Measuring Radiation Damage in the ATLAS IBL, Including Comparisons Between 3D and Planar Silicon Sensors

Abstract

Silicon pixel detectors are a fundamental part of high energy physics experiments, providing high-precision tracking of ionising radiation. The Insertable B-Layer (IBL) is a recent ATLAS upgrade, using conventional planar and novel, radiation-hard 3D sensors; it is essential to monitor the performance of the IBL, as it is exposed to high levels of radiation. Initial studies found high leakage currents in several IBL sensors, and dangerously high currents in every IBL readout chip. Ultimately, the origin of these issues was found, and there were no serious long term effects, with both planar and 3D sensors performing as expected. There was also a detailed analysis of the IBL sensor leakage currents, finding excellent agreement between observed leakage currents and Hamburg Model predictions. This analysis resulted in the most accurate measurements of silicon radiation-damage rates at the LHC. The measured rates of radiation damage were compared to expected values from the ATLAS radiation simulation group, with general agreement, but some key differences,leading to updates in the radiation simulation code. The final part of this analysis included a novel, model-independent way to check if the IBL sensors were fully depleted, which could be generalised for other existing and future experiments. Finally, 3D and planar designs were again compared, using Timepix readout chips,in order to investigate the feasibility of using radiation-hard 3D sensors for future applications. Both modules were successfully characterised, finding no significant differences.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrew Pilkington (Supervisor) & Cinzia Da Via (Supervisor)