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Muon radiography, which relies on measuring the absorption and attenuation of muons as they pass through matters, offers a new imaging technique capable of revealing the internal structure of large objects. Recent technological advancement allows for the application or testing of muon radiography in various fields, including mining, civil engineering, security check, etc. This study investigates the factors that influence muon radiography, which is used in density inversion, through simulations and experiments. The materials considered for density inversion include water, standard rock, and iron. Our simulation studies show that the number of events detected and selected has an impact on the reconstruction results, and several factors, such as multiple Coulomb scattering processes, recording time, and spatial resolution, which influence the number of muons, must be taken into account when measuring the rock density. We design and conduct a laboratory scale experiment based on the simulation results. We filter the 220 h of recording signals through time coincidence and straight-line fitting to obtain the selected events. Our results reveal that the statistical error of muons survival ratio in recording time significantly impacts the inversion result and decreases the error can improve accuracy greatly. In the experiment, the deviation between the inversion mean value and the expected value can be reduced to 2.4%–2.9% for iron, 7% for water, and 1.5% for standard rock. This density inversion approach provides insight into future density detection of underground structures. [ABSTRACT FROM AUTHOR]

The High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, located on the side of the Sierra Negra volcano in Mexico, has been fully operational since 2015. The HAWC collaboration has recently significantly improved their extensive air shower reconstruction algorithms, which has notably advanced the observatory performance. The energy resolution for primary gamma rays with energies below 1 TeV was improved by including a noise-suppression algorithm. Corrections have also been made to systematic errors in direction fitting related to the detector and shower plane inclinations, O (0.° 1) biases in highly inclined showers, and enhancements to the core reconstruction. The angular resolution for gamma rays approaching the HAWC array from large zenith angles (>37°) has improved by a factor of 4 at the highest energies (>70 TeV) as compared to previous reconstructions. The inclusion of a lateral distribution function fit to the extensive air shower footprint on the array to separate gamma-ray primaries from cosmic-ray ones based on the resulting χ 2 values improved the background rejection performance at all inclinations. At large zenith angles, the improvement in significance is a factor of 4 compared to previous HAWC publications. These enhancements have been verified by observing the Crab Nebula, which is an overhead source for the HAWC Observatory. We show that the sensitivity to Crab-like point sources (E −2.63) with locations overhead to 30° zenith is comparable to or less than 10% of the Crab Nebula's flux between 2 and 50 TeV. Thanks to these improvements, HAWC can now detect more sources, including the Galactic center. [ABSTRACT FROM AUTHOR]

Ultra-high-energy cosmic rays (UHECRs) are extremely rare energetic particles of ordinary matter in the Universe, traveling astronomical distances before reaching the Earth's atmosphere. When primary cosmic rays interact with atmospheric nuclei, cascading extensive air showers (EASs) of secondary elementary particles are developed. Radio detectors have proven to be a reliable method for reconstructing the properties of EASs, such as the shower's axis, its energy, and its maximum ( X max ). This aids in understanding fundamental astrophysical phenomena, like active galactic nuclei and gamma-ray bursts. Concurrently, data science has become indispensable in UHECR research. By applying statistical, computational, and deep learning methods to both real-world and simulated radio data, researchers can extract insights and make predictions. We introduce a convolutional neural network (CNN) architecture designed to classify simulated air shower events as either being generated by protons or by iron nuclei. The classification achieved a stable test error of 10%, with Accuracy and F 1 scores of 0.9 and an MCC of 0.8. These metrics indicate strong prediction capability for UHECR's nuclear composition, based on data that can be gathered by detectors at the world's largest cosmic rays experiment on Earth, the Pierre Auger Observatory, which includes radio antennas, water Cherenkov detectors, and fluorescence telescopes. [ABSTRACT FROM AUTHOR]

A study is made of the progressive 'decoherence' of cosmic ray extensive air-shower particle-detector signals in small air showers through measurements of coincidence rates for pairs of detectors versus the detector separation. Measurements are made both when only the two separated detectors themselves trigger in coincidence, and when that coincidence trigger also requires the detection of a local air shower by a small external air-shower array. The addition of the explicit air-shower trigger ensures that the latter data correspond to showers of a larger particle size, and triggering by very localised shower cores is then unlikely. When including a shower trigger, the decoherence results appear substantially different in form. The coincidence rate between two detectors only can be approximated by a power-law variation with separation distance. When triggering involves an air-shower array, the variation becomes close to an exponential form with characteristic exponent distances varying systematically with increasing detector and air-shower size thresholds. A result is that one can see that small air showers will exhibit clear non-Poissonian density fluctuations near their cores, out to distances of ~5 m, or at shower energies below ~0.05 PeV. These ideas can be helpful in understanding the statistical properties of signals when using large detectors in air-shower arrays. [ABSTRACT FROM AUTHOR]

Analyzing the isotopic composition of cosmic rays (CRs) provides valuable insights into the galactic environment and helps refine existing propagation models. A particular interest is devoted to secondary-to-primary ratios of light isotopic components of CRs, the measurement of which can provide complementary information with respect to secondary-to-primary ratios like B/C. Given the complexity of the concurrent measurement of velocity and momentum required to differentiate isotopes of the same Z, a task typically accomplished using magnetic spectrometers, existing measurements of these ratios only effectively characterize the low-energy region (below 1 GeV/nucl). This study introduces a novel technique for isotopic distinction in CRs at high energies up to 100 GeV/nucl based on multiple scattering, which, combined with the proposed measurement of velocity, represent an interesting alternative to magnetic spectrometers. The performance of this technique was assessed through a dedicated simulation using the GEANT4 package, with specific emphasis on Z = 1 isotopes. [ABSTRACT FROM AUTHOR]

