6,526 research outputs found
Seen and unseen tidal caustics in the Andromeda galaxy
Indirect detection of high-energy particles from dark matter interactions is
a promising avenue for learning more about dark matter, but is hampered by the
frequent coincidence of high-energy astrophysical sources of such particles
with putative high-density regions of dark matter. We calculate the boost
factor and gamma-ray flux from dark matter associated with two shell-like
caustics of luminous tidal debris recently discovered around the Andromeda
galaxy, under the assumption that dark matter is its own supersymmetric
antiparticle. These shell features could be a good candidate for indirect
detection of dark matter via gamma rays because they are located far from the
primary confusion sources at the galaxy's center, and because the shapes of the
shells indicate that most of the mass has piled up near apocenter. Using a
numerical estimator specifically calibrated to estimate densities in N-body
representations with sharp features and a previously determined N-body model of
the shells, we find that the largest boost factors do occur in the shells but
are only a few percent. We also find that the gamma-ray flux is an order of
magnitude too low to be detected with Fermi for likely dark matter parameters,
and about 2 orders of magnitude less than the signal that would have come from
the dwarf galaxy that produces the shells in the N-body model. We further show
that the radial density profiles and relative radial spacing of the shells, in
either dark or luminous matter, is relatively insensitive to the details of the
potential of the host galaxy but depends in a predictable way on the velocity
dispersion of the progenitor galaxy.Comment: ApJ accepte
Performance of the Micromegas detector in the CAST experiment
The gaseous Micromegas detector designed for the CERN Axion search experiment
CAST, operated smoothly during Phase-I, which included the 2003 and 2004
running periods. It exhibited linear response in the energy range of interest
(1-10keV), good spatial sensitivity and energy resolution (15-19% FWHM at
5.9keV)as well as remarkable stability. The detector's upgrade for the 2004
run, supported by the development of advanced offline analysis tools, improved
the background rejection capability, leading to an average rate 5x10^-5
counts/sec/cm^2/keV with 94% cut efficiency. Also, the origin of the detected
background was studied with a Monte Carlo simulation, using the GEANT4 package.Comment: Prepared for PSD7: The Seventh International Conference on Position
Sensitive Detectors, Liverpool, United Kingdom, 12-16 Sep. 200
Performances of Anode-resistive Micromegas for HL-LHC
Micromegas technology is a promising candidate to replace Atlas forward muon
chambers -tracking and trigger- for future HL-LHC upgrade of the experiment.
The increase on background and pile-up event probability requires detector
performances which are currently under studies in intensive RD activities.
We studied performances of four different resistive Micromegas detectors with
different read-out strip pitches. These chambers were tested using \sim120 GeV
momentum pions, at H6 CERN-SPS beam line in autumn 2010. For a strip pitch 500
micrometers we measure a resolution of \sim90 micrometers and a efficiency of
~98%. The track angle effect on the efficiency was also studied. Our results
show that resistive techniques induce no degradation on the efficiency or
resolution, with respect to the standard Micromegas. In some configuration the
resistive coating is able to reduce the discharge currents at least by a factor
of 100.Micromegas technology is a promising candidate to replace Atlas forward
muon chambers -tracking and trigger- for future HL-LHC upgrade of the
experiment. The increase on background and pile-up event probability requires
detector performances which are currently under studies in intensive RD
activities. We studied performances of four different resistive Micromegas
detectors with different read-out strip pitches. These chambers were tested
using \sim120 GeV momentum pions, at H6 CERN-SPS beam line in autumn 2010. For
a strip pitch 500 micrometers we measure a resolution of \sim90 micrometers and
a efficiency of \sim98%. The track angle effect on the efficiency was also
studied. Our results show that resistive techniques induce no degradation on
the efficiency or resolution, with respect to the standard Micromegas. In some
configuration the resistive coating is able to reduce the discharge currents at
least by a factor of 100.Comment: "Presented at the 2011 Hadron Collider Physics symposium (HCP-2011),
Paris, France, November 14-18 2011, 3 pages, 6 figures.
