A. Gorgi

Publications (61)66.18 Total impact

• Article: Antennas for the Detection of Radio Emission Pulses from Cosmic-Ray induced Air Showers at the Pierre Auger Observatory

  P. Abreu, M. Aglietta, M. Ahlers, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P. Allison, A. Almela, [......], J. Zhou, Y. Zhu, M. Zimbres Silva, M. Ziolkowski, D. Charrier, L. Denis, G. Hilgers, L. Mohrmann, B. Philipps, O. Seeger
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  ABSTRACT: The Pierre Auger Observatory is exploring the potential of the radio detection technique to study extensive air showers induced by ultra-high energy cosmic rays. The Auger Engineering Radio Array (AERA) addresses both technological and scientific aspects of the radio technique. A first phase of AERA has been operating since September 2010 with detector stations observing radio signals at frequencies between 30 and 80 MHz. In this paper we present comparative studies to identify and optimize the antenna design for the final configuration of AERA consisting of 160 individual radio detector stations. The transient nature of the air shower signal requires a detailed description of the antenna sensor. As the ultra-wideband reception of pulses is not widely discussed in antenna literature, we review the relevant antenna characteristics and enhance theoretical considerations towards the impulse response of antennas including polarization effects and multiple signal reflections. On the basis of the vector effective length we study the transient response characteristics of three candidate antennas in the time domain. Observing the variation of the continuous galactic background intensity we rank the antennas with respect to the noise level added to the galactic signal.
  09/2012;
• Article: The Rapid Atmospheric Monitoring System of the Pierre Auger Observatory

  The Pierre Auger Collaboration, P. Abreu, M. Aglietta, M. Ahlers, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P. Allison, [......], B. Zamorano Garcia, E. Zas, D. Zavrtanik, M. Zavrtanik, I. Zaw, A. Zepeda, J. Zhou, Y. Zhu, M. Zimbres Silva, M. Ziolkowski
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  ABSTRACT: The Pierre Auger Observatory is a facility built to detect air showers produced by cosmic rays above 10^17 eV. During clear nights with a low illuminated moon fraction, the UV fluorescence light produced by air showers is recorded by optical telescopes at the Observatory. To correct the observations for variations in atmospheric conditions, atmospheric monitoring is performed at regular intervals ranging from several minutes (for cloud identification) to several hours (for aerosol conditions) to several days (for vertical profiles of temperature, pressure, and humidity). In 2009, the monitoring program was upgraded to allow for additional targeted measurements of atmospheric conditions shortly after the detection of air showers of special interest, e.g., showers produced by very high-energy cosmic rays or showers with atypical longitudinal profiles. The former events are of particular importance for the determination of the energy scale of the Observatory, and the latter are characteristic of unusual air shower physics or exotic primary particle types. The purpose of targeted (or "rapid") monitoring is to improve the resolution of the atmospheric measurements for such events. In this paper, we report on the implementation of the rapid monitoring program and its current status. The rapid monitoring data have been analyzed and applied to the reconstruction of air showers of high interest, and indicate that the air fluorescence measurements affected by clouds and aerosols are effectively corrected using measurements from the regular atmospheric monitoring program. We find that the rapid monitoring program has potential for supporting dedicated physics analyses beyond the standard event reconstruction.
  08/2012;
• Source

  Available from: Olaf Scholten

  Article: A search for ultra-high energy neutrinos in highly inclined events at the Pierre Auger Observatory

  The Pierre Auger Collaboration, P. Abreu, M. Aglietta, M. Ahlers, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P. Allison, [......], A. Yushkov, B. Zamorano, E. Zas, D. Zavrtanik, M. Zavrtanik, I. Zaw, A. Zepeda, Y. Zhu, M. Zimbres Silva, M. Ziolkowski
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  ABSTRACT: The Surface Detector of the Pierre Auger Observatory is sensitive to neutrinos of all flavours above 0.1 EeV. These interact through charged and neutral currents in the atmosphere giving rise to extensive air showers. When interacting deeply in the atmosphere at nearly horizontal incidence, neutrinos can be distinguished from regular hadronic cosmic rays by the broad time structure of their shower signals in the water-Cherenkov detectors. In this paper we present for the first time an analysis based on down-going neutrinos. We describe the search procedure, the possible sources of background, the method to compute the exposure and the associated systematic uncertainties. No candidate neutrinos have been found in data collected from 1 January 2004 to 31 May 2010. Assuming an E^-2 differential energy spectrum the limit on the single flavour neutrino is (E^2 * dN/dE) < 1.74x10^-7 GeV cm^-2 s^-1 sr^-1 at 90% C.L. in the energy range 1x10^17 eV < E < 1x10^20 eV.
  02/2012;
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  Available from: Maria Concetta Maccarone

