Prof. Dr. rer. nat. Stefan Schönert

Courses and Dates

Offered Bachelor’s or Master’s Theses Topics

CRESST: Freezing cold, deep underground, illuminating the dark (matter)

The CRESST (Cryogenic Rare-Event Search with Superconducting Thermometers) experiment operated at the Gran Sasso underground laboratory employs highly sensitive cryogenic detectors to the search for signals of the elusive dark matter particles, a main ingredient of the Universe whose nature is still unknown. 

The energy thresholds reached in CRESST-III are the lowest in the field, making CRESST the most sensitive experiment to light dark matter. Optimisation of the tungsten thin-film thermometers and of the techniques for data analysis promise will further improve the energy threshold, which will significantly boost the physics reach of the experiment.

 

A student can contribute to:

- design, production and prototyping of new CRESST detectors in Munich 

- development of high purity crystals 

- development of new software tools for data analysis

- dark matter data analysis

 

and, if interested, can participate in the operation of the main experiment at Gran Sasso. 

 

The theses can be carried out at the Chair for astroparticle physics of the Physics Department and/or at the Max-Planck-Institute for Physics (MPP). Supervision at the Physics Deptartment by Prof. Schönert / Dr. Strauss and at the MPP by Prof. Schönert /  Dr. Federica Petricca. Please contact schoenert@ph.tum.de, raimund.strauss@ph.tum.de and petricca@mpp.mpg.de for further information. 

 

We will organize a dedicated meeting for interested (bachelor) students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320 . Also Master students are welcome to join the meeting.

suitable as

• Master’s Thesis Nuclear, Particle, and Astrophysics

Supervisor: Stefan Schönert

CRESST: Freezing cold, deep underground, illuminating the dark (matter)

The CRESST (Cryogenic Rare-Event Search with Superconducting Thermometers) experiment operated at the Gran Sasso underground laboratory employs highly sensitive cryogenic detectors to the search for signals of the elusive dark matter particles, a main ingredient of the Universe whose nature is still unknown. 

The energy thresholds reached in CRESST-III are the lowest in the field, making CRESST the most sensitive experiment to light dark matter. Optimisation of the tungsten thin-film thermometers and of the techniques for data analysis promise will further improve the energy threshold, which will significantly boost the physics reach of the experiment.

 

A student can contribute to:

- design, production and prototyping of new CRESST detectors in Munich 

- development of high purity crystals 

- development of new software tools for data analysis

- dark matter data analysis

 

and, if interested, can participate in the operation of the main experiment at Gran Sasso. 

 

The theses can be carried out at the Chair for astroparticle physics of the Physics Department and/or at the Max-Planck-Institute for Physics (MPP). Supervision at the Physics Deptartment by Prof. Schönert / Dr. Strauss and at the MPP by Prof. Schönert /  Dr. Federica Petricca. Please contact schoenert@ph.tum.de, raimund.strauss@ph.tum.de and petricca@mpp.mpg.de for further information. 

 

We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert

Design and Commissioning of a Temperature Control System for the Characterization of Wavelength Shifters at Low Temperatures

Experiments searching for dark matter or neutrinoless double-beta decay commonly use liquid Argon (LAr) as a target or instrumented shielding medium. Particle interactions in LAr produce vacuum-ultraviolet (VUV) light flashes peaking at 128 nm, which are converted to longer wavelengths by wavelength shifters (WLSs). Due to the short LAr scintillation wavelength and low LAr temperature (87 K), the characterization of WLSs requires VUV optics and a cooling system in vacuum. The VUV spectrofluorometer setup used for the characterization of WLSs is currently upgraded to cool the samples by mounting them on the coldhead of a Gifford-McMahon cryocooler in a vacuum-tight sample chamber. For the characterization at LAr temperature it is crucial to precisely control the sample temperature. The task of this project is to design and commission a temperature readout and control system. The candidate will assess the currently used temperature readout setup and combine it with a new heater system to regulate the temperature. The goal is the implementation of the system into the main data acquisition (DAQ) program of the VUV spectrofluorometer. After the commission of the new temperature control system, the candidate will characterize wavelength shifting materials used in the neutrinoless double-beta decay experiment LEGEND (https://legend-exp.org) at low-temperatures with VUV excitation for the first time. Existing skills in python and arduino programming are advantageous but not necessary. A high motivation for hands-on work in a spectroscopy laboratory and an affinity for electronics and microcontroller are beneficial. The candidate awaits a diverse project, which offers the possibility to acquire skills in VUV optics, vacuum engineering, cooling technology, sensors and microcontrollers, python and arduino programming, laboratory work and project management. Supervision at the Physics Deptartment by Prof. Schönert and Andreas Leonhardt. Please contact schoenert@ph.tum.de or andreas.leonhardt@tum.de for further information. We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert

