21. Highlights from the Auger Engineering Radio ArrayBjarni Pont, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The Auger Engineering Radio Array (AERA) at the Pierre Auger Observatory is an array of 153 radio-antenna stations that measure the 30−80 MHz radio emission produced in extensive air showers in the energy range between 0.1 and 10 EeV. It has been taking data for over a decade. In this contribution, we present the recent results of AERA. We show the measurements of the depths of the shower maxima (Xmax) using the radio footprint and using interferometry, demonstrating compatibility and competitiveness with the established fluorescence detection method. We also show the measurement of the stability of the radio signal over close to a decade determined using the Galactic radio background as a calibration source, demonstrating that a radio detector can be used to lower systematic uncertainties on the energy scale of, for example, fluorescence and water-Cherenkov detectors.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, radio emission
Objavljeno v RUNG: 28.03.2025; Ogledov: 693; Prenosov: 6
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22. Mass composition of ultra-high-energy cosmic rays at the Pierre Auger ObservatoryThomas Fitoussi, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: For the past 20 years, the Pierre Auger Observatory has collected the largest dataset of
ultra-high-energy cosmic rays (UHECRs) ever achieved using a hybrid detector. The study
of this dataset has led to numerous unexpected discoveries that enhance our understanding
of the origins of UHECRs. One of the key points in this study is their mass composition.
In this work, we will present the most recent results regarding the mass composition of UHECRs at the Pierre Auger Observatory. In particular, we will focus on the measurement of the depth
of the maximum of air-shower profiles, denoted as Xmax . This determination has been achieved through both direct measurements from the Fluorescence Detector data and the application of machine learning for estimating Xmax on an event-by-event basis using the Surface Detector data. The latter has allowed us to extend the measurement to energies up
to 100 EeV and indicates a correlation between changes in composition and three features
of the energy spectrum (ankle, instep, steepening). Moreover, the results provide evidence
of a heavy and nearly pure primary beam for energies greater than 50 EeV that is independent
of the hadronic interaction model. The implications of these findings for astrophysics and
for modelling hadronic interactions will be discussed.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, UHECR mass composition
Objavljeno v RUNG: 28.03.2025; Ogledov: 656; Prenosov: 11
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23. Testing the declination dependency of the spectrum measured by the Pierre Auger ObservatoryDiego Ravignani, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The distribution of the arrival directions of cosmic rays observed by the Pierre Auger Observatory has a dipolar component that implies a flux dependence on declination. Previously, we showed that the spectrum built from events arriving with a zenith angle less than 60° is qualitatively consistent with the dipole. In this work, we go one step further and show that the Auger spectrum cannot reject the hypothesis of a declination-independent flux. By using events of up 80°, we extend the previous survey from +25° of declination to +45°, thus covering 85% of the sky.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHECR arrival directions, large-scale dipolar anisotropy
Objavljeno v RUNG: 28.03.2025; Ogledov: 688; Prenosov: 10
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24. Measuring the proton-proton interaction cross section with hybrid data of the Pierre Auger ObservatoryOlena Tkachenko, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The depth of the maximum of an air shower development, Xmax, as observed with fluorescence telescopes, is among the most sensitive observables for studying the interaction characteristics and primary composition of ultra-high-energy cosmic rays. However, precise measurement of the interaction cross section remains challenging, as standard analyses often rely on assumptions about the composition, which are closely tied to the validity of specific hadronic interaction models. In this work, we discuss a method for the simultaneous estimation of the proton-proton interaction cross section and primary mass composition, addressing the limitations of separate measurements. The inclusion of the Xmax scale into the fit further accounts for systematic uncertainties in the data and theoretical uncertainties in particle production. The performance of the method is evaluated using simulations that include detector responses under realistic conditions and with a particular focus on assessing the systematic uncertainties of the fit.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, air shower maximum depth
Objavljeno v RUNG: 28.03.2025; Ogledov: 628; Prenosov: 11
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25. Overview of hadronic interaction studies at the Pierre Auger ObservatoryJakub Vícha, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The combination of fluorescence and surface detectors at the Pierre Auger Observatory offers unprecedented precision in testing models of hadronic interactions at center-of-mass energies around 70 TeV and beyond. However, for some time, discrepancies between model predictions and measured air-shower data have complicated efforts to accurately determine the mass composition of ultra-high-energy cosmic rays. A key inconsistency is the deficit of simulated signals compared to those measured with the surface detectors, typically interpreted as a deficit in the muon signal generated by the hadronic component of simulated showers.
Recently, a new global method has been applied to the combined data from the surface and fluorescence detectors at the Pierre Auger Observatory. This method simultaneously determines the mass composition of cosmic rays and evaluates variations in the simulated depth of the shower maximum and hadronic signals on the ground. The findings reveal not only the alleviated muon problem but also show that all current models of hadronic interactions predict depths of the shower maximum that are too shallow, offering new insights into deficiencies in these models from a broader perspective.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, hadronic interactions
Objavljeno v RUNG: 28.03.2025; Ogledov: 654; Prenosov: 9
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26. 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, objavljeni znanstveni prispevek na konferenci Opis: 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.
