255 research outputs found
A stacking method to study the gamma-ray emission of source samples based on the co-adding of Fermi LAT count maps
We present a stacking method that makes use of co-added maps of gamma-ray
counts produced from data taken with the Fermi Large Area Telescope. Sources
with low integrated gamma-ray fluxes that are not detected individually may
become detectable when their corresponding count maps are added. The combined
data set is analyzed with a maximum likelihood method taking into account the
contribution from point-like and diffuse background sources. For both simulated
and real data, detection significance and integrated gamma-ray flux are
investigated for different numbers of stacked sources using the public Fermi
Science Tools for analysis and data preparation. The co-adding is done such
that potential source signals add constructively, in contrast to the signals
from background sources, which allows the stacked data to be described with
simply structured models. We show, for different scenarios, that the stacking
method can be used to increase the cumulative significance of a sample of
sources and to characterize the corresponding gamma-ray emission. The method
can, for instance, help to search for gamma-ray emission from galaxy clusters.Comment: accepted for publication in Astronomy & Astrophysics, 10 pages, 12
figure
Neutrino physics with multi-ton scale liquid xenon detectors
We study the sensitivity of large-scale xenon detectors to low-energy solar
neutrinos, to coherent neutrino-nucleus scattering and to neutrinoless double
beta decay. As a concrete example, we consider the xenon part of the proposed
DARWIN (Dark Matter WIMP Search with Noble Liquids) experiment. We perform
detailed Monte Carlo simulations of the expected backgrounds, considering
realistic energy resolutions and thresholds in the detector. In a low-energy
window of 2-30 keV, where the sensitivity to solar pp and Be-neutrinos is
highest, an integrated pp-neutrino rate of 5900 events can be reached in a
fiducial mass of 14 tons of natural xenon, after 5 years of data. The
pp-neutrino flux could thus be measured with a statistical uncertainty around
1%, reaching the precision of solar model predictions. These low-energy solar
neutrinos will be the limiting background to the dark matter search channel for
WIMP-nucleon cross sections below 210 cm and WIMP
masses around 50 GeVc, for an assumed 99.5% rejection of
electronic recoils due to elastic neutrino-electron scatters. Nuclear recoils
from coherent scattering of solar neutrinos will limit the sensitivity to WIMP
masses below 6 GeVc to cross sections above
410cm. DARWIN could reach a competitive half-life
sensitivity of 5.610 y to the neutrinoless double beta decay of
Xe after 5 years of data, using 6 tons of natural xenon in the central
detector region.Comment: 17 pages, 4 figure
First Direct Detection Limits on sub-GeV Dark Matter from XENON10
The first direct detection limits on dark matter in the MeV to GeV mass range
are presented, using XENON10 data. Such light dark matter can scatter with
electrons, causing ionization of atoms in a detector target material and
leading to single- or few-electron events. We use 15 kg-days of data acquired
in 2006 to set limits on the dark-matter-electron scattering cross section. The
strongest bound is obtained at 100 MeV where sigma_e < 3 x 10^{-38} cm^2 at 90%
CL, while dark matter masses between 20 MeV and 1 GeV are bounded by sigma_e <
10^{-37} cm^2 at 90% CL. This analysis provides a first proof-of-principle that
direct detection experiments can be sensitive to dark matter candidates with
masses well below the GeV scale.Comment: Submitted to PR
A 83Krm Source for Use in Low-background Liquid Xenon Time Projection Chambers
We report the testing of a charcoal-based Kr-83m source for use in
calibrating a low background two-phase liquid xenon detector. Kr-83m atoms
produced through the decay of Rb-83 are introduced into a xenon detector by
flowing xenon gas past the Rb-83 source. 9.4 keV and 32.1 keV transitions from
decaying 83Krm nuclei are detected through liquid xenon scintillation and
ionization. The characteristics of the Kr-83m source are analyzed and shown to
be appropriate for a low background liquid xenon detector. Introduction of
Kr-83m allows for quick, periodic calibration of low background noble liquid
detectors at low energy.Comment: Updated to version submitted to JINS
Spatially uniform calibration of a liquid xenon detector at low energies using 83m-Kr
A difficult task with many particle detectors focusing on interactions below
~100 keV is to perform a calibration in the appropriate energy range that
adequately probes all regions of the detector. Because detector response can
vary greatly in various locations within the device, a spatially uniform
calibration is important. We present a new method for calibration of liquid
xenon (LXe) detectors, using the short-lived 83m-Kr. This source has
transitions at 9.4 and 32.1 keV, and as a noble gas like Xe, it disperses
uniformly in all regions of the detector. Even for low source activities, the
existence of the two transitions provides a method of identifying the decays
that is free of background. We find that at decreasing energies, the LXe light
yield increases, while the amount of electric field quenching is diminished.
Additionally, we show that if any long-lived radioactive backgrounds are
introduced by this method, they will present less than 67E-6 events/kg/day in
the next generation of LXe dark matter direct detection searchesComment: 9 pages, 9 figures. Accepted to Review of Scientific Instrument
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