Extensive air showers (EAS), cascades of electromagnetic radiation and ionized particles produced when primary cosmic rays (CRs) interact with atmospheric nuclei, generate a plethora of secondary particles, including electrons, muons, alpha particles, X-rays, and neutrons. These phenomena, pivotal in the exploration of high-energy CR interactions, have prompted advancements in simulating the lateral distribution function (LDF) of secondary particles. Utilizing AIR-shower extended simulations (AIRES) software (version 19.04.10), this study presents simulations of EAS to elucidate the impact on the LDF at the high energy thresholds of 1016, 1018 and 1019 eV. The focus is on secondary muons and electrons, considering the influence of primary protons and iron nuclei across zenith angles of 0°, 20°, and 40°. Through the application of an exponential function model, novel coefficients were derived, reflecting the variation of the LDF relative to the distance from the shower core. These coefficients are instrumental in astrophysics and particle physics, offering a nuanced understanding of CR interactions with earth's atmosphere. By delineating the spatial particle distribution during interactions, insights into the shower's lateral extent and configuration are gleaned, facilitating the deduction of the initiating CR's energy. Such knowledge is crucial for CR spectrum analysis. The investigation of electron and muon LDFs not only advances fundamental particle physics but also holds implications for space exploration, radiation protection, and other domains. [ABSTRACT FROM AUTHOR]

Context. The presence of clouds during observations with Imaging Atmospheric Cherenkov Telescopes can strongly affect the performance of the instrument due to additional absorption of light and scattering of light beyond the field of view of the instrument. If not corrected for, the presence of clouds leads to increased systematic errors in the results. Aims. One approach to correct for the effects of clouds is to include clouds in Monte Carlo simulations to produce models for primary particle classification, and energy and direction estimation. However, this method is challenging due to the dynamic nature of cloudy conditions and requires extensive computational resources. The second approach focuses on correcting the data themselves for cloud effects, which allows the use of standard simulations. However, existing corrections often prioritise the limitation of systematic errors without optimising overall performance. By correcting the data already at the image level, it is possible to improve event reconstruction without the need for specialised simulations. Methods. We introduce a novel analysis method based on a geometrical model that can correct the data already at the image level given a vertical transmission profile of a cloud. Using Monte Carlo simulations of an array of four of the Large-Sized Telescopes of the Cherenkov Telescope Array, we investigated the effect of the correction on the image parameters and the performance of the system. We compared the data correction at the camera level with the use of dedicated simulations for clouds with different transmissions and heights. Results. The proposed method efficiently corrects the extinction of light in clouds, eliminating the need for dedicated simulations. Evaluation using Monte Carlo simulations demonstrates improved gamma-ray event reconstruction and overall system performance. [ABSTRACT FROM AUTHOR]

Context. Hadronic interactions between cosmic rays (CRs) and interstellar gas have been probed in γ rays across the Galaxy. A fairly uniform CR distribution is observed up to a few hundred parsecs from the Sun, except in the Eridu cloud, which shows an unexplained 30–50% deficit in GeV to TeV CR flux. Aims. To explore the origin of this deficit, we studied the Reticulum cloud, which shares notable traits with Eridu: a comparable distance in the low-density region of the Local Valley and a filamentary structure of atomic hydrogen extending along a bundle of ordered magnetic-field lines that are steeply inclined to the Galactic plane. Methods. We measured the γ-ray emissivity per gas nucleon in the Reticulum cloud in the 0.16–63 GeV energy band using 14 years of Fermi-LAT data. We also derived interstellar properties that are important for CR propagation in both the Eridu and Reticulum clouds, at the same parsec scale. Results. The γ-ray emissivity in the Reticulum cloud is fully consistent with the average spectrum measured in the solar neighbourhood, but this emissivity, and therefore the CR flux, is 1.57 ± 0.09 times larger than in Eridu across the whole energy band. The difference cannot be attributed to uncertainties in gas mass. Nevertheless, we find that the two clouds are similar in many respects: both have magnetic-field strengths of a few micro-Gauss in the plane of the sky; both are in approximate equilibrium between magnetic and thermal pressures; they have similar turbulent velocities and sonic Mach numbers; and both show magnetic-field regularity with a dispersion in orientation lower than 10°–15° over large zones. The gas in Reticulum is colder and denser than in Eridu, but we find similar parallel diffusion coefficients around a few times 1028 cm2 s−1 in both clouds if CRs above 1 GV in rigidity diffuse on resonant, self-excited Alfvén waves that are damped by ion-neutral interactions. Conclusions. The loss of CRs in Eridu remains unexplained, but these two clouds provide important test cases to further study how magnetic turbulence, line tangling, and ion-neutral damping regulate CR diffusion in the dominant gas phase of the interstellar medium. [ABSTRACT FROM AUTHOR]

We observed five clusters of upper‐level compact intracloud discharges (CIDs) moving positive charge up over land and over water in Florida. The clusters each contained 3 to 6 CIDs, and the overall cluster duration ranged from 27 to 58 s. On average, the CIDs in a given cluster occurred 11 s apart and were separated by a 3D distance of about 1.5 km. All the clustered CIDs were located above the tropopause and were likely associated with convective surges that penetrated the stratosphere. The average periodicity of CID occurrence within a cluster (every 11 s) was comparable to the periodicity at which the average cluster area is expected to be bombarded by ≥1016 eV cosmic‐ray particles (every 5 s). Each of such energetic particles gives rise to a cosmic ray shower (CRS) and, in the presence of sufficiently strong electric field over a sufficiently large distance, to a relativistic runaway electron avalanche (RREA). We infer that each of our upper‐level CIDs is likely to be caused by a CRS‐RREA traversing, at nearly the speed of light, the electrified overshooting convective surge and triggering, within a few microseconds, a multitude of streamer flashes along its path, over a distance of the order of hundreds of meters (as per the mechanism recently proposed for lightning initiation by Kostinskiy et al., 2020, https://doi.org/10.1029/2020JD033191). The upper‐level CID clustering was likely made possible by the recurring action of energetic cosmic rays and the rapid recovery of the negative screening charge layer at stratospheric altitudes. Plain Language Summary: Compact intracloud discharges (CIDs) are non‐conventional lightning discharges inside the cloud that are characterized by a relatively small spatial extent (less than 1 km), very strong HF‐VHF (3–300 MHz) electromagnetic emissions, and characteristic wideband radiofrequency field pulses. It has been recently discovered, using space‐based detectors, that CIDs also produce optical signals, the so‐called blue flashes at cloud tops. Our understanding of the physics of CIDs is still poor. CIDs are usually solitary events, but we observed five clusters of CIDs, mostly at altitudes in the 18–20 km range, which were likely associated with kilometer‐scale convective surges that penetrated the stratosphere. Each cluster contained 3 to 6 CIDs, and the cluster duration ranged from 27 to 58 s. On average, the CIDs in a given cluster occurred 11 s apart and were separated by a 3D distance of about 1.5 km. Some CIDs within a cluster were essentially collocated, while being separated in time by up to several tens of seconds. We inferred that the CID clustering observed in our study was made possible by (a) the recurring action of omnipresent energetic cosmic rays and (b) the rapid recovery of the negative screening charge layer at stratospheric altitudes. Key Points: 5 clusters of 3–6 compact intracloud discharges (CIDs) moving positive charge up in convective surges overshooting the tropopause in Florida were examinedCID clustering was tight in both time and space: average time interval was 11 s and average 3D distance within a cluster was 1.5 kmCID clustering was made possible by recurring action of ≥1016 eV cosmic‐ray particles and rapid recovery of negative screening charge layer [ABSTRACT FROM AUTHOR]

