21. 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, published scientific conference contribution Abstract: 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.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHECR arrival directions, large-scale dipolar anisotropy
Published in RUNG: 28.03.2025; Views: 290; Downloads: 6
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22. 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, published scientific conference contribution Abstract: 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.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, air shower maximum depth
Published in RUNG: 28.03.2025; Views: 280; Downloads: 5
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23. 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, published scientific conference contribution Abstract: 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.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, extensive air showers, hadronic interactions
Published in RUNG: 28.03.2025; Views: 288; Downloads: 7
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27. Understanding the nanoscale organization of natural killer cell receptor NKp30 at the singlemolecule levelBarbora Kalouskova, Ondřej Skořepa, Jan Bláha, Lucia Cikatricisová, Ario De Marco, Ondřej Vaněk, Mario Brameshuber, 2024, published scientific conference contribution abstract Keywords: advanced microscopy, nanobodies, fluorescent proteins
Published in RUNG: 24.03.2025; Views: 266; Downloads: 0
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28. 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: 321; Downloads: 4
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29. 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, published scientific conference contribution Abstract: 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.
Keywords: 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
Published in RUNG: 24.03.2025; Views: 291; Downloads: 6
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30. 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, published scientific conference contribution Abstract: 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.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE photon search, diffuse photon flux
Published in RUNG: 24.03.2025; Views: 262; Downloads: 6
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