The large-scale dipole structure in the arrival directions of ultra-high-energy cosmic rays above 8 EeV observed by the Pierre Auger Collaboration is a well-established anisotropy measurement. This anisotropy is understood to be of extragalactic origin, as the maximum of the dipolar component is located $\sim115^\circ$ away from the Galactic Center. Cosmic rays interact with background...
Galactic Cosmic Rays (GCR) are a common background for measurements of solar activity. Measurements of long-lived isotopes in meteoritic data indicate the GCR flux has been constant for several Myr, but these measurements have relative systematic uncertainties exceeding 30%. By using deep-ice carbon-14 extracted from the Antarctic ice sheet at Dome C, we can reconstruct changes in the GCR...
Ground-based full-sky studies of the angular distribution of arrival directions of ultra-high-energy cosmic rays require combining data from different observatories, such as the Pierre Auger Observatory (Auger) and the Telescope Array (TA), because no single array can cover all declinations. A working group comprising members from the Auger and TA collaborations has been tasked with performing...
The GELATICA experiment (GEorgian Large-area Angle and TIme Coincidence Array) comprises several cosmic ray detector arrays located in two cities in Georgia. These observatories are designed to detect Extensive Air Showers (EAS) with high-precision timing and determine the arrival directions of cosmic ray showers. GELATICA is part of the CREDO collaboration (Cosmic Ray Extremely Distributed...
Cosmic ray secondaries produced in Earth's atmosphere present a dominant background in many experiments and equipment benchmarking efforts, especially for those requiring high levels of sensitivity. For such experiments and equipment testing, underground research facilities are an essential asset. These facilities are sought after due to the rock overburden, which provides natural protection...
We present an update on the arrival-direction analyses conducted on intermediate angular scales using the complete Phase I data of the Pierre Auger Observatory up to the end of $2022$ with a total exposure of $135,000\,\text{km}^2\,\text{sr}\,\text{yr}$. We will show the arrival-direction distribution of the ultra-high-energy cosmic rays along the supergalactic plane above...
The IceAct telescopes are Imaging Air Cherenkov telescopes installed as part of the IceCube Neutrino Observatory at the geographic South Pole. They consist of a 61 pixel camera and are small and robust to withstand the harsh environmental conditions. IceAct detects Cherenkov light produced by cosmic-ray particles with energies above approximately 10TeV interacting inside the atmosphere, which...
Observations made by the High Resolution Fly's Eye detector in stereoscopic fluorescent mode revealed correlations between arrival directions of ultra-high-energy cosmic rays and positions of distant BL Lac type objects (Gorbunov et al. 2004, Abbasi et al. 2005). They implied the existence of non-deflected particles travelling for cosmological distances, which was hard to explain within...
The Wide Field-of-view Cherenkov Telescope Array (WFCTA) at the Large High Altitude Air Shower Observatory (LHAASO) detects cosmic-ray-induced air showers by measuring Cherenkov light produced by secondary particles in the atmosphere. Precise reconstruction of primary cosmic-ray properties necessitates rigorous calibration of atmospheric attenuation effects and telescope response. This study...
Simulations of the cosmic-ray (CR) anisotropy down to TeV energies are presented, using turbulence parameters consistent with those inferred from observations of the interstellar medium. We compute the angular power spectra $C_{\ell}$ of the CR anisotropy obtained from the simulations. We show that the power spectrum depends on CR energy, and that it is sensitive to the location of the...
The cosmic-ray anisotropy is now used to help unveil nearby cosmic-ray accelerators and their local propagation environment. The LHAASO-WCDA experiment is composed of three water ponds. It covers a total detection area of 87000 m^2, which makes it an ideal detector for measuring the cosmic-ray anisotropy from hundreds of GeV to ∼PeV. In this talk, we present the measurements of the cosmic-ray...
Paleo-detectors offer a unique opportunity to probe the long-term history of cosmic ray-flux, potentially revealing evidence of nearby supernovae and other high-energy astrophysical events. This technique relies on the persistent damage tracks left in natural minerals by nuclear recoils induced by cosmic ray secondaries, providing an integrated record of particle flux over geological...
The evolution of cosmic ray large-scale anisotropy (LSA) with energy is essential for studying the origins of LSA, which are closely related to the origins and propagation of cosmic rays. However, due to both the low flux of cosmic rays and inconsistency among experiments, the observations of LSA above one hundred TeV are subject to large uncertainties. We utilize over three years data from...
With the knowledge and statistical precision derived from two decades of measurement, the Pierre Auger Observatory has significantly deepened our understanding of ultra-high-energy cosmic rays while unearthing an increasingly complex astrophysical landscape and exposing tensions with hadronic interaction models. The field now demands the mass of individual cosmic-ray primaries as an observable...
The anisotropy in different mass components of cosmic rays can provide stringent constraints on theoretical models regarding the origin of anisotropy, such as the distribution of sources, the propagation of cosmic rays, and the local magnetic field environment. This is particularly significant in the high-energy range, from hundreds of TeV to PeV, where the anisotropy exhibits considerable...
The Pierre Auger Observatory upgrade, AugerPrime, is a multi-hybrid system designed to improve the sensitivity and precision of ultra-high-energy cosmic ray measurements. It includes scintillator detectors positioned both atop the enhanced Water-Cherenkov detectors and buried nearby for direct muon measurements, along with radio and fluorescence detectors. In this contribution, we present an...
We present preliminary results on an updated full-sky analysis of the cosmic-ray arrival direction distribution with data collected by the High-Altitude Water Cherenkov (HAWC) Observatory and IceCube Neutrino Observatory with complementary field of views covering a large fraction of the sky. This study extends the energy range to higher energies. The HAWC Observatory, located at 19°N has...
Identification of primary cosmic rays on an event-by-event basis is a much-desired capability of cosmic-ray observatories. Several cosmic-ray air-shower experiments use so-called photon tags for gamma/hadron primary particle discrimination. These photon tag variables are derived from the total signals measured by an array of detectors and are correlated with the total number of muons in the...
We present a measurement for large-scale anisotropy of pure protons with the Large High Altitude Air Shower Observatory. We analyze the data collected from the full array of KM2A in three years' operation. We selected the proton data set using a cut on the muonic and electron magnetic components ratio, similar to the gamma/background discrimination technique in KM2A. The purity of the proton...