Regular measurements of radio emission produced by relativistic air shower particles were started at the Yakutsk array in 1986. After monitoring of the background noise in the array area, the frequency of 30–35 MHz was chosen, because noise level is minimal in this frequency range. During this time, air showers with highest energies of 100 EeV were registered. By means of hybrid measurements of charged particles, Cherenkov light and radio emission, it was shown that signal amplitude proportional to air shower energy and shape of lateral distribution at sea level correlates with the depth of maximum development. By these characteristics, the atomic weight of primary particles that generated air shower is estimated within QGSjetII-04 framework simulation. [ABSTRACT FROM AUTHOR]

The telescope Mini-EUSO has been observing, since 2019, the Earth in the ultraviolet band (290–430 nm) through a nadir-facing UV-transparent window in the Russian Zvezda module of the International Space Station. The instrument has a square field of view of 44°, a spatial resolution on the Earth surface of 6.3 km and a temporal sampling rate of 2.5 microseconds. The optics is composed of two 25 cm diameter Fresnel lenses and a focal surface consisting of 36 multi-anode photomultiplier tubes, 64 pixels each, for a total of 2304 channels. In addition to the main camera, Mini-EUSO also contains two cameras in the near infrared and visible ranges, a series of silicon photomultiplier sensors and UV sensors to manage night-day transitions. Its triggering and on-board processing allow the telescope to detect UV emissions of cosmic, atmospheric and terrestrial origin on different time scales, from a few microseconds up to tens of milliseconds. This makes it possible to investigate a wide variety of events: the study of atmospheric phenomena (lightning, transient luminous events (TLEs) such as ELVES and sprites), meteors and meteoroids; the search for nuclearites and strange quark matter; and the observation of artificial satellites and space debris. Mini-EUSO is also potentially capable of observing extensive air showers generated by ultra-high-energy cosmic rays with an energy above 1021 eV and can detect artificial flashing events and showers generated with lasers from the ground. The instrument was integrated and qualified in 2019 in Rome, with additional tests in Moscow and final, pre-launch tests in Baikonur. Operations involve periodic installation in the Zvezda module of the station with observations during the crew night time, with periodic downlink of data samples, and the full dataset being sent to the ground via pouches containing the data disks. In this work, the mission status and the main scientific results obtained so far are presented, in light of future observations with similar instruments. [ABSTRACT FROM AUTHOR]

In high-altitude experiments to study the central cores of EAS at E0 ≳ 1016 eV (√s ≳ 5 TeV) using X-ray emulsion chambers and ionization calorimeters, phenomena such as the coplanarity of the arrival of the most energetic particles in super families of γ-rays and hadrons and a so-called Tien Shan effect (too slow absorption of cascades initiated by high-energy hadrons in the calorimeter) were observed. These effects could not be reproduced within the framework of theoretical models of the 80s and 90s. The coplanarity is explained via a process of coplanar generation of the most energetic secondary particles in interactions of super high-energy hadrons with nuclei of air atoms. Perhaps the Tien Shan effect could be explained using a high cross section for the generation of fragmentation-region charmed hadrons. To study these phenomena, a new set of detectors has been developed, including the world's highest high-mountain ionization calorimeter, "Hadron-55". This paper presents the initial experimental results. [ABSTRACT FROM AUTHOR]

Although celestial sources emitting in the few tens of GeV up to a few TeV are being investigated by imaging atmospheric Čerenkov telescope arrays such as H.E.S.S., MAGIC, and VERITAS, at higher energies, up to PeV, more suitable instrumentation is required to detect ultra-high-energy photons, such as extensive air shower arrays, as HAWC, LHAASO, Tibet AS- γ. The Italian National Institute for Astrophysics has recently become the leader of an international project, the ASTRI Mini-Array, with the aim of installing and operating an array of nine dual-mirror Čerenkov telescopes at the Observatorio del Teide in Spain starting in 2025. The ASTRI Mini-Array is expected to span a wide range of energies (1–200 TeV), with a large field of view (about 10 degrees) and an angular and energy resolution of ∼3 arcmin and ∼10 %, respectively. The first four years of operations will be dedicated to the exploitation of Core Science, with a small and selected number of pointings with the goal of addressing some of the fundamental questions on the origin of cosmic rays, cosmology, and fundamental physics, the time-domain astrophysics and non γ -ray studies (e.g., stellar intensity interferometry and direct measurements of cosmic rays). Subsequently, four more years will be dedicated to Observatory Science, open to the scientific community through the submission of observational proposals selected on a competitive basis. In this paper, I will review the Core Science topics and provide examples of possible Observatory Science cases, taking into account the synergies with current and upcoming observational facilities. [ABSTRACT FROM AUTHOR]

