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Exploring the Universe with Ultra High Energy Cosmic Rays
Full text linkUltra High Energy Cosmic Rays (UHECR) are messengers of the most powerful astrophysical
sources in the universe and they offer the unique chance of investigating particle interactions
over an energy range well beyond the one covered by present ground-based particle accelerators.
Despite several progresses have been made in the last decade, the understanding of the nature of
UHECR and of their origin remains an open science case. A review of selected results from the
largest UHECR experiments, namely The Pierre Auger Observatory and the Telescope Array, is
presented with the emphasis given to the measurements of energy spectrum, arrival directions,
chemical composition, and the search for photons and neutrinos as primary particles. Connection
to hadronic physics and open issues will also be discussed along with the perspectives for near
future measurements
RESULTS FROM THE PIERRE AUGER OBSERVATORY
Full text linkThe Pierre Auger Observatory has been designed to investigate the origin and the nature of Ultra High Energy Cosmic Rays using a hybrid detection technique. It is located on a plateau in the Province of Mendoza, Argentina, and consists of a surface array of about 3000 km2 overlooked by 24 air fluorescence telescopes grouped in 4 sites which together provide a powerful instrument for air shower reconstruction. The Southern site of the Auger Observatory has been completed in June 2008 and is taking data smoothly since 2004. A review of selected results is presented with the emphasis given to the measurement of energy spectrum, chemical composition and search for photons and neutrinos as primary particles
Results from the Pierre Auger Observatory
No full textThe Pierre Auger Observatory has been designed to investigate the origin and the nature of Ultra High Energy Cosmic Rays using a hybrid detection technique. It is located on a plateau in the Province of Mendoza, Argentina,
and consists of a surface array of about 3000 km^2 overlooked by 24
air fluorescence telescopes grouped in 4 sites, which together provide a
powerful instrument for air shower reconstruction.
The combination of information from the surface array, measuring the
lateral distributions of secondary particles at the ground, and the
fluorescence telescopes, observing the longitudinal profile, enhances
the reconstruction capability with respect to the individual detector components.
The Observatory was completed in 2008 and it is taking data smoothly since 2004. Moreover, detector enhancements are being constructed to extend the sensitivity of the Observatory towards the lower energies.
A review of selected results is presented with the emphasis given to the measurement of energy spectrum, arrival directions, chemical composition and search for photons and neutrinos as primary particles
Measurement of the UHECR energy spectrum from hybrid data of the Pierre Auger Observatory
No full textMore than two years of fluorescence detector data collected in coincidence with at least one station of the surface detector array (“hybrid data”) are used to measure the flux and energy spectrum of cosmic rays above about 10**18 eV. The hybrid measurement extends towards lower energies the spectrum measured with the surface detector data only, and provides a cross-check with an independent data set. The determination of the fluorescence detector aperture and of its live-time, which is the major aspect of this measurement, is illustrated in detail. Our current estimate of the corresponding systematic uncertainties are given
Multiparametric topological analysis (MTA) for the study of the primary CR composition: Performances with Auger simulated data
No full textWe describe the application of a multiparametric analysis to estimate the UHE Cosmic Rays composition. The proposed method, MTA (Multiparametric Topological Analysis), is based on the study of the correlations among different shower observables. This technique is designed to fully exploit the complementarity of Auger fluorescence and ground array data. In the present work, we report the results of the application to Conex showers, fully simulated through the Auger detector, using only parameters describing the longitudinal development of air showers as recorded by fluorescence detector for hybrid data
Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory
Full text linkData from the Pierre Auger Observatory are analyzed to search for anisotropies near the direction of the Galactic Centre at EeV energies. The exposure of the surface array in this part of the sky is already significantly larger than that of the fore-runner experiments. Our results do not support previous findings of localized excesses in the AGASA and SUGAR data. We set an upper bound on a point-like flux of cosmic rays arriving from the Galactic Centre which excludes several scenarios predicting sources of EeV neutrons from Sagittarius A. Also the events detected simultaneously by the surface and fluorescence detectors (the ‘hybrid’ data set), which have better pointing accuracy but are less numerous than those of the surface array alone, do not show any significant localized excess from this direction.http://www.elsevier.com/wps/find/journaldescription.cws_home/523319/description#descriptio
Induced Effects on Extensive Air Showers Observed with the Surface Detector of the Pierre Auger Observatory
No full textAbstract: The rate of events measured with the surface detector of the Pierre Auger Observatory is found to be modulated by the weather conditions. This effect is due to the increasing amount of matter traversed by a shower as the ground pressure increases and to the inverse proportionality of the Molière radius to the air density near ground. Air-shower simulations with different realistic profiles of the atmosphere support this interpretation of the observed effects
The Pierre Auger Observatory: Review of Latest Results and Perspectives
No full textThe Pierre Auger Observatory is the world’s largest operating detection system for the observation of ultra high energy cosmic rays (UHECRs), with energies above 10 17 eV. The detector allows detailed measurements of the energy spectrum, mass composition and arrival directions of primary cosmic rays in the energy range above 10 17 eV. The data collected at the Auger Observatory over the last decade show the suppression of the cosmic ray flux at energies above 4 × 10 19 eV. However, it is still unclear if this suppression is caused by the energy limitation of their sources or by the Greisen–Zatsepin–Kuzmin (GZK) cut-off. In such a case, UHECRs would interact with the microwave background (CMB), so that particles traveling long intergalactic distances could not have energies greater than 5 × 10 19 eV. The other puzzle is the origin of UHECRs. Some clues can be drawn from studying the distribution of their arrival directions. The recently observed dipole anisotropy has an orientation that indicates an extragalactic origin of UHECRs. The Auger surface detector array is also sensitive to showers due to ultra high energy neutrinos of all flavors and photons, and recent neutrino and photon limits provided by the Auger Observatory can constrain models of the cosmogenic neutrino production and exotic scenarios of the UHECRs origin, such as the decays of super heavy, non-standard-model particles. In this paper, the recent results on measurements of the energy spectrum, mass composition and arrival directions of cosmic rays, as well as future prospects are presented
Search for Coincidences in Time and Arrival Direction of Auger Data with Astro- physical Transients
No full textAbstract: The data collected by the Pierre Auger Observatory are analyzed to search for coincidences between the arrival directions of high-energy cosmic rays and the positions in the sky of astrophysical transients. Special attention is directed towards gamma ray observations recorded by NASA's Swift mission, which have an angular resolution similar to that of the Auger surface detectors. In particular, we check our data for evidence of a signal associated with the giant flare that came from the soft gamma repeater 1806-20 on December 27, 2004
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