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Abstract: We report an investigation of the mass composition of cosmic rays with energies from 3 to 100 EeV (1 EeV = 10[sup]18 eV) using the distributions of the depth of shower maximum Xmax. The analysis relies on ∼50,000 events recorded by the surface detector of the Pierre Auger Observatory and a deep-learning-based reconstruction algorithm. Above energies of 5 EeV, the dataset offers a 10-fold increase in statistics with respect to fluorescence measurements at the Observatory. After cross-calibration using the fluorescence detector, this enables the first measurement of the evolution of the mean and the standard deviation of the Xmax distributions up to 100 EeV. Our findings are threefold: (i) The evolution of the mean logarithmic mass toward a heavier composition with increasing energy can be confirmed and is extended to 100 EeV. (ii) The evolution of the fluctuations of Xmax toward a heavier and purer composition with increasing energy can be confirmed with high statistics. We report a rather heavy composition and small fluctuations in Xmax at the highest energies. (iii) We find indications for a characteristic structure beyond a constant change in the mean logarithmic mass, featuring three breaks that are observed in proximity to the ankle, instep, and suppression features in the energy spectrum.
Keywords: ultra-high-energy cosmic rays, UHECRs, extensive air showers, Pierre Auger Observatory, UHECR mass composition, depth of shower maximum, fluorescence detector, surface detector, deep learning
Published in RUNG: 20.01.2025; Views: 718; Downloads: 8
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Abstract: A first measurement of the muon content of air showers using hybrid measurements combining radio and particle detection is presented. For inclined air showers with zenith angles above 60°, the water-Cherenkov detector (WCD) of the Pierre Auger Observatory performs an almost pure measurement of the muonic component, whereas the Auger Engineering Radio Array (AERA) allows reconstructing the electromagnetic energy independently using the radio emission of the air shower. The analysis of more than six years of AERA data shows a deficit of muons predicted by all current-generation hadronic interaction models for energies between 4 EeV and 20 EeV. This deficit, already observed in previous analyses of Auger, is now confirmed for the first time with radio data. This analysis is limited by low statistics of only 59 high-quality events due to the small area of AERA of 17 km² and the high energy threshold of 4 EeV originating from the WCD reconstruction. With the AugerPrime Radio Detector currently being deployed, this analysis can be extended to the highest energies to allow for in-depth tests of hadronic interaction models with large statistics.
Keywords: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, engineering radio array
Published in RUNG: 03.10.2024; Views: 1041; Downloads: 3
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Abstract: We use the surface detector of the Pierre Auger Observatory to search for air showers initiated by photons with an energy above 10[sup]19 eV. Photons in the zenith angle range from 30 deg. to 60 deg. can be identified in the overwhelming background of showers initiated by charged cosmic rays through the broader time structure of the signals induced in the water-Cherenkov detectors of the array and the steeper lateral distribution of shower particles reaching ground. Applying the search method to data collected between January 2004 and June 2020, upper limits at 95% CL are set to an E[sup]-2 diffuse flux of ultra-high energy photons above 10[sup]19 eV, 2 × 10[sup]19 eV and 4 × 10[sup]19 eV amounting to 2.11 × 10[sup]-3, 3.12 × 10[sup]-4 and 1.72 × 10[sup]-4 km-2 sr-1 yr-1, respectively. While the sensitivity of the present search around 2 × 10[sup]19 eV approaches expectations of cosmogenic photon fluxes in the case of a pure-proton composition, it is one order of magnitude above those from more realistic mixed-composition models. The inferred limits have also implications for the search of super-heavy dark matter that are discussed and illustrated.
Keywords: ultra-high-energy cosmic rays, UHE photons, Pierre Auger Observatory, extensive air showers, water Cherenkov detectors
Published in RUNG: 18.08.2023; Views: 2178; Downloads: 20
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Keywords: ultra-high energy cosmic rays, UHE photon flux upper limits, super-heavy dark matter models, instantons, Pierre Auger Observatory
Published in RUNG: 09.02.2023; Views: 2487; Downloads: 0
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Abstract: The Pierre Auger Observatory, being the largest air-shower experiment in the world, offers an unprecedented exposure to neutral particles at the highest energies. Since the start of data taking more than 18 years ago, various searches for ultra-high-energy (UHE, E > 10[sup]17 eV) photons have been performed: either for a diffuse flux of UHE photons, for point sources of UHE photons or for UHE photons associated with transient events like gravitational wave events. In the present paper, we summarize these searches and review the current results obtained using the wealth of data collected by the Pierre Auger Observatory.
Keywords: photons, ultra-high energies, air showers, Pierre Auger Observatory, upper limits, transients
Published in RUNG: 03.01.2023; Views: 3203; Downloads: 0
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