The interaction of cosmic rays with celestial bodies such as the Moon or the Sun produces a shadow in the arrival direction distribution of the cosmic rays reaching the Earth. Such deficits from an isotropic flux have been observed by astroparticle observatories below energies of $10^{15}\,$eV. Above this energy, measurements were limited due to the low number of events as a result of the...
Cosmic ray anisotropy at various scales has been observed over the past decade by multiple experiments in both the Northern and Southern Hemispheres. The GRAPES-3 experiment, located at 11.4 degrees North, is well positioned to study a significant portion of both hemispheres, covering nearly 70 percent of the sky at TeV energies. Observing large-scale anisotropy is particularly challenging...
Unveiling the sources of ultra-high energy cosmic rays remains one of the main challenges of high-energy astrophysics. Measurements of anisotropies in their arrival directions are key to identifying their sources, yet magnetic deflections obscure direct associations. In this work, we reconstruct the sky regions of origin of the highest-energy cosmic-ray events detected by the Pierre Auger...
The intensity of Galactic cosmic rays in the arrival directions is highly isotropic, however, many cosmic ray experiments have observed weak anisotropies of various angular sizes. In this work, we report the observation of the medium-scale structures with the square kilometer array of the Large High Altitude Air Shower Observatory (LHAASO-KM2A). We have found that the positions of the excess...
Astrophysical flares are one of the possible prominent source classes of ultra-high-energy (UHE, E > 10^17 eV) cosmic rays, which can be detected by recording clusters of extensive air showers in arrays of detectors. The search for sources of neutral particles offers distinct advantages over searching for sources of charged particles, as the former traverse cosmic distances undeflected by...
Terrestrial Gamma-ray Flashes (TGFs) are intense bursts of gamma rays originating in Earth's atmosphere, often associated with lightning activity during thunderstorms. These flashes are believed to result from relativistic runaway electron avalanches triggered by strong electric fields. In this study, we analyze multiple TGFs observed at the Telescope Array Surface Detectors site using a suite...
The large high altitude air shower observatory has comprehensively measured the information of the air showers of very high energy cosmic rays. Several important results regarding the air shower already have been published. A cosmic ray mass independent energy reconstruction method has been proposed by combining the muon content and the electromagnetic particles (or Cherenkov light) of the air...
The muon puzzle, the excess of the number of muons with respect to simulations in ultra-high energy cosmic rays, was initially reported by the Pierre Auger Observatory in 2015 and confirmed by more recent analyses. This suggests that forward meson production in hadronic interactions is not fully understood. Most scenarios to solve this issue predict less production of forward neutral pions and...
Since 2014, the Pierre Auger Observatory has exploited a dedicated trigger, and its very high time resolution to do studies on ELVES and harvest record samples of multiple ELVES using the Fluorescence Detector (FD). In 2017, after extending the readout of trace lengths to 0.9 ms, we started observing other types of light transients from the base of the ionosphere, such as HALOS, which...
The connection between cosmic ray air showers and thunderclouds has become a major research topic in recent years in high-energy atmospheric physics.
One of the open questions is whether cosmic rays are involved in triggering a “gamma-ray glow”. A “gamma-ray glow” is a phenomenon in which gamma-ray increases for tens of seconds to several minutes during the passage of thunderclouds. A strong...
Precise knowledge of high energy hadronic interaction is an important key to understand air shower development. The LHCf experiment measures neutral particles such as photons, neutral pions, and neutrons, produced in the very forward region of LHC collisions, which contribute to the air shower development. Since the LHC start, LHCf performed many operations with pp collisions at several...
Thunderstorms are intense localized convective weather phenomena, typically accompanied by strong lightning, high-energy electromagnetic radiation, and dramatic variations in atmospheric electric fields. Terrestrial Gamma-ray Flashes (TGFs) and Thunderstorm Ground Enhancements (TGE) represent high-energy radiation phenomena generated during thunderstorms. The extreme electric field...
The hadron production in the simulation of extensive air showers is a long standing problem and the origin of large uncertainties in the reconstruction of the mass of the high energy primary cosmic rays. Hadronic interaction models re-tuned after early LHC data give more consistent results among each other compared to the first generation of models, but still can't reproduce extended air...
We present a new approach to modeling cosmic ray (CR) interactions, which relies on a very basic interaction picture, while using a reasonable and transparent formalism, in the framework of the Reggeon Field Theory. Our main motivation is to provide a new CR interaction model characterized by relatively transparent physics, sufficient parameter flexibility, and high computational efficiency,...
Downward TGFs are sub-millisecond bursts of MeV gamma rays produced in thunderclouds. According to the Relativistic Runaway Electron Avalanche model, gamma rays are produced, via bremsstrahlung, from electron cascades activated by a relativistic “seed” electron. It is not clear what mechanism is responsible for the acceleration of electrons to relativistic energies in electric discharges. To...
We introduce a set of new multiparticle production variables derived from the energy spectrum of secondary hadrons in ultra-high-energy proton-air interactions. The distributions of these variables can be measured within the phase space accessible to particle detectors in accelerator experiments and are highly dependent on the hadronic interaction model. Furthermore, we demonstrate a precise,...
It is commonly understood that the atmosphere protects the Earth from harmful radiation. However, the atmosphere not only absorbs the vast energy of galactic cosmic rays but also serves as a source of particle generation, producing significant fluxes of electrons, gamma rays, and neutrons. These particles are generated through several mechanisms, including relativistic runaway electron...
Measuring proton-proton interaction cross-sections at center-of-mass energies above 40 TeV remains a significant challenge in particle physics. The Pierre Auger Observatory provides a unique opportunity to study the interactions at the highest energies through the distribution of the depth of maximum shower development ($X_\mathrm{max}$) observed by its Fluorescence Detector. In previous...
GRANDProto300 (GP300) is a prototype array of the GRAND experiment, designed to validate the technique of autonomous radio-detection of astroparticles by detecting cosmic rays with energies between $10^{17}$-$10^{18.5}$ eV. This observation will further enable the study of the Galactic-to-extragalactic source transition region. Since November 2024, 46 out of 300 antennas have been operational...