  Article: Description of Atmospheric Conditions at the Pierre Auger Observatory using the Global Data Assimilation System (GDAS)

  The Pierre Auger Collaboration, P. Abreu, M. Aglietta, M. Ahlers, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P. Allison, [......], A. Yushkov, B. Zamorano, E. Zas, D. Zavrtanik, M. Zavrtanik, I. Zaw, A. Zepeda, Y. Zhu, M. Zimbres Silva, M. Ziolkowski
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  ABSTRACT: Atmospheric conditions at the site of a cosmic ray observatory must be known for reconstructing observed extensive air showers. The Global Data Assimilation System (GDAS) is a global atmospheric model predicated on meteorological measurements and numerical weather predictions. GDAS provides altitude-dependent profiles of the main state variables of the atmosphere like temperature, pressure, and humidity. The original data and their application to the air shower reconstruction of the Pierre Auger Observatory are described. By comparisons with radiosonde and weather station measurements obtained on-site in Malarg\"ue and averaged monthly models, the utility of the GDAS data is shown.
  01/2012;
• Article: Search for Point-like Sources of Ultra-high Energy Neutrinos at the Pierre Auger Observatory and Improved Limit on the Diffuse Flux of Tau Neutrinos

  The Pierre Auger Collaboration, P Abreu, M Aglietta, M Ahlers, E J Ahn, I F M Albuquerque, D Allard, I Allekotte, J Allen, P Allison, [......], Zamorano B Garcia, E Zas, D Zavrtanik, M Zavrtanik, I Zaw, A Zepeda, J Zhou, Y Zhu, Zimbres M Silva, M Ziolkowski
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  ABSTRACT: The surface detector array of the Pierre Auger Observatory can detect neutrinos with energy E ν between 10 17 eV and 10 20 eV from point-like sources across the sky south of +55° and north of –65° declinations. A search has been performed for highly inclined extensive air showers produced by the interaction of neutrinos of all flavors in the atmosphere (downward-going neutrinos), and by the decay of tau leptons originating from tau neutrino interactions in Earth's crust (Earth-skimming neutrinos). No candidate neutrinos have been found in data up to 2010 May 31. This corresponds to an equivalent exposure of ~3.5 years of a full surface detector array for the Earth-skimming channel and ~2 years for the downward-going channel. An improved upper limit on the diffuse flux of tau neutrinos has been derived. Upper limits on the neutrino flux from point-like sources have been derived as a function of the source declination. Assuming a differential neutrino flux k PS · E –2 ν from a point-like source, 90% confidence level upper limits for k PS at the level of ##IMG## [http://ej.iop.org/icons/Entities/ap.gif] ≈ 5 × 10 –7 and 2.5 × 10 –6 GeV cm –2 s –1 have been obtained over a broad range of declinations from the searches for Earth-skimming and downward-going neutrinos, respectively.
  The Astrophysical Journal Letters. 01/2012; 755(1):L4.
• Source

  Available from: Maria Concetta Maccarone

  Article: The effect of the geomagnetic field on cosmic ray energy estimates and large scale anisotropy searches on data from the Pierre Auger Observatory

  P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, J. Alvarez-Muñiz, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: We present a comprehensive study of the influence of the geomagnetic field on the energy estimation of extensive air showers with a zenith angle smaller than $60^\circ$, detected at the Pierre Auger Observatory. The geomagnetic field induces an azimuthal modulation of the estimated energy of cosmic rays up to the ~2% level at large zenith angles. We present a method to account for this modulation of the reconstructed energy. We analyse the effect of the modulation on large scale anisotropy searches in the arrival direction distributions of cosmic rays. At a given energy, the geomagnetic effect is shown to induce a pseudo-dipolar pattern at the percent level in the declination distribution that needs to be accounted for.
  11/2011;
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  Available from: Maria Concetta Maccarone

  Article: Trigger and Aperture of the Surface Detector Array of the Pierre Auger Observatory

