1. Neural networks for photon searches with AugerPrimeEzequiel Rodriguez, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: Ultra-high-energy photons (E ≥ 10[sup]17 eV) are expected as by-products of interactions between ultra-high-energy cosmic rays (UHECRs) and background radiation fields or galactic matter, as well as from decay of super-heavy dark matter. Despite these various production mechanisms, the diffuse photon flux is too low for direct detection. Consequently, photon searches at UHE must rely on large ground-based detector arrays. In this contribution, we present a method for photon-hadron discrimination based on deep learning algorithms applied to detector simulations within the context of the Pierre Auger Observatory. Our method correlates information from the Surface Detector (SD), sensitive to air-shower particles arriving to the ground, and the Underground Muon Detector (UMD), sensitive to muons with energies above ∼ 1 GeV. We chose graph neural networks (GNNs) for their effectiveness in handling the discrimination task, allowing for an easy and flexible correlation of information from the SD and UMD. This approach is particularly suitable for handling the irregular structures found in SD and UMD configurations, where stations may be missing due to technical issues. Using simulations, the performance indicates that the method has strong potential for identifying photons, suffering at most 10[sup]−4 background contamination at 0.5 signal efficiency. Future studies will delve into how much that background contamination can be diminished.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE photons, extensive air showers, AugerPrime upgrade
Published in RUNG: 29.05.2025; Views: 354; Downloads: 5
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2. Estimation of muons on the surface and correlation with the muonic signal of AugerPrimeCarmina Perez Bertolli, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: This work focuses on estimating the muon density at ground level using simulations and investigating its correlation with the muonic signal recorded by the Water Cherenkov Detectors (WCDs) of the Pierre Auger Observatory. The study is motivated by the need to validate the estimation of the muonic signal in the WCDs. The methodology involves the development of a parameterization for the surface muon density based on simulated muon data from the Underground Muon Detector (UMD) of AugerPrime—an upgrade to the Pierre Auger Observatory. Our results indicate a negligible bias and a resolution better than 40 at energies above 10[sup]17.5 eV. Furthermore, we find a strong positive correlation between the estimated muon density and the simulated muonic signals in the WCDs.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, AugerPrime upgrade, muonic air-shower component
Published in RUNG: 29.05.2025; Views: 315; Downloads: 7
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3. Calibrating the Surface Scintillator Detector of AugerPrimePaul Filip, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: We present the methods used to calibrate the Surface Scintillator Detector of the Pierre Auger
Observatory. We describe how to obtain an accurate calibration of the scintillator by examining
peak and charge distributions of atmospheric muons. This is done whenever an extensive air
shower event measured by the Surface Detector is reconstructed. We also describe the work
towards an algorithm that uses a rate-based approach to calibrate the Surface Scintillator
Detectors independently.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, AugerPrime upgrade, detector calibration
Published in RUNG: 16.05.2025; Views: 366; Downloads: 5
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4. Improved calibration methods and reconstruction of the underground muon detector of the Pierre Auger ObservatoryJoaquín De Jesús, A. Abdul Halim, P. Abreu, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: As part of the upgrade of the Pierre Auger Observatory, known as AugerPrime, the Underground
Muon Detector is being deployed in the low-energy extension of the Surface Detector. It comprises
an array of 30 m[sup]2 plastic scintillator muon counters, buried 2.3 meters underground near the water-Cherenkov detectors, allowing for direct measurement of the muonic component of air showers in the energy range of 10[sup]16.5 − 10[sup]19 eV. To achieve an extended dynamic range, the detector operates in two modes: the binary mode, which is optimized for low muon densities, and the ADC mode, designed for high muon densities. In this contribution, we present the latest improvements to the calibration procedure of the ADC mode and to the data reconstruction of the binary mode. We assess their performance with simulations.
Keywords: ultra-high-energy cosmic rays (UHECRs), extensive air showers, Pierre Auger Observatory, AugerPrime upgrade, Auger underground muon detector (UMD), muonic air-shower component, detector calibration, data reconstruction
Published in RUNG: 30.04.2025; Views: 657; Downloads: 8
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5. Subluminal pulses in the surface-scintillator detectors of AugerPrimeTobias Schulze, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: In extensive air showers, the signals from the electromagnetic and muonic components typically span a few microseconds in scintillation detectors.
Neutrons are the only stable neutral hadrons over the timescale of air showers.
They lose energy exclusively through hadronic interactions and quasi-elastic scattering, which results in their high abundance at ground level.
These neutrons can produce delayed pulses in scintillation detectors, appearing up to several milliseconds after the primary shower signal.
This allows us to probe hadronic interactions in the development of air showers.
In this study, we characterize such subluminal pulses using the first measurements from the scintillator surface detectors of the AugerPrime upgrade of the Pierre Auger Observatory.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, AugerPrime upgrade
Published in RUNG: 28.03.2025; Views: 681; Downloads: 10
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6. A new view of UHECRs with the Pierre Auger ObservatoryDenise Boncioli, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution Abstract: In its Phase I, the Pierre Auger Observatory has led to several observations, driving the field of ultra- high-energy cosmic ray (UHECR) research over the last 20 years. Major achievements obtained so far include the unprecedented precise energy spectrum and its features, the observables linked to the UHECR mass composition and the distribution of arrival directions of the most energetic events. These results, together with the non-observation of high-energy neutrinos and photons, strongly disfavor the pre-Auger pure-proton paradigm.
