Cosmic-ray Showers Research Articles

Cosmic ray shower rate variations detected by the ARGO-YBJ experiment during thunderstorms

The ARGO-YBJ detector, located at the Yangbajing Cosmic Ray Laboratory (4300 m a. s. l., Tibet, China), was a “full coverage” air shower array. The high altitude location and the frequent occurrence of thunderstorms, made ARGO-YBJ suitable to study the effects of atmospheric electric fields (AEF) on secondary cosmic rays. By analyzing the data of the ARGO-YBJ detector recorded during thunderstorms, significant variations of the rate of detected showers have been observed. During 20 thunderstorm episodes in 2012, the variations of the shower rates (both increases and decreases of amplitudes up to a few percent) are found to be correlated to the intensity and polarity of the AEF, and strongly dependent on the primary zenith angle. To understand the observed behavior, Monte Carlo simulations have been performed with corsika and g4argo (a code based on geant4). We found that the data are well consistent with simulations, assuming the presence of a uniform electric field in a layer of thickness of 500 m in the atmosphere above the observation level. Due to the AEF accelerates/decelerates and deflects the secondary charged particles (mainly electrons and positrons) according to their charge, modifying the number and position of particles with energy exceeding the detector threshold. For the differences in electron and positron flux, spectrum, and lateral distribution, the AEF has an asymmetric effect on the shower particles, producing significant variations of the particle pattern on the ground, and, consequently, on the rate of detected showers, consistent with observations.2 MoreReceived 8 February 2022Accepted 5 July 2022DOI:https://doi.org/10.1103/PhysRevD.106.022008© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic ray & astroparticle detectorsCosmic rays & astroparticlesGravitation, Cosmology & Astrophysics

A Search for Cosmic Ray Bursts at 0.1 PeV with a Small Air Shower Array

The Cosmic Ray Extremely Distributed Observatory (CREDO) pursues a global research strategy dedicated to the search for correlated cosmic rays, so-called Cosmic Ray Ensembles (CRE). Its general approach to CRE detection does not involve any a priori considerations, and its search strategy encompasses both spatial and temporal correlations, on different scales. Here we search for time clustering of the cosmic ray events collected with a small sea-level extensive air shower array at the University of Adelaide. The array consists of seven one-square-metre scintillators enclosing an area of 10 m × 19 m. It has a threshold energy ~0.1 PeV, and records cosmic ray showers at a rate of ~6 mHz. We have examined event arrival times over a period of over 2.5 years in two equipment configurations (without and with GPS timing), recording ~300 k events and ~100 k events. We determined the event time spacing distributions between individual events and the distributions of time periods which contained specific numbers of multiple events. We find that the overall time distributions are as expected for random events. The distribution which was chosen a priori for particular study was for time periods covering five events (four spacings). Overall, these distributions fit closely with expectation, but there are two outliers of short burst periods in data for each configuration. One of these outliers contains eight events within 48 s. The physical characteristics of the array will be discussed together with the analysis procedure, including a comparison between the observed time distributions and expectation based on randomly arriving events.

Measuring temporal characteristics of the Cherenkov radiation signal from extensive air showers of cosmic rays with a wide field-of-view telescope addendum to the Yakutsk array

A wide field-of-view Cherenkov telescope has been working in the surroundings of the Yakutsk array experiment since 2012. Its main function is to measure the waveform of the optical Cherenkov radiation signal induced by extensive air showers of cosmic rays. Analysis of the dataset collected by the telescope in the vicinity of ${10}^{17}\text{ }\text{ }\mathrm{eV}$ is intended for the reconstruction of the parameters of the development of the showers in addition to the main shower characteristics measured by the rest of the array detectors. In this paper, the observed duration of the Cherenkov radiation signal as a function of the shower core distance is used to estimate the depth of the shower maximum in a different way based on the results of model simulations. The results are in general agreement with those of other works.

