Neutrons and antiprotons in ultrahigh-energy cosmic rays

The neutron fraction in the very high-energy cosmic rays near the Greisen-Zatsepin-Kuzmin (GZK) cutoff energy is analyzed by taking into account the time dilation effect of the neutron decays and also the pion photoproduction behaviors above the GZK cutoff. We predict a non-trivial neutron fraction above the GZK cutoff and a negligibly small neutron fraction below. However, there should be a large antiproton fraction in the high-energy cosmic rays below the GZK cutoff in several existing models for the observed cosmic-ray events above and near the GZK cutoff. Such a large antiproton fraction can manifest itself by the muon charge ratio μ⁺/μ^- in the collisions of the primary nucleon cosmic rays with the atmosphere, if there is no neutron contribution. We suggest to use the muon charge ratio as one of the information to detect the composition of the primary cosmic rays near or below the GZK cutoff.     

Two-decade experience of application of plastic nuclear track detectors to cosmic ray research on satellites and orbital space stations

The work generalizes the results obtained during the last two decades in our spaceborne experiments aimed at studying galactic cosmic rays and cosmic ray anomalous component and carried out using solid-state nuclear track detectors (SSNTD) mounted mostly outside spacecraft. The experimental equipment and the techniques for identifying cosmic ray ions and for calculating particle flux values are described. The experimental data are used to construct a modified model for the fluxes and spectra of cosmic ray protons and heavy nuclei to be calculated to within a higher accuracy compared with the earlier models.     

Small shower CORSIKA simulations

Extensive Air Showers (EAS) induced by cosmic ray particles of very low energies, owing to the significantly steep cosmic ray energy spectrum, dominate the secondary particle flux measured by single detectors and small shower arrays. Such arrays connected in extended networks can be used to determine potentially interesting spatial correlations between showers, which may shed new light on the nature of ultra high-energy cosmic rays. The quantitative interpretation of showers recorded by small local arrays requires a methodology that differs from that used by ordinary large EAS arrays operating in the "knee" region and above. We present "small EAS generator," a semi-analytical method for integrating cosmic ray spectra over energies of interest and summing over the mass spectra of primary nuclei in arbitrary detector configurations. Furthermore, we provide results on the EAS electron and muon fluxes and particle density spectra.     

Ionization states of cosmic rays:Anuradha (IONS) experiment in Spacelab-3

The measurements of the ionization states, composition, energy spectra and spatial distribution of heavy ions of helium to iron of energies 10–100 MeV/amu in the anomalous cosmic rays are of major importance in understanding their origin which is unknown at present.Anuradha (IONS) cosmic ray experiment in Spacelab-3 was designed to determine the above properties in near earth space and this had a highly successful flight and operations aboard the shuttle Challenger at an orbital altitude of 352 km during 29 April to 6 May 1985. The instrument employs solid state nuclear track detectors (CR-39) of high sensitivity and large collecting area of about 800 cm² and determines the arrival time information of particles with active elements. Experimental methods, flight operations and preliminary results are briefly described. Initial results indicate that relatively high fluxes of low energy cosmic ray α-particles, oxygen group and heavier ions were obtained. The flight period corresponded to that of quiet Sun and the level of solar activity was close to solar minimum. It is estimated that about 10,000 events of low energy cosmic ray alpha particles with time annotation are recorded in the detector together with similar number of events of oxygen and heavier ions of low energy cosmic rays. The authors felicitate Prof. D S Kothari on his eightieth birthday and dedicate this paper to him on this occasion.     

Modernization of the Carpet-2 array of the Baksan Neutrino Observatory

The state of the art and the project of modernization of the extensive-air-shower array Carpet-2 of the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences are described. The modernized array will allow the performance of detailed study of variations in the cosmic ray intensity, the energy spectra and composition of primary cosmic rays in the energy range 10¹³–10¹⁶ eV, and the anisotropy of primary cosmic rays with energies above 10¹³ eV.     

Lateral distribution of EAS muons measured for the primary cosmic ray energy around 100 TeV

The muonic component of the extensive air showers (EAS) is of great importance for the astroparticle physics. It carries the information about the properties of primary cosmic ray (CR) particles, such as their mass, and electromagnetic and hadronic nature. It provides a sensitive test for the hadronic interaction models, which are inevitable for describing the cascade shower development of cosmic rays in EAS experiments. The YangBaJing Hybrid Array (YBJ-HA) experiment has been in operation since the end of 2016. Surface detectors are used for the measurements of primary energy, angular direction and core position of a shower event, while underground muon detectors are used for measuring the density of muons at various locations. Using the data obtained by the YBJ-HA experiment,this work reports the first measurement of the lateral muon distribution for the primary cosmic ray energy in the 100TeV region. The punch-through effect is evaluated via MC simulation.     

