EMMA—a new underground cosmic-ray experiment

An experiment observing underground muons originating from cosmic-ray air showers is under preparation in the Pyhäsalmi mine, Finland. The aim is to cover an area of about 200–300 m², and the detector setup is capable of measuring the muon multiplicity and their lateral distribution. The detector is placed at a depth of about 85 m (corresponding about 240 m w.e.), which gives a threshold energy of muons of about 45 GeV. The detection of the multimuon events is motivated by partly unknown composition of the primary cosmic rays in the energy region of 10¹⁵–10¹⁶ eV, i.e., the knee region. In addition, by measuring only the higher energy muons of the air shower, the lowest energy muons being filtered out by the rock overburden, the data is sensitive also to the studies of the upper parts of the air shower. The experiment will be constructed mainly using drift chambers used previously in LEP detectors at CERN, but it can also be expanded using plastic scintillator detectors. The prototype detector is expected to be running in the beginning of 2006, and the full-size detector by the end of 2007.     

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.     

Behavior of the EAS in late stages of its development

In late stages of the extensive air shower (EAS) development (s ≥ 1.2–1.3) contributions to the electromagnetic component are made not only by hadrons but also partially by muons. In this case, the cascade curves are higher in comparison with the classical theory. If the number of particles is converted into the shower energy, this effect is not small in the energy range E ₀ = 10¹³?10¹⁶ eV. In the numerical simulation of the experiment, it is important to make sure that the energy cutoff thresholds for muons and electrons are close to each other (this is usually ignored).     

Electromagnetic Interactions of High Energy Cosmic Ray Muons

This paper investigates the electromagnetic interactions of muons. The various processes such as knock-on electron-, bremsstrahlung-, direct electron pair production, and nuclear interactions are described in detail. The energy range concerned extends from 10⁹ eV up to 10¹⁵ eV for primary muons and from 10⁸ eV up to 10¹⁴ eV for energy transfers to the secondaries. On the one hand the measurement of muon interactions represents a test of quantum electrodynamics. On the other hand the high energies available in cosmic rays would possibly lead to the measurement of new processes or the detection of new particles. One hopes to find in the high energy domain the answer to the question why the muon exists at all and if there are properties (apart from differences in mass, lifetime, and lepton number) which distinguish it from a mere heavy electron. The different experimental techniques are described and the various experimental results on muon interactions are presented and compared with relevant QED-theories. Observed deviations between theory and experiment and anomalies in muon interactions are critically investigated and discussed in the light of experimental difficulties and interpretation problems. In general, agreement between theory and experiment is found, i.e. QED-theories describe the results adequately. However, some experiments claim to have detected anomalies in muon physics in the cosmic ray beam. But the hypotheses on new processes and new particles in the high energy range do not withstand a critical analysis. It is concluded that the observed deviations can be understood in the framework of conventional theories.     

Identification of extragalactic cosmic-ray sources using data from various detection facilities

Showers with energies E>3.2×10¹⁹ eV and E≥10²⁰ eV detected at the AGASA (Akeno, Japan), Haverah Park, and Yakutsk arrays are investigated. The question of how the identification of sources depends on the error in determining the shower arrival directions is analyzed. Confirmation is obtained for the conclusion in the author’s earlier work, that the principal sources of shower-driven particles are Seyfert galaxies with red shifts z≤0.0092, which are weak emitters in the x-ray and radio ranges. Zh. éksp. Teor. Fiz. 116, 1121–1130 (October 1999)     

Possible observations of new physics in ultrahigh-energy cosmic rays

The muon lateral structure functions in giant air showers induced by primary photons have been simulated with the help of original codes. Particularly, the densities of muons with energies above 0.5 and 1 GeV at a distance of 1000 m from the shower core have been estimated for gamma-induced showers of various energies. A comparison with the results of calculations for hadronic showers shows a considerable deficit of muons in the gamma-induced showers. The density of muons at a distance of 1000 m from the shower core happened to be ≳ 10 times larger for the hadronic showers. Some possible constraints of the source models with superheavy-dark-matter particles and topological defects are discussed. The text was submitted by the authors in English.     