The paper is devoted to the modeling and analysis of data detected by the TAIGA-IACT installation in the stereo mode. Five Imaging Atmospheric Cherenkov Telescopes (IACT) with a viewing angle of 9.6° are expected to be included in the installation. Today there are three telescopes spaced far apart (from 320 to 500 m) in the installation. The effective area of the installation is as large as 0.6 km2; therefore, it is possible to conduct statistically significant measurements of weak γ-ray sources in the energy range above 10 TeV over a reasonable observation time (300–400 h). The Monte Carlo procedure for simulating the hadrons and γ-rays detected by the telescopes is described as is the procedure for reconstructing the parameters of extensive air showers, such as the arrival direction of an event, the axis position, the depth of the maximum of shower development (Xmax), and the primary-particle energy. In order to solve the problem of γ-hadron separation, the criteria for selecting γ-rays detected in the stereo mode have been optimized and the effective area of the installation has been calculated. [ABSTRACT FROM AUTHOR]

Here we consider the results of direct measurements of muons in extensive air showers with zenith angles and energy above eV, obtained at the Pierre Auger Observatory and Yakutsk array. In both experiments muons were registered with underground scintillation detectors with GeV energy threshold. Measured density values were compared to theoretical predictions calculated within the framework of the qgsjet-ii.04 hadron interaction model. They differ by factor (stat). We demonstrate that this difference is due to overestimation of muon densities by 1.22 times and underestimation of primary energy by 1.25 times in the Auger experiment. [ABSTRACT FROM AUTHOR]

Cosmic rays are a very valuable tool of multi‐messenger astrophysics, as they provide a very different picture of the sky. During the past decades, a large number of active astrophysical objects in our Galaxy and beyond have been discovered through the detection of gamma‐rays with Cherenkov telescopes. Cosmic rays, neutrinos have been successfully supplementing the astronomical view. Also, cosmic rays may offer to investigation of the elementary particle properties. Neutrino telescope detects the Cherenkov radiation generated in water or ice by the passage of relativistic charged particles produced by neutrino collisions with nucleons in the detector volume. Some alternative approaches have been proposed. One of them is using earth matter or mountains as a target volume for the conversion of neutrinos to leptons which then initiate extensive air showers (EAS) in the atmosphere, then showers can be detected by the Cherenkov telescope. Investigations with SHALON Cherenkov telescope have included observations of EAS from the sub‐horizontal direction Θ=97°$$ \Theta ={97}^{{}^{\circ}} $$. Five EAS of ∼10 TeV energies were detected with SHALON from the sub‐horizontal directions in the conditions with the zero expected number of showers. These events may be caused by the decay of a long‐lived penetrating particle entering the atmosphere from the ground and decaying in front of the telescope. As a possible explanation, two scenarios with an unstable neutrino of mass m≈0.5$$ m\approx 0.5 $$ GeV and cτ≈30$$ c\tau \approx 30 $$ m is discussed. Remarkably, one of these models has been proposed to explain an excess of electron‐like neutrino events at MiniBooNE. [ABSTRACT FROM AUTHOR]

Astrophysical very high energy (VHE) gamma-rays (with energies >30 GeV) are believed to result almost exclusively from the interactions of populations of highly relativistic particles with ambient matter or photon fields. The study of these VHE photons therefore allows us to examine the processes of particle acceleration in the Universe, and the extreme environments in which they occur. Gamma-rays are also highly directional, making them useful for studying the origin, acceleration, propagation, and composition of cosmic rays. This study uses the Monte Carlo method to simulate the process of extensive air showers being initiated when primary incident γ -rays with energies ranging from 10 GeV to 5 TeV interact with the atmosphere. The ultimate goal is to investigate and analyze the properties and lateral density distributions of Cherenkov light at different altitudes. The simulation considers various energies and zenith angles. The results show that a hump in the lateral density distribution of Cherenkov light is a distinctive feature of a γ -initiated shower, with the hump becoming less prominent at higher energy levels and altitudes. These significant findings not only facilitate better fitting of experimental data obtained from actual extensive air showers but also assist with estimating readings from detectors, thus advancing our understanding of these processes. [ABSTRACT FROM AUTHOR]

• We characterized the pressure wave produced by the Tonga volcano using cosmic rays. • We believe this is the first time that a Lamb wave is studied using cosmic rays. • Our high-altitude data provides additional information about this unique event. High-energy cosmic rays that hit the Earth can be used to study large-scale atmospheric perturbations. After a first interaction in the upper parts of the atmosphere, cosmic rays produce a shower of particles that sample it down to the detector level. The HAWC (High-Altitude Water Cherenkov) gamma-ray observatory in Central Mexico at 4,100 m elevation detects air shower particles continuously with 300 water Cherenkov detectors with an active area of 12,500 m2. On January 15th, 2022, HAWC detected the passage of the pressure wave created by the explosion of the Hunga volcano in the Tonga islands, 9,000 km away, as an anomaly in the measured rate of shower particles. The HAWC measurements are used to determine the propagation speed of four pressure wave passages, and correlate the variations of the shower particle rates with the barometric pressure changes. The profile of the shower particle rate and atmospheric pressure variations for the first transit of the pressure wave at HAWC is compared to the pressure measurements at the Tonga island, near the volcanic explosion. By using the cosmic-ray propagation in the atmosphere as a probe for the pressure, it is possible to achieve very high time-resolution measurements. Moreover, the high-altitude data from HAWC allows to observe the shape of the pressure anomaly with less perturbations compared to sea level detectors. Given the particular location and the detection method of HAWC, our high-altitude data provides valuable information that contributes to fully characterize this once-in-a-century phenomenon. [ABSTRACT FROM AUTHOR]

The status of the TAIGA experiment (Tunka Advanced Instrument for cosmic-ray physics and Gamma-ray Astronomy) located in the Tunka Valley is presented. The paper presents mainly the tasks, developed approaches for their solution, and first results on high-energy gamma-ray astronomy (10 TeV and higher) obtained from a two- to three-year exposure. The current tasks of gamma-ray astronomy and plans for development of the installation are discussed. [ABSTRACT FROM AUTHOR]

