The Time Evolution of the Surface Detector of the Pierre Auger Observatory
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et al.; Institute for Cosmic Ray Research (ICRR) Univeristy of Tokyo; International Union of Pure and Applied Physics (IUPAP); JPS; Nagoya Convention and Visitors Bureau; Nagoya University
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The surface detector array of the Pierre Auger Observatory, consisting of 1660 water Cherenkov tanks, has been in operation for nearly 20 years. During this long period of data acquisition, ageing effects in the detector response have been observed. The temporal evolution of the signals recorded by the surface detector is mostly compensated by continuous calibration with atmospheric muons; however, effects persist in the signal rise time and in high-level data analysis using neural networks. We have implemented a detailed description of the time evolution of the detector response and of the uptimes of individual stations in GEANT4-based detector simulations. These new simulations reproduce the observed time dependencies in the data. Using air-shower simulations that take into account the evolution of individual stations, we show that the reconstructed energy is stable at the sub-percent level, and its resolution is affected by less than 5% in 15 years. For a few specific stations, the collected light produced by muons has decreased to the point where it is difficult to distinguish it from the electromagnetic background in the calibration histograms. The upgrade of the Observatory with scintillator detectors mitigates this problem: by requiring a coincidence between the water-Cherenkov and scintillator detectors, we can enhance the muon relative contribution to the calibration histogram. We present the impact and performance of this coincidence calibration method. © Copyright owned by the author(s) under the terms of the Creative Commons.
Palabras clave
Cerenkov counters, Cosmic ray detectors, Hadrons, Heavy ions, Negative ions, Photons, Positive ions, Ageing effects, Cherenkov, Continuous calibrations, Detector arrays, Detector response, Pierre Auger observatory, Scintillator detector, Surface detectors, Temporal evolution, Time evolutions, Scintillation counters