The accurate determination of the absolute energy scale in cosmic ray
measurements is both a challenging and fundamentally important task. In this contribution, we present how measurements of radio pulses from extensive air showers with the Auger Engineering Radio Array, combined with per-event simulations of radio emission using the CoREAS extension of CORSIKA, allow us to determine the...
The combined data of fluorescence and surface detectors of the Pierre Auger Observatory has recently provided the strongest constraints on the validity of predictions from current models of hadronic interactions [Phys. Rev. D 109 (2024) 102001]. The unmodified predictions of these models on the depth of shower maximum (Xmax) and the hadronic part of the ground signal are unable to accurately...
In the physics of Ultra-High Energy Cosmic Rays (UHECR), there is a well-established disagreement between the predictions of the last generation of hadronic interaction models and the measurement of the number of muons. Lately, there have also been hints of a disagreement on the scale of shower maxima. The MOdified Characteristics of Hadronic Interactions (MOCHI) is a simulation framework...
Radio observations of cosmic ray air showers can characterize cosmic ray mass composition, via precise Xmax measurements, at the energies of the likely shift from Galactic to extragalactic sources. Advantages over other methods include lower cost instrumentation and the ability to operate in a range of weather conditions. However, detecting cosmic rays via their radio emission alone amid radio...
Over the past decade, ground-based array experiments have observed a notable muon deficit when simulating extensive air showers (EAS) induced by high-energy cosmic rays, compared to experimental measurements. This discrepancy is referred to as the muon puzzle. In this report, we present the first investigation on this topic at the China Jinping Underground Laboratory (CJPL), which, with its...
Radio detection of extensive air showers induced by ultra-high energy cosmic rays has significantly advanced in recent decades. Observables such as shower energy and depth of maximum development are largely derived by comparing experimental data with Monte Carlo simulations, making it essential to assess the systematic uncertainties associated with the simulation models. In this work, we...
Neutrons are the only neutral hadrons that remain stable over the timescale of an air-shower development.
Their energy is lost only through hadronic interactions and quasi-elastic scattering, which results in their high abundance at the ground.
The signals from the electromagnetic and muonic components in scintillation detectors typically span only a few microseconds.
In contrast, the...
Cosmic rays can induce extensive air showers whose development takes place entirely inside the atmosphere, without reaching the ground. These atmosphere-skimming events have been detected with balloon-borne experiments such as ANITA and EUSO-SPB2. In this work, we evaluate the possibility of estimating the energy of an atmosphere-skimming cosmic ray shower through measurements of radio pulses....
ALICE experiment at CERN Large Hadron Collider, located 52 meters underground, carried out a cosmic data-taking campaign in the period 2015-2018 corresponding to 62.5 days of live time. In this work the analysis of these data is limited to multimuon events defined as events with more than four detected muons. In particular the muon multiplicity distribution (MMD) is studied in the...
The Square Kilometre Array (SKA) is a radio telescope currently under construction in South Africa and Australia.
Its low-frequency part (50-350 MHz), located in Australia, features nearly 60,000 antennas in a core region of about 1 km diameter.
With such an extreme antenna density, surpassing e.g. LOFAR by two orders of magnitude, this observatory is well equipped to make the most precise...
The GRAPES-3 (Gamma Ray Astronomy at PeV EnergieS phase-3) is a globally recognized experiment that detects cosmic rays with energies in the range from 10$^{13}$ eV to 10$^{16}$ eV. It has an excellent core-reconstruction resolution, approximately 0.5 meters at 1 PeV. We are designing a radio antenna array with 60-70 antennas, envisaged to function along with the array of scintillator...
The study of the muon content in extensive air showers (EAS) is relevant for understanding the origin and nature of cosmic rays. Moreover, muons serve as a sensitive observable to hadronic interactions in air showers, offering insight into high-energy physics processes. However, discrepancies between measured and predicted shower muon content have been reported by some EAS observatories at...
The Taiwan Astroparticle Radiowave Observatory for Geosynchrotron Emissions (TAROGE) is an antenna array located atop the high mountains along Taiwan’s eastern coast, oriented toward the ocean. It is designed to detect near-horizon extensive air showers (EAS) induced by ultra-high-energy cosmic rays (UHECRs) and Earth-skimming ultra-high-energy tau neutrinos. The TAROGE array offers several...
At large zenith angles, the electromagnetic component of ordinary air showers is significantly attenuated by the atmosphere long before reaching ground level. The observation of Horizontal Air Showers (HAS) provides a "well-shielded laboratory" for detecting penetrating particles, such as high-energy muons and cosmic neutrinos, which leave a distinctive signature in this environment.
In this...
Reconstructing the longitudinal profile of extensive air showers, generated from the interaction of cosmic rays in the Earth's atmosphere, is crucial to understand their mass composition, which in turn provides valuable insight on their possible source of origin. Furthermore, the substructures within the profile allow us to probe the intricate particle interactions that occur within these air...
Air-Shower Universality is a framework that describes the regularity in the longitudinal, lateral, and energy distributions of electromagnetic shower particles, motivated by solutions to the cascade equations. We employ a universality-based model of shower development that incorporates hadronic particle components to reconstruct observables from extensive air showers produced by...
The muon content predicted by hadronic interaction models falls short of describing the data from multiple air shower experiments. This discrepancy, known as the Muon Puzzle, poses significant challenges for mass composition studies and limits our understanding of the origins and acceleration mechanisms of ultra-high-energy cosmic rays. The recent releases of the EPOS LHC-R and QGSJET-III...
To detect ultra-high-energy neutrinos, experiments such as ARA and RNO-G target the radio emission induced by these particles as they cascade in the ice, using deep in-ice antennas at the South Pole or in Greenland. In this context, it is essential to first characterize the in-ice radio signatures from cosmic ray induced particle showers, which constitute a primary background for neutrino...
The amplitude, polarization, frequency spectrum, and energy fluence of the electric field at a given measurement position are crucial parameters for extracting primary information from radio signals generated by extensive air showers. Therefore, accurate reconstruction of the electric field from recorded antenna signals is therefore essential for advancing radio detection techniques....