The investigation of cosmic rays holds significant importance in the realm of particle physics, enabling us to expand our understanding beyond atomic confines. However, the origin and characteristics of ultra-high-energy cosmic rays remain elusive, making them a crucial topic of exploration in the field of astroparticle physics. Currently, our examination of these cosmic rays relies on studying the extensive air showers (EAS) generated as they interact with atmospheric nuclei during their passage through Earth's atmosphere. Accurate comprehension of cosmic ray composition is vital in determining their source. Notably, the muon content of EAS and the atmospheric depth of the shower maximum serve as the most significant indicators of primary mass composition. In this study, we present two novel methods for reconstructing particle densities based on muon counts obtained from underground muon detectors (UMDs) at varying distances to the shower axis. Our methods were analyzed using Monte Carlo air shower simulations. To demonstrate these techniques, we utilized the muon content measurements from the UMD of the Pierre Auger cosmic ray Observatory, an array of detectors dedicated to measuring extensive air showers. Our newly developed reconstruction methods, employed with two distinct UMD data acquisition modes, showcased minimal bias and standard deviation. Furthermore, we conducted a comparative analysis of our approaches against previously established methodologies documented in existing literature. [ABSTRACT FROM AUTHOR]

The JEM-EUSO program aims to study ultra-high energy cosmic rays from space. To achieve this goal, it has realized a series of experiments installed on the ground (EUSO-TA), various on stratospheric balloons (with the most recent one EUSO-SPB2), and inside the International Space Station (Mini-EUSO), in light of future missions such as K-EUSO and POEMMA. At nighttime, these instruments aim to monitor the Earth's atmosphere measuring fluorescence and Cherenkov light produced by extensive air showers generated both by very high-energy cosmic rays from outside the atmosphere and by neutrino decays. As the two light components differ in duration (order of microseconds for fluorescence light and a few nanoseconds for Cherenkov light) they each require specialized sensors and acquisition electronics. So far, the sensors used for the fluorescence camera are the Multi-Anode Photomultiplier Tubes (MAPMTs), while for the Cherenkov one, new systems based on Silicon PhotoMultipliers (SiPMs) have been developed. In this contribution, a brief review of the experiments is followed by a discussion of the tests performed on the optical sensors. Particular attention is paid to the development, test, and calibration conducted on SiPMs, also in view to optimize the geometry, mass, and weight in light of the installation of mass-critical applications such as balloon- and space-borne instrumentation. [ABSTRACT FROM AUTHOR]

This work presents the development of a 64-channel application-specific integrated circuit (ASIC), implemented to detect the optical Cherenkov light from sub-orbital and orbital altitudes. These kinds of signals are generated by ultra-high energy cosmic rays (UHECRs) and cosmic neutrinos (CNs). The purpose of this front-end electronics is to provide a readout unit for a matrix of silicon photo-multipliers (SiPMs) to identify extensive air showers (EASs). Each event can be stored into a configurable array of 256 cells where the on-board digitization can take place with a programmable 12-bits Wilkinson analog-to-digital converter (ADC). The sampling, the conversion process, and the main digital logic of the ASIC run at 200 MHz, while the readout is managed by dedicated serializers operating at 400 MHz in double data rate (DDR). The chip is designed in a commercial 65 nm CMOS technology, ensuring a high configurability by selecting the partition of the channels, the resolution in the interval 8–12 bits, and the source of its trigger. The production and testing of the ASIC is planned for the forthcoming months. [ABSTRACT FROM AUTHOR]

The IceCube Neutrino Observatory is a cubic-kilometer Cherenkov detector that is deployed deep in the Antarctic ice at the South Pole. A square kilometer companion surface detector, IceTop, located directly above in the in-ice array, measures cosmic-ray initiated extensive air showers with primary energies between 100 TeV and 1 EeV. By combining the events measured by IceTop and the in-ice detectors of IceCube in coincidence, we can reconstruct the energy spectra for different primary mass groups. Therefore, we provide information about the origin of cosmic rays, in particular, in the transition region from galactic to extra-galactic origin of high-energy cosmic rays. In this contribution we present recent experimental results, as well as prospects by the foreseen enhancement of the surface detectors of IceTop and the future IceCube-Gen2 surface array. [ABSTRACT FROM AUTHOR]

Multi‐resolution analysis methods can reveal the underlying physical dynamics of nonstationary signals, such as those from lightning. In this paper we demonstrate the application of two multi‐resolution analysis methods: Ensemble Empirical Mode Decomposition (EEMD) and Variational Mode Decomposition (VMD) in a comparative way in the analysis of electric field change waveforms from lightning. EEMD and VMD decompose signals into a set of Intrinsic Mode Functions (IMFs). The IMFs can be combined using distance and divergence metrics to obtain noise reduction or to obtain new waveforms that isolate the physical processes of interest while removing irrelevant components of the original signal. We apply the EEMD and VMD methods to the observations of three close Narrow Bipolar Events (NBEs) that were reported by Rison et al. (2016, https://doi.org/10.1038/ncomms10721). The ΔE observations reveal the occurrence of complex oscillatory processes after the main NBE sferic. We show that both EEMD and VMD are able to isolate the oscillations from the main NBE, with VMD being more effective of the two methods since it requires the least user supervision. The oscillations are found to begin at the end of the NBEs' downward fast positive breakdown, and appear to be produced by a half‐wavelength standing wave within a weakly‐conducting resonant ionization cavity left behind in the wake of the streamer‐based NBE event. Additional analysis shows that one of the NBEs was likely initiated by an energetic cosmic ray shower, and also corrects a misinterpretation in the literature that fast breakdown is an artifact of NBE‐like events in interferometer observations. Plain Language Summary: This paper investigates the application of mode decomposition techniques to the analysis of Narrow Bipolar Events (NBEs). NBEs are high‐power discharges that often occur as the initiating event of lightning flashes, and are produced by streamer‐based activity called fast positive breakdown. We apply Ensemble Empirical Mode Decomposition (EEMD) and Variational Mode Decomposition (VMD) methods to three NBEs that were observed at Langmuir Laboratory in New Mexico to extract and interpret oscillatory behavior that occurred following the NBEs. We show that both EEMD and VMD separate the oscillations from the strong electric field change of the parent NBE, with VMD being the preferred choice. The resulting waveforms are indicative of a shock‐excited residual process that lasts for tens of microseconds, beginning at the end of the downward fast breakdown activity. Although questions remain about the physical mechanism of the oscillations, they appear to be caused by the NBE's streamers creating a weakly‐conducting resonant cavity in its wake that supports half‐wavelength standing wave oscillations, analogous to the vibrations of a plucked guitar string. Key Points: Ensemble Empirical Mode Decomposition and Variational Mode Decomposition separate out Narrow Bipolar Event (NBE) oscillations for further studies of physical mechanisms responsible for oscillationsThe results show the oscillations initiate not during the NBE but at the end of the fast positive breakdown processThe oscillatory behavior indicates that residual ionic conductivity creates a resonant cavity which emits half‐wavelength radiation [ABSTRACT FROM AUTHOR]

