The Pierre Auger Observatory Upgrade - Preliminary Design Report

Abstract

ForewordThe Pierre Auger Observatory has begun a major Upgrade of its already impressive capabilities, with an emphasis on improved mass composition determination using the surface detectors of the Observatory. Known as AugerPrime, the upgrade will include new 4 m 2 plastic scintillator detectors on top of all 1660 water-Cherenkov detectors, updated and more flexible surface detector electronics, a large array of buried muon detectors, and an extended duty cycle for operations of the fluorescence detectors.This Preliminary Design Report was produced by the Collaboration in April 2015 as an internal document and information for funding agencies. It outlines the scientific and technical case for AugerPrime 1 . We now release it to the public via the arXiv server. We invite you to review the large number of fundamental results already achieved by the Observatory and our plans for the future.The Pierre Auger Collaboration 1 As a result of continuing R&D, slight changes have been implemented in the baseline design since this Report was written. These changes will be documented in a forthcoming Technical Design Report. ix x Executive Summary Present Results from the Pierre Auger ObservatoryMeasurements of the Auger Observatory have dramatically advanced our understanding of ultra-high energy cosmic rays. The suppression of the flux around 5×10 19 eV is now confirmed without any doubt. Strong limits have been placed on the photon and neutrino components of the flux indicating that "top-down" source processes, such as the decay of superheavy particles, cannot account for a significant part of the observed particle flux. A largescale dipole anisotropy of ∼7% amplitude has been found for energies above 8×10 18 eV. In addition there is also an indication of the presence of a large scale anisotropy below the ankle. Particularly exciting is the observed behavior of the depth of shower maximum with energy, which changes in an unexpected, non-trivial way. Around 3×10 18 eV it shows a distinct change of slope with energy, and the shower-to-shower variance decreases. Interpreted with the leading LHC-tuned shower models, this implies a gradual shift to a heavier composition. A number of fundamentally different astrophysical model scenarios have been developed to describe this evolution. The high degree of isotropy observed in numerous tests of the small-scale angular distribution of UHECR above 4×10 19 eV is remarkable, challenging original expectations that assumed only a few cosmic ray sources with a light composition at the highest energies. Interestingly, the largest departures from isotropy are observed for cosmic rays with E > 5.8×10 19 eV in ∼20 • sky-windows. Due to a duty cycle of ∼15% of the fluorescence telescopes, the data on the depth of shower maximum extend only up to the flux suppression region, i.e. 4×10 19 eV. Obtaining more information on the composition of cosmic rays at higher energies will provide crucial means to discriminate between the model classes and to understand the origin of the observed flux suppre...

Uncorrelated Far Active Galactic Nuclei Flaring with Their Delayed Ultra High Energy Cosmic Rays Events

“…Since 25 years and up to now, after the early Fly's Eye event [2] (as well as the maximal, more and more puzzling, unbeaten 3 · 10 20 eV energetic event), after Akeno Giant Air Shower Array (AGASA) decade of records [3,4], the HiRes observation of a UHECR cut off [5], and the more recent hundreds of PAO and TA records [6][7][8], some (or let say most) of the UHECR are still mainly spread. In summary on years 1991-2000, up to HiRes results, we were all believing that UHECR could overcome somehow the GZK cut off: this is because some of the most energetic [2] UHECR were uncorrelated with nearby (GZK distance) sources and because AGASA didn't show the GZK cut off.…”

Review of Model Predictions for Extensive Air Showers

“…This constraint is much stronger than the traditional test limiting the results to the range between proton and iron induced showers. This is now satisfied in most of the cases, but none of the current models is able to give a fully consistent picture of the different observables within a given experiment [21][22][23].…”

“…At the same time, a new generation of hybrid cosmic ray detectors such as the Pierre Auger Observatory [8] (surface and fluorescence detectors), the IceCube/IceTop experiments [17,18] (low energy muons at the surface and high energy muons deep underground) or the KASCADE/KASCADE Grande experiment [19,20] (muons of different energies and at different distances) gives access to various precise measurements of the mean logarithmic mass of cosmic rays within the same experiment. By definition the mean logarithmic mass should be independent of the measurement technique.…”

Prospects of Silicon Photomultipliers for Ground-Based Cosmic Ray Experiments

“…A combined analysis by means of complementary detection methods is thereby a common technique to study these showers. For example, at the Pierre Auger Observatory [2], water-Cherenkov detector (WCD) stations [3] determine the distribution of charged particles on the ground, i.e. the electromagnetic and muonic component, while fluorescence telescopes [4] overlook the atmosphere above the array.…”

“…Located at the same position as the WCD stations, both detector arrays measure the same air showers, but with different response to their components. These Surface Scintillator Detectors (SSD), to be read out with standard photomultiplier tubes, are one main part of the on-going upgrade AugerPrime [5] of the Pierre Auger Observatory. Nowadays, for many of these applications, silicon photomultipliers (SiPMs) promise a high potential as an excellent choice as photosensors [6,7].…”