The GRAPES-3 experiment, located in Ooty, India, consists of a densely packed array of 400 plastic scintillator detectors and a large area ($560 m^2$) muon telescope. The muons produced in extensive air showers (EAS) are key observables for analyzing the primary cosmic ray composition. The GRAPES-3 muon telescope (G3MT) measures the muonic component in the EAS by counting the reconstructed...
The atmosphere provides a large set of experimental conditions on which cosmic-ray induced high-energy hadron interactions can take place. These conditions include: sudden changes in the atmospheric pressure, temperature, and in the local electric and magnetic fields. In this talk we introduce the Piritakua (flash of lightning, in the language of the pre-Columbian Purépecha Empire in Mexico)...
In order to interpret the radio data from extensive air showers detectors, we rely on accurate simulations. The state-of-the-art simulation frameworks use Monte-Carlo techniques which pose computational challenges. This is a limiting factor for the next generation of radio arrays, for example the upcoming Square Kilometer Array (SKA), which will have orders of magnitude more antennas than the...
Accurately measuring the energy of shower particles reaching the ground remains a challenge due to the inherent limitations of typical cosmic ray experiments. In this work, we present two experimental strategies to determine the energy spectra of the electromagnetic and muonic components of extensive air showers, leveraging a single hybrid detector station within a regular cosmic ray array....
The Radar Echo Telescope for Cosmic Rays (RET-CR) is a prototype experiment for the future neutrino detector, the Radar Echo Telescope for Neutrinos (RET-N). It is deployed at Summit Station in Greenland, with a full data-taking run conducted in the summer of 2024.
This experiment utilises the radar technique to search for an in-ice secondary cascade produced when the core of a high-energy...
The simulation of particle cascades is an essential foundation for the analysis chains of many astroparticle physics experiments, irrespective of whether they investigate primarily charged cosmic rays, very high-energy photons or neutrinos, or even dark matter. The most widely used software for simulating such particle showers is CORSIKA, originally developed as COsmic Ray Simulation for...
The simulation of extensive air showers is pivotal for advancing our understanding of high-energy cosmic ray interactions in Earth's atmosphere. The CORSIKA 8 framework is being developed as a modern, flexible, and efficient tool for simulating these interactions with a variety of high-energy hadronic models. We present the ongoing implementation and validation of Pythia 8/Angantyr within...
In this work we show that there is a strong dependence of the radio lateral distribution function (LDF) electric field amplitudes at ground level on the position of the shower maximum ($X_{max}$) in the atmosphere, even when accounting for differences in the electromagnetic (EM) energy of the showers. This $X_{max}$ dependence can be explained in terms of two competing effects on the measured...
The problem of the excess of muons in extensive air showers (EAS) initiated by very high energy cosmic rays remains an intriguing challenge even for modern upgraded and retuned models of high energy hadron interactions. Collider experiments also demonstrate many indications of some new processes taking place in pp, pA and AA interactions. While some improvements come from the consideration of...
Precise measurements of the composition of cosmic rays in the energy range of $10^{17}-10^{18}\,$eV could provide crucial insights into the long-standing questions about the origin and acceleration of these particles. Ground-based experiments typically rely on determining the position of the extensive air shower maximum ($X_\rm {max}$) to identify the type of cosmic ray particle. One...
Electromagnetic dissociation (EMD) is a well-known process which has been extensively studied with accelerator beams. On the contrary, the influence of EMD on cosmic-ray propagation in the atmosphere and in the Galaxy is still somewhat unclear. For example, the mass composition is one of the most important ingredients to understand the origin of ultra-high energy cosmic rays. It can be...
The Low Frequency Array (LOFAR) has been measuring cosmic rays for over a decade. Its dense core of antenna fields makes it an ideal tool for studying the radio emission of extensive air showers, sensitive to energies between $10^{16.5}$ eV and $10^{18}$ eV. Each air shower is recorded using a small particle detector array and hundreds of antennas. The current state-of-the-art method for...
Radio emissions from extensive air showers (EAS) provide a valuable tool for detecting ultra-high-energy (UHE) astroparticles. In this context, several radio arrays focus on detecting highly inclined EAS, as this enables the observation of Earth-skimming UHE neutrinos, in addition to cosmic rays and gamma rays.
The reconstruction of such inclined events relies heavily on a thorough...
We present a combined tune of the Pythia 8 event generator using accelerator data and evaluate its impact on air shower observables.
Reliable simulations with event generators are essential for particle physics analyses, achievable only through advanced tuning to experimental data. Pythia 8 has emerged as a promising high-energy interaction model for cosmic ray air shower simulations,...
High-energy atmospheric muon neutrinos are detected by the IceCube Neutrino Observatory with a high rate of almost a hundred thousand events per year. Being mainly produced in meson decays in cosmic-ray-induced air showers in the upper atmosphere, the flux of these neutrinos is expected to depend on atmospheric conditions and thus features a seasonal variation. The magnitude of this effect can...
The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) Balloon with Radio (PBR) is an instrument designed to be borne by a NASA suborbital Super Pressure Balloon (SPB), in a mission planned to last as long as 50 days. The PBR instrument consists of a 1.1 m aperture Schmidt telescope, similar to the POEMMA design, with two cameras in its hybrid focal surface: a Fluorescence Camera (FC) and...
There is an observed anisotropy in the arrival direction distribution of cosmic rays in the TeV-PeV regime with variations on the scale of one part in a thousand. While the origin of this anisotropy is an open question, a possible factor is cosmic-ray interactions with interstellar and heliospheric magnetic fields. These magnetic fields may change over time - for example, due to changes in...
The POEMMA-Balloon with Radio (PBR) mission is a NASA super-pressure balloon experiment designed to advance the detection of ultra-high-energy cosmic rays, high-altitude horizontal air showers, and astrophysical neutrinos. A key instrument of PBR is the Cherenkov Camera (CC), which utilizes a 2048-pixel SiPM camera to detect the optical Cherenkov emission from cosmic-ray-induced air showers...
The origin of ultra-high-energy cosmic rays (UHECRs) is one of the most intriguing mysteries in the astroparticle physics and high-energy physics. Since UHECRs with light mass compositions are less deflected by the Galactic and extragalactic magnetic fields, their arrival directions are more strongly correlated with their origins. Charged-particle astronomy with UHECRs is hence a potentially...
