114,993 research outputs found
Dark Matter vs. Neutrinos: The effect of astrophysical uncertainties and timing information on the neutrino floor
Future multi-tonne Direct Detection experiments will be sensitive to solar
neutrino induced nuclear recoils which form an irreducible background to light
Dark Matter searches. Indeed for masses around 6 GeV the spectra of neutrinos
and Dark Matter are so similar that experiments will run into a neutrino floor,
for which sensitivity increases only marginally with exposure past a certain
cross section. In this work we show that this floor can be overcome using the
different annual modulation expected from solar neutrinos and Dark Matter.
Specifically for cross sections below the neutrino floor the DM signal is
observable through a phase shift and a smaller amplitude for the time-dependent
event rate. This allows the exclusion power to be improved by up to an order of
magnitude for large exposures. In addition we demonstrate that the neutrino
floor exists over a wider mass range than has been previously shown, since the
large uncertainties in the Dark Matter velocity distribution make the signal
spectrum harder to distinguish from the neutrino background. However for most
velocity distributions the neutrino floor can still be surpassed using timing
information, though certain velocity streams may prove problematic.Comment: 18 pages, 7 figures. v2: Matches version published in JCAP. Includes
clarifications to the text and a new figur
A novel dry coal feeding concept for high-pressure gasifiers
A novel dry coal feeding concept was developed for injecting ground coal into high-pressure gasifiers. Significant power savings are projected because the coal is injected directly with a ram and there is no requirement for pumping large volumes of gas or fluid against pressure. A novel feature of the concept is that a new seal zone is formed between the ram and injection tube each cycle. The seal zone comprises a mixture of a small quantity of finely ground coal and a fluid. To demonstrate the feasibility of the concept, coal was injected into a 1000-psi chamber with an experimental device having a 7-1/2-inch-diameter ram and a 28-inch-long stroke
The Past and Future of Light Dark Matter Direct Detection
We review the status and future of direct searches for light dark matter. We
start by answering the question: `Whatever happened to the light dark matter
anomalies?' i.e. the fate of the potential dark matter signals observed by the
CoGeNT, CRESST-II, CDMS-Si and DAMA/LIBRA experiments. We discuss how the
excess events in the first two of these experiments have been explained by
previously underestimated backgrounds. For DAMA we summarise the progress and
future of mundane explanations for the annual modulation reported in its event
rate. Concerning the future of direct detection we focus on the irreducible
background from solar neutrinos. We explain broadly how it will affect future
searches and summarise efforts to mitigate its effects.Comment: Invited review article for the International Journal of Modern
Physics A. 20 pages, 3 figure
Fitting the annual modulation in DAMA with neutrons from muons and neutrinos
The DAMA/LIBRA experiment searches for evidence of Dark Matter scattering off
nuclei. Data from DAMA show 9.2 sigma evidence for an annual modulation,
consistent with Dark Matter having a cross section around 2x10^(-40) cm^2.
However this is excluded by other Direct Detection experiments. We propose an
alternative source of annual modulation in the form of neutrons, which have
been liberated from material surrounding the detector by a combination of 8B
solar neutrinos and atmospheric muons. The phase of the muon modulation lags 30
days behind the data, however we show that adding the modulated neutrino
component shifts the phase of the combined signal forward. In addition we
estimate that neutrinos and muons need around 1000 m^3 of scattering material
in order to generate enough neutrons to constitute the signal. With current
data our model gives as good a fit as Dark Matter and we discuss prospects for
future experiments to discriminate between the two.Comment: v2: Matches version published in PRL. Includes a new figure. 5 pages,
4 figure
Projections for measuring the size of the solar core with neutrino-electron scattering
We quantify the amount of data needed in order to measure the size and
position of the B neutrino production region within the solar core, for
experiments looking at elastic scattering between electrons and solar
neutrinos. The directions of the electrons immediately after scattering are
strongly correlated with the incident directions of the neutrinos, however this
is degraded significantly by the subsequent scattering of these electrons in
the detector medium. We generate distributions of such electrons for different
neutrino production profiles, and use a maximum likelihood analysis to make
projections for future experimental sensitivity. We find that with
approximately 20 years worth of data the Super Kamiokande experiment could
constrain the central radius of the shell in which B neutrinos are produced
to be less than 0.22 of the total solar radius at 95% confidence.Comment: 5 pages, 2 figures. Matches version accepted to PRL. Improved 2D
analysis and results discussio
Tumbling Motion of Elliptical Particles in Viscous Two-Dimensional Flow
The settling dynamics of spherical and elliptical particles in a viscous
Newtonian fluid are investigated numerically using a finite difference
technique. The terminal velocity for spherical particles is calculated for
different system sizes and the extrapolated value for an infinite system size
is compared to the Oseen approximation. Special attention is given to the
settling and tumbling motion of elliptical particles where their terminal
velocity is compared with the one of the surface equivalent spherical particle.Comment: 13 pages, 8 figures (within text), uses IJMPC macros (included
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