HPGe characterization for the Monument experiment

Learning skills: Gamma spectroscopy; usage of HPGe detector, DAQ, low-level analysis Hardware and management in experimental physics Requisites: Being comfortable with laboratory “hand-work” Being communicative and willing to do team-work Commitment Physics topics: 0𝜈ββ-decay, accelerator physics, experimental-techniques, ordinary muon capture, HPGe detectors… Gamma spectroscopy is a powerful tool to evaluate with outstanding resolution the energy and time of radiation in the MeV regime. This is usually realised by the use of High Purity Germanium Detectors (HPGe) cooled down at liquid nitrogen temperatures (77K). Learning how to operate HPGe detectors is a very valuable skill to gain, given the use of HPGe detectors in astroparticle physics experiments, where gamma spectroscopy is a technique widely used in their searches. As an example, the neutrinoless double beta decay (0𝜈ββ-decay) experiments GERDA (https://www.mpi-hd.mpg.de/gerda) and LEGEND (https://legend-exp.org) work under this principle. The Monument experiment is measuring ordinary muon capture (OMC) in several double beta decay (2𝜈ββ) isotopes used for 0𝜈ββ-decay experiments. These measurements involve the emission of muonic x-rays (µX) and gammas (γs) which are captured by an array of HPGe detectors. To evaluate their energy and time distributions, the Monument experiment uses gamma-spectroscopy. These measurements are performed at the Paul Schrrer Institute, in Switzerland, where a µ-beam fulfilling our requirements for the experiment is available. At TUM, in the GERDA-LEGEND group, we work on the characterisation of the experimental setup used for the Monument experiment. This involves the characterisation of the HPGe detectors to be used during the beam-time campaigns. The bachelor student working on this project, is expected to characterise a HPGe detector from the setup and get familiarised with all the experimental elements needed to perform this task; the electronics, the analysis of a gamma-spectrum, the characteristics of this kind of detector, etc. The thesis would include a potential contribution in the up-coming beam-time campaign, in Switzerland, programmed for June 2022. Supervision at the Physics Deptartment by Prof. Schönert and Elisabeth Mondragon Cortes. Please contact schoenert@ph.tum.de or elizabeth.mondragon@tum.de for further information. We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert

In Search of the Lowest Radioactive Traces Ever: Tagging BiPo Events in GERDA

ll experiments have background - may it be cosmogenic muons, accidental coincidences, or decays from unstable isotopes. A common type of background comes from radiogenic nuclei as part of longer decay chains. These nuclei might be intrinsic to the detector material or might even cause background by being present in the walls around the experiment. One way of estimating the impact of one such decay chain intrinsic to the detector is the so-called BiPo analysis. The isotope 214Bi which is part of the decay chain of 238U has a high likelihood to decay via beta decay into 214Po which itself decays via alpha decay after only several hundred microseconds. As both of these decays are very highly energetic and their decays so fast after one another, their coincidence signature is often used to estimate the activity of the total decay chain. For planned experiments, it is vitally important to estimate the impact of specific background sources. The LEGEND-1000 (https://legend-exp.org) experiment, a planned neutrinoless double beta-decay experiment, will use high purity germanium (HPGe) detectors made out of 92% 76Ge which decays via double beta-decay. The question is now how high is the contribution of radiogenic isotopes in Germanium detectors. For this, we can look at the GERDA experiment (https://www.mpi-hd.mpg.de/gerda), another neutrinoless double beta-decay experiment that used HPGes and which was completed recently. In its data, one can look for signals similar to the BiPo coincidences and with that make an estimate of how large of an impact the radiogenic background sources might have for an experiment with a similar setup. The student will work with raw GERDA data to look for the specific signature of the BiPo decays. This will include learning how the data analysis process looks like for a large experiment - from initial waveform analysis to energy estimation to final event selection. Furthermore, the student will also produce pseudo data to estimate the efficiency to find the BiPos with the proposed analysis. The analysis is performed using C++ and ROOT, so basic knowledge of these languages may be useful, but is not required. Supervision at the Physics Deptartment by Prof. Schönert and Moritz Neuberger Please contact schoenert@ph.tum.de or Moritz.Neuberger@tum.de for further information. We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert

LEGEND: Why does matter prevail over antimatter in today's Universe?