Atmospheric muons produced in cosmic-ray air showers are classified as conventional muons from pion and kaon decays and prompt muons from heavy hadron decays. Conventional muons dominate at lower energies, and the prompt component becomes more significant at PeV energies and above. Precisely measuring the atmospheric muon flux from a few GeV to several PeV is valuable for advancing our...
Ultra-high-energy cosmic rays (UHECRs) are the most energetic particles ever detected. Their production mechanisms remain unknown, but the conditions in which they are generated are likely to be extreme. Cosmic rays that achieve the highest energies are rare, and their flux at Earth is extremely low. As a result, next-generation experiments with large effective areas are required and under...
The seasonal variation of single muons is a well-understood phenomenon, mainly driven by a positive correlation with atmospheric temperature fluctuations. However, the rate of multi-muon events measured by several experiments has revealed an opposite seasonal modulation in multi-muon events, which remains unexplained by any previous studies using CORSIKA simulations. For the first time, we...
High-energy cosmic rays enter Earth's atmosphere where they interact with atmospheric particles to generate charged mesons that subsequently decay into muons. As the atmospheric temperature rises, the density decreases, increasing the mean free path of pions and kaons and thus their likelihood of decaying into cosmic ray muons. The positive correlation that results as a consequence of this...
The origin of ultra-high-energy cosmic rays is still an open question, requiring next-generation observation technology. The CRAFFT project is developing a next-generation fluorescence detector designed for low-cost and fully automated observations with a simple structure. In this study, we report the successful detection of ultra-high-energy cosmic ray air showers using a prototype telescope...
The Pierre Auger Observatory has recently undergone a major upgrade, called AugerPrime, tailored to answer the current most burning questions in the Ultra-High-Energy cosmic ray detection. The AugerPrime upgrade consists of adding, on top of each station, a scintillator detector to separate the muonic and electromagnetic component of the shower for better primary identification, and a radio...
We use the reconstructed properties of individual UHECR events to constrain the location of their unknown sources via approximate Bayesian computation. All important propagation effects, including deflections in both Galactic and extragalactic magnetic fields, are implemented via CRPropa 3. We define priors over key parameters, the source position, distance, particle energy at the source, and...
The possibility that a dominant fraction of the cosmic rays above the ankle is due the single source Centaurus A is discussed. We focus on the properties of the source spectrum and composition required to reproduce the observations, showing that the nuclei are strongly suppressed for E > 10Z EeV, either by a rigidity dependent source cutoff or by the photodisintegration interactions with the...
The highest-energy cosmic rays (CRs) with energy above $10^{20}$ eV$=100$ EeV are one of the most mysterious particles in the Universe. Recently, Telescope Array Collaboration (2024) detected the second highest energy CR in history, $244\pm29{\rm (stat.)}~^{+51}_{-76}{\rm (sys.)}$~EeV, which is named as `Amaterasu.' Unger and Farrar (2024) reported no existence of candidates among the radio...
Combining the CR measurements by AMS-02 and DAMPE in space and those by LHAASO and Auger on the ground, a Galactic cosmic ray model has been
constructed to recover all these measurements from tens of GeV to tens of EeV. The precise measurements of CR spectra for individual species by AMS-02 and DAMPE together with the newest LHAASO results clearly indicate three Galactic CR components, that...
Experimental results by Milagro, HAWC, and ARGO-YBJ have observed variations in the energy spectrum of cosmic rays at TeV scales in different regions of the sky. These findings on the spectral anisotropy provide insights into cosmic ray behavior. This work explores the impact of galactic CR interactions with the heliosphere in creating the observed spectral anisotropy features. Specifically,...
Current experimental observations of true two-dimensional (2D) anisotropy are insufficient: ground-based experiments achieve precise measurements only in right ascension (RA), while space-based experiments currently provide solely upper limits. For ground detector arrays, the accuracy of detector efficiency is lower than the anisotropy amplitude. Most experiments adopt equal-declination (Dec)...
The mass composition of ultra-high-energy cosmic rays is usually inferred from the depth of the shower maximum (Xmax) of cosmic-ray showers, which is ambiguously determined by modern hadronic interaction models. We examine a data-driven scenario in which the expectation value of Xmax is considered as a free parameter. We test the hypothesis of whether the cosmic-ray data from the Pierre Auger...
In the ultra-high-energy range, cosmic rays (UHECRs) can originate from distances as large as a few hundreds of megaparsecs, limited mainly by interactions with the infrared background light and the cosmic microwave background. Although a modest size, such volume may contain too many sources to be able to discern the origin with the capabilities of current observatories. Furthermore, the...
Magnetohydrodynamic (MHD) turbulence plays a fundamental role in shaping the interstellar medium (ISM), influencing cosmic ray transport, star formation, and plasma dynamics. However, identifying the dominant MHD modes—Alfvén, slow, and fast—from observational data remains a significant challenge. In this study, we present a novel refinement of the Synchrotron Polarization Analysis (SPA)...
Cosmic rays (CRs) remain a key uncertainty in galaxy evolution due to their poorly constrained transport and acceleration in diverse plasma environments. They may play a crucial role in shaping the multiphase structure of the Circumgalactic Medium (CGM), with their impact varying across different phases depending on their transport properties and coupling with the thermal plasma. A central...
The nature of the cosmic ray all-particle spectrum knee has been a long-standing puzzle since its discovery. The high altitude near the shower maxima of cosmic rays in the knee region has enabled the LHAASO experiment to conduct calorimetric energy measurements, significantly reducing the dependence of energy measurement on cosmic ray composition and interaction models typical in ground-based...
The Global Spline Fit (GSF) is a data-driven parameterization of cosmic-ray flux and mass composition. It combines direct and indirect measurements of the cosmic-ray flux of individual elements from 1 GeV to $10^{11}$ GeV, considering their uncertainties. At lower energies, the fluxes are corrected to the local interstellar spectra using the individual data-taking periods of the experiments....
The Pierre Auger Observatory has driven the field of ultra-high-energy cosmic ray (UHECR) physics, producing several groundbreaking observations over the last 20 years. One of the most striking findings has been the complex evolution of UHECR mass composition, as revealed by detailed analyses of observables such as the depth of shower maximum (Xmax) and the muon content of showers. As more...
