Limits on WIMP dark matter using sapphire cryogenic detectors

We present data on a detector composed of an 18 g Si crystal and a superconducting phase transition thermometer which could be operated over a wide temperature range. An energy resolution of 1 ke V (FWHM) has been obtained for 60 keV photons. The signals consist of two components: a fast one and a slow one, with decay times of 1.5 ms and 30–60 ms, respectively. In this paper we present a simple model which takes thermal and non-thermal phonon processes into account and provides a description of the observed temperature dependence of the pulse shape. The fast component, which completely dominates the signal at low temperatures, is due to high-frequency non-thermal phonons being absorbed in the thermometer. Thermalization of these phonons then leads to a temperature rise of the absorber, which causes the slow thermal component. At the highest operating temperatures (T ∼ 80 mK) the amplitude of the slow component is roughly as expected from the heat capacity of the absorber. The strong suppression of the slow component at low temperatures is explained mostly as a consequence of the weak thermal coupling between electrons and phonons in the thermometer at low temperatures.

Model for cryogenic particle detectors with superconducting phase transition thermometers

A proposal for solar axion detection via Bragg scattering

A tungsten superconducting phase transition thermometer on a 32 g sapphire crystal has given an energy resolution of 100 eV (FWHM) for 1.5 keV X-rays, increasing to 440 eV at 14 keV. A possibility to obtain similar resolution in much larger crystals by using Al films as phonon collectors is presented.

/pdf/cryogenic-particle-detectors-with-superconducting-phase-olbmdrk5ya.pdf

Cryogenic particle detectors with superconducting phase transition thermometers

A massive bolometer with a 760 g TeO2 crystal as energy absorber, the largest employed underground, has been realized and operated in the Gran Sasso Underground Laboratory for γ- and α-ray spectroscopy. A new system of mechanical suspensions was implemented to reduce vibration and thermal noise, and special care was put to the read-out electronics. As a consequence the FWHM resolution for high-energy γ-rays became comparable to that of Germanium diodes. The 4.2 keV average FWHM resolution for the 5407 keV line is the best ever obtained for α particles with any type of detector.

/pdf/a-massive-thermal-detector-for-alpha-and-gamma-spectroscopy-7bkqvaxyg1.pdf

W. Christen

Papers

Phase transition thermometers with high temperature resolution for calorimetric particle detectors employing dielectric absorbers