Specific features of studying Forbush decreases in the muon flux

The variations in the cosmic ray (CR) muon flux during the Forbush decreases (FDs), registered by the DECOR muon detector and the URAGAN muon hodoscope during the periods of their operation from 2004 to 2006, are analyzed. The unified method for determining the parameters of variations in the CR flux during FDs has been developed, and the dependences of the FD characteristics on the rigidity of primary CRs and information about the spatial-angular dynamics of the muon flux during FDs have been obtained.     

Investigation of the Energy Loss of Muon Bundles in the Cherenkov Water Calorimeter

Investigations of the energy loss of muon bundles are being conducted at the Experimental complex NEVOD. Such investigations are directed to detailed study of “muon puzzle” (the excess of multi-muon events observed in several cosmic ray experiments at ultra-high energies). Results of measurements of the muon bundle energy deposit during a long period of observations in primary cosmic ray energy range 10–1000 PeV have been obtained and have been compared with simulations performed on the basis of the CORSIKA code.     

Observation of heliospheric disturbances in the muon component of cosmic rays

The possibilities of using ground-based muon hodoscopes to study heliospheric disturbances are discussed. Mapping of the matrices of muon flux angular distributions recorded at the ground level in geocentric solar ecliptic coordinates with allowance for the asymptotic directions of primary protons of galactic cosmic rays makes it possible to observe the dynamics of heliospheric disturbances in the near-Earth space. Variations in some other characteristics of muon flux angular distributions are also analyzed.     

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.     

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.     

Investigation of cosmic rays above the knee by means of muon bundles detected in a wide range of zenith angles

The results of investigation of muon bundles at the Earth’s surface in a wide range of zenith angles on the basis of the new phenomenological characteristic of extensive air showers—spectra of local muon density—have been investigated. Features of the local-density spectra are considered within a simple analytical model. The expected distributions of muon density in a wide range of zenith angles and primary energies, calculated on the basis of the CORSIKA code, are compared with the experimental data.     

Negative muon capture in very light atoms

The transition rates for unbound muons to be captured into atomic bound states are calculated as functions of (1) incident muon center-of-mass energy, (2) muon principal quantum number n, and (3) muon (final) angular momentum l, for the hydrogen, helium, and lithium atoms. These rates reflect differences in electron binding energies. At muon energies of several hundred electron volts, lithium K-shell electrons are more likely to be ejected than the L-shell electron, while this behavior is reversed for energies ? 10 eV. However, in each case when the capture rate is folded with a muon stopping power function, the result is that more than half of the unbound muons are absorbed above 75 eV. Implications for experiments which look at muon transfer processes are noted.     

Muon bundles produced by UHE cosmic rays at large zenith angles

The first experimental results on a new EAS observable, the local muon density spectra measured with a large area coordinate detector DECOR in a wide range of zenith angles, are presented. These data correspond to the interval of primary particle energies from 10¹⁵ to 10¹⁸ eV. Some features of local muon density phenomenology are considered on the basis of an analytical model. Expected distributions of the events in the muon density have been calculated by means of the CORSIKA code and compared with experimental data. The text was submitted by the authors in English.     

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.     

Weak neutral currents in elastic muon-nucleon scattering

Elastic polarized muon scattering is considered as an independent source of information on weak neutral currents involving muons. At low energies and high intensities cross section asymmetries are measurable which are sensitive to the right-handed weak muon charge, involve new combinations of coupling constants and depend remarkably on the details of weak nucleon form factors.     

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.     

Sea level muon spectra at large zenith angles derived from the latest JACEE primary nucleon spectrum

Summary Sea level muon energy spectra at large zenith angles have been derived from the latest JACEE primary spectrum using the Fermilab Single-Arm Spectrometer data on charged-meson production. The role of increasing total cross-section on the final result for the energy spectra has been investigated here with special emphasis. The inclusion of the rising total cross-section at cosmic range of energies, it is seen, has come into much use in explaining the observed data at very high energies. The autors of this paper have agreed not to receive the proofs for correction.     