We present an analysis of ultra-high energy cosmic ray (UHECR) mass composition based on four years of data collected by Telescope Array’s expansion project, TA×4. Reconstructing events in hybrid mode, combining information from both the fluorescence detectors (FDs) and surface detectors (SDs), we measure the mass composition of UHECRs using the distribution of the depth of air shower maxima...
In this contribution, we have investigated the energy spectra of the elemental mass groups of cosmic rays for the Light (H+He), medium (C+O) and heavy (Ne-Fe) components using the HAWC observatory. The study was carried out in the energy interval from 10 TeV to 1 PeV using almost 5 years of data on hadronic air showers. The energy spectra were unfolded using the bidimensional distribution of...
We present an analysis of the correlation between the depth of the maximum of air-shower profiles and the signal in water-Cherenkov stations in events simultaneously recorded by the fluorescence and surface detectors of the Pierre Auger Observatory. The analysis allows constraints to be placed on the spread of nuclear masses in ultra-high-energy cosmic rays with a minor impact from the...
We introduced a parameterization method to analyze the mean muon content $<\ln N_{\mu}>$ and its dispersion $\sigma^{2}(\ln N_{\mu})$ in relation to the mass composition of cosmic-rays. This approach enhances the Heitler model for air showers by employing a parameterization that incorporates the first two moments of the logarithmic mass distribution $\ln A$ and $\sigma^{2}_{\ln A}$. This...
The cosmic ray energy spectrum has always been an important tool for investigating fundamental issues related to origin of cosmic rays. The so-called ”knee” around ∼4 PeV, at where the spectral index changes from-2.7 to-3.1, were observed by several experiments. The measurements of the ”knee” by the ground based experiments still have deviations. Most ground-based experiments measure the...
In this contribution, we present the status and first data from the Radio Detector (RD) at the Pierre Auger Observatory, consisting of 1660 radio antennas deployed across the 3000 km² surface detector array. These antennas measure the radio emission from extensive air showers in the 30–80 MHz band, enabling electromagnetic energy measurements for air showers with zenith angles above 60°....
The Radio Neutrino Observatory Greenland (RNO-G) is an in-ice neutrino detector currently under construction on top of the Greenlandic ice sheet. Its primary goal is to achieve detection of neutrinos beyond energies of $\sim$ 10 PeV. Each station is equipped with log-periodic dipole antennas (LPDA) oriented toward the sky, which play a crucial role for background reduction in the neutrino...
The Auger Engineering Radio Array (AERA) has played a pioneering role in the development of radio detection techniques for cosmic rays. Consisting of 153 autonomous antenna stations deployed over 17 km², AERA measures the radio emission from extensive air showers initiated by cosmic rays with energies between 0.1 and 10 EeV in the frequency range of 30 to 80 MHz. As the largest cosmic-ray...
GRANDProto300 is a pioneering prototype array of the GRAND experiment. It consists of 300 radio antennas and will cover an area of $200\, \text{km}^2$ in a radio-quiet region of western China. Serving as a test bench for the GRAND experiment, GRANDProto300 aims to achieve autonomous radio-detection and reconstruction of highly inclined air showers. It is designed to detect ultra-high-energy...
Construction of low frequency component (50 - 350 MHz) of the Square Kilometre Array has started in Australia. With an immensely dense core of almost 60 thousand antennas within a square kilometer, the telescope provides a unique opportunity to study cosmic rays in the energy range between the knee and the ankle. High resolution observations and new analysis strategies will provide more...
The Beamforming Elevated Array for COsmic Neutrinos (BEACON) is a detector concept designed to measure the flux of Earth-skimming tau neutrinos above 100 PeV. BEACON will consist of many independent, phased radio arrays placed on mountains. The long in-air propagation length of radio together with the high-elevation sites provide BEACON with a large detector volume in an efficient manner. A...
The Radar Echo Telescope for Cosmic Rays (RET-CR), a pathfinder experiment for a future ultra-high-energy neutrino detector, is an experiment designed to detect the ionization trail from a cosmic-ray-induced particle cascade penetrating a high-altitude ice sheet. In high-elevation ice sheets, a high-energy cosmic ray (E $>$ 10 PeV) at a small zenith angle deposits more than 10 percent of its...
Recent catalogue of the Faraday rotation measures (RM) of extragalactic sources, together with the synchrotron polarisation data from WMAP and Planck, provide us with a wealth of information on the magnetic fields of the Galaxy. We combine several phenomenological components of the GMF –- the spiral arms, the toroidal halo, the X-shaped field, and the field of the Local Bubble –- to construct...
Propagation effects play an important role in structuring UHECR data, altering their arrival directions, energy spectrum, and mass composition. Cosmic magnetic fields modify the trajectories of electrically charged cosmic rays as they travel from their sources to Earth. While small-scale magnetized structures do not significantly impact UHECR propagation, they influence our reconstruction of...
The Unger-Farrar 2023 models of the large scale coherent magnetic field of the Milky Way give comparably good fits to the key constraining data — Faraday rotation measures of extragalactic sources and polarized synchrotron emission -- while maximizing the differences in predictions of UHECR deflections. In this talk we report on our progress in identifying intermediate-scale structures in...
The Telescope Array (TA) experiment has reported evidence of an intermediate-scale excess in the arrival directions of ultrahigh-energy cosmic rays (UHECRs) with energies above 57 EeV, known as the TA Hotspot. Initially reported in 2014, this excess continues to be observed with a statistical significance of approximately 3$\sigma$. However, the astrophysical origin of this excess remains...
We study the propagation of ultra-high-energy cosmic rays (UHECRs) in the local intergalactic magnetic field (IGMF) within a radius of <10 Mpc around the Milky Way. Assuming that the field strength is in the range of 1–3 nG and the correlation length is between 0.01 and 1 Mpc, we demonstrate that the IGMF can not only blur the source image but also shift its position, mimicking the effect of...
Most ultra-high-energy cosmic rays (UHECRs) are charged particles. As a result, they are deflected by magnetic fields, which can act as lenses, altering their trajectories and (de)magnifying their apparent sources. In this study, we investigate the influence of Galactic magnetic fields on the propagation of UHECRs. The deflections of UHECR trajectories can lead to phenomena such as the...
