P. Colling

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

Enhanced ballistic phonon production for surface events in cryogenic silicon detector

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

Results and status 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.

A new biasing technique for transition edge sensors with electrothermal feedback

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.

Status of CDMS search for dark matter WIMPs

Abstract The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a direct search for weakly interacting massive particles in our Galaxy. The novel detectors allow a high degree of background rejection by discriminating between electron and nuclear recoils through the simultaneous measurement of the energy deposited in phonons and ionization. Exposures on the order of one kilogram-day from initial runs of our experiment yield (preliminary) upper limits on the WIMP-nucleon cross section that are comparable to much longer runs of other experiments. Current and future runs promise significant improvement, primarily due to improved detectors and reduced surface-electron backgrounds.

Results of the Cryogenic Dark Matter Search

We have developed a new operating mode for superconducting transition edge sensors (TES) used in cryogenic particle detection which use electrothermal feedback (ETF). By using the new technique with the optical photon detectors our group has developed, we have been able to reduce the decay time of the pulses from the detector by more than a factor of five. The technique involves reducing the voltage bias across the tungsten superconducting detector during a pulse. By reducing the voltage during a pulse, there is an additional reduction in joule heating which speeds up the recovery of the detector. In theory, the technique reduces the decay time of the pulses which allows for higher maximum count rates. In addition to a brief theoretical analysis of the benefits of the technique, we present experimental results and analysis demonstrating a pulse decay time reduction by a factor of five.

Recent Results from the Cryogenic Dark Matter Search for Weakly Interacting Massive Particles

We report on the latest results from the CDMS (cryogenic dark matter search) experiment. The experiment uses superconducting particle detectors, operated below 100 mK, to search for dark matter in the form of weakly interacting massive elementary particles or WIMPs. These detectors are either Si or Ge crystals, where the electron-hole production and the phonon production are measured for each event, allowing the discrimination of electron recoils (most backgrounds due to gammas and betas) from nuclear recoils (due to WIMPs and neutrons). We have recently reported new limits from the Stanford shallow site experiment (CDMS-I) which explore supersymmetric models where the lightest supersymmetric particle is often an excellent WIMP candidate. We will also report on the Soudan deep site facility for the CDMS-II experiment which is under construction, and on the status of the CDMS-II detector fabrication.

Exclusion limits on the WIMP-nucleon scattering cross-section from the Cryogenic Dark Matter Search

The Cryogenic Dark Matter Search (CDMS) employs 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. CDMS data, accounting for the neutron background, 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 > 75% CL. the entire 3σ allowed region for the WIMP signal reported by the DAMA experiment.