Ključne besede: 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
Objavljeno v RUNG: 24.03.2025; Ogledov: 715; Prenosov: 5
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27. Searches for UHE neutrinos and upward-going showers at the Pierre Auger ObservatoryJaime Alvarez-Muňiz, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The Pierre Auger Observatory, as a key actor in multi-messenger astronomy, is playing a crucial role in searching for and following-up cosmic phenomena across different channels. Data from the Observatory have been utilized for nearly 20 years to search for showers induced by Ultra-High-Energy (UHE) neutrinos with energies exceeding 0.1 EeV. Neutrino-induced showers at high zenith angles are likely to develop deep in the atmosphere, resulting in a significant electromagnetic component that distinguishes them from the cosmic-ray background. This enables the identification of candidate events from both neutrinos interacting in the atmosphere and Earth-skimming τ neutrinos. Searches have been conducted for both diffuse and point sources using data collected by the Surface Detector, a large array of over 1660 water-Cherenkov stations spread over an area of 3000 square km. Additionally, the Fluorescence Detector consisting of 27 telescopes has been employed to search for upward-developing air showers, as predicted by several interpretations of the 'anomalous' events detected by the ANITA detector. In this contribution, we summarize the main results obtained in these searches and discuss their astrophysical implications.
Ključne besede: ulti-messenger astronomy, ultra-high-energy neutrino search, down-going neutrinos, Earth-skimming τ neutrinos, search for upward-developing air showers, ANITA detector, Pierre Auger Observatory
Objavljeno v RUNG: 24.03.2025; Ogledov: 653; Prenosov: 7
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28. Searches for ultra-high-energy photons with the Pierre Auger ObservatoryNicolás González, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: Ultra-high-energy (UHE, E≳10[sup]17 eV) photons are expected to originate from the interaction of UHE cosmic rays with background radiation fields, as well as from more exotic processes like the decay of hypothetical super-heavy dark matter particles. UHE photons produced at cosmic-ray sources are key ingredients for enhancing our multimessenger understanding of the cosmic-ray acceleration and transient phenomena. Pierre Auger Observatory, designed to investigate UHE cosmic rays, offers unparalleled sensitivity to UHE photons. In this contribution, we present recent results of photon searches above 10[sup]16.7 eV obtained with data collected prior to the upgrade of the Observatory. Additionally, we discuss directional and follow-up searches conducted in coincidence with gravitational wave events detected by LIGO/Virgo, highlighting the role of the Observatory in advancing multi-messenger astronomy at the highest energies.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE photon search, diffuse photon flux
Objavljeno v RUNG: 24.03.2025; Ogledov: 660; Prenosov: 12
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29. The Pierre Auger Observatory and physics beyond the standard modelR. Aloisio, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: The Pierre Auger Observatory, the world’s largest cosmic ray detector, plays a pivotal role in exploring the frontiers of physics beyond the standard model of particle physics. By the observation of ultra-high energy cosmic rays, Auger provides critical insights into two major scenarios: super heavy dark matter and Lorentz invariance violation. Super heavy dark matter, hypothesized to originate in the early universe, offers a compelling explanation for the dark matter problem and is constrained by Auger through searches for photons and neutrinos resulting from its decay. Lorentz invariance violations, motivated by quantum gravity theories implying deviations from fundamental symmetries, are probed by Auger through alterations of the particle dispersion relation and the energy thresholds of their interactions with astrophysical photons backgrounds.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE neutrinos, UHE photons
Objavljeno v RUNG: 24.03.2025; Ogledov: 626; Prenosov: 8
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30. Large-scale cosmic-ray anisotropies measured by the Pierre Auger ObservatoryEsteban Roulet, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, objavljeni znanstveni prispevek na konferenci Opis: An update of the measurements of large-scale anisotropies in the arrival directions of ultra high-energy cosmic rays detected at the Pierre Auger Observatory is presented. The established dipolar anisotropy in right ascension has now reached a significance of 6.8σ when considering all energies above 8 EeV and 5.7 σ when only considering energies between 8 and 16 EeV. The 3D dipole amplitude and direction are reconstructed in four different energy bins above 4 EeV. At energies above 8 EeV it points more than 100∘ away from the Galactic centre, providing evidence that the anisotropy observed is of extragalactic origin. An analysis allowing for both dipolar and quadrupolar anisotropies finds qualitatively similar dipole components and no significant quadrupole components. The results for the angular power spectrum are shown, demonstrating that no other statistically significant multipoles are present. The equatorial dipole components are presented down to 0.03 EeV using a trigger which has been optimized for low energies. We find no significant departures from isotropic expectations below 8 EeV, although below 2 EeV the phases appear to be consistently aligned with the right ascension of the Galactic centre. Finally, model predictions based on source emission scenarios obtained in the combined fit of spectrum and composition data above 0.6 EeV are discussed and compared with observations.
Ključne besede: ultra-high-energy cosmic rays, Pierre Auger Observatory, large scale anisotropies
Objavljeno v RUNG: 24.03.2025; Ogledov: 676; Prenosov: 13
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