Constraints on upward-going air showers using the Pierre Auger Observatory data

The fluorescence detector (FD) of the Pierre Auger Observatory is sensitive to upward-going air showers with energies above 10¹⁷ eV. Given its operation time and wide field of view, the FD has the potential to support or constrain the “anomalous” observations by the ANITA detector, interpreted as upward-going air showers that would be indicative of Beyond Standard Model (BSM) physics. To this end, a search for upward-going air showers with the FD has been performed applying selection criteria that were optimized using 10% of FD data. Dedicated background simulations (downward-going events) have been performed to estimate our capability to distinguish candidates from false positives. Also dedicated signal simulations (upward-going events) have been used to estimate our sensitivity to such showers with a focus on the energy region close to the ANITA observations. Improved and updated results of the Pierre Auger Observatory exposure to upward-going showers will be presented after the unblinding of 14 years of FD data. Extensive simulations allow the FD exposure to be obtained at lower energies which are particularly relevant for the comparison with the ANITA results. A refinement of the method for signal discrimination and background rejection has also been applied. The implications are discussed under the assumption that the ANITA events were due to upward-going events.