Cosmic rays from the knee to the highest energies

This review summarizes recent developments in the understanding of high-energy cosmic rays. It focuses on galactic and presumably extragalactic particles in the energy range from the knee (10¹⁵ eV ) up to the highest energies observed (>10²⁰ eV). Emphasis is put on observational results, their interpretation, and the global picture of cosmic rays that has emerged during the last decade.     

Astroparticle physics with high energy neutrinos: from AMANDA to IceCube

Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of 10²⁰ eV and 10¹³ eV, respectively. The puzzle of where and how Nature accelerates the highest energy cosmic particles is unresolved almost a century after their discovery. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the science reach of its extension, IceCube. Similar experiments are under construction in the Mediterranean. Neutrino astronomy is also expanding in new directions with efforts to detect air showers, acoustic and radio signals initiated by super-EeV neutrinos. The outline of this review is as follows:

Introduction

Why kilometer-scale detectors?

Cosmic neutrinos associated with the highest energy cosmic rays

High energy neutrino telescopes: methodologies of neutrino detection

High energy neutrino telescopes: status

     

Ultra high energy cosmic rays

Ultra High Energy Cosmic Rays (UHECRs) represent the most energetic source of elementary particles available to scientists. They have macroscopic energies, exceeding 5 × 10¹⁹ eV, and as yet unidentified sources. Unfortunately, their flux is as low as one particle per century per square kilometre, requiring dedicated detectors with huge apertures to obtain high-quality and statistically significant data-sets. Over the last three to four decades, a few tens of events at extreme energies were detected by ground-based cosmic ray detectors, opening a new window in the field of astroparticle physics. In this article, the physics of cosmic rays is reviewed briefly. We present a short history and the present status of the field mainly from an experimental point of view. Special attention is given to the Pierre Auger Observatory, the world's largest operating hybrid detector. The most recent and fascinating results are also presented and discussed. Finally, some attention is given to the next generation of detectors devoted to the exploration of the highest energy ranges, which is likely to dramatically increase our knowledge about UHECRs in the near future.     

Strong signature of the active Sun in 100 years of terrestrial insolation data

Terrestrial solar irradiance data of the Smithsonian Astrophysical Observatory from 1905 to 1954 and of Mauna Loa Observatory from 1958 to 2008 are analyzed. The analysis shows that, with changing solar activity, the atmosphere modifies the solar irradiance on the percentage level, in all likelihood via cosmic ray intensity variations produced by the active sun. The analysis strongly suggests that cosmic rays cause a large part of the atmospheric aerosols. These aerosols show specific absorption and scattering properties due to an inner structure of hydrated ionic centers, most probably of O₂^‐ and O₂⁺ produced by the cosmic rays.     

Primary cosmic ray composition at energies from 10<Superscript>17</Superscript> to 10<Superscript>18</Superscript> eV according to the EAS MSU array data

EAS MSU array data on the composition of primary cosmic rays at energies above 10₁₇ eV are analyzed. The problem of existence of a cosmic ray component that is not related to the conventional mechanism of formation of galactic cosmic rays is considered and the fraction of γ rays in primary cosmic rays is estimated.     

Cosmic ray energy spectrum from measurements of air showers

This review focuses on high-energy cosmic rays in the PeV energy range and above. Of particular interest is the knee of the spectrum around 3 PeV and the transition from cosmic rays of Galactic origin to particles from extra-galactic sources. Our goal is to establish a baseline spectrum from 1014 to 10^20 eV by combining the results of many measurements at different energies. In combination with measurements of the nuclear composition of the primaries, the shape of the energy spectrum places constraints on the number and spectra of sources that may contribute to the observed spectrum.     

Measurement of peak fluence of neutron beams using Bi-fission detectors

Fission fragments and other charged particles leave tracks of permanent damage in most of the insulating solids. Damage track detectors are useful for personal dosimeters and for flux/dose determination of high-energy particles from accelerators or cosmic rays. A detector that has its principal response at nucleon energy above 50 MeV is provided by the fission of Bi-209. Neutrons produce the largest percentage of hadron dose in most high-energy radiation fields. In these fields, the neutron spectrum is typically formed by low-energy neutrons (evaporation spectrum) and high-energy neutrons (knock-on spectrum). We used Bi-fission detectors to measure neutron peak fluence and compared the result with the calculated value of neutron peak fluence. For the exposure to 100 MeV we have used the iThemba Facility in South Africa.     