The origin of cosmic rays can be deciphered by accurately measuring the components and energy spectrum in the knee region. Study of Extensive air shower (EAS) relies on information provided by secondary high energy hadrons, which generate evaporation neutrons when they interact with matter in the environment. In the early 21st century, the electron–neutron detector (EN-detector) was developed at the Institute for Nuclear Research of the Russian Academy of Science (INR RAS). The PRImary Spectrum Measurement Array (PRISMA) project was introduced to enhance the array capabilities of cosmic ray composition separation and improve measurement accuracy. Within the framework of Chinese–Russian cooperation, at the Large High Altitude Air Shower Observatory (LHAASO) at Mt. Haizi (4400 m a.s.l.) in Daocheng, Sichuan province, China, a proposal was launched to establish the EN-Detector Array (ENDA) composed of 400 detectors in area of 10000 m to measure cosmic rays up to 300 PeV. In China, in 2018, a cluster, having 16 EN-detectors, was built at Tibet University (TU, 3700 m a.s.l.) in Lhasa, Tibet, to test specification of the array, and later it was moved to the Yangbajing (YBJ) Cosmic Ray Observatory (4300 m a.s.l.) in Tibet. Since 2019, another cluster so called ENDA-16 has started running at LHAASO, and here we give the first result of thermal neutron distribution. After gaining experience from these previous works, in April 2023, we successfully extended ENDA to ENDA-64 composed of 64 EN-detectors in area of 1000 m at LHAASO to measure cosmic rays from 400 TeV to 20 PeV. Here we describe installation and running status of ENDA-64 and present first results of thermal neutron distributions at different locations and hybrid detection of cosmic ray by using ENDA and LHAASO. [ABSTRACT FROM AUTHOR]

NEVOD-DECOR is the unique experiment where systematic studies of cosmic ray muon bundles in a wide range of zenith angles and, accordingly, the energies of primary cosmic rays are carried out. Impressive experimental material (more than 100 thousand events) has been accumulated over a long time period from May 2012 to December 2022. The earlier developed method of local muon density spectra allows us to compare experimental data on muon bundles with the results of the EAS muon component simulations. The analysis showed that the observed intensity of muon bundles at primary cosmic ray energies of about 1 EeV and higher can be compatible with the expectation (in frame of widely used hadronic interaction models) only under the assumption of an extremely heavy mass composition. It is consistent with data of several other experiments on investigations of air shower muon content, but contradicts the available measurements of the depth of the shower maximum in the atmosphere by means of fluorescent technique, which favor a light mass composition at these energies. This probably leads to the need to revise the existing hadronic interaction models. [ABSTRACT FROM AUTHOR]

Experimental Complex NEVOD (MEPhI, Moscow) includes several detectors and installations for measuring different components of extensive air showers (EAS). For the development of multicomponent EAS studies with the implementation of a complementary approach to the analysis of experimental information of the scientific facilities of the complex, a specialized hardware and software system is being created. This system will speed up the obtaining of new physical results by simplification of development and implementation of both traditional approaches and modern methods for data processing, including neural networks and algorithms for analyzing large amounts of data. The hardware and software architecture of the system, its features and prospects of the further development are discussed. [ABSTRACT FROM AUTHOR]

Paper contains the first results on the development of a SPHERE-3 telescope for the primary cosmic ray studies in 1–1000 PeV energy range using reflected and direct Cherenkov light generated by extensive air showers. It also sheds some light on the development of our new approach to the design of the new telescope. [ABSTRACT FROM AUTHOR]

A comparison of the reconstruction accuracy of the shower size and coordinates of the axes of extensive air showers based on the response of the NEVOD-EAS array are presented. The reconstruction is based on various functions of the lateral distribution of particles. A comparison of the lateral distribution of EAS particles according to modeled and experimental data is given. [ABSTRACT FROM AUTHOR]

The article considers showers produced by primary particles with energies eV. The showers were registered in the course of continuous long-term observations at the Yakutsk array of extensive air showers. In the present work, the mathematical processing of showers was repeated and the phenomenology of the charged component, muons with threshold GeV in the region of highest energies was refined. Mass composition of primary particles producing air showers with energy greater than eV was made based on the muon component. [ABSTRACT FROM AUTHOR]

JEM-EUSO is an international program for the development of space-based Ultra-High Energy Cosmic Ray observatories. The program consists of a series of missions which are either under development or in the data analysis phase. All instruments are based on a wide-field-of-view telescope, which operates in the near-UV range, designed to detect the fluorescence light emitted by extensive air showers in the atmosphere. We describe the simulation software ESAF in the framework of the JEM-EUSO program and explain the physical assumptions used. We present here the implementation of the JEM-EUSO, POEMMA, K-EUSO, TUS, Mini-EUSO, EUSO-SPB1 and EUSO-TA configurations in ESAF. For the first time ESAF simulation outputs are compared with experimental data. [ABSTRACT FROM AUTHOR]

Extensive air showers induced from high-energy cosmic rays provide a window into understanding the most energetic phenomena in the universe. We present a new method for observing these showers using the silicon imaging detector Subaru Hyper Suprime-Cam (HSC). This method has the advantage of being able to measure individual secondary particles. When paired with a surface detector array, silicon imaging detectors like Subaru HSC will be useful for studying the properties of extensive air showers in detail. The following report outlines the first results of observing extensive air showers with Subaru HSC. The potential for reconstructing the incident direction of primary cosmic rays is demonstrated and possible interdisciplinary applications are discussed. [ABSTRACT FROM AUTHOR]

