846 research outputs found
A new application of emulsions to measure the gravitational force on antihydrogen
We propose to build and operate a detector based on the emulsion film
technology for the measurement of the gravitational acceleration on antimatter,
to be performed by the AEgIS experiment (AD6) at CERN. The goal of AEgIS is to
test the weak equivalence principle with a precision of 1% on the gravitational
acceleration g by measuring the vertical position of the anni- hilation vertex
of antihydrogen atoms after their free fall in a horizontal vacuum pipe. With
the emulsion technology developed at the University of Bern we propose to
improve the performance of AEgIS by exploiting the superior position resolution
of emulsion films over other particle de- tectors. The idea is to use a new
type of emulsion films, especially developed for applications in vacuum, to
yield a spatial resolution of the order of one micron in the measurement of the
sag of the antihydrogen atoms in the gravitational field. This is an order of
magnitude better than what was planned in the original AEgIS proposal.Comment: 17 pages, 14 figure
Determination of the high-pressure crystal structure of BaWO4 and PbWO4
We report the results of both angle-dispersive x-ray diffraction and x-ray
absorption near-edge structure studies in BaWO4 and PbWO4 at pressures of up to
56 GPa and 24 GPa, respectively. BaWO4 is found to undergo a pressure-driven
phase transition at 7.1 GPa from the tetragonal scheelite structure (which is
stable under normal conditions) to the monoclinic fergusonite structure whereas
the same transition takes place in PbWO4 at 9 GPa. We observe a second
transition to another monoclinic structure which we identify as that of the
isostructural phases BaWO4-II and PbWO4-III (space group P21/n). We have also
performed ab initio total energy calculations which support the stability of
this structure at high pressures in both compounds. The theoretical
calculations further find that upon increase of pressure the scheelite phases
become locally unstable and transform displacively into the fergusonite
structure. The fergusonite structure is however metastable and can only occur
if the transition to the P21/n phases were kinetically inhibited. Our
experiments in BaWO4 indicate that it becomes amorphous beyond 47 GPa.Comment: 46 pages, 11 figures, 3 table
The Far-Infrared Properties of Spatially Resolved AKARI Observations
We present the spatially resolved observations of IRAS sources from the
Japanese infrared astronomy satellite AKARI All-Sky Survey during the
performance verification (PV) phase of the mission. We extracted reliable point
sources matched with IRAS point source catalogue. By comparing IRAS and AKARI
fluxes, we found that the flux measurements of some IRAS sources could have
been over or underestimated and affected by the local background rather than
the global background. We also found possible candidates for new AKARI sources
and confirmed that AKARI observations resolved IRAS sources into multiple
sources. All-Sky Survey observations are expected to verify the accuracies of
IRAS flux measurements and to find new extragalactic point sources.Comment: 11 pages, 7 figures, accepted publication in PASJ AKARI special issu
Infrared composition of the Large Magellanic Cloud
The evolution of galaxies and the history of star formation in the Universe
are among the most important topics in today's astrophysics. Especially, the
role of small, irregular galaxies in the star-formation history of the Universe
is not yet clear. Using the data from the AKARI IRC survey of the Large
Magellanic Cloud at 3.2, 7, 11, 15, and 24 {\mu}m wavelengths, i.e., at the
mid- and near-infrared, we have constructed a multiwavelength catalog
containing data from a cross-correlation with a number of other databases at
different wavelengths. We present the separation of different classes of stars
in the LMC in color-color, and color-magnitude, diagrams, and analyze their
contribution to the total LMC flux, related to point sources at different
infrared wavelengths
The AKARI/IRC Mid-Infrared All-Sky Survey
Context : AKARI is the first Japanese astronomical satellite dedicated to
infrar ed astronomy. One of the main purposes of AKARI is the all-sky survey
performed with six infrared bands between 9 and 200um during the period from
2006 May 6 to
2007 August 28. In this paper, we present the mid-infrared part (9um and 18um
b ands) of the survey carried out with one of the on-board instruments, the
Infrar ed Camera (IRC). Aims : We present unprecedented observational results
of the 9 and 18um AKARI al l-sky survey and detail the operation and data
processing leading to the point s ource detection and measurements. Methods :
The raw data are processed to produce small images for every scan and point
sources candidates, above the 5-sigma noise level per single scan, are der
ived. The celestial coordinates and fluxes of the events are determined
statisti cally and the reliability of their detections is secured through
multiple detect ions of the same source within milli-seconds, hours, and months
from each other. Results : The sky coverage is more than 90% for both bands. A
total of 877,091 s ources (851,189 for 9um, 195,893 for 18um) are confirmed and
included in the cur rent release of the point source catalogue. The detection
limit for point source s is 50mJy and 90mJy for the 9um and 18um bands,
respectively. The position accu racy is estimated to be better than 2".
