589 research outputs found
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
Spatial confinement of muonium atoms
We report the achievement of spatial confinement of muonium atoms (the bound
state of a positive muon and an electron). Muonium emitted into vacuum from
mesoporous silica reflects between two SiO confining surfaces separated by
1 mm. From the data, one can extract that the reflection probability on the
confining surfaces kept at 100 K is about 90% and the reflection process is
well described by a cosine law. This technique enables new experiments with
this exotic atomic system and is a very important step towards a measurement of
the 1S-2S transition frequency using continuous wave laser spectroscopy.Comment: 5 pages, 6 figure
Plus forts ensemble - Swiss School of Public Health
De vénérables écoles de santé publique ont fêté leur 100 e anniversaire au cours des 20 dernières années. En Suisse, la pandémie a pris au dépourvu une institution adolescente - un modèle innovant qui fête son 16 e anniversaire cette année. L'âge adulte a-t-il été atteint
Sensitivity potential to a light flavor-changing scalar boson with DUNE and NA64
In this work, we report on the sensitivity potential of complementary
muon-on-target experiments to new physics using a scalar boson benchmark model
associated with charged lepton flavor violation. The NA64 experiment at
CERN uses a 160-GeV energy muon beam with an active target to search for excess
events with missing energy and momentum as a probe of new physics. At the same
time, the proton beam at Fermilab, which is used to produce the neutrino beam
for the Deep Underground Neutrino Experiment (DUNE) will also produce a
high-intensity muon beam dumped in an absorber. Combined with the liquid Argon
Near Detector, the system could be used to search for similar scalar boson
particles with a lower energy but higher intensity beam. We find that both
NA64 and DUNE could cover new, unexplored parts of the parameter space of
the same benchmark model, providing a complementary way to search for new
physics
NASA advanced design program: Analysis, design, and construction of a solar powered aircraft
Increase in energy demands coupled with rapid depletion of natural energy resources have deemed solar energy as the most logical alternative source of power. The major objective of this project was to build a solar powered remotely controlled aircraft to demonstrate the feasibility of solar energy as an effective, alternate source of power. The final design was optimized for minimum weight and maximum strength of the structure. These design constraints necessitated a carbon fiber composite structure. Surya is a lightweight, durable aircraft capable of achieving level flight powered entirely by solar cells
Intradural lumbar disc herniation detected by 3D CISS MRI.
A 73-year-old man who presented with right lumbosciatic pain underwent a neurosurgical operation for a voluminous L2-L3 disc herniation, seen on conventional MRI images. No disc herniation was identified in the epidural space during the surgery. Just after the operation, the patient started to present pain in the left L3 territory and was not able to walk any more. A second MRI including three-dimensional (3D) high-resolution constructive interference in steady state (CISS) sequence showed that the voluminous L2-L3 disc split the posterior longitudinal ligament and the anterior dura mater, extended intradurally and compressed the cauda equina to the right. The patient underwent a second surgery, which permitted to cure the symptoms. 3D high-resolution CISS should be considered to accurately depict intradural disc herniation in order to optimally guide the surgical approach
In vivo estimation of the shoulder joint center of rotation using magneto-inertial sensors: MRI-based accuracy and repeatability assessment
Background: The human gleno-humeral joint is normally represented as a spherical hinge and its center of rotation is used to construct humerus anatomical axes and as reduction point for the computation of the internal joint moments. The position of the gleno-humeral joint center (GHJC) can be estimated by recording ad hoc shoulder joint movement following a functional approach. In the last years, extensive research has been conducted to improve GHJC estimate as obtained from positioning systems such as stereo-photogrammetry or electromagnetic tracking. Conversely, despite the growing interest for wearable technologies in the field of human movement analysis, no studies investigated the problem of GHJC estimation using miniaturized magneto-inertial measurement units (MIMUs). The aim of this study was to evaluate both accuracy and precision of the GHJC estimation as obtained using a MIMU-based methodology and a functional approach. Methods: Five different functional methods were implemented and comparatively assessed under different experimental conditions (two types of shoulder motions: cross and star type motion; two joint velocities: ωmax = 90°/s, 180°/s; two ranges of motion: Θ = 45°, 90°). Validation was conducted on five healthy subjects and true GHJC locations were obtained using magnetic resonance imaging. Results: The best performing methods (NAP and SAC) showed an accuracy in the estimate of the GHJC between 20.6 and 21.9 mm and repeatability values between 9.4 and 10.4 mm. Methods performance did not show significant differences for the type of arm motion analyzed or a reduction of the arm angular velocity (180°/s and 90°/s). In addition, a reduction of the joint range of motion (90° and 45°) did not seem to influence significantly the GHJC position estimate except in a few subject-method combinations. Conclusions: MIMU-based functional methods can be used to estimate the GHJC position in vivo with errors of the same order of magnitude than those obtained using traditionally stereo-photogrammetric techniques. The methodology proposed seemed to be robust under different experimental conditions. The present paper was awarded as "SIAMOC Best Methodological Paper 2016"
Intense beam of metastable Muonium
Precision spectroscopy of the Muonium Lamb shift and fine structure requires
a robust source of 2S Muonium. To date, the beam-foil technique is the only
demonstrated method for creating such a beam in vacuum. Previous experiments
using this technique were statistics limited, and new measurements would
benefit tremendously from the efficient 2S production at a low energy muon
( keV) facility. Such a source of abundant low energy has
only become available in recent years, e.g. at the Low-Energy Muon beamline at
the Paul Scherrer Institute. Using this source, we report on the successful
creation of an intense, directed beam of metastable Muonium. We find that even
though the theoretical Muonium fraction is maximal in the low energy range of
keV, scattering by the foil and transport characteristics of the beamline
favor slightly higher energies of keV. We estimate that
an event detection rate of a few events per second for a future Lamb shift
measurement is feasible, enabling an increase in precision by two orders of
magnitude over previous determinations
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