1. Search for the anomalous events detected by ANITA using the Pierre Auger ObservatoryA. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, original scientific article Abstract: A dedicated search for upward-going air showers at zenith angles exceeding 110° and energies E>0.1 EeV has been performed using the Fluorescence Detector of the Pierre Auger Observatory. The search is motivated by two “anomalous” radio pulses observed by the ANITA flights I and III that appear inconsistent with the standard model of particle physics. Using simulations of both regular cosmic-ray showers and upward-going events, a selection procedure has been defined to separate potential upward-going candidate events and the corresponding exposure has been calculated in the energy range [0.1–33] EeV. One event has been found in the search period between January 1, 2004, and December 31, 2018, consistent with an expected background of 0.27 ± 0.12 events from misreconstructed cosmic-ray showers. This translates to an upper bound on the integral flux of (7.2±0.2)×10[sup]−21 cm[sup]−2 sr[sup]−1 y[sup]−1 and (3.6±0.2)×10−20 cm[sup]−2 sr[sup]−1 y[sup]−1 for an E[sup]−1 and E[sup]−2 spectrum, respectively. An upward-going flux of showers normalized to the ANITA observations is shown to predict over 34 events for an E[sup]−3 spectrum and over 8.1 events for a conservative E[sup]−5 spectrum, in strong disagreement with the interpretation of the anomalous events as upward-going showers.
Keywords: ultra-high-energy cosmic rays, extensive air showers, upward-going air showers, Pierre Auger Observatory, Fluorescence Detector, anomalous ANITA events
Published in RUNG: 28.03.2025; Views: 440; Downloads: 5
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2. Inference of the Mass Composition of Cosmic Rays with Energies from 10[sup]18.5 to 10[sup]20 eV Using the Pierre Auger Observatory and Deep LearningA. Abdul Halim, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, original scientific article Abstract: We present measurements of the atmospheric depth of the shower maximum Xmax,
inferred for the first time on an event-by-event level using the Surface Detector
of the Pierre Auger Observatory. Using deep learning, we were able to extend
measurements of the Xmax distributions up to energies of 100 EeV (10[sup]20 eV),
not yet revealed by current measurements, providing new insights into the mass
composition of cosmic rays at extreme energies.
Gaining a 10-fold increase in statistics compared to the Fluorescence Detector data,
we find evidence that the rate of change of the average Xmax with the logarithm
of energy features three breaks at 6.5 ± 0.6 (stat) ± 1 (sys) EeV,
11 ± 2 (stat) ± 1 (sys) EeV, and 31 ± 5 (stat) ± 3 (sys) EeV, in the vicinity to the three
prominent features (ankle, instep, suppression) of the cosmic-ray flux.
The energy evolution of the mean and standard deviation of the measured Xmax
distributions indicates that the mass composition becomes increasingly heavier
and purer, thus being incompatible with a large fraction of light nuclei between
50 EeV and 100 EeV.
Keywords: ultra-high-energy cosmic rays (UHECRs), extensive air showers, Pierre Auger Observatory, UHECR mass composition, depth of the shower maximum, fluorescence detector, surface detector, deep learning
Published in RUNG: 20.01.2025; Views: 732; Downloads: 5
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3. Measurement of the depth of maximum of air-shower profiles with energies between ▫$10^{18.5} and 10^{20}$▫ eV using the surface detector of the Pierre Auger Observatory and deep learningA. Abdul Halim, P. Abreu, M. Aglietta, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, original scientific article 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: 772; Downloads: 8
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4. Operations of the Pierre Auger ObservatoryR. Caruso, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2022, published scientific conference contribution Abstract: The construction of the first stage of the Pierre Auger Observatory, designed for research of ultra-high energy cosmic rays, began in 2001 with a prototype system. The Observatory has been collecting data since early 2004 and was completed in 2008. The Observatory is situated at 1400 m above sea level near Malargüe, (Mendoza province) in western Argentina, covering a vast plain of 3000 squared km, known as the Pampa Amarillo. The Observatory consists of a hybrid detector, in which there are 1660 water-Cherenkov stations, forming the Surface Detector (SD) and 27 peripheral atmospheric fluorescence telescopes, comprising the Fluorescence Detector (FD). Over time, the Auger Observatory has been enhanced with different R&D prototypes and is recently being to an important upgrade called AugerPrime. In the present contribution, the general operations of the SD and FD will be described. In particular the FD shift procedure - executable locally in Malargüe or remotely by teams in control rooms abroad within the Collaboration - and the newly SD shifts (operating since 2019) will be explained. Additionally, the SD and FD maintenance campaigns, as well as the data taking and data handling at a basic level, will be reported
Keywords: Pierre Auger Observatory, AugerPrime, indirect detection, fluorescence detectors, surface detectors, ultra-high energy, cosmic rays, detector operation
Published in RUNG: 04.10.2023; Views: 2696; Downloads: 5
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5. Constraints on BSM particles from the absence of upward-going air showers in the Pierre Auger ObservatoryBaobiao Yue, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, published scientific conference contribution Abstract: The Fluorescence Detector (FD) of the Pierre Auger Observatory has a large exposure to search for upward-going showers. Constraints have been recently obtained by using 14 years of FD data searching for upward-going showers in the zenith angle range [110◦, 180◦]. In this work, we translate these bounds to upper limits of a possible flux of ultra high energy tau-leptons escaping from the Earth into the atmosphere. Such a mechanism could explain the observation of "anomalous pulses" made by ANITA, that indicated the existence of upward-going air showers with energies above 10[sup]17 eV. As tau neutrinos would be absorbed within the Earth at the deduced
angles and energies, a flux of upward-going taus could only be resulted from an unknown type of ultra high energy Beyond Standard Model particle penetrating the Earth with little attenuation, and then creating tau-leptons through interactions within a maximum depth of about 50 km before exiting. We test classes of such models in a generic way and determine upper flux limits of ultra high energy BSM particles as a function of their unknown cross section with matter.
