1,938 research outputs found
Solar neutrino physics with low-threshold dark matter detectors
Dark matter detectors will soon be sensitive to Solar neutrinos via two
distinct channels: coherent neutrino-nucleus scattering and neutrino electron
elastic scattering. We establish an analysis method for extracting Solar model
properties and neutrino properties from these measurements, including the
possible effects of sterile neutrinos which have been hinted at by some reactor
experiments and cosmological measurements. Even including sterile neutrinos,
through the coherent scattering channel a 1 ton-year exposure with a
low-threshold Germanium detector could improve on the current measurement of
the normalization of the B Solar neutrino flux down to 3% or less.
Combining with the elastic scattering data will provide constraints on both the
high and low energy survival probability, and will improve on the uncertainty
on the active-to-sterile mixing angle by a factor of two. This sensitivity to
active-to-sterile transitions is competitive and complementary to forthcoming
dedicated short baseline sterile neutrino searches with nuclear decays.Comment: 12 pages, 4 figures, 3 table
Implication of neutrino backgrounds on the reach of next generation dark matter direct detection experiments
As direct dark matter experiments continue to increase in size, they will
become sensitive to neutrinos from astrophysical sources. For experiments that
do not have directional sensitivity, coherent neutrino scattering (CNS) from
several sources represents an important background to understand, as it can
almost perfectly mimic an authentic WIMP signal. Here we explore in detail the
effect of neutrino backgrounds on the discovery potential of WIMPs over the
entire mass range of 500 MeV to 10 TeV. We show that, given the theoretical and
measured uncertainties on the neutrino backgrounds, direct detection
experiments lose sensitivity to light (~10 GeV) and heavy (~100 GeV) WIMPs with
a spin-independent cross section below 10^{-45} cm^2 and 10^{-49} cm^2,
respectively.Comment: 15 pages, 12 figures, 7Be fluxes revised, conclusions unchange
Complementarity of dark matter detectors in light of the neutrino background
Direct detection dark matter experiments looking for WIMP-nucleus elastic
scattering will soon be sensitive to an irreducible background from neutrinos
which will drastically affect their discovery potential. Here we explore how
the neutrino background will affect future ton-scale experiments considering
both spin-dependent and spin-independent interactions. We show that combining
data from experiments using different targets can improve the dark matter
discovery potential due to target complementarity. We find that in the context
of spin-dependent interactions, combining results from several targets can
greatly enhance the subtraction of the neutrino background for WIMP masses
below 10 GeV/c and therefore probe dark matter models to lower
cross-sections. In the context of target complementarity, we also explore how
one can tune the relative exposures of different target materials to optimize
the WIMP discovery potential.Comment: 13 pages, 12 figures, 3 table
Coherent Neutrino Scattering in Dark Matter Detectors
Coherent elastic neutrino- and WIMP-nucleus interaction signatures are
expected to be quite similar. This paper discusses how a next generation
ton-scale dark matter detector could discover neutrino-nucleus coherent
scattering, a precisely-predicted Standard Model process. A high intensity
pion- and muon- decay-at-rest neutrino source recently proposed for oscillation
physics at underground laboratories would provide the neutrinos for these
measurements. In this paper, we calculate raw rates for various target
materials commonly used in dark matter detectors and show that discovery of
this interaction is possible with a 2 tonyear GEODM exposure in an
optimistic energy threshold and efficiency scenario. We also study the effects
of the neutrino source on WIMP sensitivity and discuss the modulated neutrino
signal as a sensitivity/consistency check between different dark matter
experiments at DUSEL. Furthermore, we consider the possibility of coherent
neutrino physics with a GEODM module placed within tens of meters of the
neutrino source.Comment: 8 pages, 4 figure
Steric engineering of metal-halide perovskites with tunable optical band gaps
Owing to their high energy-conversion efficiency and inexpensive fabrication
routes, solar cells based on metal-organic halide perovskites have rapidly
gained prominence as a disruptive technology. An attractive feature of
perovskite absorbers is the possibility of tailoring their properties by
changing the elemental composition through the chemical precursors. In this
context, rational in silico design represents a powerful tool for mapping the
vast materials landscape and accelerating discovery. Here we show that the
optical band gap of metal-halide perovskites, a key design parameter for solar
cells, strongly correlates with a simple structural feature, the largest
metal-halide-metal bond angle. Using this descriptor we suggest continuous
tunability of the optical gap from the mid-infrared to the visible. Precise
band gap engineering is achieved by controlling the bond angles through the
steric size of the molecular cation. Based on these design principles we
predict novel low-gap perovskites for optimum photovoltaic efficiency, and we
demonstrate the concept of band gap modulation by synthesising and
characterising novel mixed-cation perovskites.Comment: This manuscript was submitted for publication on March 6th, 2014.