This article is a brief biography and account of the scientific achievements of an inspiring Indian woman scientist, Dr Bibha Chowdhuri. Her story is one of courage, determination, and perseverance as she carved her path in a male dominated profession during a time when women faced severe obstacles even accessing basic education, let alone pursuing higher education and a career in science. [ABSTRACT FROM AUTHOR]

Ensuring the ethical use of AI in experiments, addressing data privacy concerns, and bridging the gap between traditional scientific methodologies and AI-driven approaches are pivotal steps on this journey. The integration of AI into experiments has an interesting timeline, beginning in the 1990s, when machine learning methods like neural networks were first applied to analyze physics detector data. Artificial intelligence (AI) has become deeply intertwined with scientific inquiry and experimentation. Machine learning, deep learning, and advanced AI techniques are poised to revolutionize data interpretation, enabling us to unearth hidden patterns, discover new phenomena, and explore the uncharted realms of the universe. [Extracted from the article]

In this paper, we study the similarities and differences of Forbush decreases in solar cycles 23 and 24. Groups of events associated with various types of solar sources were analyzed: coronal mass ejections from active regions accompanied by solar flares (CME1 group), filament ejections outside active regions (CME2 group), and high-velocity streams from coronal holes (CH group). The distributions and relations of various parameters were studied: the amplitude of Forbush decreases, the maximum values of the hourly decrease in the cosmic ray density, the equatorial cosmic ray anisotropy, the solar wind velocity, and the magnetic field strength, as well as the values of the solar wind velocity and the magnetic field strength 1 hour before the onset of the Forbush decrease during the event. The results showed that the number of events, parameter values, and their relations depend on the phase and cycle of solar activity. In the 24th cycle, the number of events in the CME1 group decreased, did not change in CME2, and increased in CH. The values of the parameters and the difference between them in various groups of events are higher in cycle 23, which is characterized by greater asymmetry and long "tails" of distributions. The magnitude of the Forbush decreases in the CME1 group in cycle 23 depends more strongly on the solar wind velocity while, in cycle 24, on the magnetic field strength, as in the CME2 group in both solar cycles. Multiple linear regression describes the dependences of the parameters of Forbush decreases in the CME1 and CME2 groups in the 23rd cycle and in the CME1 group in the 24th cycle well. [ABSTRACT FROM AUTHOR]

Cosmic ray air showers are a phenomenon that can be observed on Earth when high-energy particles from outer space collide with the Earth's atmosphere. These energetic particles in space are called primary cosmic rays and consist mainly of protons (about 89%), along with nuclei of helium (10%) and heavier nuclei (1%). Particles resulting from interactions in the atmosphere are called secondary cosmic rays. The composition of air showers in the atmosphere can include several high-energy particles such as mesons, electrons, muons, photons, and others, depending on the energy and type of the primary cosmic ray. Other than air, primary cosmic rays can also produce showers of particles when they interact with any type of matter; for instance, particle showers are also produced within the soil of planets without an atmosphere. In the same way, secondary cosmic particles can start showers of tertiary particles in any substance. In the 1930s, Bruno Rossi conducted an experiment to measure the energy loss of secondary cosmic rays passing through thin metal sheets. Surprisingly, he observed that as the thickness of the metal sheets increased, the number of particles emerging from the metal also increased. However, by adding more metal sheets, the number of particles eventually decreased. This was consistent with the expectation that cosmic rays were interacting with the atoms in the metals and losing energy to produce multiple secondary particles. In this paper, we describe a new–old approach for measuring particle showers in water using a cosmic ray telescope and Rossi's method. Our instrument consists of four Geiger–Müller tubes (GMT) arranged to detect muons and particle showers. GMT sensors are highly sensitive devices capable of detecting electrons and gamma rays with energies ranging from a few tens of keV up to several tens of MeV. Since Rossi studied the effects caused by cosmic rays as they pass through metals, we wondered if the same process could also happen in water. We present results from a series of experiments conducted with this instrument, demonstrating its ability to detect and measure particle showers produced by the interaction of cosmic rays in water with good confidence. To the best of our knowledge, this experiment has never been conducted before. Our approach offers a low-cost and easy-to-use alternative to more sophisticated cosmic ray detectors, making it accessible to a wider range of researchers and students. [ABSTRACT FROM AUTHOR]

Context. The number of satellites launched into Earth's orbit has almost tripled in the last three years (to over 4000) due to the increasing commercialisation of space. Multiple satellite constellations, consisting of over 400 000 individual satellites, have either been partially launched or are proposed for launch in the near future. Many of these satellites are highly reflective, resulting in a high optical brightness that affects ground-based astronomical observations. Despite this caveat, the potential effect of these satellites on gamma-ray-observing Imaging Atmospheric Cherenkov Telescopes (IACTs) has largely been assumed to be negligible due to their nanosecond-scale integration times. However, this assumption has not been verified to date. Aims. As IACTs are sensitive to optical wavelength light, we aim to identify satellite trails in data taken by the High Energy Stereoscopic System (H.E.S.S.) IACT array. In particular, this study is aimed at quantifying the potential effects on data quality and extensive air shower event classification and reconstruction. Methods. Using night sky background measurements from H.E.S.S., we determined which observation times and pointing directions are affected most by these satellite trails. We then evaluated their impact on the standard Hillas parameter variables used for event analysis. Results. Due to the brightest trails, false trigger events can occur, however, for most modern analyses, the effect on astronomical results will be minimal. We observe a mild increase in the rate of trail detections over time (approximately doubling in three years), which is partially correlated with the number of satellite launches. Overall, the fraction of H.E.S.S. data affected (~0.2% of dark time observations) is currently minimal. We note that these trails could still have a non-negligible effect on future Cherenkov Telescope Array observations if advanced analysis techniques designed to lower the energy threshold of the instrument are applied. [ABSTRACT FROM AUTHOR]

