288 research outputs found
Radio-detection of extensive air showers at the Pierre Auger Observatory - Results and enhancements
The Pierre Auger Collaboration is exploring the potential of radio-detection
techniques to measure the extensive air showers. The main advantage of these
setups is the possibility to cover a large area with no atmospheric attenuation
and having 100% duty cycle. Radio emission in the MHz range is recorded by the
Auger Engineering Radio Array (AERA), presently consisting of 124 stations
distributed over an area of approximately 6 km. This enhancement is focused
on physics of cosmic rays with an energy greater than 10 eV. In
addition, novel detection techniques based on the GHz emission from extensive
air showers are being tested at the Pierre Auger Observatory. Three different
setups are currently installed and are collecting data: MIDAS (Microwave
Detection of Air Showers) and AMBER (Air-shower Microwave Bremsstrahlung
Experimental Radiometer) are prototypes of an imaging parabolic dish detector,
while EASIER (Extensive Air Shower Identification using Electron Radiometer)
records the radio emission by antenna horns located on more than 60 surface
detector units. The status of these different activities and the new results in
MHz and GHz bands will be reported.Comment: 3 pages -- EPS-HEP'13 European Physical Society Conference on High
Energy Physics (July, 18-24, 2013) at Stockholm, Swede
Monte Carlo simulation of multiple scattered light in the atmosphere
We present a Monte Carlo simulation for the scattering of light in the case
of an isotropic light source. The scattering phase functions are studied
particularly in detail to understand how they can affect the multiple light
scattering in the atmosphere. We show that although aerosols are usually in
lower density than molecules in the atmosphere, they can have a non-negligible
effect on the atmospheric point spread function. This effect is especially
expected for ground-based detectors when large aerosols are present in the
atmosphere.Comment: 5 pages. Proceedings of the Atmospheric Monitoring for High-Energy
Astroparticle Detectors (AtmoHEAD) Conference, Saclay (France), June 10-12,
201
Atmospheric multiple scattering of fluorescence light from extensive air showers and effect of the aerosol size on the reconstruction of energy and depth of maximum
The reconstruction of the energy and the depth of maximum of an
extensive air shower depends on the multiple scattering of fluorescence photons
in the atmosphere. In this work, we explain how atmospheric aerosols, and
especially their size, scatter the fluorescence photons during their
propagation. Using a Monte Carlo simulation for the scattering of light, the
dependence on the aerosol conditions of the multiple scattered light
contribution to the recorded signal is fully parameterised. A clear dependence
on the aerosol size is proposed for the first time. Finally, using this new
parameterisation, the effect of atmospheric aerosols on the energy and on the
reconstructions is presented for a vertical extensive air shower
observed by a ground-based detector at km: for typical aerosol conditions,
multiple scattering leads to a systematic over-estimation of for
the energy and g/cm for the , where the
uncertainties refer to a variation of the aerosol size.Comment: 12 pages, 9 figures, journal paper, accepted in Astroparticle
Physics. arXiv admin note: text overlap with arXiv:1310.170
Atmospheric considerations for CTA site search using global models
The Cherenkov Telescope Array (CTA) will be the next high-energy gamma-ray
observatory. Selection of the sites, one in each hemisphere, is not obvious
since several factors have to be taken into account. Among them, and probably
the most crucial, are the atmospheric conditions. Indeed, CTA will use the
atmosphere as a giant calorimeter, i.e. as part of the detector. The Southern
Hemisphere presents mainly four candidate sites: one in Namibia, one in Chile
and two in Argentina. Using atmospheric tools already validated in other air
shower experiments, the purpose of this work is to complete studies aiming to
choose the site with the best quality for the atmosphere. Three strong
requirements are checked: the cloud cover and the frequency of clear skies, the
wind speed and the backward trajectories of air masses travelling above the
sites and directly linked to the aerosol concentrations. It was found, that the
Namibian site is favoured, and one site in Argentina is clearly not suited.
