Navigation auf uzh.ch
Navigation auf uzh.ch
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
A new method for calibrating photosensor responses in direct dark matter searches
Xenon-based dark matter detectors such as XENONnT aim to detect the faint signals from dark matter particles interacting with xenon atom. The light released in such interactions is registered by photomultiplier tubes (PMTs) that can detect single photons by converting them to millions of electrons that can be registered as an electrical current. The photon to electron conversion factor is called gain and needs to be known precisely for data analysis in the experiments. Traditionally, the gain is determined using a faint artificial light source in a detector such as an LED. Since this calibration requires pausing the dark matter search, it is only carried out on the timescale of weeks. Short-time variations in gain cannot be monitored in this way. This master thesis looks at a new method for continuous gain calibration that uses thermally-induced signals in the PMTs as well as background-photons. As these are always present in the detector, they can augment the dedicated gain calibrations and provide more precise gain estimates for the world’s most sensitive dark matter detectors. The thesis work will allow the student to get an in-depth look at data analysis in the XENONnT dark matter experiment. It entails data-analysis, statistical inference of PMT parameters and simulations.
Contact Dr. Christian Wittweg
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
Optimization of Electric Field Calculations for Pulse Shape Simulation in LEGEND-200
This project focuses on optimizing electric field calculations in high-purity germanium detectors (HPGe) for the LEGEND-200 experiment. Using SolidStateDetectors.jl, you will study the effects of various detector geometries, impurity densities, and bias voltages on the electric potential and field distribution. The project will explore the Successive Over-Relaxation (SOR) method and red-black grid division techniques for computational efficiency.
Objectives:
Contact: Dr. Marta Babicz
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:
Contact: Dr. Marta Babicz