Polarisation signatures in radio for inclined cosmic-ray induced air-shower identification

Autonomous radio-detection, i.e., detection of air-showers with standalone radio arrays, is one of the major technical challenges to overcome for the next generation astroparticle detectors. In this context, we study polarisation signatures of simulated radio signals to perform an identification of the associated air-showers initiated by cosmic-rays and neutrinos. We compare the two sources of radio emission (the charge excess and geomagnetic) and show that the former is almost negligible for inclined (zenith angle >65°) cosmic-ray air-showers. This provides an efficient background rejection criterion at the DAQ level, based on the projection of the total electric field along the direction of the local magnetic field. This relevant quantity can be computed, — even in an online treatment — for antennas measuring three orthogonal polarisations. Independently of the experimental antenna layout, we estimate that assuming a random polarisation of noise events, a rejection from ≈72% (for a non favourable detector location) to ≈93% (for a favourable one) of the noise induced events and a trigger efficiency of 86% (93%) with a 3σ (5σ) trigger threshold level should be achievable. We also show that neutrino-induced showers present a charge excess to geomagnetic signal ratio up to ∼10 times higher than for cosmic ray showers. Although this characteristic makes the identification of neutrino-induced showers challenging via the method developed here, it provides an efficient criterion to perform an offline discrimination between cosmic-ray and neutrino primaries. The stronger charge excess emission will also help the reconstruction of air-shower parameters, such as the core position.

Conceptual design report of the MPD Cosmic Ray Detector (MCORD)

This report presents a concept of constructing a detector dedicated for detection of muons observed during measurements carried out at the MPD (Multi-Purpose Detector) detector that is currently under construction at the NICA facility, Russia, Dubna. It has been proposed to design and build an additional detector that will complement the current MPD set and increase its measurement capabilities. The main goal of this project is to provide information from cosmic muons that pass the MPD detector in both in-beam and off-beam experiments. Hence, the detector is called the MPD COsmic Ray Detector (MCORD).The conceptual design of MCORD is proposed by a Polish consortium NICA-PL comprising several Polish scientific institutions.The data from cosmic ray muons could be used as a trigger for calibration of other detection systems comprising the MPD detector. Large surface covered by the MCORD offers also possibility for efficient registration of muons generated in expanding atmospheric showers induced by distant sources. Moreover, beyond some energy threshold, observation of muons originating from decays of collision products will also be possible. In this report examples of the MCORD functionality as a part of the MPD detector are presented.The MCORD is designed as a universal, fast triggering system built as a modular reconfigurable construction. The detection system will be based on plastic scintillators equipped with wavelength shifting fibers, and silicon photomultipliers (SiPM) will be used for scintillation readout. The online analysis of received signals will be performed using digital FPGA modules. Due to the modular design, the same system (its small part) can be used for both laboratory testing of other MPD sub-detectors, and the calibration of these detectors after placing them inside the MPD in off-beam mode. The full detector will support these systems as an additional trigger, calibrator, and muon identifier during the normal operation of the MPD detector with the beam. Thanks to its unique construction, it will expand the possibilities of collecting scientific data of the MPD detector with astrophysical observations.The publication will show the assumptions of the mechanical structure and electronic systems of the planned detector. The installation site of the detector as part of the MPD detector will be described in detail. In the following, the results of simulations made in preparation for this project will be presented. In particular, simulations with the CORSIKA code present angular distributions of particles in cosmic showers in the Dubna city region. Since muons dominate the cosmic ray showers, the MPD detector response to expected cosmic muon flux was also simulated. The results provide information about the muon cut-off thresholds depending on the MPD detector composition during the installation campaign. Simulations of muon events that could be used for MPD subsystems calibration were also performed. The results shown for various configuration of MCORD detector modules will enable the estimation of the time necessary to perform such tests in the future.Simulations with UrQMD model shows the muon abundances due to beam-beam collisions. Approximately 90% of muons are created from pions, whereas the number of muons that reach the MCORD detector is 10 times greater than the number of pions. The MPD detector response was also simulated under the influence of a stream of various particles, especially muons. It shows energy dependence of muon transmission coefficient for MPD with and without ECal assembled. Assuming requirement for muon transmission above 95%, the muon cut-off thresholds are 1.6 GeV and 2.0 GeV, respectively.MCORD detector performance evaluation is also reported. In the case when we used scintillators with one fiber with a diameter of 1 mm, the time resolution of about 1.0 ns was recorded, which corresponds to the positional accuracy (σx) of 7.1 cm. The results of laboratory tests show that application of a 2 mm diameter WLS fiber instead of the previously used 1 mm diameter fiber improves the time resolution to 0.80 ns.

