing communication with and control of the detector. During the development phase, my role was to replicate a section of the ST in a test stand at UZH. The test stand was comprised of the ST electronics, some pixel modules, and a slice of the CMS DAQ system. I tested the ST electronics and developed the necessary verification and calibration procedures. I helped assemble and test the four final ST half-cylinders at UZH before they were shipped to PSI, where they were connected to the BPIX detector modules. I was part of the team that tested the system as a whole after the transport and assembly. Chapter four explains a simulation I developed to model spatial resolution for a future silicon sensor that is to be used in the CMS phase-two pixel detector. This new detector is designed to efficiently operate at higher pile-up, and extending the 𝜂 coverage from 2.4 to 4.0. It will feature improved technologies for the pixel modules, a more optimized layout, and a faster readout. A simulation software called tkLayout has been used to estimate the performance of different detector layouts. The tkLayout parametric simulation relies on basic physics principles, a detector layout configuration, and the resolution of the detector’s sensors. My toy simulation predicted the sensor’s resolution performance years before test beam results were available, and allowed for the optimisation of the detector layout while working in parallel on the sensor study. Chapter five covers my research into silicon pixel sensors with precise timing resolution, which are considered as an option for pixel detectors in a stage after the phase-two pixel upgrade. During my last years of the PhD I was lucky enough to work with low-gain avalanche diode (LGAD) detector technology. These interesting detectors achieve extremely good time resolution, of the order of 20-30 ps for charged particles and 5-10 ps for photons. I implemented a new lab setup at UZH with a radioactive strontium source that would allow us to measure the time resolution of these detectors. After characterising LGADs from different production batches and vendors, like FBK and CNM, I moved on to characterise a new promising type of detector, the AC-coupled LGAD. One of the setbacks of the LGAD is the relatively large region without multiplication (gain) between the pads, such that there is effectively a dead area with a width of 45-100 𝜇m, depending on the different design choices. This translates into a decreased active area or fill factor, especially in the case of a pixel-like implementation. The AC- LGAD technology resolves these problems and has a theoretical fill factor of 100%, while keeping an excellent time resolution performance, and also achieving spatial resolutions that outperform standard devices.