The Micromegas detector of the CAST experiment
A low background Micromegas detector has been operating in the CAST
experiment at CERN for the search of solar axions during the first phase of the
experiment (2002-2004). The detector, made out of low radioactivity materials,
operated efficiently and achieved a very low level of background rejection (5 x
10^-5 counts/keV/cm^2/s) without shielding.Comment: 13 pages, 12 figures and images, submitted to New Journal o
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Turbocharger Lubrication - Lubricant Behavior and Factors That Cause Turbocharger Failure
This paper is a review of the turbocharger lubrication system and at the same time an attempt to point out and analyze the factors responsible for turbocharger wear, damage and failures. In particular, the conditions under which the lubricant works are presented, from its entrance up to its exit from the turbocharger bearing housing. Additionally, the consequences of failure to comply with the instructions for appropriate turbocharger operation are provided by the various manufacturers. Water cooled turbochargers (for which engine coolant is used), contribute significantly to the reduction of lubricant temperature, in the critical zones of its operation. This is achieved by reducing, the danger of the oil “coking” effect (charred oil residues) or its decomposition, because of high temperature occurring in these zones. Turbochargers shaft support development using semi-floating bush bearings has a significant impact on turbocharger manufacturing cost, as well as on their operational features. Further benefit may be had, when ball bearings are used (usually angular contact bearings are used) for turbocharger shaft support as they provide: a) a reduction of the kinetic friction coefficient, b) reduction of turbocharger lag during turbocharger shaft acceleration from low to high speeds, and c) reduced sealing problems. Regarding the failures that occur in turbochargers, their majority - up to 50% - is caused by problematic lubrication [1]. The rest of the failures are divided between causes related to human factors (such as misuse and inadequate maintenance of a turbocharged vehicle) and external factors such as foreign objects entering either the compressor or turbine housings
CAST microbulk micromegas in the Canfranc Underground Laboratory
During the last taking data campaigns of the CAST experiment, the micromegas
detectors have achieved background levels of keVcms between 2 and 9 keV. This performance has
been possible thanks to the introduction of the microbulk technology, the
implementation of a shielding and the development of discrimination algorithms.
It has motivated new studies towards a deeper understanding of CAST detectors
background. One of the working lines includes the construction of a replica of
the set-up used in CAST by micromegas detectors and its installation in the
Canfranc Underground Laboratory. Thanks to the comparison between the
performance of the detectors underground and at surface, shielding upgrades,
etc, different contributions to the detectors background have been evaluated.
In particular, an upper limit keVcms
for the intrinsic background of the detector has been obtained. This work means
a first evaluation of the potential of the newest micromegas technology in an
underground laboratory, the most suitable environment for Rare Event Searches.Comment: 6 pages, 8 figures. To appear in the proceedings of the 2nd
International Conference on Technology and Instrumentation for Particle
Physics (TIPP 2011
Progress on a spherical TPC for low energy neutrino detection
The new concept of the spherical TPC aims at relatively large target masses
with low threshold and background, keeping an extremely simple and robust
operation. Such a device would open the way to detect the neutrino-nucleus
interaction, which, although a standard process, remains undetected due to the
low energy of the neutrino-induced nuclear recoils. The progress in the
development of the fist 1 m prototype at Saclay is presented. Other physics
goals of such a device could include supernova detection, low energy neutrino
oscillations and study of non-standard properties of the neutrino, among
others.Comment: 3 pages, talk given at the 9th Workshop on Topics in Astroparticle
and Underground Physics, Zaragoza, September 10-1
A low background Micromegas detector for the CAST experiment
A low background Micromegas detector has been operating on the CAST
experiment at CERN for the search of solar axions during the first phase of the
experiment (2002-2004). The detector operated efficiently and achieved a very
low level of background rejection ( counts
keVcms) thanks to its good spatial and energy resolution
as well as the low radioactivity materials used in the construction of the
detector. For the second phase of the experiment (2005-2007), the detector will
be upgraded by adding a shielding and including focusing optics. These
improvements should allow for a background rejection better than two orders of
magnitude.Comment: 6 pages, 3 figures To appear on the proceedings of the 9th ICATPP
Conference on AStroparticle, Particle, Space Physics, Detectors and Medical
Physics Application
X-ray detection with Micromegas with background levels below 10 keVcms
Micromegas detectors are an optimum technological choice for the detection of
low energy x-rays. The low background techniques applied to these detectors
yielded remarkable background reductions over the years, being the CAST
experiment beneficiary of these developments. In this document we report on the
latest upgrades towards further background reductions and better understanding
of the detectors' response. The upgrades encompass the readout electronics, a
new detector design and the implementation of a more efficient cosmic muon veto
system. Background levels below 10keVcms have been
obtained at sea level for the first time, demonstrating the feasibility of the
expectations posed by IAXO, the next generation axion helioscope. Some results
obtained with a set of measurements conducted in the x-ray beam of the CAST
Detector Laboratory will be also presented and discussed
Towards a new generation axion helioscope
We study the feasibility of a new generation axion helioscope, the most
ambitious and promising detector of solar axions to date. We show that large
improvements in magnetic field volume, x-ray focusing optics and detector
backgrounds are possible beyond those achieved in the CERN Axion Solar
Telescope (CAST). For hadronic models, a sensitivity to the axion-photon
coupling of \gagamma\gtrsim {\rm few} \times 10^{-12} GeV is
conceivable, 1--1.5 orders of magnitude beyond the CAST sensitivity. If axions
also couple to electrons, the Sun produces a larger flux for the same value of
the Peccei-Quinn scale, allowing one to probe a broader class of models. Except
for the axion dark matter searches, this experiment will be the most sensitive
axion search ever, reaching or surpassing the stringent bounds from SN1987A and
possibly testing the axion interpretation of anomalous white-dwarf cooling that
predicts of a few meV. Beyond axions, this new instrument will probe
entirely unexplored ranges of parameters for a large variety of axion-like
particles (ALPs) and other novel excitations at the low-energy frontier of
elementary particle physics.Comment: 37 pages, 11 figures, accepted for publication in JCA
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