The Influence of Heavy Cosmic Rays in Energy Deposition in Molecular Clouds Employing the GEANT4 Code and Voyager I Data

Abstract Galactic and extragalactic cosmic rays fully illuminate and trigger several physical and physicochemical changes in molecular clouds (MCs), including gas and grain heating, molecular destruction and formation, and molecular and atomic desorption (sputtering) from dust/ices to gas phase. Besides the major component in cosmic ray inventory (in flux) being electrons, protons, and alphas, particles with larger atomic numbers have a higher rate of energy delivery (due to richer cosmic ray showers) than the lighter particles, and this may add extra energy input into MCs. To understand this issue, we perform complementary calculations to the previous work on MCs, now adding the heavy ions (12 ≤ Z ≤ 29) in the cosmic ray incoming inventory. Once more, the calculations were performed employing the Monte Carlo toolkit GEANT4 code (considering nuclear and hadron physics). We observe that most projectiles in the heavy ion group have lower deposited energies (roughly 10 times less) than iron with the exception of magnesium (Z = 12) and silicon (Z = 14) which are about double. Cobalt presents the lowest deposited energies with respect to iron (only 0.5%). The total energy deposition in the current model was only roughly 10% higher (outer layers) and virtually the same at the center of the cloud when compared with the previous model (with only protons + alphas + electrons sources). The results show that energy deposition by heavy ions is small compared with the values from light particles, and also suggest a very low temperature enhancement due to heavy ions within the MC, being the protons the dominant agent in the energy delivery and also in the cloud’s heating.

Starting track events in IceCube

The IceCube Neutrino Observatory is a cubic kilometer-sized detector designed to detect neutrinos of astrophysical origin. We summarize an ongoing dataset that will identify starting track neutrino events above 1 TeV over the entire sky. We discuss a method using a boosted decision tree (BDT) to classify and reduce the cosmic ray muon rates from billions per year to ∼1 per year while selecting ∼1000 starting track events per year. Muon tagging with the BDT also improves our sensitivity to astrophysical neutrinos from the southern sky, since it removes atmospheric neutrinos accompanied by muons from parent cosmic ray showers. Next, we introduce a Random Forest to reconstruct the energy of astrophysical neutrino candidates interacting inside the detector volume, with an energy resolution of 25% made possible by identification of the hadronic and muonic components of the neutrino interaction. Finally, the outgoing muon track is used to reconstruct the direction of the astrophysical neutrino candidates with an estimated median angular resolution of 1.6° at 1 TeV improving to 0.5° at 1 PeV. This dataset will eventually be used to measure the astrophysical diffuse flux, so we summarize the impact of systematic uncertainties on such a measurement.

Supercomputers face a cosmic challenge

Fast neutrons from cosmic-ray showers can cause significant errors in supercomputers. But by measuring the scale of the problem, physicists hope not only to make such devices less prone to cosmic corruption but also protect everything from self-driving cars to quantum computers, as Rachel Brazil finds out

Design and implementation of the AMIGA embedded system for data acquisition

The Auger Muon Infill Ground Array (AMIGA) is part of the AugerPrime upgrade of the Pierre Auger Observatory. It consists of particle counters buried 2.3 m underground next to the water-Cherenkov stations that form the 23.5 km2 large infilled array. The reduced distance between detectors in this denser area allows the lowering of the energy threshold for primary cosmic ray reconstruction down to about 1017 eV. At the depth of 2.3 m the electromagnetic component of cosmic ray showers is almost entirely absorbed so that the buried scintillators provide an independent and direct measurement of the air showers muon content. This work describes the design and implementation of the AMIGA embedded system, which provides centralized control, data acquisition and environment monitoring to its detectors. The presented system was firstly tested in the engineering array phase ended in 2017, and lately selected as the final design to be installed in all new detectors of the production phase. The system was proven to be robust and reliable and has worked in a stable manner since its first deployment.