Keywords: ultra-high energy cosmic rays, Pierre Auger Observatory, fluorescence detector, upward-going air showers, Beyond Standard Model particles
Published in RUNG: 26.09.2023; Views: 2313; Downloads: 33
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6. Cosmic Ray Shower Profile Track Finding for Telescope Array Fluorescence DetectorsJon Paul Lundquist, 2016, published scientific conference contribution Abstract: A simple cosmic ray track finding pattern recognition analysis (PRA) method for fluorescence detectors (FD) has been developed which significantly improves Xmax resolution and its dependence on energy. Events which have a clear rise and fall in the FD view contain information on Xmax that can be reliably reconstructed. Shower maximum must be extrapolated for events with Xmax outside the field of view of the detector, which creates a systematic dependence on the fitting function. The PRA method is a model and detector independent approach to removing
these events, by fitting shower profiles to a set of triangles and applying limits on the allowable geometry.
Keywords: UHECR, cosmic rays, fluorescence detector, track finding, pattern recognition
Published in RUNG: 29.04.2020; Views: 4195; Downloads: 117
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7. TA Anisotropy SummaryK. Kawata, Jon Paul Lundquist, 2019, published scientific conference contribution Abstract: The Telescope Array (TA) is the largest ultra-high-energy cosmic-ray (UHECR) detector in the northern hemisphere. It consists of an array of 507 surface detectors (SD) covering a total 700 km^2 and three fluorescence detector stations overlooking the SD array. In this proceedings, we summarize recent results on the search for directional anisotropy of UHECRs using the latest dataset collected by the TA SD array. We obtained hints of the anisotropy of the UHECRs in the northern sky from the various analyses.
Keywords: cosmic radiation, UHE detector, fluorescence detector, surface, Telescope Array Experiment, anisotropy, experimental results
Published in RUNG: 28.04.2020; Views: 4697; Downloads: 82
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8. The energy spectrum of cosmic rays above 1017.2 eV measured by the fluorescence detectors of the Telescope Array experiment in seven yearsR.U. Abbasi, Jon Paul Lundquist, 2016, original scientific article Abstract: The Telescope Array (TA) experiment is the largest detector to observe ultra-high-energy cosmic rays in the northern hemisphere. The fluorescence detectors at two stations of TA are newly constructed and have now completed seven years of steady operation. One advantage of monocular analysis of the fluorescence detectors is a lower energy threshold for cosmic rays than that of other techniques like stereoscopic observations or coincidences with the surface detector array, allowing the measurement of an energy spectrum covering three orders of magnitude in energy. Analyzing data collected during those seven years, we report the energy spectrum of cosmic rays covering a broad range of energies above 10^17.2eV measured by the fluorescence detectors and a comparison with previously published results.
Keywords: Cosmic rays, Ultra-high energy, Fluorescence detector, Energy spectrum, Ankle, GZK cutoff
Published in RUNG: 27.04.2020; Views: 4113; Downloads: 0
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9. Improvements to aerosol attenuation measurements at the Pierre Auger ObservatoryMax Malacari, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2017, published scientific conference contribution Keywords: aerosol attenuation measurements, Pierre Auger Observatory, fluorescence detector
Published in RUNG: 19.02.2018; Views: 6236; Downloads: 173
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10. Automated procedures for the Fluorescence Detector calibration at the Pierre Auger ObservatoryGaetano Salina, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Darko Veberič, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, 2015, published scientific conference contribution Abstract: The quality of the physics results, derived from the analysis
of the data collected at the Pierre Auger Observatory depends
heavily on the calibration and monitoring of the components of
the detectors. It is crucial to maintain a database containing complete information on the absolute calibration of all
photomultipliers and their time evolution. The low rate of the
physics events implies that the analysis will have to be made
over a long period of operation. This requirement imposes a
very organized and reliable data storage and data management
strategy, in order to guarantee correct data preservation and
high data quality. The Fluorescence Detector (FD) consists of
27 telescopes with about 12,000 phototubes which have to be
calibrated periodically. A special absolute calibration system
is used. It is based on a calibrated light source with a
diffusive screen, uniformly illuminating photomultipliers
of the camera. This absolute calibration is performed every few
years, as its use is not compatible with the operation of the
detector. To monitor the stability and the time behavior,
another light source system operates every night of data
taking. This relative calibration procedure yields more than
2×10[sup]4 raw files each year, about 1 TByte/year. In this
paper we describe a new web-interfaced database architecture
to manage, store, produce and analyse FD calibration data.
It contains the configuration and operating parameters of the
detectors at each instant and other relevant functional
parameters that are needed for the analysis or to monitor
possible instabilities, used for the early discovery of
malfunctioning components. Based on over 10 years of
operation, we present results on the long term performance
of FD and its dependence on environmental variables. We also
report on a check of the absolute calibration values by
analysing the signals left by stars traversing the FD field of
view.
Keywords: Pierre Auger Observatory, Fluorescence Detector, detector calibration and monitoring, automated calibration procedure
Published in RUNG: 03.03.2016; Views: 5739; Downloads: 215
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