64 research outputs found
Energy resolution of alpha particles in a microbulk Micromegas detector at high pressure Argon and Xenon mixtures
The latest Micromesh Gas Amplification Structures (Micromegas) are achieving
outstanding energy resolution for low energy photons, with values as low as 11%
FWHM for the 5.9 keV line of Fe in argon/isobutane mixtures at
atmospheric pressure. At higher energies (MeV scale), these measurements are
more complicated due to the difficulty in confining the events in the chamber,
although there is no fundamental reason why resolutions of 1% FWHM or below
could not be reached. There is much motivation to demonstrate experimentally
this fact in Xe mixtures due to the possible application of Micromegas readouts
to the Double Beta Decay search of Xe, or in other experiments needing
calorimetry and topology in the same detector. In this paper, we report on
systematic measurements of energy resolution with state-of-the-art Micromegas
using a 5.5 MeV alpha source in high pressure Ar/isobutane mixtures. Values as
low as 1.8% FWHM have been obtained, with possible evidence that better
resolutions are achievable. Similar measurements in Xe, of which a preliminary
result is also shown here, are under progress.Comment: 16 pages, 19 figures, version after referees comments. Accepted for
publication in Nuclear Instruments and Methods
Micromegas in a Bulk
In this paper we present a novel way to manufacture the bulk Micromegas
detector. A simple process based on the PCB (Printed Circuit Board) technology
is employed to produce the entire sensitive detector. Such fabrication process
could be extended to very large area detectors made by the industry. The low
cost fabrication together with the robustness of the electrode materials will
make it extremely attractive for several applications ranging from particle
physics and astrophysics to medicineComment: 6 pages, 4 figure
A novel large-volume Spherical Detector with Proportional Amplification read-out
A new type of radiation detector based on a spherical geometry is presented.
The detector consists of a large spherical gas volume with a central electrode
forming a radial electric field. Charges deposited in the conversion volume
drift to the central sensor where they are amplified and collected. We
introduce a small spherical sensor located at the center acting as a
proportional amplification structure. It allows high gas gains to be reached
and operates in a wide range of gas pressures. Signal development and the
absolute amplitude of the response are consistent with predictions. Sub-keV
energy threshold with good energy resolution is achieved. This new concept has
been proven to operate in a simple and robust way and allows reading large
volumes with a single read-out channel. The detector performance presently
achieved is already close to fulfill the demands of many challenging projects
from low energy neutrino physics to dark matter detection with applications in
neutron, alpha and gamma spectroscopy.Comment: 13 pages, 13 figure
Excited Leptonic States in Polarized e^-\gamma and e^+ e^- Collisions
We analyze the capability of the next generation of linear electron--positron
colliders to unravel the spin and couplings of excited leptons predicted by
composite models. Assuming that these machines will be able to operate both in
the and modes, we study the effects of the excited
electrons of spin and in the reactions and . We show how the
use of polarized beams is able not only to increase the reach of these
machines, but also to determine the spin and couplings of the excited states.Comment: 22 pages, RevTeX, 8 figure
Shifts of Gamma Phase across Primary Visual Cortical Sites Reflect Dynamic Stimulus-Modulated Information Transfer
Distributed neural processing likely entails the capability of networks to reconfigure dynamically the directionality and strength of their functional connections. Yet, the neural mechanisms that may allow such dynamic routing of the information flow are not yet fully understood. We investigated the role of gamma band (50–80 Hz) oscillations in transient modulations of communication among neural populations by using measures of direction-specific causal information transfer. We found that the local phase of gamma-band rhythmic activity exerted a stimulus-modulated and spatially-asymmetric directed effect on the firing rate of spatially separated populations within the primary visual cortex. The relationships between gamma phases at different sites (phase shifts) could be described as a stimulus-modulated gamma-band wave propagating along the spatial directions with the largest information transfer. We observed transient stimulus-related changes in the spatial configuration of phases (compatible with changes in direction of gamma wave propagation) accompanied by a relative increase of the amount of information flowing along the instantaneous direction of the gamma wave. These effects were specific to the gamma-band and suggest that the time-varying relationships between gamma phases at different locations mark, and possibly causally mediate, the dynamic reconfiguration of functional connections
PHENOMENOLOGIE DES INTERACTIONS FORTES
Nous présentons certains développements récents de la phénoménologie des interactions fortes. En particulier nous essayons de répondre à quelques questions sur le Pomeron : pente, structure géométrique, conservation de l'hélicité, violation du théorème de Pomeranchuk. Nous discutons ensuite les propriétés caractéristiques des coupures de Regge et des modèles d'absorption, notamment des modèles à coupures faibles ou fortes. Enfin, nous comparons leurs prescriptions et leurs prédictions à l'ensemble des résultats expérimentaux concernant les réactions à deux corps ou quasi deux corps.We discuss some recent developments of strong interaction phenomenology. More precisely we try to answer to some questions related to the Pomeron : slope, geometric structure, helicity conservation, Pomeranchuk theorem violation. Then we discuss the characteristic properties of Regge cuts and absorption models with weak or strong cuts. At last we compare their prescriptions and predictions with the whole set of experimental data for two body or quasi two body reactions
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