82 research outputs found
Exploring the hidden interior of the Earth with directional neutrino measurements
Roughly 40% of the Earth's total heat flow is powered by radioactive decays
in the crust and mantle. Geo-neutrinos produced by these decays provide
important clues about the origin, formation and thermal evolution of our
planet, as well as the composition of its interior. Previous measurements of
geo-neutrinos have all relied on the detection of inverse beta decay reactions,
which are insensitive to the contribution from potassium and do not provide
model-independent information about the spatial distribution of geo-neutrino
sources within the Earth. Here we present a method for measuring previously
unresolved components of Earth's radiogenic heating using neutrino-electron
elastic scattering and low-background, direction-sensitive tracking detectors.
We calculate the exposures needed to probe various contributions to the total
geo-neutrino flux, specifically those associated to potassium, the mantle and
the core. The measurements proposed here chart a course for pioneering
exploration of the veiled inner workings of the Earth.Comment: 18 pages, 11 figures, 8 table
The Maximum Patch Method for Directional Dark Matter Detection
Present and planned dark matter detection experiments search for WIMP-induced
nuclear recoils in poorly known background conditions. In this environment, the
maximum gap statistical method provides a way of setting more sensitive cross
section upper limits by incorporating known signal information. We give a
recipe for the numerical calculation of upper limits for planned directional
dark matter detection experiments, that will measure both recoil energy and
angle, based on the gaps between events in two-dimensional phase space.Comment: 13 pages, 11 figures; minor textual corrections, filled in an
important missing detail relating to the method, publication versio
Directional Dark Matter Detection Beyond the Neutrino Bound
Coherent scattering of solar, atmospheric and diffuse supernovae neutrinos
creates an irreducible background for direct dark matter experiments with
sensitivities to WIMP-nucleon spin-independent scattering cross-sections of
10^(-46)-10^(-48) cm^2, depending on the WIMP mass. Even if one could eliminate
all other backgrounds, this "neutrino floor" will limit future experiments with
projected sensitivities to cross-sections as small as 10^(-48) cm^2.
Direction-sensitive detectors have the potential to study dark matter beyond
the neutrino bound by fitting event distributions in multiple dimensions:
recoil kinetic energy, recoil track angle with respect to the sun, and event
time. This work quantitatively explores the impact of direction-sensitivity on
the neutrino bound in dark matter direct detection.Comment: matches the published version, figure 4 updated plus extended
discussion about neutrino flux uncertainties and detector resolutions, 13
pages, 11 figure
Track Reconstruction Progress from the DMTPC Directional Dark Matter Experiment
he Dark Matter Time Projection Chamber (DMTPC) collaboration is developing prototype detectors to measure both the energies and directions of nuclear recoils. The intended application is to exploit the expected directional anisotropy of dark matter velocities at Earth to unambiguously observe dark matter induced recoils. The detector consist of low-pressure CF[subscript 4] TPC's with CCD cameras, PMT's, and charge amplifiers for readout. This talk gives an overview of the experiment and describes recent advances in hardware and analysis
Measurement of the directional sensitivity of Dark Matter Time Projection Chamber detectors
The Dark Matter Time Projection Chamber (DMTPC) is a direction-sensitive
detector designed to measure the direction of recoiling F and C
nuclei in low-pressure CF gas using optical and charge readout systems. In
this paper, we employ measurements from two DMTPC detectors, with operating
pressures of 30-60 torr, to develop and validate a model of the directional
response and performance of such detectors as a function of recoil energy.