The detection of cosmic-ray antinuclei holds the potential to be a groundbreaking method for identifying signatures of dark matter. The dominant background for cosmic antinuclei arises from interactions of cosmic-ray protons with interstellar hydrogen gas. However, prevalent (anti)nuclei formation models—the thermal and coalescence models—are based on different underlying physics. A deeper...
One of the indirect detection method of dark matter (DM) is based on the search of the products of DM annihilation or decay. They should appear as distortions in the gamma rays spectra and in the rare Cosmic Ray (CR) components, like antiprotons, positrons and antideuterons, on top of the standard astrophysical production. In particular, the antiprotons in the Galaxy are mainly of secondary...
The creation of anti-nuclei in the Galaxy has been discussed as a possible signal of exotic production mechanisms such as primordial black hole evaporation or dark matter decay/annihilation in addition to the more conventional production from cosmic-ray interactions. Tentative observations of cosmic-ray andideuteron and antihelium by the AMS-02 collaboration have re-energized the quest to use...
The PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project focuses on the experimental and theoretical study of photo-nuclear reactions involving light nuclei with masses below A = 60. This research is particularly relevant to the study of ultra-high-energy cosmic rays (UHECRs), where energy and mass loss is primarily driven by the electromagnetic...
Out in the universe, when ultra-high energy charged cosmic rays (UHECR) propagate from their source and/or acceleration site, they may interact with the environment (gas), producing high-energy gamma rays and neutrinos. One of the main uncertainties in the prediction of the flux of gamma rays and neutrinos from such UHECR interactions is due to the uncertainties in the modeling of hadronic...
Antiprotons and antideuterons in cosmic rays (CRs) are studied to search for potential signals of exotic physics—such as dark matter annihilation—beyond the expected astrophysical background produced by collisions between primary CRs and the interstellar medium.
In particular, it has been argued that the production of secondary antideuterons should be suppressed at kinetic energies below a...
We fit the cosmic-ray spectrum measured with the Pierre Auger Observatory's surface detectors above an energy of $10^{17}$ eV, along with composition information inferred from the depth of shower maximum measured with its fluorescence detectors above an energy threshold of $10^{17.8}$ eV. We consider astrophysical scenarios with two distinct extragalactic source populations: one dominating the...
The recent detection of a multi-PeV neutrino event by KM3NeT/ARCA opens a new window into the origins of ultra-high-energy cosmic rays (UHECRs). We revise the possibility of a cosmogenic origin for this event while considering constraints from the diffuse extragalactic gamma-ray background (EGRB) observed by Fermi-LAT and the non-detection of ultra-high-energy (UHE) photons ($\gtrsim$ EeV) by...
The origin of ultra-high-energy cosmic rays (UHECRs) is still an elusive question, mainly because the arrival directions do not point to a preferred source location. However, it has recently been observed that the amplitude of the dipole anisotropy detected by the Pierre Auger Observatory increases with the energy. This can be interpreted as an indication of the presence of a dominant source...
Over the past decade, giant surface arrays such as the Pierre Auger Observatory and the Telescope Array have detected cosmic rays with energies reaching hundreds of EeV, yet their sources remain unidentified. The detection of a large-scale dipole anisotropy pointing away from the Galactic plane, combined with the attenuation of ultra-high-energy cosmic rays (UHECRs) during propagation,...
Despite all that we have learned from observational data, the sources of ultra-high-energy cosmic rays (UHECRs) have not yet been identified. Among the candidates discussed in the literature, starburst galaxies and active galactic nuclei (AGNs) are likely the most popular. Studies from the Pierre Auger Observatory indicate that the mass composition of particles with energies above $10^{19.3}$...
Various models were proposed to explain the observed spectrum and composition of ultra-high-energy cosmic rays (UHECRs), but they remain inconclusive in constraining their source of origin. A significant neutrino event with an estimated energy between 72 PeV and 2.6 EeV was recently observed by the KM3NeT experiment (henceforth referred to as KM3-230213A). When interpreted as cosmogenic in...
Mini-EUSO is the first space-borne detector of the JEM-EUSO (Joint Exploratory Missions for Extreme Universe Space Observatory) program, operating on the International Space Station (ISS) since October 2019. Mounted on the Zvezda module, Mini-EUSO observes the Earth's atmosphere through a nadir-facing UV-transparent window. The size of this window determines the optical system, which consists...
The JEM-EUSO (Joint Exploratory Missions for Extreme Universe Space Observatory) collaboration is an international initiative studying ultra-high-energy cosmic rays (UHECRs) and related phenomena. These particles, with energies exceeding 10$^{20}$ eV, provide insights into extreme astrophysical processes but remain challenging to detect due to their low flux.
At the heart of JEM-EUSO's...
The POEMMA-Balloon with Radio (PBR) is a Ultra Long Duration Balloon payload scheduled for launch in Spring 2027 from Wanaka, New Zealand. It will circle over the Southern Ocean for a mission duration as long as 50 days, serving as a precursor to the dual satellite mission, Probe of Extreme Multi-Messenger Astrophysics (POEMMA). The PBR mission represents a significant step towards...
Mini-EUSO is the first mission of the JEM-EUSO program on board the
International Space Station. It was launched in August 2019 and it is operating since October 2019 being located in the Russian section (Zvezda module) of the station and viewing our planet from a nadir-facing UV-transparent window. The instrument is based on the concept of the original JEM-EUSO mission and consists of an...
The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) flew in May of 2023, marking an important step towards the observation of ultra-high-energy cosmic rays (UHECR) and neutrino-induced showers from space. The ultimate goal of this endeavor is to complement ground-based detectors and achieve unprecedented exposure and nearly uniform full-sky coverage at the highest...
The Terzina payload on board the NUSES space mission is being built in collaboration with TAS-I by GSSI, INFN and the University of Geneva. It is a Cherenkov Schmidt-Cassegrain compact telescope with effective focal length of 925 m and a camera focal assembly composed of 640 pixels (16 vertically x 40 horizontally) organized in 8x8 tiles produced by FBK with sensitive area 2.73 x 2.34...