  J. Abraham, P Abreu, M Aglietta, C Aguirre, E. J. Ahn, D. Allard, I. Allekotte, J Allen, J. Alvarez-Muñiz, M. Ambrosio, [......], T Yamamoto, P. Younk, G. Yuan, A. Yushkov, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M Ziolkowski
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  ABSTRACT: The surface detector array of the Pierre Auger Observatory consists of 1600 water-Cherenkov detectors, for the study of extensive air showers (EAS) generated by ultra-high-energy cosmic rays. We describe the trigger hierarchy, from the identification of candidate showers at the level of a single detector, amongst a large background (mainly random single cosmic ray muons), up to the selection of real events and the rejection of random coincidences. Such trigger makes the surface detector array fully efficient for the detection of EAS with energy above $3\times 10^{18}$ eV, for all zenith angles between 0$^\circ$ and 60$^\circ$, independently of the position of the impact point and of the mass of the primary particle. In these range of energies and angles, the exposure of the surface array can be determined purely on the basis of the geometrical acceptance.
  11/2011;
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  Available from: Maria Concetta Maccarone

  Article: The Lateral Trigger Probability function for the Ultra-High Energy Cosmic Ray Showers detected by the Pierre Auger Observatory

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: In this paper we introduce the concept of Lateral Trigger Probability (LTP) function, i.e., the probability for an extensive air shower (EAS) to trigger an individual detector of a ground based array as a function of distance to the shower axis, taking into account energy, mass and direction of the primary cosmic ray. We apply this concept to the surface array of the Pierre Auger Observatory consisting of a 1.5 km spaced grid of about 1600 water Cherenkov stations. Using Monte Carlo simulations of ultra-high energy showers the LTP functions are derived for energies in the range between 10^{17} and 10^{19} eV and zenith angles up to 65 degs. A parametrization combining a step function with an exponential is found to reproduce them very well in the considered range of energies and zenith angles. The LTP functions can also be obtained from data using events simultaneously observed by the fluorescence and the surface detector of the Pierre Auger Observatory (hybrid events). We validate the Monte-Carlo results showing how LTP functions from data are in good agreement with simulations.
  11/2011;
• Source

  Available from: Maria Concetta Maccarone

  Article: Search for signatures of magnetically-induced alignment in the arrival directions measured by the Pierre Auger Observatory

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: We present the results of an analysis of data recorded at the Pierre Auger Observatory in which we search for groups of directionally-aligned events (or `multiplets') which exhibit a correlation between arrival direction and the inverse of the energy. These signatures are expected from sets of events coming from the same source after having been deflected by intervening coherent magnetic fields. The observation of several events from the same source would open the possibility to accurately reconstruct the position of the source and also measure the integral of the component of the magnetic field orthogonal to the trajectory of the cosmic rays. We describe the largest multiplets found and compute the probability that they appeared by chance from an isotropic distribution. We find no statistically significant evidence for the presence of multiplets arising from magnetic deflections in the present data.
  11/2011;
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  Available from: Luis Del Peral

  Article: The Pierre Auger Observatory IV: Operation and Monitoring

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtnik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: Technical reports on operations and monitoring of the Pierre Auger Observatory
  07/2011;
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  Available from: Luis Del Peral

  Article: The Pierre Auger Observatory V: Enhancements

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtnik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: Ongoing and planned enhancements of the Pierre Auger Observatory
  07/2011;
• Article: The Pierre Auger Observatory I: The Cosmic Ray Energy Spectrum and Related Measurements

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtnik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: Studies of the cosmic ray energy spectrum at the highest energies with the Pierre Auger Observatory
  07/2011;
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  Available from: Maria Concetta Maccarone

  Article: The Pierre Auger Observatory II: Studies of Cosmic Ray Composition and Hadronic Interaction models

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtnik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: Studies of the composition of the highest energy cosmic rays with the Pierre Auger Observatory, including examination of hadronic physics effects on the structure of extensive air showers.
  07/2011;
• Article: The Pierre Auger Observatory III: Other Astrophysical Observations

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtnik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: Astrophysical observations of ultra-high-energy cosmic rays with the Pierre Auger Observatory
  07/2011;
• Article: The Pierre Auger Observatory IV: Operation and Monitoring

  The Pierre Auger Collaboration, P. Abreu, M. Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D. Zavrtanik, M. Zavrtnik, I. Zaw, A. Zepeda, M. Zimbres-Silva, M. Ziolkowski
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  ABSTRACT: Technical reports on operations and monitoring of the Pierre Auger Observatory
  06/2011;
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  Available from: Maria Concetta Maccarone

