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Abstract: The low energy modes of the surface detector array of the Pierre Auger Observatory record variations in the flux of low energy secondary particles with extreme detail. These two modes consist of recording (1) the rate of signals for energies between ∼15 MeV and ∼100 MeV (the Scaler mode) and (2) the calibration charge histograms of the individual pulses detected by each water-Cherenkov station, covering different energy channels up to ∼1 GeV (the Histogram mode). Previous work has studied the flux of galactic cosmic rays on short and intermediate time scales (i.e. from minutes to weeks) using these low energy modes. In this work, after including a long- term correction to the response of the detectors, we present the first long-term analysis of the flux of cosmic rays using scalers and two energy bands of the calibration histograms. We show its sensitivity to the solar cycle variation and its relation to the solar modulation of cosmic rays for an 8-year period.
Keywords: Pierre Auger Observatory, Surface Detector, secondary cosmic rays, scaler mode, charge histogram mode, solar cycle modulation
Published in RUNG: 03.03.2016; Views: 6062; Downloads: 209
Full text (533,18 KB)

Abstract: In addition to the standard Xmax and energy, the longitudinal profiles of extensive air showers contain some more interesting information. For energies above 10[sup]17.8 eV, we present the average profiles as a function of atmospheric depth measured for the first time at the Pierre Auger Observatory. The profile shapes for different energy ranges are all well reproduced by a Gaisser-Hillas function within the range studied. A detailed analysis of the systematic uncertainties is performed using data and a full detector simulation, and the results are compared with predictions of hadronic interaction models for different primaries.
Keywords: Pierre Auger Observatory, extensive air showers, longitudinal shower profile, Gaisser-Hillas finction
Published in RUNG: 03.03.2016; Views: 5283; Downloads: 191
Full text (684,20 KB)

Abstract: The muon content of extensive air showers is an observable sensitive to the primary composition and to the hadronic interaction properties. We present here different methods which allow us to estimate the muon number at the ground level and the muon production depth by exploiting the measurement of the longitudinal, lateral and temporal distribution of particles in air showers recorded at the Pierre Auger Observatory. The results, obtained at about 10[sup]19 eV (E[inf]CM ∼ 140 TeV center-of-mass energy for proton primaries), are compared to the predictions of LHC-tuned hadronic interaction models with different primary masses and suggest a deficit in the muon content at the ground predicted by simulations. The Pierre Auger Observatory uses water-Cherenkov detectors to measure particle densities at the ground and therefore has a good sensitivity to the muon content of air showers. Moreover, due to its hybrid design, the combination of muon measurements with other independent mass composition analyses such as Xmax provides additional constraints on hadronic interaction models.
Keywords: Pierre Auger Observatory, ultra-high energy cosmic rays, muons, mass composition, hadronic interactions
Published in RUNG: 03.03.2016; Views: 5954; Downloads: 221
Full text (298,46 KB)

Abstract: Ultra-high energy neutrinos and photons, with energies above 1 EeV and 10 EeV respectively, can be detected with the Surface Detector array (SD) of the Pierre Auger Observatory. Downward- going neutrinos of all flavours interacting in the atmosphere at zenith angles θ > 60◦, upward-going tau neutrinos (“Earth- skimming”), as well as photons in the zenith range 30◦ − 60◦ can be identified through the broad time-structure of the signals expected to be induced in the SD stations. An additional signature for photon-induced air showers is the steeper lateral distribution of secondary particles at ground with respect to the nucleonic showers. Stringent limits are set to the diffuse flux of ultra-high energy (UHE) neutrinos and photons, using data collected between 2004 and mid-2013, under the hypothesis of an E[sup]−2 spectrum for signal primaries.
Keywords: ultra-high energy neutrinos, ultra-high energy photons, cosmic rays, elemental composition, Pierre Auger Observatory
Published in RUNG: 03.03.2016; Views: 6082; Downloads: 242
Full text (398,21 KB)

Abstract: For the first time the Pierre Auger Collaboration presents〈Xmax〉and σ(Xmax) measurements covering nearly three decades of energy. In this analysis we include new Xmax data obtained with the High Elevation Auger Telescopes (HEAT) enhancement. The HEAT telescopes cover a field of view ranging from 30◦ to 60◦ of elevation and are located next to one of the standard fluorescence detector sites (Coihueco). The combination of the HEAT and Coihueco telescopes covers a field of view from ∼2◦ up to ∼60◦ of elevation. Thus, the combination can sample the longitudinal profile of nearby lower energy showers, allowing us to extend the energy range down to 10[sup]17 eV.
Keywords: extensive atmospheric showers, longitudinal shower profile, depth of the shower maximum, Pierre Auger Observatory
Published in RUNG: 03.03.2016; Views: 6421; Downloads: 239
Full text (718,30 KB)