Measurement and simulation of the neutron propagation time distribution inside a neutron monitor

Using a setup for testing a prototype for a satellite-borne cosmic-ray ion detector, we have operated a stack of scintillator and silicon detectors on top of the Princess Sirindhorn Neutron Monitor (PSNM), an NM64 detector at 2560-m altitude at Doi Inthanon, Thailand (18.59∘N, 98.49∘E). Monte Carlo simulations have indicated that about 15% of the neutron counts by PSNM are due to interactions (mostly in the lead producer) of GeV-range protons among the atmospheric secondary particles from cosmic ray showers, which can be detected by the scintillator and silicon detectors. Those detectors can provide a timing trigger for measurement of the propagation time distribution of such neutrons as they scatter and propagate through the NM64, processes that are similar whether the interaction was initiated by an energetic proton (for 15% of the count rate) or neutron (for 80% of the count rate). This propagation time distribution underlies the time delay distribution between successive neutron counts, from which we can determine the leader fraction (inverse multiplicity), which has been used to monitor Galactic cosmic ray spectral variations over ∼1-40 GV. Here we have measured and characterized the propagation time distribution from both the experimental setup and Monte Carlo simulations of atmospheric secondary particle detection. We confirm a known propagation time distribution with a peak (at ≈70 μs) and tail over a few ms, dominated by neutron counts. We fit this distribution using an analytic model of neutron diffusion and absorption, for both experimental and Monte Carlo results. In addition we identify a group of prompt neutron monitor pulses that arrive within 20 μs of the charged-particle trigger, of which a substantial fraction can be attributed to charged-particle ionization in a proportional counter, according to both experimental and Monte Carlo results. Prompt pulses, either due to neutrons or charged-particle ionization, are associated with much higher mean multiplicity than typical pulses. These results validate and point the way to some improvements in Monte Carlo simulations and the resulting yield functions used to interpret the neutron monitor count rate and leader fraction.

Polarized Radiation and the Emergence of Biological Homochirality on Earth and Beyond

Abstract It has been proposed that spin-polarized cosmic radiation can induce asymmetric changes in helical biopolymers that may account for the emergence of biological homochirality. The parity violation in the weak interaction has direct consequences on the transport of polarization in cosmic ray showers. In this paper, we show that muons retain their polarization down to energies at which they can initiate enantioselective mutagenesis. Therefore, muons are most likely to succeed in establishing the connection between broken symmetries in the standard model of particle physics and that found in living organisms. We calculate the radiation doses deposited by primary and secondary cosmic rays at various prime targets for the searches of life in the solar system: Mars, Venus, Titan, icy moons and planetesimals, and discuss the implications for the enantioselective mutagenesis proposed as to be the driver of homochiralization. Earth is unusual in that spin-polarized muons dominate the cosmic radiation at its surface.

Fair Weather Neutron Bursts From Photonuclear Reactions by Extensive Air Shower Core Interactions in the Ground and Implications for Terrestrial Gamma‐ray Flash Signatures

AbstractWe report on anomalously long duration (2 ms) count rate bursts following the impact of cosmic ray showers near a 7.62 cm x⊘7.62 cm LaBr3 scintillation detector at the High Altitude Water Cherenkov array in Mexico, previously described by Stenkin et al. (2001), and termed “neutron bursts.” The largest burst produced 198 counts within 2 ms in our LaBr3 detector. We simulate the neutron burst albedo flux (that is, secondary emissions from an extensive air shower core impacting the ground), and show that (1) the characteristic spectra and count rates are well explained by neutron absorption in the ground and (2) any cosmic ray secondary that produces neutrons, either through hadron inelastic collisions, or photoneutron production by gamma‐rays, produces the same characteristic spectra. This implies that other natural phenomena that produce downward beams of gamma‐rays, like Terrestrial gamma ray flashes, should produce a similar “neutron burst” signature from the photoneutron reactions occurring in the soil.

