3,820 research outputs found
Atmospheric Calorimetry above 10 eV: Shooting Lasers at the Pierre Auger Cosmic-Ray Observatory
The Pierre Auger Cosmic-Ray Observatory uses the earth's atmosphere as a
calorimeter to measure extensive air-showers created by particles of
astrophysical origin. Some of these particles carry joules of energy. At these
extreme energies, test beams are not available in the conventional sense. Yet
understanding the energy response of the observatory is important. For example,
the propagation distance of the highest energy cosmic-rays through the cosmic
microwave background radiation (CMBR) is predicted to be strong function of
energy. This paper will discuss recently reported results from the observatory
and the use of calibrated pulsed UV laser "test-beams" that simulate the
optical signatures of ultra-high energy cosmic rays. The status of the much
larger 200,000 km companion detector planned for the northern hemisphere
will also be outlined.Comment: 6 pages, 11 figures XIII International Conference on Calorimetry in
High Energy Physic
Role of the experimental filter in obtaining the Arrhenius plot in multifragmentation reactions
Recently it has been argued that the linear relation between the transverse
energy and the apparent probability to emit a fragment proves that the total
system is in thermal equilibrium. It is shown, for a specific reaction Xe+Sn at
50 A.MeV, that the same behavior is obtained in the context of Quantum
Molecular Dynamical without invoking the idea of equilibrium. The linear
dependance is shown to be a detector effect.Comment: 11 pages, 4 Postscript figures. Submitted Phys. Rev. Let
The Environments of Low and High Luminosity Radio Galaxies at Moderate Redshifts
In the local Universe, high-power radio galaxies live in lower density
environments than low-luminosity radio galaxies. If this trend continues to
higher redshifts, powerful radio galaxies would serve as efficient probes of
moderate redshift groups and poor clusters. Photometric studies of radio
galaxies at 0.3 < z < 0.5 suggest that the radio luminosity-environment
correlation disappears at moderate redshifts, though this could be the result
of foreground/background contamination affecting the photometric measures of
environment. We have obtained multi-object spectroscopy of in the fields of 14
lower luminosity (L_1.4GHz
1.2x10^25 W/Hz) radio galaxies at z ~ 0.3 to spectroscopically investigate the
link between the environment and the radio luminosity of radio galaxies at
moderate redshifts. Our results support the photometric analyses; there does
not appear to be a correlation between the luminosity of a radio galaxy and its
environment at moderate redshifts. Hence, radio galaxies are not efficient
signposts for group environments at moderate redshifts.Comment: 7 pages, 9 figures, Accepted for publication in A
Studying the nuclear mass composition of Ultra-High Energy Cosmic Rays with the Pierre Auger Observatory
The Fluorescence Detector of the Pierre Auger Observatory measures the
atmospheric depth, , where the longitudinal profile of the high energy
air showers reaches its maximum. This is sensitive to the nuclear mass
composition of the cosmic rays. Due to its hybrid design, the Pierre Auger
Observatory also provides independent experimental observables obtained from
the Surface Detector for the study of the nuclear mass composition. We present
-distributions and an update of the average and RMS values in
different energy bins and compare them to the predictions for different nuclear
masses of the primary particles and hadronic interaction models. We also
present the results of the composition-sensitive parameters derived from the
ground level component.Comment: Proceedings of the 12th International Conference on Topics in
Astroparticle and Underground Physics, TAUP 2011, Munich, German
Global Production Increased by Spatial Heterogeneity in a Population Dynamics Model
Spatial and temporal heterogeneity are often described as important factors having a strong impact on biodiversity. The effect of heterogeneity is in most cases analyzed by the response of biotic interactions such as competition of predation. It may also modify intrinsic population properties such as growth rate. Most of the studies are theoretic since it is often difficult to manipulate spatial heterogeneity in practice. Despite the large number of studies dealing with this topics, it is still difficult to understand how the heterogeneity affects populations dynamics. On the basis of a very simple model, this paper aims to explicitly provide a simple mechanism which can explain why spatial heterogeneity may be a favorable factor for production.We consider a two patch model and a logistic growth is assumed on each patch. A general condition on the migration rates and the local subpopulation growth rates is provided under which the total carrying capacity is higher than the sum of the local carrying capacities, which is not intuitive. As we illustrate, this result is robust under stochastic perturbations
