1,567 research outputs found
The DRIFT Directional Dark Matter Detector and First Studies of the Head-Tail Effect
Measurement of the direction of the elastic nuclear recoil track and
ionization charge distribution along it, gives unique possibility for
unambiguous detection of the dark matter WIMP particle. Within current
radiation detection technologies only Time Projection Chambers filled with low
pressure gas are capable of such measurement. Due to the character of the
electronic and nuclear stopping powers of low energy nuclear recoils in the
gas, an asymmetric ionization charge distribution along their tracks may be
expected. Preliminary study of this effect, called Head-Tail, has been carried
out here using the SRIM simulation program for Carbon and Sulfur in 40 Torr
carbon disulfide, as relevant to the DRIFT detector. Investigations were
focused on ion tracks projected onto the axis of the initial direction of
motion in the energy range between 10 and 400 keV. Results indicate the likely
existence of an asymmetry influenced by two competing effects: the nature of
the stopping power and range straggling. The former tends to result in the Tail
being greater than the Head and the latter the reverse. It has been found that
for projected tracks the mean position of the ionization charge flows from
'head' to 'tail' with the magnitude depending on the ion type and its energy.Comment: To appear in the proceedings of Dark 2007 Sixth International
Heidelberg conference on "Dark Matter in Astro & Particle Physics", Sydney,
Australia 24th-28th September 200
The expected background spectrum in NaI dark matter detectors and the DAMA result
Detailed Monte Carlo simulations of the expected radioactive background rates
and spectra in NaI crystals are presented. The obtained spectra are then
compared to those measured in the DAMA/NaI and DAMA/LIBRA experiments. The
simulations can be made consistent with the measured DAMA spectrum only by
assuming higher than reported concentrations of some isotopes and even so leave
very little room for the dark matter signal. We conclude that any
interpretation of the annual modulation of the event rate observed by DAMA as a
dark matter signal, should include full consideration of the background
spectrum. This would significantly restrict the range of dark matter models
capable of explaining the modulation effect.Comment: 17 pages, 6 figure
A small angle neutron scattering and Mössbauer spectrometry study of magnetic structures in nanocrystalline Ni3Fe
Results are reported from small angle neutron scattering and Mössbauer spectrometry measurements on nanocrystalline Ni3Fe. The nanocrystalline materials were prepared by mechanical attrition and studied in the as-milled state, after annealing at 265 °C to relieve internal stress, and after annealing 600 °C to prepare a control sample comprising large crystals. The small angle neutron scattering (SANS) measurements were performed for a range of applied magnetic fields. Small differences were found in how the different samples reached magnetic saturation. From the SANS data obtained at magnetic saturation, we found little difference in the nuclear scattering of the as-milled material and the material annealed at 265 °C. Reductions in nuclear scattering and magnetic scattering were observed for the control sample, and this was interpreted as grain growth. The material annealed at 265 °C also showed a reduction in magnetic SANS compared to the as-milled material. This was interpreted as an increase in magnetic moments of atoms at the grain boundaries after a low temperature annealing. Both Mössbauer spectroscopy and small angle neutron scattering showed an increase in the grain boundary magnetic moments after the 265 °C annealing (0.2 and 0.4µB/atom, respectively), even though there was little change in the grain boundary atomic density
Narrow muon bundles from muon pair production in rock
We revise the process of muon pair production by high-energy muons in rock
using the recently published cross-section. The three-dimensional Monte Carlo
code MUSIC has been used to obtain the characteristics of the muon bundles
initiated via this process. We have compared them with those of conventional
muon bundles initiated in the atmosphere and shown that large underground
detectors, capable of collecting hundreds of thousands of multiple muon events,
can discriminate statistically muon induced bundles from conventional ones.