Design, upgrade and characterization of the silicon photomultiplier front-end for the AMIGA detector at the Pierre Auger Observatory

AMIGA (Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory to complement the study of ultra-high-energy cosmic rays (UHECR) by measuring the muon content of extensive air showers (EAS). It consists of an array of 61 water Cherenkov detectors on a denser spacing in combination with underground scintillation detectors used for muon density measurement. Each detector is composed of three scintillation modules, with 10 m2 detection area per module, buried at 2.3 m depth, resulting in a total detection area of 30 m2. Silicon photomultiplier sensors (SiPM) measure the amount of scintillation light generated by charged particles traversing the modules. In this paper, the design of the front-end electronics to process the signals of those SiPMs and test results from the laboratory and from the Pierre Auger Observatory are described. Compared to our previous prototype, the new electronics shows a higher performance, higher efficiency and lower power consumption, and it has a new acquisition system with increased dynamic range that allows measurements closer to the shower core. The new acquisition system is based on the measurement of the total charge signal that the muonic component of the cosmic ray shower generates in the detector.

Preliminary analysis of neutron time-delay histograms from Changvan latitude surveys

The name “Changvan” is given to a transportable neutron monitor, modernized by researchers in Thailand and housed inside a standard-size shipping container. It contains three neutron-sensitive proportional counters, which contain enriched 10BF3 gas, to detect cosmic ray showers. Primary cosmic rays are high-energy particles arriving from outer space. By colliding with atoms in the atmosphere, they produce a shower of sub-atomic particles, called secondary particles. Some particles can reach the Earth’s surface, including neutrons. The Changvan is designed to measure atmospheric neutrons during a latitude survey. The side counter tubes are ringed with lead producer to produce evaporation neutrons when secondary particles collide with it. The center counter lacks the lead producer but can receive neutrons from nearby counters. The reflector and moderator made from polyethylene thermalize the evaporation neutrons and protect against disturbance by external low-energy neutrons. In this work, we pursue methods to determine spectral changes in Galactic cosmic rays using data from the Changvan, avoiding the systematic inconsistencies of cross-station comparisons. We examine neutron time delay histograms from the three counter tubes, as recorded by specially designed readout electronics, where the time delay refers to the time interval between consecutive neutron detections in one counter. We perform a preliminary analysis of such histograms to measure the leader fraction (L) of neutrons that do not follow a previous neutron from the same primary cosmic ray. The electronic dead time will be considered in the L calculation.

