Project D - Detector technologies

H. Fischer,  G. Herten, K. Jakobs, U. Parzefall, M. Schumann, S. Zimmermann 

Research and development (R&D) of particle detectors forms an integral part of experimental particle physics. In the framework of the RTG, three different areas of detector R&D are pursued. Two of these are related to the silicon tracker and the muon spectrometer of the ATLAS Experiment at CERN, while the third one consists of development for the DARWIN dark matter experiment. 

The ATLAS-related projects are important as the LHC luminosity will be gradually increased in the coming years, culminating in the "high-luminosity LHC" (HL-LHC) starting 2026. The detector components must thus tolerate much higher radiation doses, which makes upgrades essential. Other aspects that are upgraded are granularity and readout speed. The muon detector system (New Small Wheel) is based on micropattern gas detectors and will first be upgradeddetectors. The tracking system will be complete replaced by 2024, Freiburg is deeply involved in the silicon strip detectors for one endcap. The ultimate dark matter experiment DARWIN aims at probing WIMP-nucleaon scattering cross sections at which coherent neutrino nucleus scattering constitute the dominating background. This requires the develoment of time projection chambers with a 40 ton liquid xenon target.

Descriptions for possible PhD projects for all areas are outlined below. These should be seen as exemplary descriptions. Individual PhD topics can be adapted  to include promising up-to-date R&D areas, and tailored to the inclination and skills of the PhD candidate.


D.1 Development of novel Silicon Strip Detectors for the ATLAS-Upgrade


Development of Novel Silicon Strip Detectors for the ATLAS-Upgrade and Beyond

In the framework of a PhD project, a range of prototype silicon strip detectors will get irradiated to several fluences up to and exceeding the dose expected for the HL-LHC after 4000 fb-1. These sensors are then subjected to a comparative study of radiation hardness. Detectors in this study will include prototype sensors from the on-going prototyping efforts for the ATLAS ITk upgrade as well as sensors from RD50 projects, such as CMOS, Nitrostrip, Low Gain Avalanche Detectors (LGADs) and charge multiplication sensors. The aim of the study is twofold: First, to achieve a large and quantitative overview of the radiation hardness of standard as well as more exotic detector options. Second, to validate the performance in all stages of irradiation of the sensors to be used in the upgraded ATLAS silicon tracker. For this purpose, some of the ATLAS sensors should be assembled into modules with final front-end electronics and then irradiated. One additional long-term goal of this project is to identify sensor options for Colliders beyond the LHC, e.g. the Future Circular Collider (FCC).


Development of Assembly Procedures and QA/QC of Modules and Test Beam Measurements for the Endcaps of the ATLAS Strip Upgrade

A further PhD project aims at systematically developing the procedures for assembling modules in the pre-series and series production of modules for the Endcaps of the ATLAS-Upgrade. In connection with these procedures, strict criteria for the Quality Assurance (QA) and Quality Control (QC) have to be drawn up, established and validated as the module assembly progresses from a few prototypes to pre-series production and ultimately the series production. Another challenge is to monitor the quality of the incoming components to module production, such as sensors, front-end electronics, glues and power boards. It will also be required to regularly irradiate components and modules and study their radiation tolerance throughout the process, which links this PhD topic to the one on radiation hardness studies. Several modules in various stages of irradiation should also be examined for their performance in a test beam at DESY or CERN, which constitutes an essential component of this PhD project. The project requires close cooperation with the other German and international groups working in module production and test beam studies, primarily DESY, Berlin.


D.2 Development of New Muon Detectors for the ATLAS-Upgrade

The present ATLAS Muon Spectrometer chambers are not able to cope with the background rates expected in the High Luminosity LHC phase; a upgrade is therefore needed, and will happen in 2 steps -- first with a replacement of the innermost endcap muon stations with a new detector assembly known as the "New Small Wheels", and in a second phase a replacement of chambers in the inner part of the barrel and a complete overhaul of the Muon electronics. the New Small Wheels are in construction, while the Barrel chamber upgrade is targeted for installation in 2024-2026.

In the framework of a PhD project studies on the NSW Micromegas chambers resolution and efficiency shall be carried out, with the final detector and its electronics, and using either cosmic ray data or beam data. The work will build on results from a test bam campaign in 2018, with individual chambers, and extend the analysis to complete detector sectors within the final geometry and configuration. One emphasis will be on the Micro-TPC mode; a second focus will be on studying the  improvements in reconstruction efficiency and track resolution from including alignment corrections.


D.3 Development of a dual-phase xenon TPC for DARWIN and fast readout electronics

Single scatter nuclear recoils are the characteristic signature of WIMP dark matter. The same signature is generated by coherent neutrino nucleus scattering which thus constitutes an irreducible background for the WIMP search ("neutrino floor"). DARWIN is a dual-phase liquid xenon time (LXe) projection chamber (TPC) with an active target mass of 40t. It will explore the WIMP parameter space down to the neutrino floor. Its low background will allow exploring physics channels beyond WIMPs such as solar pp-neutrinos, neutrinoless double beta decay of 136Xe, axions and ALPs as well as supernova neutrinos.

The DARWIN TPC will have dimensions of 2.6m. R&D is required to realize such a massive detector with minimal backgrounds. Achieving the required high electric fields of the TPC is also challenging. New solutions need to be developed and tested at the real scale.

The trigger rate of low-background detectors is very small, however, the very low detector threshold and the complex data stucture (prompt light and delayed proportional scintillation signal) lead to large data rates. High rates during detector calibration are also challenging. The current data acquisition (DAQ) system provide a high degree of parallelization, however, extensive development is required for the fast DARWIN readout and veto systems. This is based on our experience with the DAQ systems for XENON (LNGS) and COMPASS (CERN) for which we developed solutions using FPGA-based ADCs.


Thesis topics:

  • Readout electronics for large dark matter detectors
  • New methods to reduce radioactive background in LXe-TPCs
  • Electrodes for the ultimate dark matter detector


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