Iskanje po repozitoriju

A+ | A- | | SLO | ENG

Opis: The azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of information on shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolution of the shower and geometrical effects related to the angles of incidence of the particles into the detectors. The magnitude of the effect depends upon the zenith angle and state of development of the shower and thus provides a novel observable sensitive to the mass composition of cosmic rays above 3 × 10[sup]18 eV. By comparing measurements with predictions from shower simulations, we find for both of our adopted models of hadronic physics (QGSJetII- 04 and Epos-LHC) an indication that the mean cosmic-ray mass increases with energy, as has been inferred from other studies. However the absolute values derived for the mass are dependent on the shower model and on the range of distance from the shower core selected. Thus the method has uncovered further deficiencies in our understanding of shower modelling that must be resolved before the mass composition can be inferred from (sec θ)max.
Ključne besede: Pierre Auger Observatory, Surface Detector, risetime of detector signal, azimuthal asymmetry, extensive air showers
Objavljeno v RUNG: 03.03.2016; Ogledov: 5549; Prenosov: 199
Celotno besedilo (243,04 KB)

Opis: Ultra-relativistic magnetic monopoles, possibly a relic of phase transitions in the early universe, would deposit an amount of energy comparable to UHECRs in their passage through the atmosphere, producing highly distinctive air shower profiles. We have performed a search for ultra-relativistic magnetic monopoles in the sample of air showers with profiles measured by the fluorescence detector of the Pierre Auger Observatory. No candidate was found to satisfy our selection criteria and we establish upper limits on the flux of ultra-relativistic magnetic monopoles - the first from an UHECR detector - improving over previous results by up to an order of magnitude.
Ključne besede: ultra-relativistic magnetic monopoles, extensive air showers, Pierre Auger Observatory
Objavljeno v RUNG: 03.03.2016; Ogledov: 5510; Prenosov: 198
Celotno besedilo (188,24 KB)

Opis: We report for the first time on the measurement of the correlation between the depth of shower maximum and the signal in water-Cherenkov stations for events reconstructed by both the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlated measurement is a unique feature of a hybrid air-shower observatory and allows us to determine the purity of the cosmic-ray composition. The observed correlation in the energy range around the “ankle” lg(E/eV) = 18.5−19.0 differs significantly from the expectations for pure beams, indicating that the primary composition in this range is mixed, unless the hadronic interactions at these energies behave very differently than in conventional, LHC-tuned event generators.
Ključne besede: ultra-high energy cosmic rays, elemental composition, depth of shower maximum, secondary cosmic rays, Pierre Auger Observatory
Objavljeno v RUNG: 02.03.2016; Ogledov: 6171; Prenosov: 244
Celotno besedilo (388,00 KB)

Opis: The large-scale distribution of arrival directions of high-energy cosmic rays carries major clues to understanding their origin. The Pierre Auger Collaboration have implemented different analyses to search for dipolar and quadrupolar anisotropies in different energy ranges spanning four orders of magnitude. A common phase ≈270◦ of the first harmonic modulation in right-ascension was found in adjacent energy intervals below 1 EeV, and another common phase ≈100◦ above 4 EeV. A constancy of phase measurements in ordered energy intervals originating from a genuine anisotropy is expected to appear with a smaller number of events than those needed to achieve significant amplitudes. This led us to design a prescribed test aimed at establishing whether this consistency in phases is real at 99% CL. The test required a total independent exposure of 21,000 km2 sr yr. We report on the status of this prescription. We also report the results of the search for a dipole anisotropy for cosmic rays with energies above 4 EeV using events with zenith angles between 60◦ and 80◦. Compared to previous analyses of events with zenith angles smaller than 60◦, this extension increases the size of the data set by 30%, and enlarges the fraction of exposed sky from 71% to 85%. The largest departure from isotropy is found in the energy range above 8 EeV, with an amplitude for the first harmonic in right ascension r1 = (4.4 ± 1.0) × 10[sup]−2, that has a chance probability P(≥ r1) = 6.4×10[sup]−5, reinforcing the hint previously reported with vertical events alone.
Ključne besede: high-energy cosmic rays large-scale distribution anisotropy studies Pierre Auger Observatory
Objavljeno v RUNG: 02.03.2016; Ogledov: 6056; Prenosov: 243
Celotno besedilo (862,90 KB)

Opis: The flux of ultra-high energy cosmic rays has been measured with unprecedented precision at the Pierre Auger Observatory. We report an update of the all-sky flux of cosmic rays above 3 x 10 [sup] 17 eV obtained by combining four independent data sets. These measurements are based on data from the surface detector arrays (divided into two sets according to the shower zenith angle), from a nested, denser, detector array, and hybrid events measured simultaneously with both the fluorescence detector and the surface detector array. The spectral features are presented in detail and the systematic uncertainties are addressed. The huge amount of data collected to date, with a total exposure exceeding 50,000 km2 sr yr, together with the wide range of sky observed (in declination from -90[deg] to 45[deg]) also allow us to measure the energy spectrum from different regions of the sky. We present the results of the search for a dependence of the measured flux on the declination of the incoming directions.
Ključne besede: ultra-high energy cosmic rays energy spectrum Pierre Auger Observatory
Objavljeno v RUNG: 02.03.2016; Ogledov: 6558; Prenosov: 228
Celotno besedilo (755,08 KB)