Uncertainties in the in-flight absolute flux calibration are estimated to be 3%
for the 9um band and 4% for the 18um ban d. The coordinates and fluxes of
detected sources in this survey are also compar ed with those of the IRAS
survey and found to be statistically consistent.Comment: Accepted for publication in AandA AKARI special issu
Spectroscopy of 32Ne and the Island of Inversion
We report on the first spectroscopic study of the N=22 nucleus 32Ne at the
newly completed RIKEN Radioactive Ion Beam Factory. A single gamma-ray line
with an energy of 722(9) keV was observed in both inelastic scattering of a 226
MeV/u 32Ne beam on a Carbon target and proton removal from 33Na at 245 MeV/u.
This transition is assigned to the de-excitation of the first J^pi = 2+ state
in 32Ne to the 0+ ground state. Interpreted through comparison with
state-of-the-art shell model calculations, the low excitation energy
demonstrates that the Island of Inversion extends to at least N=22 for the Ne
isotopes.Comment: Accepted for publication in Phys. Rev. Lett. 11 pages, 3 figure
Charged-Particle Multiplicities in Charged-Current Neutrino-- and Anti-Neutrino--Nucleus Interactions
The CHORUS experiment, designed to search for
oscillations, consists of a nuclear emulsion target and electronic detectors.
In this paper, results on the production of charged particles in a small sample
of charged-current neutrino-- and anti-neutrino--nucleus interactions at high
energy are presented. For each event, the emission angle and the ionization
features of the charged particles produced in the interaction are recorded,
while the standard kinematic variables are reconstructed using the electronic
detectors. The average multiplicities for charged tracks, the pseudo-rapidity
distributions, the dispersion in the multiplicity of charged particles and the
KNO scaling are studied in different kinematical regions. A study of
quasi-elastic topologies performed for the first time in nuclear emulsions is
also reported. The results are presented in a form suitable for use in the
validation of Monte Carlo generators of neutrino--nucleus interactions.Comment: 17 pages, 5 figure
Determination of the muon charge sign with the dipolar spectrometers of the OPERA experiment
The OPERA long-baseline neutrino-oscillation experiment has observed the
direct appearance of in the CNGS beam. Two large muon
magnetic spectrometers are used to identify muons produced in the
leptonic decay and in interactions by measuring their charge and
momentum. Besides the kinematic analysis of the decays, background
resulting from the decay of charmed particles produced in
interactions is reduced by efficiently identifying the muon track. A new method
for the charge sign determination has been applied, via a weighted angular
matching of the straight track-segments reconstructed in the different parts of
the dipole magnets. Results obtained for Monte Carlo and real data are
presented. Comparison with a method where no matching is used shows a
significant reduction of up to 40\% of the fraction of wrongly determined
charges.Comment: 10 pages. Improvements in the tex
Evidence for appearance in the CNGS neutrino beam with the OPERA experiment
The OPERA experiment is designed to search for oscillations in appearance mode i.e. through the direct observation
of the lepton in charged current interactions. The
experiment has taken data for five years, since 2008, with the CERN Neutrino to
Gran Sasso beam. Previously, two candidates with a decaying
into hadrons were observed in a sub-sample of data of the 2008-2011 runs. Here
we report the observation of a third candidate in the
decay channel coming from the analysis of a sub-sample of the
2012 run. Taking into account the estimated background, the absence of
oscillations is excluded at the 3.4
level.Comment: 9 pages, 5 figures, 1 table
Observation of nu_tau appearance in the CNGS beam with the OPERA experiment
The OPERA experiment is searching for nu_mu -> nu_tau oscillations in
appearance mode i.e. via the direct detection of tau leptons in nu_tau charged
current interactions. The evidence of nu_mu -> nu_tau appearance has been
previously reported with three nu_tau candidate events using a sub-sample of
data from the 2008-2012 runs. We report here a fourth nu_tau candidate event,
with the tau decaying into a hadron, found after adding the 2012 run events
without any muon in the final state to the data sample. Given the number of
analysed events and the low background, nu_mu -> nu_tau oscillations are
established with a significance of 4.2sigma.Comment: Submitted to Progress of Theoretical and Experimental Physics (PTEP
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