The extensive air shower muon number spectrum beyond the knee in the cosmic-ray energy spectrum

The extensive air shower (EAS) muon number spectrum is obtained with increased statistics using the central muon detector of the EAS MSU array, which records muons with energies above 10 GeV. The dependence of the mass composition of primary cosmic rays on the energy is considered. The conclusion is confirmed that for energies from 3 × 10¹⁵ eV (the primary energy spectrum knee) up to 10¹⁷ eV a change in the composition associated with an increase in the proportion of heavy nuclei occurs; however, after the energy of 10¹⁷ eV, the proportion of heavy nuclei begins to decrease and the composition becomes lighter. A comparison with similar data from other experiments is conducted. The existence of an additional component of cosmic rays is confirmed; earlier an indication of its presence was derived from data on the EAS electron number spectrum.     

Properties of giant air showers and the problem of estimating the primary-particle energy

The main errors in energy estimation in individual events detected at the Yakutsk EAS array are analyzed. The data on the fraction of muons are considered. For inclined showers with energies exceeding 10¹⁹ eV, it is much larger than the value given by approximation at lower energies. This difference may be due to new processes arising upon interaction between particles with such energies, which leads to a significant increase in the muon component in the total primary-particle energy.     

Electrons and muons in extensive air showers of energies E 0≥3×1017 eV: Yakutsk array data and QGSJET model

The results obtained from an analysis of the 1974–1998 Yakutsk array data on muons with threshold energy E _μ ≈ 1.0 × secθ GeV and on all charged particles (electrons and muons) in extensive air showers (EAS) are reported and compared with the results of calculations based on the model of quark-gluon strings with jets. For energies of E ₀≤3×10¹⁸ eV and zenith angles of θ≤45°, the results of the model calculations are consistent with the measured properties of the showers, while, for higher energy EASs, there are considerable discrepancies, which are probably due to the change in the development of the shower cascade in the region E ₀≥3×10¹⁸ eV.     

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.

     

Nonstationary phenomena in cosmic rays with <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≤ 10<Superscript>18</Superscript> eV according to the data of the Yakutsk EAS array

The energy spectrum of cosmic rays and the fraction of muons with the threshold 1.0secθ GeV in the total number of charged particles in extensive air showers with energy E ₀ ≥ 10¹⁷ eV according to Yakutsk array data collected during 35 years of its continuous operation in 1978–2012 have been analyzed. It has been shown that these characteristics are noticeably different in different time periods. Before 1996, the integral intensity of the spectrum at E ₀ = 10¹⁷ eV varied near one stable position and then began to increase. It increased by (45 ± 5)% in seven years and, then, began to decrease. This phenomenon was accompanied a similar change in the fraction of muons and was caused by a significant increase in the average weight of the chemical composition of cosmic rays after 1996 as compared to preceding years.     

Modeling and parameterization of the spatial distribution of Čerenkov light from extensive air showers

Spatial distribution of Čerenkov radiation of extensive air shower particles with energies 10¹³–10¹⁶ eV is simulated by the CORSIKA code for conditions and configuration of the Tunka-25 facility. Based on the calculated results, sets of approximating functions are constructed for different primary particles and zenith angles. A comparison of the calculated spatial distribution functions of Čerenkov light with the functions measured on the Tunka-25 facility demonstrates the feasibility of identification of the particle initiating the shower and determination of its energy in the vicinity of the bend point of the cosmic ray spectrum. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 7–13, October, 2005.     

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.     

The proton-air cross-section at 1016 eV

Summary A study of the Čerenkov light lateral distribution function for cosmic-ray showers with energies of about 10¹⁶ eV has been used to determine the distribution of depths of shower maximum at these energies. This distribution has an exponential tail due to fluctuations in the depths of early interactions of the proton primary component. The form of this tail may be used to infer an inelastic proton-air cross-section of (590±70) mb at ≈10¹⁶ eV.

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Riassunto Si usa uno studio della distribuzione laterale della luce di Čerenkov per sciami cosmici con energie di circa 10¹⁶ eV per determinare la distribuzione di profondità del massimo degli sciami a queste energie. Questa distribuzione ha una coda esponenziale dovuta a fluttuazioni nelle profondità delle prime interazioni della componente protonica delle primarie. La forma di questa coda si può usare per inferire una sezione d'urto anelastica protone-aria di (590±70) mb a ≈10¹⁶ eV.

