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...     

Cluster of scintillation counters for the shower array in the NEVOD EAS project

A shower array for investigations of primary cosmic rays in the knee region in the energy spectrum of extensive air showers is being designed on the basis of the NEVOD experimental complex. Features of the cluster organization of the array and the results of the study of the characteristics of both the basic scintillation counter and the counter cluster, which is the basic element for triggering, detecting, and data collection and treatment systems, are discussed.     

Atmospheric effects in the intensity of cosmic ray muon bundles

We analyze experimental data on cosmic ray muon bundles collected with a DECOR coordinate detector. Substantial variations in the intensity of the events are observed during the experiment. These variations are found to be caused by changes in atmospheric conditions. This study is the first to obtain experimental estimates of the temperature and barometric coefficients for muon bundles. It is shown that the observed effect can be explained by changes in the side distribution function of EAS muons.     

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.     

Direct observation of muon-pair production by high-energy muons in the liquid-argon calorimeter BARS

Experimental data accumulated over a long-term exposure of the big liquid-argon spectrometer BARS at the Institute for High Energy Physics (IHEP, Protvino) in a horizontal flux of cosmic rays are analyzed with the aim of selecting events that correspond to muon-pair production by muons in the sensitive volume of the detector. The results obtained in this way make it possible to perform, for the first time, a direct experimental test of various theoretical estimates of the total cross section for electromagnetic muon-pair production by high-energy muons.     

Meteorological effects in the intensity of muon groups

The data of the experimental study of cosmic ray muon groups using the DEKOR setup for the period of 2004–2007, during which significant changes in the intensity of groups at the Earth’s surface were detected, are analyzed. It was found that these variations are caused by variations of weather conditions (temperature and atmospheric pressure); barometric and temperature coefficients were determined. It turned out that magnitudes of these coefficients for muon groups are significantly higher than available values for singlemuons. Possible physicalmechanismof the effect is discussed. Since muon groups are formed at high altitudes (of the order of several kilometers), the detected effect can be used for monitoring air temperature variations in the upper troposphere.     

Muons of very and ultra-high energy cosmic rays

In many cosmic rays experiments at very and ultra-high energies, an excess of muons (including those of very high energy, >100 TeV) is observed that cannot be explained within existing models of hadron interactions. This excess is usually explained in terms of the heavier mass composition of primary cosmic rays. However, the excess over the predicted values even for extremely heavy compositions, and especially the observed excesses of muons with energies of >100 TeV, requires that we consider other possibilities with respect to the generation of muons, including changes in models of hadron interaction.     

Energy spectrum of cascade showers generated in water by near-horizontal muons

We discuss measuring cascade shower energy using the NEVOD Cherenkov water detector with a spatial lattice of quasi-spherical modules (QSMs). Dense QSM spacing makes it possible to reconstruct a number of cascade particles along the shower axis from the PMT response amplitude. Our cascade curve reconstruction technique is applied to showers generated by near-horizontal high-energy muons selected using the DECOR coordinate detector deployed around NEVOD. The first results from cascade energy spectrum measurements are reported.     

Restoration of parameters of high-energy cascades in Cherenkov water calorimeter with a dense array of quasispherical modules

A problem concerning the restoration of the parameters of a cascade shower with an unknown axis originating by muons in a Cherenkov water calorimeter is considered. A method for estimating the direction and geometric position of the cascade’s axis, which is based on the analysis of responses of quasispherical modules, and the criteria of selection of the events with cascades among the events with a large energy liberation are proposed. The method and the criteria are tested on events with cascades generated by near-horizontal muons of high energies detected by a DECOR coordinate-track detector. The preliminary results of measurements of the energy spectrum of cascade showers are presented.