8,179 research outputs found
Solar neutrino detection in a large volume double-phase liquid argon experiment
Precision measurements of solar neutrinos emitted by specific nuclear
reaction chains in the Sun are of great interest for developing an improved
understanding of star formation and evolution. Given the expected neutrino
fluxes and known detection reactions, such measurements require detectors
capable of collecting neutrino-electron scattering data in exposures on the
order of 1 ktonne yr, with good energy resolution and extremely low background.
Two-phase liquid argon time projection chambers (LAr TPCs) are under
development for direct Dark Matter WIMP searches, which possess very large
sensitive mass, high scintillation light yield, good energy resolution, and
good spatial resolution in all three cartesian directions. While enabling Dark
Matter searches with sensitivity extending to the "neutrino floor" (given by
the rate of nuclear recoil events from solar neutrino coherent scattering),
such detectors could also enable precision measurements of solar neutrino
fluxes using the neutrino-electron elastic scattering events. Modeling results
are presented for the cosmogenic and radiogenic backgrounds affecting solar
neutrino detection in a 300 tonne (100 tonne fiducial) LAr TPC operating at
LNGS depth (3,800 meters of water equivalent). The results show that such a
detector could measure the CNO neutrino rate with ~15% precision, and
significantly improve the precision of the 7Be and pep neutrino rates compared
to the currently available results from the Borexino organic liquid
scintillator detector.Comment: 21 pages, 7 figures, 6 table
Bayesian analysis of multiple direct detection experiments
Bayesian methods offer a coherent and efficient framework for implementing
uncertainties into induction problems. In this article, we review how this
approach applies to the analysis of dark matter direct detection experiments.
In particular we discuss the exclusion limit of XENON100 and the debated hints
of detection under the hypothesis of a WIMP signal. Within parameter inference,
marginalizing consistently over uncertainties to extract robust posterior
probability distributions, we find that the claimed tension between XENON100
and the other experiments can be partially alleviated in isospin violating
scenario, while elastic scattering model appears to be compatible with the
frequentist statistical approach. We then move to model comparison, for which
Bayesian methods are particularly well suited. Firstly, we investigate the
annual modulation seen in CoGeNT data, finding that there is weak evidence for
a modulation. Modulation models due to other physics compare unfavorably with
the WIMP models, paying the price for their excessive complexity. Secondly, we
confront several coherent scattering models to determine the current best
physical scenario compatible with the experimental hints. We find that
exothermic and inelastic dark matter are moderatly disfavored against the
elastic scenario, while the isospin violating model has a similar evidence.
Lastly the Bayes' factor gives inconclusive evidence for an incompatibility
between the data sets of XENON100 and the hints of detection. The same question
assessed with goodness of fit would indicate a 2 sigma discrepancy. This
suggests that more data are therefore needed to settle this question.Comment: 29 pages, 8 figures; invited review for the special issue of the
journal Physics of the Dark Universe; matches the published versio
Dark Matter 2014
This article gives an overview on the status of experimental searches for
dark matter at the end of 2014. The main focus is on direct searches for weakly
interacting massive particles (WIMPs) using underground-based low-background
detectors, especially on the new results published in 2014. WIMPs are excellent
dark matter candidates, predicted by many theories beyond the standard model of
particle physics, and are expected to interact with the target nuclei either
via spin-independent (scalar) or spin-dependent (axial-vector) couplings.
Non-WIMP dark matter candidates, especially axions and axion-like particles are
also briefly discussed.Comment: 8 pages, 4 figures. Contribution to DHF201
A new approach for the ortho-positronium lifetime determination in a vacuum cavity
Currently, the experimental uncertainty for the determination of the
ortho-positronium (o-Ps) decay rate is at 150 ppm precision; this is two orders
of magnitude lower than the theoretical one, at 1 ppm level. Here we propose a
new proof of concept experiment aiming for an accuracy of 100 ppm to be able to
test the second-order correction in the calculations, which is ppm. The improvement relies on
a new technique to confine the o-Ps in a vacuum cavity. Moreover, a new method
was developed to subtract the time dependent pick-off annihilation rate of the
fast backscattered positronium from the o-Ps decay rate prior to fitting the
distribution. Therefore, this measurement will be free from the systematic
errors present in the previous experiments. The same experimental setup
developed for our recent search for invisible decay of ortho-positronium is
being used. The precision will be limited by the statistical uncertainty, thus,
if the expectations are fulfilled, this experiment could pave the way to reach
the ultimate accuracy of a few ppm level to confirm or confront directly the
higher order QED corrections. This will provide a sensitive test for new
physics, e.g. a discrepancy between theoretical prediction and measurements
could hint the existence of an hidden sector which is a possible dark matter
candidate.Comment: 12 pages, 8 Figures, prepared for the proceedings of the PSAS2018
conference, Vienna (Austria
Chaos and Turbulent Nucleosynthesis Prior to a Supernova Explosion
Three-dimensional (3D), time dependent numerical simulations, of flow of
matter in stars, now have sufficient resolution to be fully turbulent. The late
stages of the evolution of massive stars, leading up to core collapse to a
neutron star (or black hole), and often to supernova explosion and
nucleosynthesis, are strongly convective because of vigorous neutrino cooling
and nuclear heating. Unlike models based on current stellar evolutionary
practice, these simulations show a chaotic dynamics characteristic of highly
turbulent flow. Theoretical analysis of this flow, both in the
Reynolds-averaged Navier-Stokes (RANS) framework and by simple dynamic models,
show an encouraging consistency with the numerical results. It may now be
possible to develop physically realistic and robust procedures for convection
and mixing which (unlike 3D numerical simulation) may be applied throughout the
long life times of stars. In addition, a new picture of the presupernova stages
is emerging which is more dynamic and interesting (i.e., predictive of new and
newly observed phenomena) than our previous one.Comment: 11 pages, 2 figures, Submitted to AIP Advances: Stardust, added
figures and modest rewritin
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