Susan Cooper

Abstract:

In the early stages of running of the CRESST dark matter search using sapphire detectors at very low temperature, an unexpectedly high rate of signal pulses appeared. Their origin was finally traced to fracture events in the sapphire due to the very tight clamping of the detectors. During extensive runs the energy and time of each event was recorded, providing large data sets for such phenomena. We believe this is the first time the energy release in fracture has been directly and accurately measured on a microscopic event-by-event basis. The energy threshold corresponds to the breaking of only a few hundred covalent bonds, a sensitivity some orders of magnitude greater than that of previous technique. We report some features of the data, including energy distributions, waiting time distributions, autocorrelations and the Hurst exponent. The energy distribution appear to follow a power law, d N / d E ∝ E- β, similar to the power law for earthquake magnitudes, and after appropriate translation, with a similar exponent. In the time domain, the waiting time w or gap distribution between events has a power law behavior at small w and an exponential fall-off at large w, and can be fit ∝ w- α e -w / w0. The autocorrelation function shows time correlations lasting for substantial parts of an hour. An asymmetry is found around large events, with higher count rates after, as opposed to before, the large event. © 2006 Elsevier B.V. All rights reserved.

Abstract:

In the early stages of running of the CRESST dark matter search with sapphire crystals as detectors, an unexpectedly high rate of signal pulses appeared. Their origin was finally traced to fracture events in the sapphire due to the very tight clamping of the detectors. During extensive runs the energy and time of each event was recorded, providing large data sets for such phenomena. We believe this is the first time that the energy release in fracture has been accurately measured on a microscopic event-by-event basis. The energy distributions appear to follow a power law, dN/dE proportional to E-beta, similar to the Gutenberg-Richter power law for earthquake magnitudes, and after appropriate translation, with a similar exponent. In the time domain, the autocorrelation function shows time correlations lasting for substantial parts of an hour. Some remarks are made concerning the possible role Of Such mechanical stress release processes in the noise of sensitive cryodetectors. (c) 2006 Elsevier B.V. All rights reserved.

Abstract:

The ANTARES neutrino telescope, to be immersed depth in the Mediterranean Sea, will consist of a three-dimensional matrix of 900 large area photomultiplier tubes housed in pressure-resistant glass spheres. The selection of the optimal photomultiplier was a critical step for the project and required an intensive phase of tests and developments carried out in close collaboration with the main manufacturers worldwide. This paper provides an overview of the tests performed by the collaboration and describes in detail the features of the photomultiplier tube chosen for ANTARES. © 2005 Elsevier B.V. All rights reserved.

Abstract:

Data taken by CRESST with a cryogenic detector system based on 262 g sapphire crystals has been used to place limits on WIMP dark matter. The experiment was especially sensitive for low-mass WIMPs with spin-dependent cross sections and improves on existing limits in this region.