Neutrinos were discovered in 1956, but only at the turn of the millennium was it experimentally proven that the three known neutrino types can convert into one another. These flavor oscillations are possible only if neutrinos have nonzero mass, which is currently the only established contradiction to the standard model (SM) of particle physics.

 

From tritium beta decay experiments and cosmological observations, we know that their masses are very small—less than 10^{-5} of the electron mass. Neutrinos are the only fundamental spin-1/2 particles (fermions) without electric charge. As a consequence, they might be Majorana fermions, particles identical to their antiparticles.

 

This is a key ingredient for the explanation for why matter is so much more abundant than antimatter in today’s Universe and why neutrinos are so much lighter than the other elementary particles.

 

Majorana neutrinos would lead to nuclear decays that violate lepton number conservation and are therefore forbidden in the Standard Model of particle physics. The so-called neutrinoless double-beta (0nbb) decay simultaneously transforms two neutrons inside a nucleus into two protons with the emission of two electrons. The LEGEND-200 experiment, currently under commissioning at the Italian Gran Sasso underground laboratory aims to be the first experiment to probe half-lives beyond 1E27 years.

 

We offer the opportunity to carry out exciting experimental BSc (and MSc) theses with a focus on:

- liquid argon detector development: SiPMs, VUV light detection and wavelength shifting, xenon-doping, trace analysis;

- germanium detectors: detector design, modeling of signal generation, pulse shape analysis, surface event discrimination;

- new software tools and algorithms: classical techniques, machine learning methods;

- data analysis: rare line searches, exotic decays, time and spatial coincidence searches;

- Monte Carlo simulations: light propagation and detection in liquid argon, gamma rays from radioactive decays, isotope production deep underground by cosmic rays;

 

and, if interested, can participate in the operation of the main experiment at Gran Sasso. 

 

You would be fully integrated into the research team and would work closely together with our international partners.

 

The theses can be carried out at the Chair for astroparticle physics of the Physics Department. Supervision at the Physics Deptartment by Prof. Schönert and his team. Please contact schoenert@ph.tum.de for further information. 

 

We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert

LEGEND: Why does matter prevail over antimatter in today's Universe?

Neutrinos were discovered in 1956, but only at the turn of the millennium was it experimentally proven that the three known neutrino types can convert into one another. These flavor oscillations are possible only if neutrinos have nonzero mass, which is currently the only established contradiction to the standard model (SM) of particle physics.

 

From tritium beta decay experiments and cosmological observations, we know that their masses are very small—less than 10^{-5} of the electron mass. Neutrinos are the only fundamental spin-1/2 particles (fermions) without electric charge. As a consequence, they might be Majorana fermions, particles identical to their antiparticles.

 

This is a key ingredient for the explanation for why matter is so much more abundant than antimatter in today’s Universe and why neutrinos are so much lighter than the other elementary particles.

 

Majorana neutrinos would lead to nuclear decays that violate lepton number conservation and are therefore forbidden in the Standard Model of particle physics. The so-called neutrinoless double-beta (0nbb) decay simultaneously transforms two neutrons inside a nucleus into two protons with the emission of two electrons. The LEGEND-200 experiment, currently under commissioning at the Italian Gran Sasso underground laboratory aims to be the first experiment to probe half-lives beyond 1E27 years.

 

We offer the opportunity to carry out exciting experimental BSc (and MSc) theses with a focus on:

- liquid argon detector development: SiPMs, VUV light detection and wavelength shifting, xenon-doping, trace analysis;

- germanium detectors: detector design, modeling of signal generation, pulse shape analysis, surface event discrimination;

- new software tools and algorithms: classical techniques, machine learning methods;

- data analysis: rare line searches, exotic decays, time and spatial coincidence searches;

- Monte Carlo simulations: light propagation and detection in liquid argon, gamma rays from radioactive decays, isotope production deep underground by cosmic rays;

 

and, if interested, can participate in the operation of the main experiment at Gran Sasso. 

 

You would be fully integrated into the research team and would work closely together with our international partners.

