Michael F. Altmann

Status of the Germanium Detector Array (GERDA) in the search of neutrinoless ββ decays of 76Ge at LNGS

The Germanium Detector Array (GERDA) in the search for neutrinoless ββ decays of 76Ge at LNGS will operate bare germanium diodes enriched in 76Ge in an (optional active) cryogenic fluid shield to investigate neutrinoless ββ decay with a sensitivity of T1/2 > 2 × 1026 yr after an exposure of 100 kg yr. Recent progress includes the installation of the first underground infrastructures at Gran Sasso, the completion of the enrichment of 37.5 kg of germanium material for detector construction, prototyping of low-mass detector support and contacts, and front-end and DAQ electronics, as well as the preparation for construction of the cryogenic vessel and water tank.

Dark matter search with CRESST cryogenic detectors

Results of the CRESST experiment at Gran Sasso using 262-g sapphire calorimeters with tungsten phase transition thermometers are presented. Calibration and analysis methods are described. Data taken in 2000 have been used to place limits on WIMP dark matter particles in the Galactic halo. The sapphire detectors are especially sensitive to low-mass WIMPs with spin-dependent interaction and improve on existing limits in this region.

Cryogenic microcalorimeters and tunnel junctions for high-resolution energy dispersive x-ray spectrometry

We have been developing cryogenic detectors for astro- particle physics applications including search for Dark Matter, neutrino physics and x-ray astronomy. Most recently we started the development of high resolution x-ray detectors based on superconducting tunnel junctions and superconducting phase transition thermometers/transition edge sensors for microanalysis applications. Both types of sensors are being investigated as well as the cryogenic setup for applications on a scanning electron microscope.

The CRESST Dark Matter Search Status and Future

Data taken by CRESST in 2000 with a cryogenic detector system based on 262 g sapphire crystals is used to place limits on WIMP dark matter in the Galactic Halo. The detector is especially sensitive for low-mass WIMPS with spin-dependent cross sections and improves on existing limits in this region. CRESST is now preparing for a second phase, which will use a 10 kg detector consisting of 300 g CaWO4 crystals with simultaneous detection of phonons and scintillation light to reduce background.

Cryogenic microcalorimeters for high-resolution energy-dispersive x-ray spectrometry

We are developing both superconducting tunnel junctions and phase transition thermometers for high resolution x-ray spectroscopy. A resolution of 12 eV has been achieved for aluminum tunnel junctions when irradiated by 5.9 keV x-rays. These devices show linear energy response in the range between 200 eV and 6.5 keV. Phase transition thermometers consisting of an iridium/gold bi-layer and a gold absorber gave a resolution of 15.5 eV at 5.9 keV. The application of both sensor types is facilitated considerably by the use of an ADR cryostat. This mobile system allowed to characterize tunnel junctions at the Bessy I synchrotron.