Using our model as a benchmark, we formulate the necessary specifications for a
scalable directional detector with sensitivity comparable to that of
current-generation counting (non-directional) experiments, which measure only
recoil energy. Assuming the performance of existing DMTPC detectors, as well as
current limits on the spin-dependent WIMP-nucleus cross section, we find that a
10-20 kg scale direction-sensitive detector is capable of correlating the
measured direction of nuclear recoils with the predicted direction of incident
dark matter particles and providing decisive (3) confirmation that a
candidate signal from a non-directional experiment was indeed induced by
elastic scattering of dark matter particles off of target nuclei.Comment: 13 pages, 10 figures. Accepted for publication in Phys. Rev. D. Added
color figures, switched to more compact layout, and fixed some reference
Index of refraction, Rayleigh scattering length, and Sellmeier coefficients in solid and liquid argon and xenon
Large liquid argon detectors have become widely used in low rate experiments,
including dark matter and neutrino research. However, the optical properties of
liquid argon are not well understood at the large scales relevant for current
and near-future detectors.The index of refraction of liquid argon at the scin-
tillation wavelength has not been measured, and current Rayleigh scattering
length calculations disagree with measurements. Furthermore, the Rayleigh
scattering length and index of refraction of solid argon and solid xenon at
their scintillation wavelengths have not been previously measured or
calculated. We introduce a new calculation using existing data in liquid and
solid argon and xenon to extrapolate the optical properties at the
scintillation wavelengths using the Sellmeier dispersion relationship.Comment: 11 pages, 4 figure
Characterisation of SiPM Photon Emission in the Dark
In this paper, we report on the photon emission of Silicon Photomultipliers (SiPMs) from avalanche pulses generated in dark conditions, with the main objective of better understanding the associated systematics for next-generation, large area, SiPM-based physics experiments. A new apparatus for spectral and imaging analysis was developed at TRIUMF and used to measure the light emitted by the two SiPMs considered as photo-sensor candidates for the nEXO neutrinoless double-beta decay experiment: one Fondazione Bruno Kessler (FBK) VUV-HD Low Field (LF) Low After Pulse (Low AP) (VUV-HD3) SiPM and one Hamamatsu Photonics K.K. (HPK) VUV4 Multi-Pixel Photon Counter (MPPC). Spectral measurements of their light emissions were taken with varying over-voltage in the wavelength range of 450ā1020 nm. For the FBK VUV-HD3, at an over-voltage of 12.1Ā±1.0 V, we measured a secondary photon yield (number of photons (Ī³) emitted per charge carrier (eā)) of (4.04Ā±0.02)Ć10ā6Ī³/eā. The emission spectrum of the FBK VUV-HD3 contains an interference pattern consistent with thin-film interference. Additionally, emission microscopy images (EMMIs) of the FBK VUV-HD3 show a small number of highly localized regions with increased light intensity (hotspots) randomly distributed over the SiPM surface area. For the HPK VUV4 MPPC, at an over-voltage of 10.7Ā±1.0 V, we measured a secondary photon yield of (8.71Ā±0.04)Ć10ā6Ī³/eā. In contrast to the FBK VUV-HD3, the emission spectra of the HPK VUV4 did not show an interference patternālikely due to a thinner surface coating. The EMMIs of the HPK VUV4 also revealed a larger number of hotspots compared to the FBK VUV-HD3, especially in one of the corners of the device. The photon yield reported in this paper may be limited if compared with the one reported in previous studies due to the measurement wavelength range, which is only up to 1020 nm
A random mutation capture assay to detect genomic point mutations in mouse tissue
Herein, a detailed protocol for a random mutation capture (RMC) assay to measure nuclear point mutation frequency in mouse tissue is described. This protocol is a simplified version of the original method developed for human tissue that is easier to perform, yet retains a high sensitivity of detection. In contrast to assays relying on phenotypic selection of reporter genes in transgenic mice, the RMC assay allows direct detection of mutations in endogenous genes in any mouse strain. Measuring mutation frequency within an intron of a transcribed gene, we show this assay to be highly reproducible. We analyzed mutation frequencies from the liver tissue of animals with a mutation within the intrinsic exonuclease domains of the two major DNA polymerases, Ī“ and Īµ. These mice exhibited significantly higher mutation frequencies than did wild-type animals. A comparison with a previous analysis of these genotypes in Big Blue mice revealed the RMC assay to be more sensitive than the Big Blue assay for this application. As RMC does not require analysis of a particular gene, simultaneous analysis of mutation frequency at multiple genetic loci is feasible. This assay provides a versatile alternative to transgenic mouse models for the study of mutagenesis in vivo
Can tonne-scale direct detection experiments discover nuclear dark matter?
Models of nuclear dark matter propose that the dark sector contains large
composite states consisting of dark nucleons in analogy to Standard Model
nuclei. We examine the direct detection phenomenology of a particular class of
nuclear dark matter model at the current generation of tonne-scale liquid noble
experiments, in particular DEAP-3600 and XENON1T. In our chosen nuclear dark
matter scenario distinctive features arise in the recoil energy spectra due to
the non-point-like nature of the composite dark matter state. We calculate the
number of events required to distinguish these spectra from those of a standard
point-like WIMP state with a decaying exponential recoil spectrum. In the most
favourable regions of nuclear dark matter parameter space, we find that a few
tens of events are needed to distinguish nuclear dark matter from WIMPs at the
level in a single experiment. Given the total exposure time of
DEAP-3600 and XENON1T we find that at best a distinction is
possible by these experiments individually, while sensitivity is
reached for a range of parameters by the combination of the two experiments. We
show that future upgrades of these experiments have potential to distinguish a
large range of nuclear dark matter models from that of a WIMP at greater than
.Comment: 23 pages, 7 multipanel figure
- ā¦