We investigate Tidal Disruption Events (TDEs) as potential sources of Ultra-High-Energy Cosmic Rays (UHECRs), motivated by recent associations between high-energy neutrinos and individual TDEs. A key challenge is bridging the gap between these few identified neutrino sources and a broader population of UHECR accelerators. Additionally, we assess the nuclear composition required to match UHECR...
The origin of ultra-high-energy cosmic rays (UHECRs) remains an open questions in astrophysics. We explore two primary scenarios for the distribution of UHECR sources, assuming that their production rate follows either the cosmic star-formation-rate or stellar-mass density. By jointly fitting the UHECR energy spectrum and mass composition measured by the Pierre Auger Observatory above the...
We investigate ultra-fast outflows (UFOs) in active galactic nuclei (AGN) as potential sources of ultra-high-energy cosmic rays (UHECRs), focusing on cosmic-ray nuclei, an aspect not explored previously. These large-scale, mildly-relativistic outflows are a common feature of AGN. We study the cosmic-ray spectrum and maximum energy attainable in these environments with 3D CRPropa simulations...
Circumstantial evidence points to binary neutron star (BNS) mergers as the principal source of ultrahigh energy cosmic rays (UCRs), as will be briefly reviewed. This motivates trying to predict consequences of the BNS merger scenario for the UCR spectrum and composition, and also multi-messenger implications in particular gravitational wave-EHE neutrino coincidences. In this talk I will
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We investigate the propagation of ultraheavy (UH) nuclei as ultrahigh-energy cosmic rays (UHECRs). We show that their energy loss lengths at $\lesssim300$~EeV are significantly longer than those of protons and intermediate-mass nuclei, and that the highest-energy cosmic rays with energies beyond $\sim100$~EeV, including the Amaterasu particle, may originate from such UH-UHECRs. We derive...
Ultra-high-energy cosmic rays (UHECRs) have long been assumed to entirely consist of iron and/or lighter atomic nuclei, and this assumption has been hard-coded in a great deal of software for UHECR simulations and data analysis. However, in the last few years several authors have started questioning this assumption and entertaining the possibility that UHECRs might at least partly consist of...
The TA Low-energy Extension (TALE) experiment extends the reach of the TA experiment on the low-energy side to below $10^{16}$ eV. A primary objective of TALE is to study the transition from galactic to extragalactic cosmic rays. The TALE detector is a hybrid observatory composed of fluorescence telescopes and a surface detector array of scintillation counters. The surface detectors are...
The surface detector (SD) array of the Telescope Array (TA) experiment, covering an area of 700 km$^2$ with 507 plastic scintillators, observes ultra-high-energy cosmic rays (UHECRs). In this presentation, we discuss the evaluation of various systematic uncertainties in the cosmic ray energy spectrum measured by the TA SD array, including those arising from the choice of hadronic interaction...
The Telescope Array (TA) experiment has been observing extensive air showers (EAS) induced by ultrahigh energy cosmic rays (UHECR) since 2008. The TAx4 upgrade aims to expand the detection area of TA at the highest energies to four times its original size with 500 additional surface detectors (SD) with the nearest neighbor spacing extended from 1.2km to 2.08km. Half of the new detectors were...
The Pierre Auger -Telescope Array joint working group on the UHECR energy spectrum was established in 2012 to analyze energy scale uncertainties in both experiments and to investigate their systematic differences, particularly in the spectral shape of the flux measurements. Previous studies have indeed shown that, within systematic uncertainties, the energy spectra measured by the two...
We present the spectrum of cosmic rays with energies above 2.5 EeV measured at the Pierre Auger Observatory after 19 years of operation, covering the period before the AugerPrime upgrade. Two independent event sets from the surface array of 1500 m-spaced detectors are combined, yielding a total exposure of approximately 100,000 km² sr yr. The first set includes events with zenith angles less...
Ultra-high energy cosmic rays (UHECRs) are extremely energetic charged particles that originate from outer space. The Telescope Array (TA) experiment, the largest UHECR observatory in the Northern Hemisphere, has provided high-precision measurements of the cosmic ray energy spectrum due to its stable operation and efficient data collection. These measurements have revealed three significant...
The IceTop array at the surface of the IceCube Neutrino Observatory measures extensive air showers produced by cosmic-ray particles with energies from PeV up to EeV, covering the transition region from galactic to extragalactic sources. This contribution presents significant improvements that will enhance the measurement of the IceTop energy spectrum. (I) To analyze more than a decade of data...
The NICHE array at Telescope Array is a non-imaging Cherenkov light detector situated close to the Telescope Array Middle Drum fluorescence detector site. It has been operating since September 2017. Data collected between June 2020 and July 2024 has been analyzed and we will present the energy spectrum of the cosmic rays observed. The threshold energy of the detector is about 1 PeV and the...
The Large High-Altitude Air Shower Observatory (LHAASO) is a hybrid detector experiment, including one square kilometer array of scintillator detectors and muon detectors, a 78,000 square meter water Cherenkov detector array and 18 wide field of view Cherenkov telescopes. This multi-parameter observation of air showers enables LHAASO to measure the energy spectrum and composition of individual...
The Large High Altitude Air Shower Observatory (LHAASO) provides unprecedented capabilities for measuring cosmic-ray (CR) properties in the high energy regime. The LHAASO experiment has achieved unprecedented precision in measuring the cosmic ray all-particle energy spectrum and its mean logarithmic mass in the "knee" region. As statistics accumulate, it becomes feasible to accurately assess...
The GRAPES-3 experiment, located in Ooty, India (11.0^{o}N, 76.7^{o}E, 2200 m a.s.l.), uses a dense array of 400 plastic scintillator detectors and a 560 m^{2} tracking muon detector to measure all charged particles and the muonic components of cosmic ray showers, respectively. The experiment has measured the cosmic ray proton spectrum in the energy range of 50 TeV to 1.3 PeV, and the relative...
Iron cosmic rays represent the most abundant heavy nuclei at energies above 1 TeV, with their production thought to be primarily originated by astrophysical sources. Therefore, measuring the iron spectrum provides crucial insights into the origin, acceleration, and propagation mechanisms of cosmic rays. Recent results from space-based detectors have revealed unexpected energy dependences in...
