Search for upward-going showers with the Fluorescence Detector of the Pierre Auger Observatory

PIERRE AUGER COLLABORATION; A. MARIAZZI

Berlin

Conferencia; 37th International Cosmic Ray Conference (ICRC2021); 2021

Given its operation time and wide field of view, the Fluorescence Detector (FD) of the PierreAuger Observatory is sufficiently sensitive to detect upward-going events when used in monocularmode. Upward-going air showers are a possible interpretation of the recent events reported by theANITA Collaboration in the energy range above 1017 eV. The Pierre Auger FD data can be usedto support or constrain this interpretation. If confirmed, it would require either new phenomenaor significant modifications to the standard model of particle physics.To prepare this search, a set of quality selection criteria was defined by using 10% of the availableFD data from 14 years of operation. This subset was mainly used to clean the data from improperlylabelled laser events that had been used to monitor the quality of the atmosphere. The potentialbackground for this search consists of cosmic-ray induced air showers with specific geometricconfigurations which, in a monocular reconstruction, can be reconstructed erroneously as upwardgoing events. To distinguish candidates from these false positives, to calculate the exposure,and to estimate the expected background, dedicated simulations for signal (upward-going events)and background (downward-going events) have been performed. The detector exposure is largeenough to strongly constrain the interpretation of ANITA anomalous events. Preliminary resultsof the analysis after unblinding the data set are presented.