In this talk, we will provide an overview on the main results of the Observatory, and describe possible astrophysical scenarios for their interpretation. The prospects of improving the current understanding about UHECR characteristics during the Phase II of the Observatory will be also shown.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE neutrinos, UHE photons, Auger Phase I, AugerPrime upgrade, Auger Phase II, UHECR mass composition, UHECR energy spectrum, UHECR anisotropy studies, UHECR astrophysical scenarios, UHECR data interpretation
Published in RUNG: 24.03.2025; Views: 665; Downloads: 5
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7. Simulations of antenna response for the Radio Detector of the Pierre Auger ObservatoryU. G. Giaccari, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2023, published scientific conference contribution Abstract: After more than 15 years of successful operation, the Pierre Auger Observatory is currently undergoing a major upgrade called AugerPrime. The aim is to study the mass composition of ultra-high-energy cosmic rays. Part of the upgrade program consists in installing a Short Aperiodic Loaded Loop Antenna (SALLA) atop each of the 1660 water-Cherenkov detectors.
To obtain an absolute calibration for the SALLA, the frequency and directionally dependent antenna response (or vector effective length) must be known. The characteristics of the SALLA depend on various parameters, most prominent is the considered frequency of reception and the antenna geometry. Moreover, the interaction with the structure elements and the presence of the ground has an impact. The measurement of the characteristics of the SALLA is a complex experimental effort. In this view, investigation by numerical antenna simulations provides an important and useful tool. In this contribution, we describe the method used to calculate the vector equivalent length of the SALLA with an advanced and widely used software for antenna simulations like the Numerical Electromagnetics Code (NEC).
Keywords: Pierre Auger Observatory, ultra-high-energy cosmic rays, extensive air showers, AugerPrime upgrade
Published in RUNG: 03.10.2024; Views: 1007; Downloads: 5
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8. With AugerPrime to the phase II of the Pierre Auger ObservatoryDaniele Martello, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution Abstract: AugerPrime, the upgrade of the Pierre Auger Observatory, is nearing completion and the Observatory is now prepared to collect physics data after the commissioning of the new components. The Pierre Auger Observatory has demonstrated, based on the data collected thus far, the existence of the cutoff in the spectrum with high accuracy. However, the origin of this cutoff remains incompletely understood. The upgraded Observatory is designed to address the unresolved questions regarding the nature of the cosmic ray flux cutoff thanks to its capability to disentangle the muon and electromagnetic components of extensive air showers. Furthermore, the measurement of the muon component at ground level can verify the accuracy of hadronic interaction models currently used. This presentation will provide an overview of the status of the Observatory and the accurate commissioning done before the start of the physics run. Furthermore, we will present the initial data from Phase II data mainly dedicated to proving the continuity of operation of the Observatory from Phase I to Phase II.
Keywords: Pierre Auger Observatory, ultra-high energy cosmic rays, AugerPrime detector upgrade, Pierre Auger data
Published in RUNG: 24.01.2024; Views: 3989; Downloads: 13
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9. Latest results from the searches for ultra-high-energy photons and neutrinos at the Pierre Auger ObservatoryMarcus Niechciol, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution Abstract: The Pierre Auger Observatory is the largest air-shower experiment in the world, offering an unprecedented exposure not only to ultra-high-energy (UHE, �>10^17 eV) cosmic rays, but also to UHE neutral particles, specifically photons and neutrinos. Since the beginning of data taking almost 20 years ago, a number of searches for UHE photons and neutrinos using the different detector systems of the Observatory have been carried out. These searches led to some of the most stringent upper limits on the diffuse—i.e., direction-independent, unresolved—fluxes of photons and neutrinos in the UHE regime. These limits severely constrain current models for the origin of UHE cosmic rays and underline the capabilities of the Pierre Auger Observatory and its leading role in the context of multimessenger astronomy at the highest energies. In this contribution, we give an overview of the current activities concerning searches for UHE photons and neutrinos in the data from the Pierre Auger Observatory. The latest results of the searches for diffuse fluxes of photons and neutrinos will be shown. Furthermore, the follow- up searches for UHE photons
and neutrinos in association with transient events, such as gravitational wave events, will be summarized. In addition, future perspectives in view of the ongoing AugerPrime detector upgrade will be discussed, which will further improve the sensitivity of the Pierre Auger Observatory to neutral particles at the highest energies.
Keywords: Pierre Auger Observatory, ultra-high energy cosmic rays, AugerPrime, multimessenger astronomy
Published in RUNG: 24.01.2024; Views: 3140; Downloads: 11
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10. Deep-learning-based cosmic-ray mass reconstruction using the water-Cherenkov and scintillation detectors of AugerPrimeNiklas Langner, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution Abstract: At the highest energies, cosmic rays can be detected only indirectly by the extensive air showers they create upon interaction with the Earth’s atmosphere. While high-statistics measurements of the energy and arrival directions of cosmic rays can be performed with large surface detector arrays like the Pierre Auger Observatory, the determination of the cosmic-ray mass on an event-by-event basis is challenging. Meaningful physical observables in this regard include the depth of maximum of air-shower profiles, which is related to the mean free path of the cosmic ray in the atmosphere and the shower development, as well as the number of muons that rises with the
number of nucleons in a cosmic-ray particle.
In this contribution, we present an approach to determine both of these observables from combined measurements of water-Cherenkov detectors and scintillation detectors, which are part of the AugerPrime upgrade of the Observatory. To characterize the time-dependent signals of the two detectors both separately as well as in correlation to each other, we apply deep learning techniques. Transformer networks employing the attention mechanism are especially well-suited for this task. We present the utilized network concepts and apply them to simulations to determine the precision of the event-by-event mass reconstruction that can be achieved by the combined measurements of the depth of shower maximum and the number of muons.
Keywords: Pierre Auger Observatory, ultra-high energy cosmic rays, muons, extensive air showers, surface detectors, AugerPrime, deep learning techiniques
Published in RUNG: 23.01.2024; Views: 2224; Downloads: 9
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