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.     

Estimate of the mass composition of cosmic rays above 4×10<Superscript>19</Superscript> eV

The arrival directions of extensive air showers are analyzed on the basis of world data. It is found that the zenith-angle distributions for energies E>10¹⁹ eV and E>4×10¹⁹ eV differ from each other. According to our estimates, the SUGAR array detects no showers above 10²⁰ eV. The mass composition of ultrahigh-energy cosmic rays is estimated. Cosmic rays with E>4×10¹⁹ eV most likely consist of superheavy nuclei.     

Ordered structure of the directions of arrival of E<Subscript>0</Subscript>∼5×10<Superscript>17</Superscript> eV cosmic rays according to data from the Yakutsk array for recording extensive air showers

Results are presented that were obtained by analyzing arrival directions for cosmic rays recorded by the Yakutsk array between 1974 and 2001 in the energy range E₀=10^17.6–17.9 eV for zenith angles in the region θ≤53°. It is shown that their flux consists of two components—an isotropic (about 75%) and a cluster (about 25%) one—that are characterized by sharply different degrees of anisotropy. At E₀=10^17.7–17.8 eV, the observed showers are found to be strongly correlated with the Supergalaxy plane.     

Depth of the maximum of extensive air showers and mass composition of primary cosmic radiation at an energy of 4 × 10<Superscript>17</Superscript> eV according to data on radioemission from extensive air showers

The results of a reanalysis of experimental data on extensive-air-shower radioemission that were obtained previously at the Moscow State University array for studying extensive air showers are presented. The lateral distribution of radioemission is given for showers characterized by a primary energy of 4 × 10¹⁷ eV and a zenith angle of θ = 35°. On the basis of an analysis of a lateral distribution of radioemission, the average value of the shower-maximum depth at a primary energy of 4 × 10¹⁷ eV is estimated at X _max = 655 ± 13 g/cm². Estimates of themass content of primary radiation that were obtained from an analysis of the distribution of X _max are compatible with the hypothesis that the role of light nuclei becomes more pronounced at energies above 10¹⁷ eV.     

Energy spectrum and anisotropy of cosmic rays with <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript>≥10<Superscript>17</Superscript> eV from Yakutsk EAS array data

Data from the Yakutsk extensive air shower array for the period 1974–2004 are used to analyze the energy spectrum and anisotropy of primary cosmic rays (PCRs) with energy E₀≥10¹⁷ eV. The spectra from different regions of the sky are shown to differ in shape. Enhanced and reduced particle fluxes come from the disks of the Galaxy and the Supergalaxy (the Local Supercluster of galaxies) at E₀≥5×10¹⁸ eV and E₀≤ (2?3)×10¹⁸ eV, respectively. This is interpreted as a manifestation of the possible interaction between extragalactic PCRs and the matter of these spatial structures.     

On the sensitivity of the spatial-angular distribution of the Cherenkov light in extensive air showers to the mass composition of primary cosmic rays with energies of 10<Superscript>15</Superscript>–10<Superscript>16</Superscript> eV

This paper analyses the possibility of separating distinct groups of nuclei of primary cosmic rays with energies of 10¹⁵–10¹⁶ eV from the data on the spatial-angular distribution of Cherenkov light in extensive air showers. The paper shows that using an array of a few (3–4) telescopes with a moderately sized angular cell ∼0.5° placed at a distance ∼100 m from one another, one can achieve almost complete separation of the showers initiated by these nuclei (the Bayesian classification error is a few percentage points for the case of separating primary protons and nitrogen nuclei). The authors propose new parameters of the angular Cherenkov image that can greatly enhance the separability of the shower classes as compared to the approach based on the traditional parameters.     

On the anisotropy of <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ⩾ 5.5× 10<Superscript>19</Superscript> eV cosmic rays according to data of the Pierre Auger Collaboration

The Pierre Auger Collaboration discovered, in a solid angle of radius about 18°, a local group of cosmic rays having energies in the region E ₀ ≥ 5.5 × 10¹⁹ eV and coming from the region of the Gen A radio galaxy, whose galactic coordinates are l _G = 309.5° and b _G = 19.4°. Near it, there is the Centaur supercluster of galaxies, its galactic coordinates being l _G = 302.4° and b _G = 21.6°. It is noteworthy that the Great Attractor, which may have a direct bearing on the observed picture, is also there.     

