Search

A model for charge trapping and impact ionization and an experiment to measure these parameters are presented for the SuperCDMS HVeV detector. A procedure to isolate and quantify the main sources of noise (bulk and surface charge leakage) in the measurements is also described. This sets the stage to precisely measure the charge trapping and impact ionization probabilities in order to incorporate this model into future dark matter searches. [ABSTRACT FROM AUTHOR]

We report recent results obtained from several W/Al test devices on Si wafers fabricated specifically to better understand energy collection in phonon sensors used for the Cryogenic Dark Matter Search (CDMS) experiment. The devices under study consist of three different lengths of 250 $$\upmu $$ m-wide by 300 nm-thick Al absorber films, coupled to 250 $$\upmu $$ m x 250 $$\upmu $$ m (40 nm thick) W-TESs at each end of the Al film. An $$^{55}$$ Fe source was used to excite a NaCl reflector producing 2.6 keV Cl X-rays that were absorbed in our test device after passing through a collimator. The impinging X-rays broke Cooper pairs in the Al film, producing quasiparticles that we detected after they propagated into the W-TESs. We studied the diffusion of these quasiparticles in the Al, trapping effects in the Al film, and energy transmission at the Al/W interfaces. [ABSTRACT FROM AUTHOR]

Amplifying the phonon signal in a semiconductor dark matter detector can be accomplished by operating at high voltage bias and converting the electrostatic potential energy into Luke-Neganov phonons. This amplification method has been validated at up to | E|=40 V/cm without producing leakage in CDMS II Ge detectors, allowing sensitivity to a benchmark WIMP with mass M=8 GeV/c and σ=1.8×10 cm (with significant sensitivity for M>2 GeV/c) assuming flat electronic recoil backgrounds near threshold. Furthermore, for the first time we show that differences in Luke-Neganov gain for nuclear and electronic recoils can be used to discriminate statistically between low-energy background and a hypothetical WIMP signal by operating at two distinct voltage biases. Specifically, 99% of events have p-value <10 for a simulated 20 kg-day experiment with a benchmark WIMP signal with M=8 GeV/c and σ=3.3×10 cm. [ABSTRACT FROM AUTHOR]

SuperCDMS is the next phase of the Cryogenic Dark Matter Search experiment, which measures both phonon and charge signals generated by particle recoils within a germanium target mass. Charge signals are employed both in the definition of a fiducial volume and in the rejection of electron recoil background events. Alternatively, phonons generated by the charge carriers can also be used for the same two goals. This paper describes preliminary efforts to observe and quantify these contributions to the phonon signal and then use them to reject background events. A simple analysis using only one pulse shape parameter shows bulk electron recoil vs. bulk nuclear recoil discrimination to the level of 1:10 (limited by the statistics of the data), with little degradation in discrimination ability down to at least 7 keV recoil energy. Such phonon-only discrimination can provide a useful cross-check to the standard discrimination methods, and it also points towards the potential of a device optimized for a phonon-only measurement. [ABSTRACT FROM AUTHOR]

Interleaved ionization electrode geometries offer the possibility of efficient rejection of near-surface events. The CDMS collaboration has implemented this interleaved approach for the charge and phonon readout for our germanium detectors. During a recent engineering run with negligible ambient radiation, the detectors were found to lose ionization stability more quickly than expected. This paper summarizes studies done in order to determine the underlying cause of the instability, as well as possible running modes that maintain stability without unacceptable loss of livetime. Additionally, first results are shown for the new version IZIP mask which attempts to improve the overall stability of the detectors. [ABSTRACT FROM AUTHOR]

This paper describes an impedance matching network which allows charge impulses to be measured by a SQUID amplifier with an RMS charge noise of less than 100 e, assuming the SQUID amplifier has a current noise of 2 $\mathrm{pA}/\sqrt{\mathrm{Hz}}$, and the current pulse has a duration of about 1 μs or shorter. The component values are provided for an example system which has an RMS charge noise of 91 e, assuming all dissipative circuit elements are cooled to a temperature of 100 mK. [ABSTRACT FROM AUTHOR]

The Cryogenic Dark Matter Search (CDMS) utilizes large mass, 3″ diameter×1″ thick target masses as particle detectors. The target is instrumented with both phonon and ionization sensors, the later providing a ∼1 V cm electric field in the detector bulk. Cumulative radiation exposure which creates ∼200×10 electron-hole pairs could be sufficient to produce a comparable reverse field in the detector thereby degrading the ionization channel performance, if it was not shielded by image charges on the electrodes. To study this, the existing CDMS detector Monte Carlo has been modified to allow for an event by event evolution of the bulk electric field, in three spatial dimensions. Surprisingly, this simple model is not sufficient to explain the degradation of detector performance. Our most recent results and interpretation are discussed. [ABSTRACT FROM AUTHOR]

The SuperCDMS collaboration is a dark matter search effort aimed at detecting the scattering of WIMP dark matter from nuclei in cryogenic germanium targets. The CDMS Detector Monte Carlo (CDMS-DMC) is a simulation tool aimed at achieving a deeper understanding of the performance of the SuperCDMS detectors and aiding the dark matter search analysis. We present results from validation of the phonon physics described in the CDMS-DMC and outline work towards utilizing it in future WIMP search analyses. [ABSTRACT FROM AUTHOR]

We briefly review a simple model of superconducting-normal phase-separation in transition-edge sensors (TESs) in the SuperCDMS experiment. After discussing some design considerations relevant to the TESs in the experiment, we study noise sources in both the phase-separated and phase-uniform cases. Such simulations will be valuable for optimizing the critical temperature and TES length of future SuperCDMS detectors. [ABSTRACT FROM AUTHOR]

The purpose of this study was to obtain more information on the nature of the macromolecule to which Pseudomonas aeruginosa adheres. Acid-injured tracheal epithelium was treated with trypsin or lipase to determine whether the receptor molecule was a protein or a lipid. Lipase treatment significantly reduced adherence to these cells, whereas trypsin had no effect. Since the receptor appeared to be a lipid containing sialic acid, gangliosides were used to test whether they would inhibit adherence. Crude ganglioside preparations inhibited adherence in a dose-dependent manner when added to the bacteria before exposure to tracheal cells. Lastly, fibronectin, which presumably binds to gangliosides, significantly reduced the adherence of these organisms. According to these findings Pseudomonas aeruginosa appears to adhere to a sialic acid-containing glycolipid on cell surfaces, probably a ganglioside. [ABSTRACT FROM AUTHOR]