Atmospheric measurements at these sites will be performed in the coming months
and will help with the selection of a CTA site.Comment: 4 pages, 4 figures, ECRS'12 - 23rd European Cosmic Ray Symposium
(July, 3-7, 2012) at Mosco
Ramsauer approach for light scattering on non-absorbing spherical particles and application to the Henyey-Greenstein phase function
We present a new method to study light scattering on non-absorbing spherical
particles. This method is based on the Ramsauer approach, a model known in
atomic an nuclear physics. Its main advantage is its intuitive understanding of
the underlying physics phenomena. We show that although the approximations are
numerous, the Ramsauer analytical solutions describe fairly well the scattering
phase function and the total cross section. Then this model is applied to the
Henyey-Greenstein parameterisation of scattering phase function to give a
relation between its asymmetry parameter and the mean particle size.Comment: 25 pages, 12 figures, journal paper, accepted in Applied Optics.
arXiv admin note: text overlap with arXiv:0903.297
Atmospheric Monitoring at the Pierre Auger Observatory - Status and Update
International audienceCalorimetric measurements of extensive air showers are performed with the uorescence detector of the PierreAuger Observatory. To correct these measurements for the effects introduced by atmospheric uctuations, the Observa-tory operates several instruments to record atmospheric conditions across and above the detector site. New developmentshave been made in the study of the aerosol optical depth, the aerosol phase function and cloud identication. Also,for cosmic ray events meeting certain criteria, a rapid monitoring program has been developed to improve the accuracyof the reconstruction. We present an updated overview of performed measurements and their application to air shower reconstruction
Atmospheric effects in astroparticle physics experiments and the challenge of ever greater precision in measurements
Astroparticle physics and cosmology allow us to scan the universe through
multiple messengers. It is the combination of these probes that improves our
understanding of the universe, both in its composition and its dynamics. Unlike
other areas in science, research in astroparticle physics has a real
originality in detection techniques, in infrastructure locations, and in the
observed physical phenomenon that is not created directly by humans. It is
these features that make the minimisation of statistical and systematic errors
a perpetual challenge. In all these projects, the environment is turned into a
detector medium or a target. The atmosphere is probably the environment
component the most common in astroparticle physics and requires a continuous
monitoring of its properties to minimise as much as possible the systematic
uncertainties associated. This paper introduces the different atmospheric
effects to take into account in astroparticle physics measurements and provides
a non-exhaustive list of techniques and instruments to monitor the different
elements composing the atmosphere. A discussion on the close link between
astroparticle physics and Earth sciences ends this paper.Comment: 27 pages, 8 figures, review paper, submitted to Astroparticle Physic
Origin of atmospheric aerosols at the Pierre Auger Observatory using backward trajectory of air masses
The Pierre Auger Observatory is the largest operating cosmic ray observatory
ever built. Calorimetric measurements of extensive air showers induced by
cosmic rays are performed with a fluorescence detector. Thus, one of the main
challenges is the monitoring of the atmosphere, both in terms of atmospheric
state variables and optical properties. To better understand the atmospheric
conditions, a study of air mass trajectories above the site is presented. Such
a study has been done using an air-modelling program well known in atmospheric
sciences. Its validity has been checked using meteorological radiosonde
soundings performed at the Pierre Auger Observatory. Finally, aerosol
concentration values measured by the Central Laser Facility are compared to
backward trajectories.Comment: 4 pages, 6 figures -- ECRS'12 European Cosmic Ray Symposium (July,
3-7, 2012) at Moscow, Russi
Atmospheric aerosols at the Pierre Auger Observatory and environmental implications
The Pierre Auger Observatory detects the highest energy cosmic rays.
Calorimetric measurements of extensive air showers induced by cosmic rays are
performed with a fluorescence detector. Thus, one of the main challenges is the
atmospheric monitoring, especially for aerosols in suspension in the
atmosphere. Several methods are described which have been developed to measure
the aerosol optical depth profile and aerosol phase function, using lasers and
other light sources as recorded by the fluorescence detector. The origin of
atmospheric aerosols traveling through the Auger site is also presented,
highlighting the effect of surrounding areas to atmospheric properties. In the
aim to extend the Pierre Auger Observatory to an atmospheric research platform,
a discussion about a collaborative project is presented.Comment: Regular Article, 16 pages, 12 figure
Ramsauer approach to Mie scattering of light on spherical particles
The scattering of an electromagnetic plane wave by a spherical particle was
solved analytically by Gustav Mie in 1908. The Mie solution is expressed as a
series with very many terms thus obscuring the physical interpretations of the
results. The purpose of the paper is to try to illustrate this phenomenon
within the Ramsauer framework used in atomic and nuclear physics. We show that
although the approximations are numerous, the Ramsauer analytical formulae
describe fairly well the differential and the total cross sections. This allows
us to propose an explanation for the origin of the different structures in the
total cross section
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