Multimodal imaging of muon based on scattering and secondary induced neutrons

Muon scattering imaging technology can be used to detect nuclear material and is of considerable significance in nuclear safety. However, it is difficult to distinguish special nuclear materials from high-Z objects effectively by using the existing muon scattering imaging technologies. Muon-induced neutrons emitted from special nuclear materials can help to identify the existence of special nuclear materials. However, this method has long imaging time and low imaging quality. Multimodal imaging of muon uses both the information about scattering muons penetrating the material and the information about muons stopped by material and generating secondary induced neutrons, which can overcome the shortcomings of single imaging method effectively. The detection model is set up based on Geant4. The simulation programs of muon imaging in coincidence with muon induced neutrons, scattering imaging of muon, and multimodal imaging of muon are developed by using Cosmic-ray Shower Library as particle source, and the imaging algorithms are implemented respectively on the basis of the simulated data. Two imaging models are designed for muon scattering imaging. The first one is a single <sup>235</sup>U cube, and the second one is composed of four cubes, namely <sup>235</sup>U cube, <sup>239</sup>Pu cube, lead cube and aluminum cube. This simulation has completed muon scattering imaging of single cube and four cubes. In the part of muon imaging in coincidence with muon induced neutrons, the neutronic gain of the HEU (90% <sup>235</sup>U) plate, LEU (20% <sup>235</sup>U) plate, and DU (0.2% <sup>235</sup>U) plate, as well as the relationship between the neutronic gain of these three uranium plates and the energy and charged properties of the muon are obtained by simulation, and then two imaging models are set up. The first one is composed of four cubes, namely <sup>235</sup>U cube, <sup>239</sup>Pu cube, lead cube, and aluminum cube, and the other is comprised of multilayer nuclear components. The 2D and 3D reconstruction results of multi-objects and multilayer nuclear components are obtained through muon imaging in coincidence with muon induced neutrons. Then the multimodal imaging of muon for three cubes is realized in the presence or absence of iron shielding shell. The imaging capabilities are compared with the muon scattering imaging capacities and muon imaging capacities in coincidence with muon induced neutrons. Simulation studies indicate that multimodal imaging of muon based on scattering and secondary induced neutrons can effectively combine the advantages of every single imaging method. The multimodal imaging of muon can take advantage of available information more efficiently, which is helpful in improving the imaging quality. Multimodal imaging of muon not only has the advantages of short imaging time and high imaging quality, but also can distinguish special nuclear material from other high-Z materials clearly, which is vital for detecting special nuclear materials.

Lightning Interferometry Uncertainty, Beam Steering Interferometry, and Evidence of Lightning Being Ignited by a Cosmic Ray Shower

AbstractWe present an uncertainty analysis on correlation‐based time delay estimate, the basis for broadband lightning interferometry. A normal interferometry would yield much higher uncertainties than the theoretically predicted lower bound due to finite correlation window lengths. However, if the signals are aligned in time, the uncertainties approach the lower bound and can be used to indicate the interferometric uncertainties. Based on this, we introduce a beam steering interferometry technique. It first estimates a direction centroid for the lightning sources with a normal interferometry and computes the time delays among the signals. It then shifts the raw data with the time delays to align the signals roughly in time and reprocess the aligned signals. It finally pushes the reprocessed results to their correct positions, based on the time delays estimated in the first step. We apply this technique on a fast positive breakdown (FPB) process that started a normal intracloud lightning. The FPB process is shown to have a much more complex structure and development than a normal interferometry would provide. More importantly, from both interferometric and polarization analyses, the FPB appears to be ignited by a cosmic ray shower (CRS). We estimate the radio frequency strength and frequency content related to a presumed CRS in a thunderstorm electric field and find that they are in agreement with the observations. We examine the electric field effect of the CRS front and find that it could raise the field above the threshold for positive breakdown and is capable of igniting the FPB (and the lightning).

Diseño, mejora y caracterización del front-end con fotomultiplicadores de silicio para los detectores de AMIGA del Observatorio Pierre Auger

AMIGA (Auger Muons and Infill for the Ground Array) es una mejora del Observatorio Pierre Auger con el objetivo de complementar el estudio de los rayos cósmicos de ultra alta energía (UHECR) mediante la medición del contenido muónico de las cascadas atmosféricas extensas (EAS). Éste consiste en un arreglo de 61 detectores de agua de efecto Cherenkov ubicado en un espacio más denso en combinación con detectores de centelleo enterrados bajo tierra utilizados para la medición de densidad de muones. Cada detector esta compuesto por tres módulos centelladores, con un área de detección de 10 m2 por módulo, enterrados a 2.3 m de profundidad, resultando un área total de detección de 30 m2. Fotomultiplicadores de silicio (SiPM) miden la cantidad de luz de centelleo generada por las partículas cargadas que atraviesan los módulos. En este trabajo, el diseño de la electrónica del front-end para procesar las señales de esos SiPMs, y los resultados de pruebas realizadas en el laboratorio como también en el sitio del Observatorio Pierre Auger son descriptos. Comparado con el diseño anterior, esta nueva electrónica muestra un mayor rendimiento, una mayor eficiencia y un menor consumo de potencia, e incluye además, un nuevo sistema de adquisición con un rango dinámico ampliado que permite realizar mediciones cercanas al núcleo de la lluvia. El nuevo sistema de adquisición esta basado en la medición de la carga total que la componente muónica de la lluvia cósmica genera en el detector.

