Reconstruction of inclined air showers detected with the Pierre Auger Observatory

Abstract

Abstract. We describe the method devised to reconstruct inclined cosmic-ray air showers with zenith angles greater than 60 • detected with the surface array of the Pierre Auger Observatory. The measured signals at the ground level are fitted to muon density distributions predicted with atmospheric cascade models to obtain the relative shower size as an overall normalization parameter. The method is evaluated using simulated showers to test its performance. The energy of the cosmic rays is calibrated using a sub-sample of events reconstructed with both the fluorescence and surface array techniques. The reconstruction method described here provides the basis of complementary analyses including an independent measurement of the energy spectrum of ultra-high energy cosmic rays using very inclined events collected by the Pierre Auger Observatory.

Observation of inclined EeV air showers with the radio detector of the Pierre Auger Observatory

“…We analyzed a data set recorded between 26 June 2013 and 28 February 2015 employing a hybrid analysis of the surface-detector and radio-detector data with the Offline analysis framework of the Pierre Auger Observatory [15]. For the particle component of the air shower, we apply the standard reconstruction for inclined showers with zenith angles greater than 60 • measured with the 1500 m surface-detector array [16]. While the maximum zenith angle of this reconstruction is normally limited to 80 • to ensure bias-free reconstruction parameters, we here extend the analysis to zenith angles up to 84 • , resulting in a minor degradation in reconstruction performance not relevant for the analysis presented here.…”

“…For a subset of the 561 events, the surface-detector reconstruction for inclined air showers [16] allows us to determine the cosmic-ray energy after the calibration with the fluorescence detector. This is normally done for showers with zenith angles between 60 • and 80 • , signals measured in a complete hexagon [19] of surface detector stations around the station with the largest energy deposit (thus in particular excluding events for which the impact point is not contained inside the area of the surface detector), and a minimum reconstructed energy of 10 18.6 eV.…”

“…This is normally done for showers with zenith angles between 60 • and 80 • , signals measured in a complete hexagon [19] of surface detector stations around the station with the largest energy deposit (thus in particular excluding events for which the impact point is not contained inside the area of the surface detector), and a minimum reconstructed energy of 10 18.6 eV. This energy determination is bias-free and achieves a resolution of 19.3% [16]. As discussed above, we here extended the zenith-angle range to include showers with zenith angles up to 84 • .…”

The Pierre Auger Observatory: Review of Latest Results and Perspectives

“…The right ascension anisotropy found in the two energy bins has amplitudes 0.5 +0. 6 −0.2 % and 4.7 +0.8 +0.7 %, respectively. The events in the lower energy bin follow an arrival direction distribution consistent with isotropy, but in the higher energy bin a significant anisotropy was found, with a p-value of 2.6 × 10 −8 under the isotropic null hypothesis.…”

“…The parameter chosen to characterize the size of an SD event for the SD-1500 array is the signal at 1000 m from the shower axis, normalized to mean zenith angle of the events of 38 • (S 38 ) according to the method described in [5]. For the SD-750 array the mean zenith angle of the events of 35 • (S 35 ) is used, while for inclined showers (with the zenith angle larger than 60 • seen by SD-1500 array), the (N 19 ) energy estimator is used [6]. Following this method the overall systematic uncertainty of the energy scale remains at 14% [7].…”