The Muon Puzzle in High-Energy Air Showers

The Muon Puzzle is a long-standing issue in the observation of high-energy cosmic rays. In 2018, eight leading air shower experiments combined their data on muons in high-energy air showers and established the existence of an energy-dependent offset with a significance of 8σ. The muon abundance is an important indicator for the cosmic ray mass. The Muon Puzzle needs to be solved to infer the cosmic-ray mass composition unambiguously. It also presents a unique opportunity to learn more about nonperturbative QCD in hadron—nucleus collisions. We will review the status of the Muon Puzzle and discuss an outlook for the future.     

Lorentz Invariance Violation: Modification of the Compton Scattering and the GZK Cutoff and Other Effects

This paper deals with the violation of Lorentz symmetry. The approach is based on Compton scattering which becomes modified due to a modified dispersion relation arising from a minimum spacetime cut off as in modern Quantum Gravity approaches. With this amendment, we find that two high-energy rays of different energies develop a time-lag. This time separation becomes prominent when the energies of the considered photons is ≥ 1GeV. Extending our approach to gamma rays of cosmic origin we predict that they undergo innumerable such scattering processes before reaching us. Therefore, it accounts for the time-lag phenomena of gamma ray bursts (GRB)’s which have been claimed to be observed. Also, we find that resorting to the modified Snyder-Sidharth Hamiltonian it is possible to extend the GZK cut off beyond its normal limit, 10²⁰ eV. Some observations of ultra high energy cosmic rays support this. This extends the limits of special theory of relativity.     

Modeling Source Spectra and Composition of Ultrahigh Energy Cosmic Rays

The inverse problem of cosmic ray transport of ultra-high energy cosmic rays is considered. The source spectrum and composition are derived based on the recent Auger data on energy spectrum, energy dependence of mean logarithm of atomic mass number and its variance. The dependence of results on the extrapolation of observable spectrum beyond energies 10²⁰ eV is investigated.

     

Estimation of The Cosmic Ray Mass Composition at Energy Above 10 17 eV According to Scintillation Detectors of the Yakutsk Array

The lateral distribution of cascade particles was studied in extensive air showers initiated by cosmic rays with energies above 1017 eV. The study is based on experimental data of ground-based and ground-shielded (with ∼1-GeV energy threshold) scintillation detectors of the Yakutsk EAS array collected during the continuous observational period from 1977 to 2017. Particle density measured in experiment is compared to the results of simulations performed with the use of several ultra-high energy hadron interaction models. The best agreement between theory and experiment was obtained for qgsjet01 and qgsjet ii-04 models. Interpretation of our data has indicated that within the energy range (1–30) × 1017 eV the cosmic ray mass composition changes from nuclei of intermediate group towards protons.     

Search for anisotropy in arrival directions of ultrahigh-energy cosmic rays by using the marr wavelet on the equatorial sphere

The arrival direction distribution of cosmic rays for energies E>10¹⁸ eV detected at the Yakutsk EAS array is analyzed using the Marr wavelet. Deviation from the isotropic distribution of 361 showers above 10¹⁹ eV is found at a significance level of 0.007, which corroborates previous evidence of the cosmic ray anisotropy in this energy range. In contrast to the previous methods, the wavelet analysis makes it possible to localize both a celestial-sphere domain containing a supposed source of excess cosmic ray flux and the scale parameter of the two-dimensional wavelet.     

A Statistic Model for Galactic Cosmic Rays

Supposed that all of cosmic ray particles of energy below 3×10¹⁸eV are mainly originated and accelerated in an individual explosion of the galactic supernovae(SNs).By using an isotropic diffusion propagation model,non-steady state density of the iron nucleus is investigated.Considering the effect of extra-galactic cosmic rays and the variety of the galactic cosmic ray nuclei,the statistic model of galactic cosmic rays with a reasonable distribution of the SNs in space and time can account for the spectrum of cosmic ray in the energy range of 10¹²—10²⁰eV quitewell.     

Energetic neutrons and gamma rays measured on the Aryabhata satellite

An experiment to measure energetic neutrons and gamma rays in space was launched in the first Indian scientific satellite,Aryobhata, on April 19, 1975. From this experiment, the first measurements in space of the Earth’s albedo fiux of neutrons of energy between 20 and 500 MeV have been made; the values obtained for two mean geomagnetic vertical cut-off rigidities of 5.6 and 17.0 GV are (6.3±0.4)×10⁻² and (1.4±0.3)×10⁻² neutrons cm⁻² sec⁻¹ respectively. These measurements confirm that protons arising from cosmic ray albedo neutron decay, can adequately account for the protons in the inner radiation belt. Observations on gamma rays of energy between 0.2 and 24 MeV have enabled the determination of the total background gamma ray flux in space as a function of latitude. This in turn has permitted useful information on the diffuse cosmic gamma rays. We have also observed four events that showed sudden increases in the gamma ray counting rates between 0.2 and 4.0 MeV. Observational details of these events are given.