 

The theses can be carried out at the Chair for astroparticle physics of the Physics Department. Supervision at the Physics Deptartment by Prof. Schönert and his team. Please contact schoenert@ph.tum.de for further information. 

 

We will organize a dedicated meeting for interested bachelor students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320 . Also Master students are welcome to join.

suitable as

• Master’s Thesis Nuclear, Particle, and Astrophysics

Supervisor: Stefan Schönert

Optimal digital processing of the LEGEND-200 liquid argon instrumentation signals

The LEGEND project (https://legend-exp.org) aims at testing the fundamental laws of nature by searching for neutrinoless double-beta decay. A fundamental part of the experimental setup is composed by a liquid argon cryostat, instrumented with optical light sensors in order to suppress unwanted background events. TUM has a leading role in developing and deploying the LEGEND-200 liquid argon instrumentation, composed of light-guiding fibers coupled to silicon photomultiplier (SiPM) light sensors. Data recorded by these devices are analyzed to search for signals above noise ( due to, for example, a nearby radioactive decay), and discard them as background. The signal searched by LEGEND, neutrinoless double beta decay, is not accompanied by emission of light in liquid argon. The thesis project consists in analyzing early SiPM data collected during tests of the LEGEND-200 instrumentation at the Laboratori Nazionali del Gran Sasso in Italy at the end of 2021. In particular, the candidate is expected to develop optimal Digital Signal Processing (DPS) algorithms to estimate parameters like energy and timing of the recorded traces. The result of these studies are critical to evaluate the performance of the experimental setup and determine the best data analysis strategy. The candidate will learn to use the existing software tools to analyze digital signals. Notions of Python programming are beneficial. The candidate will acquire skills in developing DSP routines in Python, including popular tools in the scientific computing community (e.g. NumPy, HDF5 file format), and work on remote high-performance computing facilities. The theses can be carried out at the Chair for astroparticle physics of the Physics Department. Supervision at the Physics Deptartment by Prof. Schönert and Dr. Luigi Pertoldi. Please contact schoenert@ph.tum.de or luigi.pertoldi@tum.de for further information. We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert

Simulation of optical photons in the LEGEND-200 liquid argon

The LEGEND project (https://legend-exp.org) aims at testing the fundamental laws of nature by searching for neutrinoless double-beta decay. A fundamental part of the experimental setup is composed by a liquid argon cryostat, instrumented with optical light sensors in order to suppress unwanted background events. Starting from February 2022, the LEGEND group at TUM is looking for a student to study the performance of the liquid argon detector. The thesis project consists in a simulation of optical photon propagation and detection in liquid argon from within the LEGEND-200 cryostat. The candidate will develop a software package, based on existing Monte Carlo simulation tools, that reproduces the experimental setup in terms of dimensions, material (optical) properties and light sensors. The results of this simulation will be benchmarked against physics data acquired with radioactive sources during tests of the LEGEND-200 instrumentation at the Laboratori Nazionali del Gran Sasso in Italy at the end of 2021. Notions of Python and C++ programming are beneficial. The candidate will learn how to develop an application based on the particle tracking software GEANT4 (https://geant4.web.cern.ch), and will have the possibility to run it on a remote high-performance computing facility. The acquired skills include processing of the simulation output to extract physical quantities of interest. An additional, optional work package for the motivated candidate, would be to investigate the possibility to perform a significantly more efficient simulation on graphic cards (GPUs), by exploiting their ray-tracing capabilities. Supervision at the Physics Deptartment by Prof. Schönert and Dr. Luigi Pertoldi. Please contact schoenert@ph.tum.de or luigi.pertoldi@tum.de for further information. We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert

