G. Smith

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

First Results from the Cryogenic Dark Matter Search in the Soudan Underground Laboratory

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

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

Installation of the cryogenic dark matter search (CDMS)

We report the first results from a search for weakly interacting massive particles (WIMPs) in the Cryogenic Dark Matter Search (CDMS) experiment at the Soudan Underground Laboratory. Four Ge and two Si detectors were operated for 52.6 live days, providing 19.4 kg-d of Ge net exposure after cuts for recoil energies between 10--100 keV. A blind analysis was performed using only calibration data to define the energy threshold and selection criteria for nuclear-recoil candidates. Using the standard dark-matter halo and nuclear-physics WIMP model, these data set the worlds lowest exclusion limits on the coherent WIMP-nucleon scalar cross-section for all WIMP masses above 15 GeV, ruling out a significant range of neutralino supersymmetric models. The minimum of this limit curve at the 90% C.L. is 4 x 10^{-43} cm^2 at a WIMP mass of 60 GeV.

Gas scintillation drift chambers with wave shifter fiber readout

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.

The first cryogenic dark matter experiment

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.

Performance of a 60 gram cryogenic germanium detector

Results for a prototype xenon gas scintillation drift chamber are presented. Its operation is discussed using two types of light detection schemes: one based on an Anger camera geometry and one based on an array of wave-shifting light fibers. The results are judged to demonstrate the instruments potential. >

A cryogenic detector with simultaneous phonon and ionization measurement for background rejection

An experimental search for dark matter particle candidates using cryogenic detectors requires a low radioactive background environment. We discuss the status of a cryogenic dark matter experiment to be performed 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. Details of the cryostat design and its operating performance are presented. The effectiveness of the multi-level shield surrounding the cryostat, as well as the background levels we expect to achieve in the pilot experiment are discussed. Finally, we examine the limits which can be set on dark matter candidates with such an experiment.

Particle detection and non-equilibrium phonons: Experience with large germanium crystals and NTD Ge thermistors

A 60-g particle detector which utilizes the ionization and the phonons produced by a particle interaction has been developed. Six NDT (neutron transmutation doped) Ge thermistors are attached to a pure germanium crystal which has implanted contacts for drifting charge. The authors have operated the detectors at 30 mK and have studied its response to irradiation by 18- and 60-keV photons from an /sup 241/Am source. An analysis of the resolution of the detector which addresses the noise of the front-end electronics and signals from extraneous sources such as microphonics is presented. The simultaneous measurement of phonons and ionization has been demonstrated to have a resolution of 4 keV. This joint detection should prove to be very valuable in distinguishing between candidate dark matter interaction events and competing background processes. >

SIGHT: a balloon hard X-ray telescope

We report on the performance of a 60 g Ge detector that measures both ionization and phonons at cryogenic (∼ 25 mK) temperatures. This simultaneous measurements is a powerful new tool in experiments where the primary signal is a nuclear recoil (e.g., WIMP dark matter) that must be distinguished from a background of photons or charged particles that produce electron recoils. We have measured nuclear recoils produced by neutrons from a 252Cf source, and can distinguish them from photons at energies as low as 2 keV in the ionization measurement. An important effect that can limit the efficiency of the background rejection technique is incomplete charge collection. We have tested our detector at ionization drift fields as low as 5 mV/cm and find that the phonon energy measured for each event depends on the amount of charge collected. From this we deduce details about charge trapping mechanisms.