We offer several topics for bachelor and master theses within the framework of our research projects. Examples are: tests of new photosensors in liquid xenon and argon at UZH; material screening with a high-purity Ge detector (Gator) LNGS; data analysis of XENONnT and LEGEND-200 data; MC simulations for the DARWIN demonstrator, for XENONnT and for LEGEND; hardware and computing projects in the framework of Xenoscope, a full-scale vertical DARWIN demonstrator at UZH.

Please have a look at our research page and contact one of us for details and the timescales of possible projects.

Shine bright like a diamond

Dual-phase liquid xenon time projection chambers (TPCs) are at the forefront of particle detectors used to search for the enigmatic dark matter in our universe. To detect a dark matter interaction inside these cryogenic detectors, they rely on the propagation of electrons liberated by particle interactions. This requires the application of an electric drift field. To ensure proper reconstruction of interactions in the detector, the homogeneity of this field needs to be ensured. Traditionally, this is achieved with a field-cage made of individual field-shaping rings. However, we are pioneering a novel approach of using a low-conductivity surface coating on insulating materials such as PTFE. An ideal candidate for such a coating is diamond-like carbon (DLC), which is a very fascinating and versatile material. Your task will include conceptual design, electric field simulation using COMSOL Multiphysics, and testing the sheet resistivity and adhesion of DLC coatings at cold temperatures. If time allows, we will study the reflectivity of such a coating to the light produced by particle interactions in the liquid xenon.

Contact florian.joerg@physik.uzh.ch

Radiogenic simulations for XENON and DARWIN dark matter experiments.

Experiments using liquid xenon as an active material are at the forefront of direct detection of dark matter. These types of experiments, like the existing XENONnT and the projected DARWIN, need to have a very detailed knowledge of the backgrounds. In particular, the background originated by the radiation emitted by the materials of the detector itself and the experimental hall, such as rock, concrete or other components. Simulations are a fundamental tool to understand and quantify these backgrounds. Codes, such as Geant4, are widely used to perform these simulations. The main goal of this master thesis is to study, through simulations, the radiogenic background for the XENONnT and DARWIN experiments. To do this, it is necessary to test existing software and incorporate it into the main code in Geant4. In addition to this, the impact on other physics channels, such as the neutrinoless double beta decay, can be studied.

Contact Dr. Jose Cuenca and Dr. Diego Ramirez

Shining light on trace impurities in liquid xenon

Liquid xenon detectors located deep underground are on the forefront of our ongoing effort to detect dark matter particles. They rely on the detection of very faint light signals which are emitted in the interaction of the dark matter particles in our detector. Since certain impurities such as water can attenuate this light, an exceptional purity level of the liquid xenon is required. Traces of water in gaseous xenon can be detected using cavity ring-down spectrometry (CRDS). This technique works by bouncing a laser beam back and forth inside a cavity filled with the test gas and measuring its attenuation. In this work, you will be responsible for the integration of a commercial CRDS device (HALO KA - M7500-S) into our local large-scale liquid xenon detector (Xenoscope). The skills you will acquire during this work are widely applicable inside, as well as outside of academia. Among others, you will gain knowledge in operation and maintenance of a high-flow gas handling system, integration of hardware components into automated process control frameworks as well as trace impurity analysis of ultrapure gases.

Contact Dr. Florian Jörg

Modeling Charge Drift and Diffusion Effects on Pulse Shapes in LEGEND-200 HPGe Detectors

This project will investigate charge drift, diffusion, and self-repulsion effects on pulse shapes within LEGEND-200's germanium detectors. You will use SolidStateDetectors.jl to simulate charge carrier drift paths, integrating models for temperature-dependent mobility and anisotropic drift in germanium. The project will explore the influence of charge diffusion and self-repulsion on pulse formation, aiming to refine signal generation accuracy.
Objectives:

• Develop simulations of electron and hole drift under various electric field strengths
• Quantify the impact of diffusion and self-repulsion on pulse shape accuracy
• Validate the simulations with experimental data to improve model reliability

Contact: Dr. Marta Babicz