  Article: Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], P. Younk, G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M Ziolkowski
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  ABSTRACT: The Pierre Auger Collaboration has reported evidence for anisotropy in the distribution of arrival directions of the cosmic rays with energies $E>E_{th}=5.5\times 10^{19}$ 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 $E>E_{th}$ are heavy nuclei with charge $Z$, the proton component of the sources should lead to excesses in the same regions at energies $E/Z$. We here report the lack of anisotropies in these directions at energies above $E_{th}/Z$ (for illustrative values of $Z=6,\ 13,\ 26$). If the anisotropies above $E_{th}$ are due to nuclei with charge $Z$, and under reasonable assumptions about the acceleration process, these observations imply stringent constraints on the allowed proton fraction at the lower energies.
  06/2011;
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  Available from: Olaf Scholten

  Article: Search for first harmonic modulation in the right ascension distribution of cosmic rays detected at the Pierre Auger Observatory

  Pierre The, Collaboration P Auger, Abreu, M Aglietta, E J Ahn, I F M Albuquerque, D Allard, I Allekotte, J Allen, P Allison, [......], H Wahlberg, P Wahrlich, O Wainberg, D Warner, A A Watson, M Weber, K Weidenhaupt, A Weindl, S Westerhoff, B J Whelan
  J. Kleinfeller N. Krohm Martínez Bravo H.J. Mathes J. Matthews J.A.J. Matthews C. Morello P.T. Nhung N. Nierstenhoefer V.M. Olmos-Gilbaja N. Pacheco D. Pakk Selmi-Dei J. Pallotta N. Palmieri E. Parizot J. Parrisius R.D. Parsons J. Pkala I.M. Pepe R. Pesce E. Petermann R.C. Shellard A Smiałkowski G.R. Snow J. Sorokin J. Stapleton J. Stasielak J. Swain Z. Szadkowski J. Tiffenberg C.J. Todero Peixoto D.B. Tridapalli J.F. Valdés Galicia J.R. Vázquez. 04/2011; 23(91):74-68.
• Source

  Available from: Olaf Scholten

  Article: Search for First Harmonic Modulation in the Right Ascension Distribution of Cosmic Rays Detected at the Pierre Auger Observatory

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], B. Wundheiler, T Yamamoto, P. Younk, G. Yuan, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda
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  ABSTRACT: We present the results of searches for dipolar-type anisotropies in different energy ranges above $2.5\times 10^{17}$ eV with the surface detector array of the Pierre Auger Observatory, reporting on both the phase and the amplitude measurements of the first harmonic modulation in the right-ascension distribution. Upper limits on the amplitudes are obtained, which provide the most stringent bounds at present, being below 2% at 99% $C.L.$ for EeV energies. We also compare our results to those of previous experiments as well as with some theoretical expectations.
  03/2011;
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  Available from: Maria Concetta Maccarone

  Article: Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, D. Allard, I. Allekotte, J Allen, J. Alvarez Castillo, J. Alvarez-Muñiz, M. Ambrosio, [......], P. Younk, G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M Ziolkowski
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  ABSTRACT: 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{$6\times 10^{19}$eV}. The anisotropy was measured by the fraction of arrival directions that are less than $3.1^\circ$ from the position of an active galactic nucleus within 75 Mpc (using the V\'eron-Cetty and V\'eron $12^{\rm th}$ 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 $(38^{+7}_{-6})%$, compared with $21%$ expected for isotropic cosmic rays. This is down from the early estimate of $(69^{+11}_{-13})%$. 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 2010
  09/2010;
• Article: Measurement of the depth of maximum of extensive air showers above 10{18} eV.

  J Abraham, P Abreu, M Aglietta, E J Ahn, D Allard, I Allekotte, J Allen, J Alvarez-Muñiz, M Ambrosio, L Anchordoqui, [......], T Yamamoto, P Younk, G Yuan, A Yushkov, E Zas, D Zavrtanik, M Zavrtanik, I Zaw, A Zepeda, M Ziolkowski
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  ABSTRACT: We describe the measurement of the depth of maximum, X{max}, of the longitudinal development of air showers induced by cosmic rays. Almost 4000 events above 10;{18} eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106{-21}{+35}) g/cm{2}/decade below 10{18.24+/-0.05} eV, and (24+/-3) g/cm{2}/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm{2}. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.
  Physical Review Letters 03/2010; 104(9):091101. · 7.37 Impact Factor