ATLAS ITk Silicon Strip Detector Performance Studies based on the System Test with Cosmic Muons at DESY

Abstract

The ATLAS experiment is the world’s largest collider-based particle physics experiment, located at the LHC in Geneva. An upgrade of the LHC will greatly increase the radiation environment and track density in the inner region of the detector. Therefore, an upgraded version of the innermost tracking detector, the ITk, is being developed. This thesis presents systems and experiments surrounding the ITk strip detector end cap. <br /> As an ATLAS authorship qualification task, components of this detector, the bus tapes, were tested using a custom flying probe robot. <br /> A System Test setup was constructed at DESY as a test bench for the end cap and its services. It allows the operation of the silicon strip modules in a realistic environment with cooling. A system for monitoring the safety and environmental variables of the setup was constructed. It was used to measure the tightness of the gas volume enclosing the System Test, showing that the petals are safe from condensation even in the event of a sudden stop of the external dry air supply. An additional setup for testing single petals, the petal coldbox, was developed. With the petal coldbox, the temperature-dependent on-module cooling performance was studied. <br /> Both setups were used to study the noise of the detector modules. The repeatability of the noise measurements was studied, and the results were compared to an alternative DAQ system. A way of mitigating noise artefacts by treatment with ionised air was successfully tested with one of the petals. The noise environment before and after loading the modules onto the petal, as well as the difference between the noise environments in the coldbox and System Test, were studied. Finally, a successful measurement of the noise crosstalk between the petal’s primary and secondary sides was performed. Using an external trigger setup, a cosmic muon signal was measured with a petal inserted into the System Test by performing a latency scan. This muon signal was clearly visible as an extended plateau when performing a threshold scan with the same setup. This constitutes the first measurement of a real particle signal with a fully loaded petal. <br /> During this thesis, simulation methods for the ITk strip end cap modules have been developed. In particular, a way to perform hit clustering in the native module coordinate system before transforming the cluster position and resolution into Cartesian coordinates is presented. The new simulation method was verified using a beam telescope made out of R0 modules, achieving the expected track reconstruction performance. Afterwards, a possible cosmic muon telescope setup in the System Test was investigated using Monte-Carlo simulations. The reconstruction of the cosmic muon flux from the simulated data was demonstrated, showing the feasibility of future cosmic muon tracking measurements with the System Test setup. The angular resolution of this setup was also determined and shown to be sufficient for measuring the flux. Finally, a method for determining the module efficiency exploiting the stereo module geometry is presented and demonstrated in a simulation scenario.