However, we find that the enhancement of the measured muon decoherence function
over that predicted at small distances, recently reported by the MACRO
experiment, cannot be explained by the effect of muon pair production alone,
unless its cross-section is underestimated by a factor of 3.Comment: 10 pages, 1 table, 2 figures, to be published in Physics Letters
Measurement of the Scintillation Efficiency of Na Recoils in NaI(Tl) down to 10 keV Nuclear Recoil Energy relevant to Dark Matter Searches
We present preliminary results of measurements of the quenching factor for Na
recoils in NaI(Tl) at room temperature, made at a dedicated neutron facility at
the University of Sheffield. Measurements have been performed with a 2.45 MeV
mono-energetic neutron generator in the energy range from 10 keV to 100 keV
nuclear recoil energy. A BC501A liquid scintillator detector was used to tag
neutrons. Cuts on pulse-shape discrimination from the BC501A liquid
scintillator detector and neutron time-of-flight were performed on pulses
recorded by a digitizer with a 2 ns sampling time. Measured quenching factors
range from 19% to 26%, in agreement with other experiments. From pulse-shape
analysis, a mean time of pulses from electron and nuclear recoils are compared
down to 2 keV electron equivalent energy.Comment: to appear in Proc. 6th Int. Workshop on the Identification of Dark
Matter, 11-16 September 2006, Rhodes, Greece; 6 pages, 4 figures; corrected
preliminary theoretical estimation curve plotted in figure
The Supersymmetric Origin of Matter
The Minimal Supersymmetric extension of the Standard Model (MSSM) can provide
the correct neutralino relic abundance and baryon number asymmetry of the
universe. Both may be efficiently generated in the presence of CP violating
phases, light charginos and neutralinos, and a light top squark. Due to the
coannihilation of the neutralino with the light stop, we find a large region of
parameter space in which the neutralino relic density is consistent with WMAP
and SDSS data. We perform a detailed study of the additional constraints
induced when CP violating phases, consistent with the ones required for
baryogenesis, are included. We explore the possible tests of this scenario from
present and future electron Electric Dipole Moment (EDM) measurements, direct
neutralino detection experiments, collider searches and the b -> s gamma decay
rate. We find that the EDM constraints are quite severe and that electron EDM
experiments, together with stop searches at the Tevatron and Higgs searches at
the LHC, will provide a definite test of our scenario of electroweak
baryogenesis in the next few years.Comment: 30 pages, 14 figure
Limits on WIMP Dark Matter
The current state searches for dark matter in the form of Weakly Interacting
Massive Particles (WIMPs) using both direct and indirect techniques is
reviewed. Advances in recent years by various direct search experiments,
utilising technology able to record the nuclear recoil events expected from
elastic scattering by WIMPs, have allowed progress towards lower limits to be
made. In particular, the Edelweiss and CDMS collaborations are achieving
sensitiviy able to challenge data from DAMA interpreted as evidence for WIMPs
of mass in the region of 60 GeV. Meanwhile, indirect searches, based on
observing the annihilation products of neutralino-neutralino interactions in
the Earth, Sun and Galaxy, have produced intriguing results. For instance,
analysis by Superkamiokande now suggests limits comparable with the best direct
search results.Comment: 8 pages, 5 figures, International Europhysics Conference on High
Energy Physic
Graph reasoning with context-aware linearization for interpretable fact extraction and verification
This paper presents an end-to-end system for fact extraction and verification using textual and tabular evidence, the performance of which we demonstrate on the FEVEROUS dataset. We experiment with both a multi-task learning paradigm to jointly train a graph attention network for both the task of evidence extraction and veracity prediction, as well as a single objective graph model for solely learning veracity prediction and separate evidence extraction. In both instances, we employ a framework for per-cell linearization of tabular evidence, thus allowing us to treat evidence from tables as sequences. The templates we employ for linearizing tables capture the context as well as the content of table data. We furthermore provide a case study to show the interpretability our approach. Our best performing system achieves a FEVEROUS score of 0.23 and 53% label accuracy on the blind test data
Developing a Core Outcome Set for Prognostic Research in Palliative Cancer Care: Protocol for a Mixed Methods Study
Background: Studies exploring the impact of receiving end-of-life prognoses in patients with advanced cancer use a variety of different measures to evaluate the outcomes, and thus report often conflicting findings. The standardization of outcomes reported in studies of prognostication in palliative cancer care could enable uniform assessment and reporting, as well as intertrial comparisons. A core outcome set promotes consistency in outcome selection and reporting among studies within a particular population. We aim to develop a set of core outcomes to be used to measure the impact of end-of-life prognostication in palliative cancer care. Objective: This protocol outlines the proposed methodology to develop a core outcome set for measuring the impact of end-of-life prognostication in palliative cancer care. Methods: We will adopt a mixed methods approach consisting of 3 phases using methodology recommended by the Core Outcome Measure in Effectiveness Trials (COMET) initiative. In phase I, we will conduct a systematic review to identify existing outcomes that prognostic studies have previously used, so as to inform the development of items and domains for the proposed core outcome set. Phase II will consist of semistructured interviews with patients with advanced cancer who are receiving palliative care, informal caregivers, and clinicians, to explore their perceptions and experiences of end-of-life prognostication. Outcomes identified in the interviews will be combined with those found in existing literature and taken forward to phase III, a Delphi survey, in which we will ask patients, informal caregivers, clinicians, and relevant researchers to rate these outcomes until consensus is achieved as to which are considered to be the most important for inclusion in the core outcome set. The resulting, prioritized outcomes will be discussed in a consensus meeting to agree and endorse the final core outcome set. Results: Ethical approval was received for this study in September 2022. As of July 2023, we have completed and published the systematic review (phase I) and have started recruitment for phase II. Data analysis for phase II has not yet started. We expect to complete the study by October 2024. Conclusions: This protocol presents the stepwise approach that will be taken to develop a core outcome set for measuring the impact of end-of-life prognostication in palliative cancer care. The final core outcome set has the potential for translation into clinical practice, allowing for consistent evaluation of emerging prognostic algorithms and improving communication of end-of-life prognostication. This study will also potentially facilitate the design of future clinical trials of the impact of end-of-life prognostication in palliative care that are acceptable to key stakeholders
The DRIFT Project: Searching for WIMPS with a Directional Detector
A low pressure time projection chamber for the detection of WIMPs is
discussed. Discrimination against Compton electron background in such a device
should be very good, and directional information about the recoil atoms would
be obtainable. If a full 3-D reconstruction of the recoil tracks can be
achieved, Monte Carlo studies indicate that a WIMP signal could be identified
with high confidence from as few as 30 detected WIMP-nucleus scattering events.Comment: 5 pages, 3 figures. Presented at Dark 98, Heidelberg, July 1998, and
to appear in conference proceeding
- …