The Hunt for the Rarest Cosmogenic Nuclei

As you have probably seen many times in various calculations in special relativity, a large amount of muons are produced in the atmosphere in so-called particle showers. These incredibly fast muons can reach the Earth's surface and even penetrate it to some degree. This is a problem because most low background experiments want to avoid having these muons corrupt their data. Therefore, many experiments are conducted in underground laboratories. Yet they cannot completely avoid their influence. A large part of the background caused by atmospheric muons can be removed by so-called muon vetoes, which check whether the signal in the detector matches a particle coming from outside. However, the muons can still cause some background in the form of cosmogenic radioactive nuclei. These are produced during high-energy muon crossings through the detector and can decay with a significant delay to the muon crossing which makes it hard to veto them. This is the case for LEGEND-1000 (https://legend-exp.org), an experiment planned to look for neutrinoless double beta decay. To estimate the impact of specific isotopes on the final data we use Monte-Carlo simulations. These simulate how a muon will interact with the detector and which nuclei will be produced. The student's task will be to perform simulations to estimate the production rate of certain cosmogenic nuclei and their possible impact on the final experiment. In doing so, they will learn about the processes by which cosmogenic nucleons are produced, what signal their decay will leave in the detectors, and what strategies one has to filter them out. The work will involve using C++ to modify the simulation and ROOT to analyze the results. A basic understanding in these would be beneficial but not necessary. The theses can be carried out at the Chair for astroparticle physics of the Physics Department. Supervision at the Physics Deptartment by Prof. Schönert and Moritz Neuberger Please contact schoenert@ph.tum.de or Moritz.Neuberger@tum.de for further information. We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert

The P+ spoiler: from minerals to alpha-decay tagging

In the last decade, experiments searching for neutrinoless double-beta decay of 76Ge provided the most stringent limits on the half-life of the process. This was possible thanks to the careful choice of clean materials and very efficient background reduction techniques. The combination of the two allowed to simplify the search for neutrinoless double-beta decay into the search for an energy peak on a null background. This work will focus on one source of background, which is the alpha-decays of radioactive contaminants on the surface of germanium detectors. Such a contamination can occur when detectors are exposed to air, thus Radon, which can deposit its radioactive progeny on their surface. The tagging of these alpha events with small anode detectors has proved to be very efficient; indeed, no events in the alpha peak have survived the analysis cuts in the full dataset of the GERDA experiment, and only a limit for the tagging efficiency has been extracted. In view of the future LEGEND experiment, the “p+ spoiler” setup was designed to build a high statistics sample of alpha decays on the surface of germanium detectors and extract the central value of their tagging efficiency. This is done by exposing detectors to an Autunite mineral, which, containing Uranium, works as a constant Radon emanator. In this thesis, the student will work on the data acquired from a germanium detector which has been “spoiled” for several months. They will be guided to the analysis of its data and to the final extraction of the tagging efficiency of alpha-decays. A background in programming in C/C++ is welcome, but not mandatory. The theses will be carried out at the Chair for astroparticle physics of the Physics Department. Supervision at the Physics Department by Prof. Schönert and Tommaso Commelato. Please contact schoenert@ph.tum.de or tommaso.comellato@tum.de for further information. We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert

Xenon doped liquid argon - mixing, measuring, modeling

At the first glance, liquid argon as a detector material might seem to be a peculiar choice: its low boiling point of 87 K makes it difficult to handle and puts hard constraints on any material touching it. Nonetheless, many experiments in the field of astroparticle physics employ it as a detection medium - from dark matter search to neutrinoless double beta decay. This is due to its superior properties as a scintillation medium. Via the scintillation process, energy depositions (e.g. from a dark matter particle scattering off a nucleus or gamma particles interacting) lead to light emission in the liquid argon volume. A high light output is key for a good energy reconstruction, as exhibited by liquid argon. Current efforts are made in doping liquid argon with small traces of Xenon (at parts-per-million levels), in order to further enhance the light output. Properties like the time spectrum and total light output of the light emitted by this noble gas mixture are not sufficiently understood as of now. Measurement runs in a 1m³ liquid argon cryostat located in a shallow underground lab at TUM are conducted to study these effects at various Xenon concentrations. An optical detection and monitoring system (LLAMA) is used to obtain time-resolved optical properties. The Bachelor candidate works on the modeling of the light emission process of this Xe-Ar-mixture using data obtained so far. Furthermore, they will take part in setting up, conducting and analyzing data obtained in a new measurement run planned to commence in June 2022. As the work includes the fitting of data present in ROOT format, basic C++ skills are beneficial, but not required. Skills in programming, data analysis and modeling are acquired by the student, in addition to knowledge in the handling of gas and cryogenic liquids by hands-on laboratory work. The theses can be carried out at the Chair for astroparticle physics of the Physics Department. Supervision at the Physics Deptartment by Prof. Schönert and Mario Schwarz. Please contact schoenert@ph.tum.de or Mario.Schwarz@tum.de for further information. We will organize a dedicated meeting for interested students on Tuesday, February 1, 14:00-16:00. For more information please check https://www.moodle.tum.de/course/view.php?id=75320

suitable as

• Bachelor’s Thesis Physics

Supervisor: Stefan Schönert