Particle Astrophysics at the University of Zürich

Welcome to the
particle astrophysics group!

We are conducting research in experimental particle astrophysics and are a member of two large international research collaborations: XENON and GERDA. We are involved in projects which pursue research and development towards next generation low background experiments (DARWIN, SILENT) or focus on the phenomenology of neutrinos and dark matter (Invisibles). Additionally, we perform experiments addressing general questions regarding our detection methods in our laboratory at UZH.

On these pages, we give a brief overview on our activities.


The aim of the XENON experiment is to directly detect the Dark Matter Particle. We have installed a very sensitive detector, XENON100, underground in the Gran Sasso Laboratory (LNGS), Italy, in order to suppress background interactions from cosmic ray muons that could mimic a possible signal.

The XENON experiment is designed to look for dark matter particles originating from the Milky Way halo. The detection medium is liquid xenon. Change and scintillation light from particle interactions with the xenon are detected simultaneous in a time projection chamber which allows excellent energy resolution, 3D vertex reconstruction, and effective discrimination between signal and background.

The first prototype, XENON10, with a target mass of only a few kg of liquid xenon, has proven that liqiod xenon based dark matter detectors can deliververy competitive results (Phys. Rev. Lett. 100, 2008). The current detector, XENON100, with a 62 kg liquid xenon target is installed underground at LNGS and is taking WIMP search data continuously. Once more, it has recently published the most stringent limit on spin-independent WIMP-nucleon scattering cross sections for a large range of WIMP masses (accepted by Phys. Rev. Lett.). A detailed explanation of the detector can be found in Astropart. Phys. 35, 2012.

The next step of the XENON program is XENON1T, a detector with about 1 tonne of liquid xenon in its fiducial volume (3 tonnes in total). This experiment will not only have a fair chance of detecting dark matter particles, but may also be able to measure their mass and interaction rate with high precision. It is currently in the desig phase and dedicated test experiments are under way in order to solve technical challenges. XENON1T has been approved by INFN/LNGS, is supported by many national funding agencies, and will be installed in Hall B of LNGS. First works underground are expected to commence in early 2013.

For a more detailed description see the UZH XENON site, as well as the XENON website at Columbia University.
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The GERDA (GERmanium Detector Array) experiment aims to observe theyet undiscovered neutrinoless double beta decay in ultra-pure, enriched 76Ge crystals. An experimental setup of several meters height is currently being operated underground in the Gran Sasso Laboratory (LNGS), Italy.

The GERDA detectors are operated in liquid argon, which is used as a cooling medium and as a shield against the radioactivity of the surroundings. An extremely radiopure environment is absolutely crucial for this experiment. Therefore, the stainless steel cryostat of 4.2m outer diameter and 8.9m height is additionally surrounded by 3m of active water shield.

The first phase of GERDA, which aims to test the Heidelberg-Moscow claim, is currently ongoing at the Gran Sasso Laboratory. First results are expected in 2012. Concomitantly the production and testing of the GERDA Phase II 76Ge detectors is under way.

A more detailed description can be found on the UZH GERDA site, and on the official GERDA website at the MPIK Heidelberg.
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Low-Background Physics

The search for rare events, as in dark matter and neutrinoless double beta-decay detectors, requires experimental conditions with the lowest possible contamination of natural or man-made radioactive isotopes. We are actively involved in the selection and characterization of radiopure materials and components for low backgroundexperiments.

We use several methods to identify the intrinsic radioactive contamination of materials. The main one is gamma-spectroscopy using our high purity, low background Germanium detector Gator (JINST 6 P08010, 2011), which is installed underground at LNGS, in a joint low background laboratory, operated together with the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg, Germany. Other methods used to measure radioactive traces are mass spectroscopy (ICP-MS) done by LNGS or neutron activation analysis. The activations are performed at the Swiss Spallation Neutron Source of PSI (Switzerland) or using the TRIGA Mark II reactor at Mainz University (Germany).

Additionally, we are interested in characterizing the environmental background in underground laboratories, mainly at LNGS where our main experiments are located. Depending on the type of experiment, the critical backgrounds are from gamma rays, neutrons, muons, or radon gas emanated from the rock.
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last modified 07.11.2012 by MS