Multipolar anisotropy of <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ⩾ 10<Superscript>17</Superscript> eV cosmic rays according to data of the Yakutsk array for studying extensive air showers

The results obtained by analyzing arrival directions for primary cosmic particles characterized by energies in the region E ₀ ⩾ 10¹⁷ eV and zenith angles in the range θ ⩽ 60° and detected at the Yakutsk array for studying extensive air showers (EASs) over the period spanning 1974 and 2009 are presented. It is shown that these events exhibit different anisotropies in different energy intervals.     

Study of the energy spectrum and mass composition of primary cosmic rays in the energy range of 10<Superscript>18</Superscript>–10<Superscript>20</Superscript> eV using a balloon setup in antarctica (SPHERE-antarctica project)

An Antarctic balloon experiment for measuring the energy spectrum and elemental composition of cosmic rays in the ultrahigh-energy range (10¹⁸–10²⁰) eV is proposed. Scientific equipment will measure fluorescence caused by an extensive air shower formed in the atmosphere by an ultrahigh energy particle and Cherenkov light of this shower reflected from a snow surface. It is assumed that the balloon will fly in the circumpolar orbit in Antarctica at a height of ~25 km for (2–3) winter (in the Southern Hemisphere)months. For this time, ~3000 events caused by particles with energies above 10¹⁸ eV and (200–300) events caused by particles with energies above 10¹⁹ eV will be detected.     

Small-scale anisotropy and composition of <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≈ 10<Superscript>17</Superscript> eV cosmic rays according to data from the Yakutsk array for studying extensive air showers

Results are presented that were obtained from an analysis of arrival directions for cosmic rays of energy in the range E ₀ ≈ 10^16.9–17.2 eV that were recorded by the Yakutsk array between 1974 and 2001 at zenith angles of θ ≤ 45°. It is shown that a considerable part of them form clusters that have small-scale cellular structure. In all probability, these showers are generated by neutral particles of an extragalactic origin.     

On the origin of <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≥ 10<Superscript>17</Superscript> eV cosmic rays according to data from the Yakutsk array for studying extensive air showers

Results are presented that were obtained by analyzing the energy spectrum and anisotropy of E ₀ ≥ 10¹⁷ eV primary cosmic rays on the basis of data accumulated at the Yakutsk array for studying extensive air showers over the period between 1974 and 2004. It is shown that spectra corresponding to different regions of the sky differ in shape. Particle fluxes going from the Galaxy and Supergalaxy (a local supercluster of galaxies) disks are enhanced for E ₀ ≥ 5 × 10¹⁸ eV and are reduced for E ₀ ≤ (2–3) × 10¹⁸ eV. This observation is interpreted as a manifestation of the possible interaction between extragalactic primary cosmic rays and matter of the above structures of space.     

Local anisotropy of cosmic rays with <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≥ 10<Superscript>17</Superscript> eV from Yakutsk EAS array data

The arrival directions of primary cosmic ray particles with energies E ₀ ≥ 10¹⁷ eV and zenith angles θ ≤ 60° recorded on the Yakutsk array over the period 1974–2009 are analyzed. These events are shown to have different anisotropies in different energy ranges.     

On EAS spectrum with extremely low content of hadrons in the primary-energy range ∼10<Superscript>14</Superscript>−10<Superscript>15</Superscript> eV

The distribution of energy fluxes of the hadron component of extensive air showers through an ion-ization calorimeter in the primary-energy range ～3 × 10¹³?10¹⁶ eV is considered. Extensive air showers with zero and minimum energy fluxes of the hadron component are selected. It is concluded that the primary-energy range E ₀ ≈ 1 × 10¹⁴?2 × 10¹⁵ eV contains isotropic γ radiation with a spectrum close to bell-shaped, having a maximum near E ₀ ≈ 2.2 × 10¹⁴ eV and an additional peak near E ₀ ≈ 1.6 × 10¹⁵ eV.     