Many of the results presented in this manuscript were presented at the
International Conference on Solution processed Semiconductor Solar Cells,
held in Oxford, UK, on 10-12 September 2014. The manuscript is 37 pages long
and contains 8 figure
Watching the games: Critical media literacy and students’ abilities to identify and critique the politics of sports
Sport can be the source of fitter, healthier and better lifestyles. However, sport can also be a vehicle for the reproduction of problematic notions of gender, race, nationality, industry, et cetera. If people who consume and participate in sport are unequipped to identify and question these issues, they will continue reproducing these conceptions uncritically. As a proponent of Critical Media Literacy (CML), through this dissertation I encourage educators to teach students the skills and knowledge to recognize and critically assess these and other problematic discourses in sports media. In this dissertation, I set out to discover if adolescents possess these skills and knowledge.
Two main questions drive this research: First, what type of knowledge do the participants have about the socio-cultural, political and economic implications of sport in our societies? And second, can the participants identify socio-political issues (e.g. gender, race, nationality, political economy) in sports media texts as they consume them? To answer these questions, I first attempted a study with youth and later I recruited 20 first year university students to participate in a 90 minute session where I showed them three sports clips and asked them to complete a short qualitative questionnaire and partake in a focus group discussion. Using Qualitative Content Analysis (QCA), I examined both the questionnaires and the transcripts from the discussions leading to a critical analysis.
I found that the participants had a limited knowledge of the general and critical media issues we discussed. Though the students demonstrated some understanding of the way the sports media operates, they consistently drew from stereotypes and common sense tropes when analyzing issues of race, nationality and gender in sports. I also found that students were generally unable to identify and/or critique problematic representations present in the videos. There were only 5.6% of instances where the participants questioned these problems in the clips. Most of the time (86.23%) the participants were either unaware of the issues or saw them as normal and saw no need to resist or critique. These findings support the idea that students would benefit from receiving a critical media literacy education that teaches them to identify and question hegemonic discourses in sports media
Plasma Processing of Large Curved Surfaces for SRF Cavity Modification
Plasma based surface modification of niobium is a promising alternative to
wet etching of superconducting radio frequency (SRF) cavities. The development
of the technology based on Cl2/Ar plasma etching has to address several crucial
parameters which influence the etching rate and surface roughness, and
eventually, determine cavity performance. This includes dependence of the
process on the frequency of the RF generator, gas pressure, power level, the
driven (inner) electrode configuration, and the chlorine concentration in the
gas mixture during plasma processing. To demonstrate surface layer removal in
the asymmetric non-planar geometry, we are using a simple cylindrical cavity
with 8 ports symmetrically distributed over the cylinder. The ports are used
for diagnosing the plasma parameters and as holders for the samples to be
etched. The etching rate is highly correlated with the shape of the inner
electrode, radio-frequency (RF) circuit elements, chlorine concentration in the
Cl2/Ar gas mixtures, residence time of reactive species and temperature of the
cavity. Using cylindrical electrodes with variable radius, large-surface
ring-shaped samples and d.c. bias implementation in the external circuit we
have demonstrated substantial average etching rates and outlined the
possibility to optimize plasma properties with respect to maximum surface
processing effect
Measuring Active-to-Sterile Neutrino Oscillations with Neutral Current Coherent Neutrino-Nucleus Scattering
Light sterile neutrinos have been introduced as an explanation for a number
of oscillation signals at eV. Neutrino oscillations at
relatively short baselines provide a probe of these possible new states. This
paper describes an accelerator-based experiment using neutral current coherent
neutrino-nucleus scattering to strictly search for active-to-sterile neutrino
oscillations. This experiment could, thus, definitively establish the existence
of sterile neutrinos and provide constraints on their mixing parameters. A
cyclotron-based proton beam can be directed to multiple targets, producing a
low energy pion and muon decay-at-rest neutrino source with variable distance
to a single detector. Two types of detectors are considered: a germanium-based
detector inspired by the CDMS design and a liquid argon detector inspired by
the proposed CLEAR experiment.Comment: 10 pages, 7 figure
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