Variations in the cutoff rigidities of cosmic rays (ΔR) depending on the parameters of the solar wind, the interplanetary magnetic field (IMF), and geomagnetic activity were studied at different phases of the strong magnetic storm on May 15, 2005. We found that the trajectories ΔR, i.e., the successive values that ΔR takes depending on the parameters under study during the main phase of the storm did not coincide with the trajectories in the recovery phase, which led to the formation of hysteresis loops. The clearest hysteresis loops are formed for the relationship between ΔR and the Bz component of the IMF, the density and pressure of the solar wind, and the Dst index of geomagnetic activity. The area of the hysteresis loops increases with the latitude of the cosmic ray observation station. [ABSTRACT FROM AUTHOR]

A possibility to implement in well-known program CORSIKA user-made changes connected with heavy particles' production in nucleus–nucleus interactions is considered. Program PYTHIA8.3 and the developed interface between it and CORSIKA are used for that. It is shown that implementation of PYTHIA leads to the increase in the number of muons at the ground level () and electrons (up to 10 ). At the same time, the introduction of the top quark in first nucleus–nucleus collisions does not result in the increase of the number of particles in extensive air showers at the ground level. [ABSTRACT FROM AUTHOR]

A scintillation experiment is a part of the TAIGA astrophysical complex located in the Tunka Valley, 50 km from Lake Baikal. It consists of the Tunka-Grande and TAIGA-Muon arrays. Its scientific program is devoted to the study of cosmic rays (CRs) and search for astrophysical gamma rays by detecting charged particles (electrons and muons) of extensive air showers (EASs). We present the current status of the scintillation experiment, methods of EAS and CR parameters' reconstruction, the main results obtained by the Tunka-Grande array and our scientific program for the future. [ABSTRACT FROM AUTHOR]

Positive muons can be implanted into silicon carbide (SiC), where they model the isolated hydrogen defect in the negative, neutral, or positive charge states and act as either an acceptor or a donor with midgap energy levels [Lichti et al., Phys. Rev. B 70, 165204 (2004); Lichti et al., Phys. Rev. Lett. 101, 136403 (2008)]. The charge states evolve after implantation depending on the temperature and material doping. We have measured optically induced effects on muons implanted in 6H-SiC using a pulsed, tunable laser [Yokoyama et al., Rev. Sci. Instrum. 87, 125111 (2016)]. In n-type 6H-SiC at 85 K and 40 K, with a laser pulse of energy below the bandgap, we observe photoionization of the doubly occupied level ( Mu −) to the neutral defect Mu 0 and also ionization of Mu 0 to Mu +. Varying the timing of the laser pulse relative to muon arrival confirms that the laser interacts directly with the muons in a stable or metastable state. There is no evidence of any interaction when the laser pulse is timed to arrive before the muons, so either few free carriers are generated by absorption at other dopant sites or the excess carriers have a very short lifetime (≪ 100 ns). Wavelength scans show absorption edges corresponding to the possible interstitial sites within the structure. Combining these data and the existing muon results shows that at low temperature, we have co-existence of Mu 0 and Mu − charge states, with the muon or hydrogen acting as a deep compensating impurity. The technique can be applied to many other semiconductors where the muon has been observed to be electrically active, modeling hydrogen. [ABSTRACT FROM AUTHOR]

Strong quantum zero-point motion (ZPM) of light nuclei and other particles is a crucial aspect of many state-of-the-art quantum materials. However, it has only recently begun to be explored from an ab initio perspective, through several competing approximations. Here we develop a unified description of muon and light nucleus ZPM and establish the regimes of anharmonicity and positional quantum entanglement where different approximation schemes apply. Via density functional theory and path-integral molecular dynamics simulations we demonstrate that in solid nitrogen, α–N2, muon ZPM is both strongly anharmonic and many-body in character, with the muon forming an extended electric-dipole polaron around a central, quantum-entangled [N2–μ–N2]+ complex. By combining this quantitative description of quantum muon ZPM with precision muon quadrupolar level-crossing resonance experiments, we independently determine the static 14N nuclear quadrupolar coupling constant of pristine α–N2 to be –5.36(2) MHz, a significant improvement in accuracy over the previously-accepted value of –5.39(5) MHz, and a validation of our unified description of light-particle ZPM. Quantum entanglement and uncertainty in the positions of light nuclei and implanted particles can crucially impact our understanding of advanced materials. This paper develops a unified theoretical description of these effects and applies it to muon spectroscopy measurements of a material constant to significantly improve their accuracy. [ABSTRACT FROM AUTHOR]

Particle lateral distributions were investigated in cosmic ray air showers with energy eV registered at the Yakutsk array with surface and underground scintillation detectors with GeV threshold during the period of continuous observations from 1986 to 2016. The analysis covers events with arrival direction zenith angles within five intervals with step . Experimental values were compared to simulation results obtained with the use of CORSIKA code within the framework of QGSJet-01-d hadron interaction model. The whole dataset points at probable cosmic ray composition which is close to proton one. [ABSTRACT FROM AUTHOR]

In this paper, Forbush decrease (FD) profiles are compared for events associated with (i) coronal mass ejections from active regions accompanied by solar flares (AR CMEs), (ii) filament eruptions away from active regions (non-AR CMEs), and (iii) high-speed streams (HSSs) from coronal holes (CHs). FD profiles are described by time parameters that are delayed from an FD onset to the registration of maximum values of cosmic ray (CR) density variations, CR density hourly decrease, CR equatorial anisotropy, solar wind (SW) speed, interplanetary magnetic field (IMF) strength and minimum Dst index. Distributions of these parameters from 1997 to 2020 and within maxima and minima of the last solar cycles (SCs) were compared by statistical methods. The results obtained reveal that statistical properties of the time parameters depend both on the FD source and on the solar activity period. FDs associated with AR CMEs develop even at close values of SW parameters faster than those associated with non-AR CMEs and HSS from CHs. Differences between typical FD profiles for events associated with AR and non-AR CMEs are more significant when the interplanetary disturbance contains a magnetic cloud. The difference between FD profiles for events associated with AR and non-AR CMEs is less distinguishable within maximum SC 24 than within maximum SC 23. For FDs associated with HSS from CHs, the main phase durations and the time delays of maximal SW speed are longer within SC 23–24 minimum, while the time delays of maximal IMF strength differ insignificantly between 23–24 and 24–25 minima. [ABSTRACT FROM AUTHOR]