We present results from a 54.7 live-day shielded run of the DRIFT-IId detector, the world's most sensitive, directional, dark matter detector. Several improvements were made relative to our previous ...work including a lower threshold for detection, a more robust analysis and a tenfold improvement in our gamma rejection factor. After analysis, no events remain in our fiducial region leading to an exclusion curve for spin-dependent WIMP-proton interactions which reaches 0.28pb at 100GeV/c2, a fourfold improvement on our previous work. We also present results from a 45.4 live-day unshielded run of the DRIFT-IId detector during which 14 nuclear recoil-like events were observed. We demonstrate that the observed nuclear recoil rate of 0.31 ± 0.08 events per day is consistent with detection of ambient, fast neutrons emanating from the walls of the Boulby Underground Science Facility.
We described the relationship between relatedness as full or maternal half siblings and expression of social play and other social behaviors in juvenile Belding's ground squirrel (Urocitellus ...beldingi) litters and evaluated the possible role of play in establishing social bonds between juvenile females. We used microsatellite analysis to determine relatedness. Juvenile females did not interact preferentially with full over half siblings, suggesting that they may form bonds equally with full and half sisters. The probability that females will have a surviving full sister beyond the juvenile period may be low in U. beldingi, and establishing a cooperative relationship with a half sister may sometimes be the best available option in adulthood. As the proportion of females within litters increased, rates of play decreased, suggesting that low social play may be adequate for social bonding among females. Among juvenile male U. beldingi, play bouts lasted longer between full than half brothers; however, juvenile males did not interact preferentially with full brothers in play or other social interactions. Body mass differences were smaller between full than half brothers, and in both full and half brother pairings, play bouts lasted longest when body mass differences were small. Because male U. beldingi do not ordinarily interact with littermate siblings after emigrating from the natal area, it is unlikely that play behavior functions to establish long-term social bonds between full brothers. Rather, young males may favor play interactions with phenotypically similar partners who can provide optimal challenges in interactions that promote motor development.
Reducing DRIFT backgrounds with a submicron aluminized-mylar cathode Battat, J.B.R.; Daw, E.; Dorofeev, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2015, Letnik:
794
Journal Article
Recenzirano
Odprti dostop
Background events in the DRIFT-IId dark matter detector, mimicking potential WIMP signals, are predominantly caused by alpha decays on the central cathode in which the alpha particle is completely or ...partially absorbed by the cathode material. We installed a 0.9μm thick aluminized-mylar cathode as a way to reduce the probability of producing these backgrounds. We study three generations of cathode (wire, thin-film, and radiologically clean thin-film) with a focus on the ratio of background events to alpha decays. Two independent methods of measuring the absolute alpha decay rate are used to ensure an accurate result, and agree to within 10%. Using alpha range spectroscopy, we measure the radiologically cleanest cathode version to have a contamination of 3.3±0.1 ppt 234U and 73±2 ppb 238U. This cathode reduces the probability of producing an RPR from an alpha decay by a factor of 70±20 compared to the original stainless steel wire cathode. First results are presented from a texturized version of the cathode, intended to be even more transparent to alpha particles. These efforts, along with other background reduction measures, have resulted in a drop in the observed background rate from 500/day to 1/day. With the recent implementation of full-volume fiducialization, these remaining background events are identified, allowing for background-free operation.
Commercially available computer-controlled SQUID electronics are usually delivered with software providing a basic user interface for adjustment of superconducting quantum interference device (SQUID) ...tuning parameters, such as bias current, flux offset, and feedback loop settings. However, in a research context it would often be useful to be able to modify this code and/or to have full control over all these parameters from researcher-written software. In the case of the STAR Cryoelectronics PCI/PFL family of SQUID control electronics, the supplied software contains modules for automatic tuning and noise characterization, but does not provide an interface for user code. On the other hand, the Magnicon SQUIDViewer software package includes a public application programming interface, but lacks auto-tuning and noise characterization features. To overcome these and other limitations, we are developing an "open-source" framework for controlling SQUID electronics, which should provide maximal interoperability with user software, a unified user interface for electronics from different manufacturers, and a flexible platform for the rapid development of customized SQUID auto-tuning and other advanced features. We have completed a first implementation for the STAR Cryoelectronics hardware and have made the source code for this ongoing project available to the research community on SourceForge (http://opensquid.sourceforge.net) under the GNU public license.
The DRIFT-IId dark matter detector is a m3-scale low-pressure TPC with directional sensitivity to WIMP-induced nuclear recoils. Its primary backgrounds were due to alpha decays from contamination on ...the central cathode. Efforts to reduce these backgrounds led to replacing the 20μm wire central cathode with one constructed from 0.9μm aluminized mylar, which is almost totally transparent to alpha particles. Detailed modeling of the nature and origin of the remaining backgrounds led to an in-situ, ppt-sensitive assay of alpha decay backgrounds from the central cathode. This led to further improvements in the thin-film cathode resulting in over 2 orders of magnitude reduction in backgrounds compared to the wire cathode. Finally, the addition of O2 to CS2 gas was found to produce multiple species of electronegative charge carriers, providing a method to determine the absolute position of nuclear recoils and reject all known remaining backgrounds while retaining a high efficiency for nuclear recoil detection.
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