High-energy cosmic ray muons in the Earth’s atmosphere

We present the calculations of the atmospheric muon fluxes at energies 10–10⁷ GeV based on a numerical-analytical method for solving the hadron-nucleus cascade equations. It allows the non-power-law behavior of the primary cosmic ray (PCR) spectrum, the violation of Feynman scaling, and the growth of the total inelastic cross sections for hadron-nucleus collisions with increasing energy to be taken into account. The calculations have been performed for a wide class of hadron-nucleus interaction models using directly the PCR measurements made in the ATIC-2 and GAMMA experiments and the parameterizations of the primary spectrum based on a set of experiments. We study the dependence of atmospheric muon flux characteristics on the hadronic interaction model and the influence of uncertainties in the PCR spectrum and composition on the muon flux at sea level. Comparison of the calculated muon energy spectra at sea level with the data from a large number of experiments shows that the cross sections for hadron-nucleus interactions introduce the greatest uncertainty in the energy region that does not include the knee in the primary spectrum.     

Temperature coefficients for muons at different zenith angles

Differential temperature coefficients for a muon flux have been calculated for different threshold energies and zenith angles. Comparison with the results of previous investigations shows only qualitative agreement, whereas the quantitative differences are significant. Possible reasons for such a discrepancy are discussed.     

Fluxes of high- and ultrahigh-energy cosmic-ray muons

The positive excess of cosmic-ray muons at energies higher than 1 TeV is estimated taking into account the data obtained from accelerator experiments on the production of particle and antiparticles in proton-proton interactions at energies of ～20 TeV. The fluxes of cosmic-ray muons at energies up to ～10¹¹ GeV and the production functions of muon bremsstrahlung photons at different depths in the atmosphere are calculated with due regard for the contribution from the decay of J/ψ mesons. The analysis performed is based on the accelerator data and their extrapolation to higher energies.     

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.     

Analysis of Forbush decreases observed using a muon telescope in Antarctica starting on 21 June 2015

A cosmic-ray muon telescope has been collecting data since the end of 2014, which was shortly after the telescope was built in the Zhongshan Station of Antarctica. The telescope is the first observation device to be built by Chinese scientists in Antarctica. The pressure change is very strong in Zhongshan station. The count rate of the pressure correction results shows that the large variations in the count rate are likely caused by pressure fluctuations. During the period from 18 June to 22 June 2015, four halo coronal mass ejections(CMEs) were ejected from the Sun. These CMEs initiated a series of Forbush decreases(FD) when they reached the Earth. We conducted a comprehensive study of the intensity fluctuations of galactic cosmic rays recorded during FDs. The intensity fluctuations used in this study were collected by cosmic ray detectors of multiple stations(Zhongshan, McMurdo,South Polar, and Nagoya), and the solar wind measurements were collected by ACE and WIND. The profile of the FD of 22 June demonstrated a four-step decrease. The traditional one-or two-step FD classification method does not adequately explain the FD profile results. The interaction between the faster CME that occurred on 21 June 2015 and the two slow CMEs of the earlier few days should be considered. The cosmic ray intensities of the South Pole,McMurdo, and Zhongshan stations have similar hourly variations, whereas the galactic cosmic rays recorded between polar and non-polar locations are distinct. The FD pre-increase of 22 June 2015 for the Nagoya muon telescope(non-polar location) lags those of the McMurdo and Zhongshan stations(polar locations) by 1 h. The FD onset of22 June 2015 for the Nagoya muon telescope lags those of the polar locations by 1 h.     

Search for UHE cosmic sources with a large-area underground muon detector

Summary The newly discovered gamma-ray emission from Cyg-X 3 with energies up to 2·10¹⁶eV gives the first evidence that particle acceleration in galactic gamma-ray sources can reach energies of the order of 10⁴ TeV. We discuss the detectability of this type of sources by an underground muon tracking detector with area of the order of ∼1000 m² and the physical information which could be obtained in this way. Paper presented at the 2° Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May–2 June 1984.     

Muon capture rates on 16O leading to bound states of 16N

The partial muon capture rates on ¹⁶O leading to all four particle-stable states in ¹⁶N have been measured. The results obtained are compared to previous measurements and are also used to extract a value for the induced pseudoscalar coupling constant in muon capture.     

Forbush decreases recorded by the URAGAN muon hodoscope in 2006–2011

Variations in the cosmic ray muon flux on Earth’s surface during Forbush decreases (FD) recorded by the URAGAN muon hodoscope in 2006–2011 are investigated. The dependence of the rate of amplitude reduction on the primary particle energy in a range above 10 GeV at different phases of FD development is studied by analyzing the variations in the cosmic ray muon flux recorded with the hodoscope. Analytical data on the spatial and angular dynamics of the muon flux are used to estimate variations in the spatial anisotropy of the muon flux during FDs.