ATLAS

Abstract:

We have developed multichannel SQUID systems for two particle physics experiments: a 66-channel system for detector readout in the CRESST dark matter search, and a 12-channel magnetometry system for the CryoEDM neutron electric dipole moment experiment. These different applications have different requirements, for example in the CRESST system it is important to minimise crosstalk, while the CryoEDM system must be shielded from magnetic noise. Future experiments such as the EURECA dark matter project may require systems with a much higher number of channels. (c) 2006 Elsevier B.V. All rights reserved.

Abstract:

The plasmon excitations of the degenerate free-electron gas in the surface space-charge region of InSb have been studied using high-resolution electron-energy-loss spectroscopy. Semiclassical dielectric theory simulations of the energy-loss spectra have been performed using the hydrodynamic and Boltzmann-Mermin models. While both analyses include the effects of temperature, conduction band nonparabolicity, spatial dispersion and collisional damping, the hydrodynamic model is not able to quantitatively reproduce the experimental spectra at higher excitation wave vectors. The measured spectral shapes are only accurately reproduced when collisionless plasmon damping is included explicitly using the Boltzmann-Mermin dielectric function. © 2006 The American Physical Society.

Abstract:

We show that doubly peaked electric fields are necessary to describe grazing-angle charge collection measurements of irradiated silicon pixel sensors. A model of irradiated silicon based upon two defect levels with opposite charge states and the trapping of charge carriers can be tuned to produce a good description of the measured charge collection profiles in the fluence range from 0.5x10^{14} Neq/cm^2 to 5.9x10^{14} Neq/cm^2. The model correctly predicts the variation in the profiles as the temperature is changed from -10C to -25C. The measured charge collection profiles are inconsistent with the linearly-varying electric fields predicted by the usual description based upon a uniform effective doping density. This observation calls into question the practice of using effective doping densities to characterize irradiated silicon. The model is now being used to calibrate pixel hit reconstruction algorithms for CMS.

Abstract:

CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) employs cryogenic detectors for the direct search for weakly interacting massive dark matter particles (WIMPs). In the second phase of the experiment scintillating calcium tungstate crystals are used to discriminate background by means of different light yield for background and WIMP signals. After first results with this novel technique have been obtained, the experimental setup is being upgraded for further background reduction and larger target mass. The results and present status of the experiment will be presented. © 2006 IOP Publishing Ltd.