R. M. Clarke

Detection of single infrared, optical, and ultraviolet photons using superconducting transition edge sensors

We have demonstrated the use of superconducting transition edge sensors for the wide-band detection of individual photons from the mid infrared (IR), through the optical, and into the far ultraviolet (UV). These tungsten transition edge sensors are squares about 18 μm on a side and detect single photon events above a threshold of 0.3 eV (4 μm wavelength), with an energy resolution of 0.15 eV full width at half maximum, and with a risetime (falltime) of .5 μs (60 μs). The calibration data extend up to the UV cutoff of the fiber optic feed at 3.5 eV (350 nm).

Exclusion limits on the WIMP-nucleon cross section from the cryogenic dark matter search.

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for WIMPs via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data give limits on the spin-independent WIMP-nucleon elastic-scattering cross-section that exclude unexplored parameter space above 10 GeV c^{-2} WIMP mass and, at>84% CL, the entire 3

Exclusion limits on the WIMP nucleon cross-section from the cryogenic dark matter search

\sigma

Low-threshold analysis of CDMS shallow-site data

allowed region for the WIMP signal reported by the DAMA experiment.

Installation of the cryogenic dark matter search (CDMS)

The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with>99.9% efficiency, and surface events are rejected with>95% efficiency. The estimate of the background due to neutrons is based primarily on the observation of multiple-scatter events that should all be neutrons. Data selection is determined primarily by examining calibration data and vetoed events. Resulting efficiencies should be accurate to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons in all ways tested. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}. These limits border, but do not exclude, parameter space allowed by supersymmetry models and accelerator constraints. Results are compatible with some regions reported as allowed at 3-sigma by the annual-modulation measurement of the DAMA collaboration. However, under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the DAMA most likely value at>99.9% CL, and are incompatible with the model-independent annual-modulation signal of DAMA at 99.99% CL in the asymptotic limit.

Design of QET phonon sensors for the CDMS ZIP detectors

Data taken during the final shallow-site run of the first tower of the Cryogenic Dark Matter Search (CDMS II) detectors have been reanalyzed with improved sensitivity to small energy depositions. Four {approx}224 g germanium and two {approx}105 g silicon detectors were operated at the Stanford Underground Facility (SUF) between December 2001 and June 2002, yielding 118 live days of raw exposure. Three of the germanium and both silicon detectors were analyzed with a new low-threshold technique, making it possible to lower the germanium and silicon analysis thresholds down to the actual trigger thresholds of {approx}1 and {approx}2 keV, respectively. Limits on the spin-independent cross section for weakly interacting massive particles (WIMPs) to elastically scatter from nuclei based on these data exclude interesting parameter space for WIMPs with masses below 9 GeV/c{sup 2}. Under standard halo assumptions, these data partially exclude parameter space favored by interpretations of the DAMA/LIBRA and CoGeNT experiments data as WIMP signals, and exclude new parameter space for WIMP masses between 3 and 4 GeV/c{sup 2}.

SQUID based WAl quasiparticle trapping assisted transition edge sensor

Abstract We discuss the status of a cryogenic dark matter search beginning operation in the Stanford Underground Facility. The detectors will be cooled in a specially designed cryostat connected to a modified side access Oxford 400 dilution refrigerator. We discuss two detector designs and performance, the cryostat construction and operation, and the multi-level shield surrounding the cryostat. Finally, we will examine the limits which we will be able to set on WIMP dark matter with this experiment.

Enhanced ballistic phonon production for surface events in cryogenic silicon detector

Abstract The Cryogenic Dark Matter Search (CDMS) ZIP detectors utilize quasiparticle trapping as the mechanism for coupling the energy of a particle interaction in the Ge (or Si) absorber into a tungsten (W) transition edge sensor (TES). Consequently, the dynamics of quasiparticle propagation and loss significantly impact the energy collection and resolution of the detector. This paper describes the considerations necessary in optimizing the detector surface geometry in order to have maximal quasiparticle collection.

Development of wide-band, time and energy resolving, optical photon detectors with application to imaging astronomy

Abstract We have demonstrated a new type of phonon sensor for cryogenic particle detectors with a high-bandwidth SQUID readout. Our Quasiparticle trapping assisted Electrothermal feedback Transition edge sensor (QET) utilizes aluminum quasiparticle traps attached to a tungsten superconducting transition edge sensor patterned on a silicon substrate. The tungsten lines are voltage biased and self-regulate in the transition region. We have tested three versions of these detectors. One detector consisted of four QET sensors patterned on the surface of a 1 cm × 1 cm × 1 mm silicon substrate. With this detector, we have shown an energy resolution of ∼400 eV FWHM and position sensitivity of ∼0.3 mm for 6 keV X-rays from an 55 Fe source. We tested a second detector identical to the first but with the addition of an ionization sensor. With information from the ionization channel, we were able to distinguish electron-recoil events from nuclear-recoil events. Most recently, we have tested a 2 cm × 2 cm × 2 mm detector with four QET sensors.

Results and status of the Cryogenic Dark Matter Search (CDMS)

We present evidence of an enhanced ballistic phonon component resulting from surface events in a 100 g silicon cryogenic dark matter detector. Surface events, calibrated using a 14C electron source, were found to have faster rise times (∼5 μs) than bulk gamma and neutron events (∼7 μs). Using this effect, we were able to discriminate bulk nuclear recoil events from a surface electron background at better than the 97% level above 25 keV recoil energy. The phonon risetime for bulk gamma events was dependent on the applied voltage, confirming that phonons produced from electron-hole emission are ballistic.