Investigation of the structure of a muon disk for <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≥ 5 × 10<Superscript>16</Superscript> eV according to data of the Yakutsk array for studying extensive air showers

The results are presented that were obtained at the Yakutsk array by investigating the time structure of a muon disk in extensive air showers of primary energy in the region E ₀ ≥ 5 × 10¹⁶ eV at distances of 250 to 1500 m from the shower core. The measurements were performed with a large muon detector that has an area of 184 m² and a detection threshold of E _μ≈0.5secθ GeV and which began operating in November 1995. Two components having different muon-disk thicknesses were discovered, and this requires strong modifications in the currently prevalent idea of the development of extensive air showers. The problem of the existence of E ₀ ≥ 10²⁰ eV events is considered. __________ Translated from Yadernaya Fizika, Vol. 68, No. 1, 2005, pp. 74–88. Original Russian Text Copyright ? 2005 by Glushkov, Dedenko, Sleptsov.     

Investigation of the reaction D(<Superscript>4</Superscript>He, γ)<Superscript>6</Superscript>Li at ultralow energies

The cross section of the reaction D(⁴He, γ)⁶Li with titanium and zirconium deuterides as targets is measured for incident ⁴He⁺ ion energies of 30 and 36 keV, respectively. The ion beam is generated by a Hall pulsed plasma accelerator. For the first time, upper limits on the cross section of the reaction D(⁴He, γ)⁶Li at ultralow energies are imposed (at 90% confidence level): σ ≤ 1.2 × 10^?35 cm² for the TiD₂ target and E(⁴He⁺) = 30 keV, and σ ≤ 7 × 10^?36 cm² for the ZrD₂ target and E(⁴He⁺) = 36 keV     

Spatio-temporal structure of the muon disk at <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≥ 5 × 10<Superscript>16</Superscript> eV from Yakutsk EAS array data

We present the results of our study of the temporal structure of the muon disk at the Yakutsk array in extensive air showers with primary energies E₀ ≥ 5 × 10¹⁶ eV at distances of 250–1500 m from the shower axis obtained using a large muon detector with an area of 184 m² and a detection threshold of E_μ ≈ 0.5 sec θ GeV. We have found two components with different muon disk thicknesses that require significant revisions of our view of the development of extensive air showers.     

Energy spectra of secondary particles in γ families and their sensitivity to the spectrum of primary cosmic rays

Spectra of secondary particles (γ-rays) in γ-families detected in the X-ray chambers in the Pamirs (H = 600 g cm^?2) have been analyzed. These γ-ray spectra show a bend at the energy E* _γ ≈ (ΣE _γ )^min, where (ΣE _γ )^min is the lowest total energy of γ-rays in the families above which γ-families were selected. The bend is not related to the knee in the spectrum of primary particles; it is due to the use of the ΣE _γ selection criterion. The E _γ spectrum slope is sensitive to the spectrum of the primary cosmic rays in the region E _γ ≥ (ΣE _γ )^min.     

Radio signals from extensive air showers with the energies <Emphasis Type="Italic">E</Emphasis> <Subscript>0</Subscript> ≥ 10<Superscript>19</Superscript> eV according to data from the Yakutsk extensive air shower array

A radio instrument and results obtained from the measurements of the 32-MHz radio signal from particles of extensive air showers (EASs) with energies E₀ ≥ 1×10¹⁹ eV are reported in brief. The data were obtained at the Yakutsk EAS array in 1987–1989 (the first series of measurements) and in 2009–2014 (new series of measurements). The radio signal from EASs with energies above 10²⁰eV was detected at the Yakutsk EAS array for the first time, including the shower with the record energy of ~2×10²⁰ eV for the Yakutsk EAS array.     

Energy dependence of Lévy stability and multi-fractal spectrum in e<Superscript>+</Superscript>e<Superscript>−</Superscript> collisions

Various nuclear reactions like quasi-fission, fusion-fission or particle and cluster evaporation from excited compound nuclei were studied in heavy-ion reactions at the velocity filter SHIP of GSI. The velocity filter offers the possibility to detect all reaction products under zero degree relative to the beam direction. Together with the measurement of the product velocity distribution this allows for an identification of the underlying reaction mechanism. This article is focussed on reactions of ²⁵Mg and ⁶⁴Ni beams on ^{206, 207}Pb targets at energies of 5.9×AMeV and 8.7×AMeV . Besides evaporation residues from ²⁵Mg + ²⁰⁶Pb collisions we found evidence for rotation and quasi-fission of nuclear molecules formed in the entrance channel after the capture stage. The break-up of the systems showed a preferred clustering leading to isotopes in the region 84 ⩽ Z ⩽ 88 and 122 ⩽ N ⩽ 127 of the chart of nuclei.