278 research outputs found
Highlights from the Pierre Auger Observatory
We present a review of recent results from the Pierre Auger Observatory, including the measurement of the cosmic ray energy spectrum above 1018 eV, searches for anisotropy of the arrival directions, and studies of cosmic ray mass
composition. The flux exhibits hardening at 4 × 1018 eV followed by suppression consistent with the GZK effect above 3 × 1019 eV. Correlation of cosmic ray air shower arrival directions with the distribution of the nearby extragalactic matter is observed at energies above 5.5×1019 eV. The observed longitudinal development of air showers suggests that the interaction cross-section increases with energy more rapidly than current models predict for proton primaries, perhaps due to a transition to heavier composition. No clear candidates for neutrinos and photons in the ultra-high energy cosmic ray flux have yet been found
Nitrogen fluorescence in air for observing extensive air showers
Extensive air showers initiate the fluorescence emissions from nitrogen
molecules in air. The UV-light is emitted isotropically and can be used for
observing the longitudinal development of extensive air showers in the
atmosphere over tenth of kilometers. This measurement technique is
well-established since it is exploited for many decades by several cosmic ray
experiments. However, a fundamental aspect of the air shower analyses is the
description of the fluorescence emission in dependence on varying atmospheric
conditions. Different fluorescence yields affect directly the energy scaling of
air shower reconstruction. In order to explore the various details of the
nitrogen fluorescence emission in air, a few experimental groups have been
performing dedicated measurements over the last decade. Most of the
measurements are now finished. These experimental groups have been discussing
their techniques and results in a series of Air Fluorescence Workshops
commenced in 2002. At the 8 Air Fluorescence Workshop 2011, it was
suggested to develop a common way of describing the nitrogen fluorescence for
application to air shower observations. Here, first analyses for a common
treatment of the major dependences of the emission procedure are presented.
Aspects like the contributions at different wavelengths, the dependence on
pressure as it is decreasing with increasing altitude in the atmosphere, the
temperature dependence, in particular that of the collisional cross sections
between molecules involved, and the collisional de-excitation by water vapor
are discussed.Comment: 12 pages, 17 figures, 2 tables, International Symposium on Future
Directions in UHECR Physics, 13-16 February 2012, CERN, Geneva (Switzerland);
the updated version corrects for a typo in Eq. (1
The MIDAS experiment: A prototype for the microwave emission of Ultra-High Energy Cosmic Rays
Recent measurements suggest that extensive air showers initiated by
ultra-high energy cosmic rays (UHECR) emit signals in the microwave band of the
electromagnetic spectrum caused by the collisions of the free-electrons with
the atmospheric neutral molecules in the plasma produced by the passage of the
shower. Such emission is isotropic and could allow the detection of air showers
with 100% duty cycle and a calorimetric-like energy measurement, a significant
improvement over current detection techniques. We have built MIDAS (MIcrowave
Detection of Air Showers), a prototype of microwave detector, which consists of
a 4.5 m diameter antenna with a cluster of 53 feed-horns in the 4 GHz range.
The details of the prototype and first results will be presented.Comment: To appear in the proceedings of 12th Topical Seminar on Innovative
Particle and Radiation Detectors (IPRD10), Siena, Italy, 7 - 10 June 201
A novel method for the absolute fluorescence yield measurement by AIRFLY
One of the goals of the AIRFLY (AIR FLuorescence Yield) experiment is to
measure the absolute fluorescence yield induced by electrons in air to better
than 10% precision. We introduce a new technique for measurement of the
absolute fluorescence yield of the 337 nm line that has the advantage of
reducing the systematic uncertainty due to the detector calibration. The
principle is to compare the measured fluorescence yield to a well known process
- the Cerenkov emission. Preliminary measurements taken in the BFT (Beam Test
Facility) in Frascati, Italy with 350 MeV electrons are presented. Beam tests
in the Argonne Wakefield Accelerator at the Argonne National Laboratory, USA
with 14 MeV electrons have also shown that this technique can be applied at
lower energies.Comment: presented at the 5th Fluorescence Workshop, El Escorial - Madrid,
Spain, 16 - 20 September 200
Temperature and Humidity Dependence of Air Fluorescence Yield measured by AIRFLY
The fluorescence detection of ultra high energy cosmic rays requires a
detailed knowledge of the fluorescence light emission from nitrogen molecules
over a wide range of atmospheric parameters, corresponding to altitudes typical
of the cosmic ray shower development in the atmosphere. We have studied the
temperature and humidity dependence of the fluorescence light spectrum excited
by MeV electrons in air. Results for the 313.6 nm, 337.1 nm, 353.7 nm and 391.4
nm bands are reported in this paper. We found that the temperature and humidity
dependence of the quenching process changes the fluorescence yield by a
sizeable amount (up to 20%) and its effect must be included for a precise
estimation of the energy of ultra high energy cosmic rays.Comment: presented at the 5th Fluorescence Workshop, El Escorial - Madrid,
Spain, 16 - 20 September 2007, to appear in Nuclear Instruments and Methods
Precise Measurement of the Absolute Yield of Fluorescence Photons in Atmospheric Gases
We have performed a measurement of the absolute yield of fluorescence photons
at the Fermilab Test Beam. A systematic uncertainty at 5% level was achieved by
the use of Cherenkov radiation as a reference calibration light source. A
cross-check was performed by an independent calibration using a laser light
source. A significant improvement on the energy scale uncertainty of Ultra-High
Energy Cosmic Rays is expected.Comment: To appear in the Proceedings of CRIS 2010, Cosmic Ray International
Seminar -- 100 years of Cosmic Ray Physics: from pioneering experiments to
physics in space, Catania, Italy, 13-17 September 201
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
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