A Three-Point Cosmic Ray Anisotropy Method
The two-point angular correlation function is a traditional method used to
search for deviations from expectations of isotropy. In this paper we develop
and explore a statistically descriptive three-point method with the intended
application being the search for deviations from isotropy in the highest energy
cosmic rays. We compare the sensitivity of a two-point method and a
"shape-strength" method for a variety of Monte-Carlo simulated anisotropic
signals. Studies are done with anisotropic source signals diluted by an
isotropic background. Type I and II errors for rejecting the hypothesis of
isotropic cosmic ray arrival directions are evaluated for four different event
sample sizes: 27, 40, 60 and 80 events, consistent with near term data
expectations from the Pierre Auger Observatory. In all cases the ability to
reject the isotropic hypothesis improves with event size and with the fraction
of anisotropic signal. While ~40 event data sets should be sufficient for
reliable identification of anisotropy in cases of rather extreme (highly
anisotropic) data, much larger data sets are suggested for reliable
identification of more subtle anisotropies. The shape-strength method
consistently performs better than the two point method and can be easily
adapted to an arbitrary experimental exposure on the celestial sphere.Comment: Fixed PDF erro
Educational studies of cosmic rays with telescope of Geiger-Muller counters
A group of high school students (XII Liceum) in the framework of the Roland
Maze Project has built a compact telescope of three Geiger-Muller counters. The
connection between the telescope and PC computer was also created and programed
by students involved in the Project. This has allowed students to use their
equipment to perform serious scientific measurements concerning the single
cosmic ray muon flux at ground level and below. These measurements were then
analyzed with the programs based on the 'nowadays' knowledge on statistics. An
overview of the apparatus, methods and results were presented at several
students conferences and recently won the first prize in a national competition
of high school students scientific work. The telescope itself, in spite of its
'scientific' purposes, is built in such a way that it is hung on a wall in a
school physics lab and counts muons continuously. This can help to raise the
interest for studying physics among others. At present a few (3) groups of
young participants of the Roland Maze Project have already built their own
telescopes for their schools and some others are working on it. This work is a
perfect example of what can be done by young people when respective
opportunities are created by more experienced researchers and a little help and
advice is given.Comment: 5 figures, 10 page
On the influence of statistics on the determination of the mean value of the depth of shower maximum for ultra high energy cosmic ray showers
The chemical composition of ultra high energy cosmic rays is still uncertain.
The latest results obtained by the Pierre Auger Observatory and the HiRes
Collaboration, concerning the measurement of the mean value and the
fluctuations of the atmospheric depth at which the showers reach the maximum
development, Xmax, are inconsistent. From comparison with air shower
simulations it can be seen that, while the Auger data may be interpreted as a
gradual transition to heavy nuclei for energies larger than ~ 2-3x10^18 eV, the
HiRes data are consistent with a composition dominated by protons. In Ref. [1]
it is suggested that a possible explanation of the observed deviation of the
mean value of Xmax from the proton expectation, observed by Auger, could
originate in a statistical bias arising from the approximated exponential shape
of the Xmax distribution, combined with the decrease of the number of events as
a function of primary energy. In this paper we consider a better description of
the Xmax distribution and show that the possible bias in the Auger data is at
least one order of magnitude smaller than the one obtained when assuming an
exponential distribution. Therefore, we conclude that the deviation of the
Auger data from the proton expectation is unlikely explained by such
statistical effect.Comment: To be published in Journal of Physics G: Nuclear and Particle Physic
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