Cosmic microwave background (CMB) measurements are fundamentally limited by photon statistics. Therefore, ground-based CMB observatories have been increasing the number of detectors that are ...simultaneously observing the sky. Thanks to the advent of monolithically fabricated transition edge sensor arrays, the number of on-sky detectors has been increasing exponentially for over a decade. The next-generation experiment CMB-S4 will increase this detector count by more than an order of magnitude from the current state of the art to 500,000. The readout of such a huge number of exquisitely precise sub-Kelvin sensors is feasible using an existing technology: frequency-domain multiplexing. To further optimize this system and reduce complexity and cost, we have recently made significant advances including the elimination of 4 K electronics, a massive decrease in parasitic in-series impedances, and a significant increase in multiplexing factor.
We report a model that can be used to calculate superconducting transition temperature of a transition-edge sensor (TES), which is either a normal metal-superconductor-normal metal trilayer or a ...normal metal-superconductor bilayer. The model allows the T C estimation of a trilayer when the normal metals at the bottom and at the top are different. Furthermore, the model includes the spin flip time of the normal metals. We use the T C calculations from this model for selected Ir-based trilayers and bilayers to help understand potential designs of low T C TESs. A Au/Ir/Au trilayer can have a low T C because the superconducting order parameter is reduced with normal metals at both sides. On the other hand, an Ir/Pt bilayer can have a low T C because the much larger electron density of states of Pt reduces the superconducting order parameter more effectively. Moreover, the spin flip scattering of paramagnetic Pt also contributes to the T C reduction.
Overwhelming astrophysical evidence indicates that non-baryonic Dark Matter constitutes most of the mass of the Universe. Nevertheless, the particle nature of Dark Matter remains a long standing ...mystery. The use of noble liquids as scintillators in single and dual-phase detectors are some of the most promising scalable WIMP detectors currently planned and under construction. The MiniCLEAN experiment will have 92 photomultiplier tubes (PMTs) looking at a liquid Argon detector mass of over 500 kg in a single-phase configuration. It will use Pulse Shape Discrimination (PSD) techniques to search for low-energy WIMP nuclear recoils inside a fiducial volume. Liquid Argon would be interchangeable with liquid Neon to study A2 dependence of a potential signal and examine backgrounds external to the cryogenic liquid. For the Argon run, MiniCLEAN projects a sensitivity in terms of spin-independent WIMP-nucleon cross-section of 2×10-45cm2 for a mass of 100 GeV/c2. A status report of MiniCLEAN will be presented as well as plans to deploy the experiment at SNOLAB.
Astrophysical observations indicate that dark matter constitutes most of the mass in our universe, but its nature remains unknown. Over the past decade, the Cryogenic Dark Matter Search (CDMS II) ...experiment has provided world-leading sensitivity for the direct detection of weakly interacting massive particle (WIMP) dark matter. The final exposure of our low-temperature germanium particle detectors at the Soudan Underground Laboratory yielded two candidate events, with an expected background of 0.9 ± 0.2 events. This is not statistically significant evidence for a WIMP signal. The combined CDMS II data place the strongest constraints on the WIMP-nucleon spin-independent scattering cross section for a wide range of WIMP masses and exclude new parameter space in inelastic dark matter models.
We report results from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory (CDMS II) featuring the full complement of 30 detectors. A blind analysis of data taken between October ...2006 and July 2007 sets an upper limit on the weakly interacting massive particle (WIMP) nucleon spin-independent cross section of 6.6x10;{-44} cm;{2} (4.6x10;{-44} cm;{2} when combined with previous CDMS II data) at the 90% confidence level for a WIMP mass of 60 GeV/c;{2}. This achieves the best sensitivity for dark matter WIMPs with masses above 44 GeV/c;{2}, and significantly restricts the parameter space for some favored supersymmetric models.
To improve surface event rejection for the SuperCDMS experiment, we have designed, fabricated and tested a new detector concept where ionization electrodes are interleaved with phonon sensors on both ...sides of the detector. This i-(interleaved)-ZIP concept has electrical fields tangential to all detector surfaces. A surface event will produce an ionization signal in one charge read out channel, whereas an event within the bulk of the crystal will cause a signal in both charge read out channels. In addition, the symmetric phonon channels on both sides of the crystal, two semicircles on one side for
x
and two on the other for
y
, allow three-dimensional reconstruction of event locations through time delays and relative energy collection between the four phonon channels. Preliminary results from a 100
g Si prototype are presented.
We report new results from the Cryogenic Dark Matter Search (CDMS II) at the Soudan Underground Laboratory. Two towers, each consisting of six detectors, were operated for 74.5 live days, giving ...spectrum-weighted exposures of 34 (12) kg d for the Ge (Si) targets after cuts, averaged over recoil energies 10-100 keV for a weakly interacting massive particle (WIMP) mass of 60 GeV/c2. A blind analysis was conducted, incorporating improved techniques for rejecting surface events. No WIMP signal exceeding expected backgrounds was observed. When combined with our previous results from Soudan, the 90% C.L. upper limit on the spin-independent WIMP-nucleon cross section is 1.6 x 10(-43) cm2 from Ge and 3 x 10(-42) cm2 from Si, for a WIMP mass of 60 GeV/c2. The combined limit from Ge (Si) is a factor of 2.5 (10) lower than our previous results and constrains predictions of supersymmetric models.
Present Status of the SuperCDMS program Akerib, D. S.; Bailey, C. N.; Bauer, D. A. ...
Journal of low temperature physics,
05/2008, Letnik:
151, Številka:
3-4
Journal Article
Recenzirano
The expected final reach of the Weakly Interacting Massive Particle (WIMP) search experiment CDMS-II by the end of 2007 is a WIMP-nucleon cross-section sensitivity of 2.1×10
−44
cm
2
. To proceed ...further in our search, we have proposed the SuperCDMS Phase A project that would deploy 42 1-inch thick Ge detectors, at a site deeper than the location of CDMS II, and reach a desired sensitivity goal of 1.3×10
−45
cm
2
. These cross-sections are of interest and are complementary to Supersymmetry searches at the Large Hadron Collider (LHC) and future linear colliders.
The Cryogenic Dark Matter Search (CDMS) experiment is searching for Weakly Interacting Massive Particles (WIMPs) using detectors with the ability to discriminate between candidate (nuclear recoil) ...and background (electron recoil) events by measuring both phonon and ionization signals from recoils in the detector crystals. As CDMS scales up to greater WIMP sensitivity, it is necessary to increase the detector mass and further improve background discrimination. CDMS is engaged in ongoing fabrication and development of new detector designs in order to meet these criteria for the proposed SuperCDMS experiment. Thicker detector prototypes have been produced with new photolithographic masks. These masks have greater surface coverage of the quasi particle trap and transition edge sensor system to provide superior athermal phonon collection. Results from continuing laboratory tests are presented which already indicate improvement in discrimination parameters.
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