1,396 research outputs found
Note on the Origin of the Highest Energy Cosmic Rays
In this note we argue that the galactic model chosen by E.-J. Ahn, G.
Medina-Tanco, P.L. Bierman and T. Stanev in their paper discussing the origin
of the highest energy cosmic rays, is alone responsible for the focussing of
positive particles towards the North galactic pole. We discuss the validity of
this model, in particular in terms of field reversals and radial extensions. We
conclude that with such a model one cannot retreive any directional information
from the observed direction of the cosmic rays. In particular one cannot
identify point sources at least up to energies of about 200 EeV. Therefore the
apparent clustering of the back-traced highest energy cosmic rays observed to
date cannot be interpreted as an evidence for a point source nor for the
identification of M87, which happens to be close to the North pole, as being
such a source.Comment: 3 pages, 2 figure
Evaluation of the Primary Energy of UHE Photon-induced Atmospheric Showers from Ground Array Measurements
A photon induced shower at eV exhibits very specific
features and is different from a hadronic one. At such energies, the LPM effect
delays in average the first interactions of the photon in the atmosphere and
hence slows down the whole shower development. They also have a smaller muonic
content than hadronic ones. The response of a surface detector such as that of
the Auger Observatory to these specific showers is thus different and has to be
accounted for in order to enable potential photon candidates reconstruction
correctly. The energy reconstruction in particular has to be adapted to the
late development of photon showers. We propose in this article a method for the
reconstruction of the energy of photon showers with a surface detector. The key
feature of this method is to rely explicitly on the development stage of the
shower. This approach leads to very satisfactory results (). At
even higher energies ( eV and above) the probability for the photon
to convert into a pair of ee in the geomagnetic field becomes non
negligible and requires a different function to evaluate the energy with the
proposed method. We propose several approaches to deal with this issue in the
scope of the establishment of an upper bound on the photon fraction in UHECR.Comment: 10 page
Kalman Filter Track Fits and Track Breakpoint Analysis
We give an overview of track fitting using the Kalman filter method in the
NOMAD detector at CERN, and emphasize how the wealth of by-product information
can be used to analyze track breakpoints (discontinuities in track parameters
caused by scattering, decay, etc.). After reviewing how this information has
been previously exploited by others, we describe extensions which add power to
breakpoint detection and characterization. We show how complete fits to the
entire track, with breakpoint parameters added, can be easily obtained from the
information from unbroken fits. Tests inspired by the Fisher F-test can then be
used to judge breakpoints. Signed quantities (such as change in momentum at the
breakpoint) can supplement unsigned quantities such as the various chisquares.
We illustrate the method with electrons from real data, and with Monte Carlo
simulations of pion decays.Comment: 27 pages including 10 figures. To appear in NI
Layered water Cherenkov detector for the study of ultra high energy cosmic rays
We present a new design for the water Cherenkov detectors that are in use in
various cosmic ray observatories. This novel design can provide a significant
improvement in the independent measurement of the muonic and electromagnetic
component of extensive air showers. From such multi-component data an event by
event classification of the primary cosmic ray mass becomes possible. According
to popular hadronic interaction models, such as EPOS-LHC or QGSJetII-04, the
discriminating power between iron and hydrogen primaries reaches Fisher values
of 2 or above for energies in excess of eV with a detector
array layout similar to that of the Pierre Auger Observatory.Comment: 17 pages, 15 figures, submitted to Nuclear Instruments and Methods
A coverage independent method to analyze large scale anisotropies
The arrival time distribution of cosmic ray events is well suited to extract
information regarding sky anisotropies. For an experiment with nearly constant
exposure, the frequency resolution one can achieve is given by the inverse of
the time during which the data was recorded. For larger than one
calendar year the resolution becomes sufficient to resolve the sidereal and
diurnal frequencies. Using a Fourier expansion on a modified time parameter, we
show in this note that one can accurately extract sidereal modulations without
knowledge of the experimental coverage. This procedure also gives the full
frequency pattern of the event sample under studies which contains important
information about possible systematics entering in the sidereal analysis. We
also show how this method allows to correct for those systematics. Finally, we
show that a two dimensional analysis, in the form of the spherical harmonic
() decomposition, can be performed under the same conditions for all
.Comment: 8 pages, 6 figure
A phenomenological model of the muon density profile on the ground of very inclined air showers
Ultra-high energy cosmic rays generate extensive air showers in Earth's
atmosphere. A standard approach to reconstruct the energy of an ultra-high
energy cosmic rays is to sample the lateral profile of the particle density on
the ground of the air shower with an array of surface detectors. For cosmic
rays with large inclinations, this reconstruction is based on a model of the
lateral profile of the muon density observed on the ground, which is fitted to
the observed muon densities in individual surface detectors. The best models
for this task are derived from detailed Monte-Carlo simulations of the air
shower development. We present a phenomenological parametrization scheme which
allows to derive a model of the average lateral profile of the muon density
directly from a fit to a set of individual Monte-Carlo simulated air showers.
The model reproduces the detailed simulations with a high precision. As an
example, we generate a muon density model which is valid in the energy range
1e18 eV < E < 1e20 eV and the zenith angle range 60 deg < theta < 90 deg. We
will further demonstrate a way to speed up the simulation of such muon profiles
by three orders of magnitude, if only the muons in the shower are of interest.Comment: Corresponding author: Hans Dembinsk
Estimates of multipolar coefficients to search for cosmic ray anisotropies with non-uniform or partial sky coverage
We study the possibility to extract the multipolar moments of an underlying
distribution from a set of cosmic rays observed with non-uniform or even
partial sky coverage. We show that if the degree is assumed to be upper bounded
by , each multipolar moment can be recovered whatever the coverage, but with
a variance increasing exponentially with the bound if the coverage is zero
somewhere. Despite this limitation, we show the possibility to test predictions
of a model without any assumption on by building an estimate of the
covariance matrix seen through the exposure function.Comment: 20 pages, 8 figure
A new composition-sensitive parameter for Ultra-High Energy Cosmic Rays
A new family of parameters intended for composition studies in cosmic ray
surface array detectors is proposed. The application of this technique to
different array layout designs has been analyzed. The parameters make exclusive
use of surface data combining the information from the total signal at each
triggered detector and the array geometry. They are sensitive to the combined
effects of the different muon and electromagnetic components on the lateral
distribution function of proton and iron initiated showers at any given primary
energy. Analytical and numerical studies have been performed in order to assess
the reliability, stability and optimization of these parameters. Experimental
uncertainties, the underestimation of the muon component in the shower
simulation codes, intrinsic fluctuations and reconstruction errors are
considered and discussed in a quantitative way. The potential discrimination
power of these parameters, under realistic experimental conditions, is compared
on a simplified, albeit quantitative way, with that expected from other surface
and fluorescence estimators.Comment: 27 pages, 17 figures. Submitted to a refereed journa
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