Detector Development for the Next Phases of the Cryogenic Dark Matter Search: Results from 1 Inch Ge and Si Detectors

Bailey, C. N.; Ahmed, Zeeshan; Akerib, D. S.; Brink, P. L.; Cabrera, B.; Castle, J. P.; Cooley, J.; Danowski, M. E.; Dragowsky, M. R.; Filippini, J. P.; Grant, D.; Hennings‐Yeomans, R.; Mirabolfathi, N.; Novák, L.; Ogburn, R. W.; Pyle, M.; Ruderman, Joshua T.; Sadoulet, B.; Schnee, R. W.; Seitz, D. N.; Serfass, B.; Sundqvist, K. M.; Tomada, A.; Young, B. A.

doi:10.1007/s10909-007-9645-x

Cited by 10 publications

(4 citation statements)

References 3 publications

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“…Both the CDMS II and EDELWEISS-I detectors have a surface 'dead-layer' of ~ 1 micron within which electron-recoils events do not generate the full ionization signal expected, due to electron back-diffusion 12 . Note that the voltage applied across the Ge crystal for the ionization measurement needs to be kept small, a few Volts, otherwise the drifting electrons and holes would generate a large population of phonons that would swamp the discrimination technique of identifying bulk electron vs nuclear recoil events by the ratio of ionization signal to intrinsic recoil phonon energy.…”

Section: Direct-detection Backgroundsmentioning

confidence: 99%

“…3. The SuperCDMS towers contain improved Ge detectors 12 with thicker substrates (25 mm) and improved phonon sensor designs that a cover larger effective surface area of the Ge. The aggregation of the phonon sensors into read-out channels has been re-arranged from the fourquadrants style of CDMS II into one where 3 inner channels are surrounded by an outer-ring comprising the fourth phonon sensor readout channel.…”

Section: Supercdms Programmentioning

confidence: 99%

“…The aggregation of the phonon sensors into read-out channels has been re-arranged from the fourquadrants style of CDMS II into one where 3 inner channels are surrounded by an outer-ring comprising the fourth phonon sensor readout channel. This rearrangement gives enhanced radial information on the event location and improved identification of surface events 12 . The discrimination performance of these new detectors is expected to be adequate for the SuperCDMS Soudan zero-background event goal, with an expected sensitivity (90% CL) of 5 x 10 -45 cm 2 for the WIMP-nucleon scalar cross-section after operation for 3 years.…”

Section: Supercdms Programmentioning

confidence: 99%

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Dark Matter search with Ge detectors

Brink¹

2010

Proceedings of VERTEX 2009 (18th Workshop) — PoS(VERTEX 2009)

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The direct detection of Dark Matter, the relic abundance of weakly-interacting particles in the Universe responsible for large-scale galactic clustering, and inferred from studies of weaklensing and the cosmic microwave background, requires very sensitive detectors here on Earth. The Cryogenic Dark Matter Search (CDMS) collaboration has lead the field for most of the last decade in setting increasingly sensitive exclusion limits on the cross-section of these particles with ordinary baryonic matter.The detectors used by CDMS are crystals of Ge, cooled to sub-Kelvin temperatures and instrumented with advanced phonon sensors to detect the small energy depositions, of order 10keV, from these particles recoiling off the target nuclei. The expected event rate is less than 1 event per kg of target material per year, requiring significant measures to shield the detectors from radioactive backgrounds and powerful discrimination techniques. A description of the CDMS detector technology will be given, along with the present status of the field, and future plans for continuing the search for the Dark Matter of the Universe.

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Section: Direct-detection Backgroundsmentioning

confidence: 99%

Section: Supercdms Programmentioning

confidence: 99%

Section: Supercdms Programmentioning

confidence: 99%

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Dark Matter search with Ge detectors

Brink¹

2010

Proceedings of VERTEX 2009 (18th Workshop) — PoS(VERTEX 2009)

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“…While initial tests hydrogenating the aSi layer in 1-inch silicon detectors resulted in promising results, that under specific bias conditions the asymmetry would disappear [9], the technique needed to be tested with germanium detectors (since most CDMS detectors are made from Ge rather than Si). Three Ge test devices were fabricated: one "control" device with no hydrogen added to the aSi layer on either detector face (like CDMS-II detectors), one device with 20% hydrogen added to the aSi layer on the ionization face, and the final device with 8% hydrogen added to the aSi layer on the phonon face (Table 1).…”

Section: Hydrogenated Amorphous Siliconmentioning

confidence: 99%

Bulk and Surface Charge Collection: CDMS Detector Performance and Design Implications

Bailey¹,

Ahmed²,

Akerib³

et al. 2009

AIP Conference Proceedings

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Abstract. The Cryogenic Dark Matter Search (CDMS) searches for Weakly Interacting Massive Particles (WIMPs) with cryogenic germanium particle detectors. These detectors discriminate between nuclear-recoil candidate and electron-recoil background events by collecting both phonon and ionization energy from interactions in the crystal. Incomplete ionization collection results in the largest background in the CDMS detectors as this causes electron-recoil background interactions to appear as false candidate events. Two primary causes of incomplete ionization collection are suface and bulk charge trapping. Recent work has been focused on reducing surface trapping through the modification of fabrication methods for future detectors. Analyzing data taken with test devices shows that hydrogen passivation of the amorphous silicon blocking layer does not reduce the effects of surface trapping. Other data shows that the iron-ion implantation used to lower the critical temperature of the tungsten transition-edge sensors increases surface trapping, causing a degradation of the ionization collection. Using selective implantation on future detectors may improve ionization collection for events near the phonon side detector surface. Bulk trapping is minimized by neutralizing ionized lattice impurities. Detector investigations at testing facilities and at the experimental site in Soudan, MN have provided methods to optimize the neutralization process and monitor running conditions to maintain maximal ionization collection.

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