Energy spectrum and mass composition of primary cosmic rays at energies 10<Superscript>15</Superscript>–10<Superscript>18</Superscript> eV

Data on muon and electron components of extensive air showers (EAS) (obtained with the EAS MSU array) were used to derive the primary cosmic ray (PCR) mass composition. It is shown that for energies beyond the knee at energy 3 × 10¹⁵ eV the abundance of heavy nuclei increases with energy. But at energies above 10¹⁷ eV the abundance of light nuclei starts to grow. The primary cosmic ray spectrum in the range 10¹⁵–10¹⁸ eV is analyzed. It is shown that at energies above 10¹⁷ eV the additional component appears and it differs from the bulk of Galactic cosmic rays generated by shocks in SN remnants.     

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.     

Dependence of the energy spectrum of UHE cosmic rays on the latitude of an extensive air shower array

Several energy spectra of cosmic rays with energies E ₀ ≥ 10¹⁷ eV measured at the Yakutsk EAS, AGASA, Haverah Park, HiRes, Auger, and SUGAR arrays are considered. It is shown that the fairly good mutual agreement of the spectrum shapes can be achieved if the energy of each spectrum is multiplied by a factor K specific for each spectrum. These factors exhibit a pronounced dependence on the latitude of the above-mentioned arrays.     

Mass Composition of Cosmic Rays with Energies above 1017 eV According to the Data from the Muon Detectors of the Yakutsk EAS Array

The lateral distribution of muons in extensive air showers with energies above 1017 eV detected by underground scintillation detectors with a threshold of 1.0 GeV at the Yakutsk array in 1986–2016 has been analyzed. The experimental data on the muon flux density at a distance of 300 m from the shower axis have been compared to the calculations within various models of hadron interactions at ultrahigh energies. The experimental data are in the best agreement with the QGSJet01 and QGSJet II-04 models. The mass composition of cosmic rays in the energy range of (1–30) × 10¹⁷ eV changes from middle nuclei to a purely proton composition.

     

Evidence for changing of cosmic ray composition between 10(17) and 10(18) eV from multicomponent measurements

The average mass composition of cosmic rays with primary energies between 10(17) and 10(18) eV has been studied using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum and the muon density as a function of energy. The results show that the composition is changing from a heavy to lighter mix as the energy increases.     

Investigation of the PCR energy spectrum shape by the means of the local EAS muon density technique

The results of studying the primary cosmic radiation (PCR) flux in the energy range 10¹⁵–10¹⁸ eV at the NEVOD-DECOR experimental array using local muon density spectra are reported. The experimental distributions and the spectra obtained by simulation of EAS muon LDF using the CORSIKA code are compared. Possibilities of using a new method for analysis of muon bundle events on the basis of the primary energy estimator are discussed.     

Arrival directions and chemical composition of ultrahigh-energy cosmic rays

Chemical composition of ultrahigh-energy cosmic rays is estimated through the reliably determined (both experimentally and theoretically) distribution of the number of showers in the galactic latitude. Experimental data at energies of ～10¹⁹ eV agree with the theoretical calculations, provided that cosmic rays involve predominantly heavy nuclei. An enhanced flux of cosmic rays from the galactic plane is detected at energies of ～10¹⁹ eV.     

Intensity of muon bundles at large zenith angles and hadron interaction models at energy of 1018 eV

Characteristics of muon bundles detected with the DECOR detector are compared to predictions based on different hadron interaction models and various assumptions as to the spectrum and mass composition of primary cosmic rays. The intensity of primary cosmic rays derived from the muon bundle data is considerably higher than that measured by means of the fluorescence technique. Either changes in the hadron interaction characteristics at ultrahigh energies or a revision of the energy calibration in the fluorescence technique of measuring EAS energy is required to explain these results.     

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.     

Cosmic ray spectrum obtained from the energy scattered by the particles of extensive air showers in the atmosphere and the galactic model

The differential energy spectrum of cosmic rays that is obtained on the basis of the measurements of Cherenkov radiation from extensive air showers in an energy range of 10¹⁵–10²⁰ eV is compared with the model of the propagation of primary particles in the interstellar medium with fractal properties. It is found that the shape of the experimental spectrum is in good agreement with the shape of the calculated spectrum of “all particles” at 10¹⁵–10¹⁸ eV. The average mass composition of cosmic rays that is calculated on the basis of five components does not contradict the average mass composition obtained from the experimental data for several parameters in this energy range.     

Search for extragalactic sources of ultrahigh-energy cosmic rays

Possible extragalactic sources of cosmic rays with energies above 4 × 10¹⁹ eV detected at the Yakutsk EAS array are sought. The correlation of the shower arrival directions with objects from Véron’s catalog that are located closer than 100 Mpc from the Earth confirms the observations at the Pierre Auger Observatory, as well as the Greisen-Zatsepin-Kuzmin effect on the spectrum of cosmic rays. The detailed analysis of the data reveals the classes of objects belonging to the active galactic nuclei that are the most probable sources of ultrahigh-energy cosmic rays.     

