Updated results on Ultra-High Energy Neutrinos with the Pierre Auger Observatory

The Pierre Auger Observatory is the world's largest cosmic- ray observatory. Updated results on the search for ultra-high energy (UHE) neutrinos with Auger data are presented. The search method and the detection channels are introduced and neutrino flux limits are given in the energy range 0.1− 100 EeV. Finally the sensitivity to point-like sources of ul tra-high energy neutrinos over a broad range of declinations is demonstrated

Study of the performance of the Pierre Auger Observatory and search for primary cosmic ray photons

Astroparticle physics is now entering the very exciting phase in which the efforts to enhance the detection capabilities of our instruments begin to turn out into clear answers. In this context the Pierre Auger Observatory (PAO) has been conceived to study the extensive air showers produced by the primary cosmic rays at energies above 1018eV in their interaction with the Earth’s atmosphere, in order to solve the mystery of the origin and nature of the highest energy particles. The PAO design combines the most advanced detection techniques and the largest exposure, to provide high data quality together with unprecedented statistics. In addition, two experimental sites, one nearly completed in the southern hemisphere and the other to be built in the northern one will achieve full sky coverage, and the largest exposure ever. The PAO collaboration benefits from the contribution of about 300 scientists from 17 countries. The Wuppertal group is highly involved in physics analysis and the study and monitoring of the detector performance. Moreover its tasks involve hardware development and testing. More than half of the 11 000 optical modules for the fluorescence detector telescopes have been qualified with a highly automatised test setup. Details on the experimental requirements and test results are presented in Section 4.3, (see [24]). The performance of the fluorescence detector (FD) reconstruction algorithm has been studied at different selection levels with dedicated simulations. In Chapter 5 the FD trigger efficiency and the geometry resolutions are calculated. A realistic estimate of the hybrid resolution of the physics observables (depth of shower maximum and energy) is also given, see [108]. This work includes the extension of the reconstruction capabilities to the highest energies covered by the FD dynamic range [136]. Discrimination of different primaries is based on their expected shower features, for instance the depth shower maximum, Xmax. In Chapter 6 the composition sensitivity of other parameters connected to the shape of the longitudinal shower profile is evaluated in order to achieve an enhancement of the separation power between photon and hadron primaries [139]. No claim for photon observation at the highest energies has been reported so far. For this work an update of the first limit to the fraction of photons in cosmic rays above 10 EeV [119], based on the measurement of Xmax has been performed, see Section 7.2, reported in [21]. Finally, limits above 2, 3.16, 5 and 10 EeV are derived using the Pierre Auger hybrid data sample Jan 2004–July 2007, see Section 7.3. The expected impact of a photon contamination of this order on the measurement of the inelastic proton-air cross section is briefly discussed in Section 7.4. Our limits confirm the ones derived by ground-based experiments at higher energies and they strongly constrain the non-acceleration models invoked to explain the origin of the ultra high energy cosmic rays, thus favoring astrophysical scenarios

Measurement of the cosmic ray spectrum above 4×10184{\times}10^{18} eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$ eV, the "ankle", the flux can be described by a power law $E^{-\gamma}$ with index $\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by a smooth suppression region. For the energy ($E_\text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$ eV.Comment: Replaced with published version. Added journal reference and DO

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI. Supplemental material in the ancillary file

Combined fit to the spectrum and composition data measured by the Pierre Auger Observatory including magnetic horizon effects

The measurements by the Pierre Auger Observatory of the energy spectrum and mass composition of cosmic rays can be interpreted assuming the presence of two extragalactic source populations, one dominating the flux at energies above a few EeV and the other below. To fit the data ignoring magnetic field effects, the high-energy population needs to accelerate a mixture of nuclei with very hard spectra, at odds with the approximate E$^{-2}$ shape expected from diffusive shock acceleration. The presence of turbulent extragalactic magnetic fields in the region between the closest sources and the Earth can significantly modify the observed CR spectrum with respect to that emitted by the sources, reducing the flux of low-rigidity particles that reach the Earth. We here take into account this magnetic horizon effect in the combined fit of the spectrum and shower depth distributions, exploring the possibility that a spectrum for the high-energy population sources with a shape closer to E$^{-2}$ be able to explain the observations