     

Particles of primary cosmic radiation generating extensive air showers of energy above 10<Superscript>20</Superscript> eV in the atmosphere

In order to construct the energy spectrum on the basis of data from the Yakutsk array, a method similar to that employed at the AGASA array is applied in addition to the standard approach based on experimental procedures. Moreover, a new, original, method underlying the calculation of the spectrum in the region of energies above 10²⁰ eV is used to estimate energies. In order to compare data obtained at different arrays, it is proposed to harness the universal spectrum based on HiRes data. Within the QGSJET2 model, it is shown that a shower of energy 2 × 10²⁰ eV was observed at the Yakutsk array. In the same energy region (above 2 × 10²⁰ eV), the AGASA array recorded four showers, while the Fly’s Eye array and Pierre Auger Observatory (PAO) recorded one shower each. These data do not confirm the conclusion that the flux of primary-cosmic-ray particles decreases because of the Greisen-Zatsepin-Kuzmin effect.     

Simulation of muon-induced air showers affecting CMS tracking detectors

We study the propagation of energetic muons produced by ultrahigh energy cosmic rays which could penetrate the cavern of a giant experiment called Compact Muon Solenoid (CMS) at CERN. The present work is based on our previous simulation model proposed in [1]. We have improved this model by (1) eliminating the ambiguity via adding Landau-Pomeranchuk-Migdal effect to the Monte-Carlo code, (2) using different incidence angles of the simulated air showers, (3) defining the actual contents of the CMS cavern concrete. We estimate the energy spectrum of muons produced by air showers of primary protons and photons, which could be detected as a background in the CMS tracking detectors. Our results show that muons produced by air showers within the energy range 10¹⁷–10²⁰ eV injected to the CMS site could penetrate the cavern with cutoff energy 36.5 GeV. The article is published in the original.     

Experiments with low-energy muons

Two experiments with low-energy muons are described: the determination of the stopping power of C, Si, Ti and Au for muons at energies down to 2 keV and the measurement of the diffusion times for pµ and dµ atoms in low-pressure (0.25–12 hPa) hydrogen gas. A pronounced Barkas effect was found for muons at the Bragg peak (about 10 keV): the stopping power for µ^– in C, e.g., is about 30% lower than that for µ⁺. The mean kinetic energy of pµ atoms at the end of the cascade in 1 hPa hydrogen gas was determined to be (2.6 ± 0.6) eV (preliminary value).     

Cosmic rays and supernova SN 1987a

Summary We discuss the possibility of obtaining information on the contribution to the galactic cosmic-ray flux by young pulsars searching for high-energy gamma-rays from SN 1987a. A small extensive air shower array operating in Chacaltaya (Bolivia, 5200 m a.s.l.) could give significant information at primary energiesE ₀∼10¹⁴ eV.     

On possible role of neutrons in appearance of delayed muons in MUON-T setup at the Tien Shan high-altitude station

The MUON-T setup operated at the Tien Shan high-altitude station of the Lebedev Physical Institute (3340 m above sea level) at a soil depth of ∼10 m (∼20 m m.w.e.). Muons with delay times of 30–150 ns with respect to the extensive air shower front were observed at this setup. Calculations showed that delay times of relativistic muons, taking into account their deviations in the geomagnetic field, do not exceed ∼30 ns. To elucidate the possible role of neutrons in the appearance of delayed events due to the n-p reaction in the plastic scintillator material, the problem of neutron transport in a medium with a density of 2 g/cm³ and a humidity of 10% was solved by the Monte Carlo method. Calculations for a point source of neutrons with energies of 5, 10, and 20 MeV (such neutrons can be generated, in particular, in cascades in soil from hadrons of the shower core) showed that the neutron flux decreases more than by a factor of 10⁴ at a distance of 2.8 m of soil from the source. Neither neutron crosses the boundary of 3m at the total statistics of 3 · 10⁵ events. Since the MUON-T setup is at a depth of 10 m, it is clear that neutrons from the atmosphere and soil upper layer are absorbed, scattered, and do not reach the detector. Thus, the formation of delayed muons in the MUON-T setup cannot be explained by these neutrons.     

Reestimation of the energy of extensive air showers at the Yakutsk EAS array with the CORSIKA package

The responses of ground and underground muon scintillation detectors of the Yakutsk extensive air shower (EAS) array from primary particles with the energy E ₀ ≥ 10¹⁷ eV have been calculated within the QGSJET-01-d, QGSJET-II-04, SIBILL, and EPOS-LHC models with the CORSIKA package. A new estimate obtained for E ₀ is lower by a factor of about 1.41 than that previously obtained within the calorimetric method for EASs.