Remote update solution for LHAASO wide field-of-view Cherenkov telescope array electronic readout system

The wide field-of-view Cherenkov telescope array (WFCTA), which consists of 18 wide field telescopes, is one of the main detectors used in the Large High Altitude Air Shower Observatory (LHAASO) . The WFCTA collects Cherenkov light and fluorescence signals from cosmic ray showers and converts them into electrical signals that are then processed by an electronic system based on a field-programmable gate array (FPGA) for later physical analysis. The high altitude of the array and the difficulties involved in disassembling the electronics inside the telescope mean that an electronic remote update solution with high fault tolerance and simple operation is required. The proposed remote update solution for the LHAASO-WFCTA electronic readout system is based on Xilinx Multiboot and is intended to implement remote updates without appended circuits. When compared with other remote update solutions based on Multiboot, the solution used on the WFCTA saves numerous resources in the original FPGA program, eases the timing constraint burden, and enhances security. This solution has been successfully implemented and used in remote updating of FPGAs in the LHAASO-WFCTA several times.

Reconstruction of Cherenkov radiation signals from extensive air showers of cosmic rays using data of a wide field-of-view telescope

The operation of a wide field-of-view (WFOV) Cherenkov telescope is described. The detection of extensive air showers (EASs) of cosmic rays (CRs) is based upon the coincidence with signals from the Yakutsk array. The data acquisition system of the telescope yields signals connected with EAS development parameters: presumably, shower age and position of shower maximum in the atmosphere. Here, we describe the method of signal processing used to reconstruct Cherenkov radiation signals induced by CR showers. An analysis of signal parameters results in the confirmation of the known correlation of the duration of the Cherenkov radiation signal with the distance to the shower core. The measured core distance dependence is used to set an upper limit to the dimensions of the area along the EAS axis where the Cherenkov radiation intensity is above half-peak amplitude.

The shape of the cosmic ray proton spectrum

Recent observations of cosmic ray protons in the energy range 102–105 GeV have revealed that the spectrum cannot be described by a simple power law. A hardening of the spectrum around an energy of order a few hundred GeV, first observed by the magnetic spectrometers PAMELA and AMS02, has now been confirmed by several calorimeter detectors (ATIC, CREAM, CALET, NUCLEON and DAMPE). These new measurements reach higher energy and indicate that the hardening corresponds to a larger step in spectral index than what was estimated by the magnetic spectrometers. Data at still higher energy (by CREAM, NUCLEON and DAMPE) show that the proton spectrum undergoes a marked softening at E ≈ 104 GeV. Understanding the origin of these unexpected spectral features is a significant challenge for models of the Galactic cosmic rays. An important open question is whether additional features are present in the proton spectrum between the softening and the “Knee”. Extensive Air Shower detectors, using unfolding procedures that require the modeling of cosmic ray showers in the atmosphere, estimated the proton flux below and around the Knee (at E ≃ 3 PeV). These results however have large systematic uncertainties and are in poor agreement with each other. The measurement in the PeV energy range, recently presented by IceTop/IceCube, indicates a proton flux higher than extrapolations of the direct measurements calculated assuming a constant slope, and therefore requires the existence of an additional spectral hardening below the Knee. A clarification of this point is very important for an understanding of the origin of the Galactic cosmic rays, and is also essential for a precise calculation of the spectra of atmospheric neutrinos in the energy range (E ≳ 10 TeV) where they constitute the foreground for the emerging astrophysical ν signal.