Prospects for Solving the Muon Puzzle on the NEVOD-DECOR-TREK Complex

Physics of Atomic Nuclei - The muon puzzle is an excess of muon bundles generated by primary cosmic rays (PCR) at energies above 10 $${}^{17}$$ eV compared to estimations that assume even a heavy...     

Efficiency of the production of γ families with halos and the fraction of protons at an energy of 10<Superscript>16</Superscript> eV

γ Families with halos detected in the “Pamir” experiment have been analyzed. Comparison of the experimental data with the results of calculation within the quark-gluon string model (MC0 code) made it possible to determine the efficiency of halo formation by protons, α particles, and heavy nuclei, as well as the fraction of protons in the mass composition of primary cosmic rays at an energy of 10¹⁶ eV. It is shown that halos are formed predominantly by protons. The fraction of protons in the mass composition of primary cosmic rays at an energy of 10¹⁶ eV is 20%.     

Local Muon Density Spectra at Various Zenith Angles Measured with NEVOD-DECOR

Data on cosmic ray muon bundles accumulated at the NEVOD-DECOR complex over the period from May 2012 to December 2018 have been analyzed. Local muon density spectra at various zenith angles have been reconstructed and compared with CORSIKA-based simulations. At large zenith angles and high muon multiplicities corresponding to primary particle energies more than about 3 × 1017 eV an excess of multi-muon events compared to simulations is clearly seen. Present data are compatible with the expectation for recent LHC-adjusted hadron interaction models only under assumption of extremely heavy (iron group nuclei) primary composition. The assumption of a heavy composition is however in contradiction with other EAS observables, such as maximum depth and its fluctuations.     

Ultrahigh-energy cosmic rays: Possible origin and spectrum

The complicated shape of the cosmic ray spectrum recorded by giant arrays in the energy range 10¹⁷–10²⁰ eV is analyzed. It is shown that in the energy region ∼10¹⁸–10¹⁹ eV the spectrum probably coincides with the injection spectrum whose exponent is equal approximately to 3.2–3.3. The flatter component in the energy region (3.2–5.0)×10¹⁹ eV is due to braking of extragalactic protons on primordial photons (the cosmic background radiation). At energies exceeding 3.2×10¹⁹ eV the spectrum does not have a blackbody cutoff. The possibility of determining the distances at which cosmic rays originate and investigating the evolution of their sources on the basis of ultrahigh-energy cosmic ray data is discussed. Zh. éksp. Teor. Fiz. 113, 12–20 (January 1998)     

On the composition of cosmic rays with E 0 ≥ 1017 eV according to the Yakutsk EAS array data

The energy spectrum and anisotropy of primary cosmic rays, as well as the lateral distribution functions of electrons and muons in extensive air showers (EASs) with E ₀ ≥ 10¹⁷ eV, are presented according to the Yakutsk EAS array data. It has been shown that the spectrum and lateral distribution functions in some energy ranges have different shapes for the particles that arrive from the disc of the Supergalaxy (Local Supercluster of galaxies) and from the other part of the celestial sphere. This is interpreted as the manifestation of the interaction of extragalactic primary cosmic rays with the gas of the Supergalaxy that possibly leads to the production of new ultra-high-energy particles.     

Muon content of ultrahigh-energy air showers: Yakutsk data versus simulations

A sample of 33 extensive air showers (EASs) with estimated primary energies above 2 × 10¹⁹ eV and high-quality muon data recorded by the Yakutsk EAS array is analyzed. The observed muon density is compared event-by-event to that expected from CORSIKA simulations for primary protons and iron using SIBYLL and EPOS hadronic interaction models. The study suggests the presence of two distinct hadronic components, “light” and “heavy.” Simulations with EPOS are in good agreement with the expected composition in which the light component corresponds to protons and the heavy component to iron-like nuclei. With SIBYLL, simulated muon densities for iron primaries are a factor of ∼ 1.5 less than those observed for the heavy component for the same electromagnetic signal. Assuming a two-component proton-iron composition and the EPOS model, the fraction of protons with energies E > 10¹⁹ eV is 0.52_−0.20^+0.19 at the 95% C.L. The text was submitted by the authors in English.     

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.     

Determining the primary cosmic ray energy from the total flux of Cherenkov light measured at the Yakutsk EAS array

We present a method for determining the energy of the primary particle that generates an extensive air shower (EAS) of comic rays based on measuring the total flux of Cherenkov light from the shower. Applying this method to Cherenkov light measurements at the Yakutsk EAS array has allowed us to construct the cosmic ray energy spectrum in the range 10¹⁵ ? 3 × 10¹⁹ eV.