Abstract
In this work, we use muon bundles, which are formed in extensive air showers and detected at the ground level, as a tool for searching for anisotropy in high-energy cosmic rays. Such choice ...is explained by the penetrating ability of muons that allows them to retain the direction of primary particles with good accuracy. In 2012–2022, we performed long-term muon-bundle detection with the coordinate-tracking detector DECOR, which is a part of the Experimental Complex NEVOD (MEPhI, Moscow). To search for cosmic-ray anisotropy, muon bundles arriving at zenith angles in the range from 15° to 75° in the local coordinate system are used. During the entire period of data taking, about 14 million of such events have been accumulated. In this paper, we describe some methods developed in the Experimental Complex NEVOD and implemented in our research, including: the method for compensating for the influence of meteorological conditions on the intensity of muon bundles at the Earth’s surface, the method for accounting for the design features of the detector and the inhomogeneity of the detection efficiency for different directions, as well as the method for estimating the primary energies of cosmic rays. Here we present the results of the search for the dipole anisotropy of cosmic rays with energies in the PeV region and also compare them with the results obtained at other scientific facilities.
Underground cosmic-ray experiments, including very large volume neutrino telescopes, depend on a precise description of the interaction cross sections of muons, which can travel large distances ...before reaching the detector. High-energy muons lose their energy almost exclusively via four processes: ionization, electron-positron pair production, bremsstrahlung and inelastic interaction with nuclei. At low energies, ionization is the dominant process, while above energies of about a TeV, the three other processes dominate the energy loss. We discuss the uncertainties of the cross sections of the energy loss processes used in the simulation chain of current very large volume neutrino telescopes and review recent theoretical improvements.
Four most widely used models of hadronic interactions at high energies implemented in CORSIKA program were compared basing on the simulation of the first nucleus–nucleus interactions of cosmic rays ...with the atmosphere. For this comparison the distributions of the number of produced particles of different types were obtained, as long as the mean values of these numbers. The dependences of the fraction of the collision energy carried by different secondary particles on the mass of the primary particle were calculated for each model. The check of the electric charge conservation law implementation was performed. Comparison shows vast differences between the models in some cases that may result in different interpretation of experimental data.
Investigation of lepton propagation through matter is of importance for cosmic-ray physics and neutrino astronomy. The diffractive scattering of virtual photons is considered as a process that leads ...to the energy loss of leptons emitting these photons. The interference between this process and bremsstrahlung makes a contribution that depends on the sign of the lepton charge.
The muon puzzle is an excess of muon bundles generated by primary cosmic rays (PCR) at energies above 10
eV compared to estimations that assume even a heavy composition of PCR. The appearance of such ...excess of muons can be caused both by cosmophysical (the change in the spectrum and composition of cosmic rays) and nuclear-physical (the changing features of the hadron interaction) reasons. To separate these two possibilities it is necessary to measure energy characteristics of muon bundles and their dependence on energy of primary particles. Today the complex NEVOD-DECOR is the only one for such type experiment conduction. To improve the conditions of this experiment a further development of the experimental complex is planned: construction of new coordinate-tracking detector TREK for increasing of the area and improving of spatial resolution of muon track detection, modernization of the Cherenkov water detector for optimization of its structure and improvement of accuracy of energy deposit of muon bundle measurement, inclusion of the installation NEVOD-EAS in the experiment for independent evaluation of primary particle energy.
Experimental data on cosmic ray muons obtained with the coordinate-tracking detector DECOR in 2012 - 2017 are analyzed. The rate of the events exhibits variations significantly exceeding the ...statistical errors. It is shown that these variations are related to changes in the meteorological conditions (atmospheric pressure and air temperature). Barometric coefficient for near-horizontal muons has been estimated.
NEVOD-DECOR is the unique experiment where systematic studies of cosmic ray muon bundles in a wide range of zenith angles and, accordingly, the energies of primary cosmic rays are carried out. ...Impressive experimental material (more than 100 thousand events) has been accumulated over a long time period from May 2012 to December 2022. The earlier developed method of local muon density spectra allows us to compare experimental data on muon bundles with the results of the EAS muon component simulations. The analysis showed that the observed intensity of muon bundles at primary cosmic ray energies of about 1 EeV and higher can be compatible with the expectation (in frame of widely used hadronic interaction models) only under the assumption of an extremely heavy mass composition. It is consistent with data of several other experiments on investigations of air shower muon content, but contradicts the available measurements of the depth of the shower maximum in the atmosphere by means of fluorescent technique, which favor a light mass composition at these energies. This probably leads to the need to revise the existing hadronic interaction models.
Data of NEVOD-DECOR experiment on investigations of inclined cosmic ray muon bundles for a long time period (May 2012 - May 2020) are presented. Their comparison with the results of calculations ...based on simulations of extensive air shower hadron and muon components is carried out. The analysis showed that the observed intensity of muon bundles at primary particle energies of about 1018 eV and higher can be compatible with the expectation only under the assumption of an extremely heavy mass composition of cosmic rays. On the contrary, measurements of the depth of the shower maximum in the atmosphere in the experiments using air fluorescence technique, favour a light mass composition of primary cosmic rays at these energies.
The neutrino telescope IceCube is capable to reconstruct the energy spectrum of muons in very high energy region by means of measurements of muon-induced cascades. To compare with experimental data, ...the expected spectra of cascades were theoretically estimated. Calculations were performed for two variants of muon spectrum on the ice surface: a simple power-law energy spectrum with a differential slope index −3.7, and a composite spectrum combined of two power spectra with differential indexes −3.7 and −2.7. The differential spectra of cascades for different zenith angles and integral cascade spectra calculated for two variants of muon spectra are discussed.
Parameters of extensive air showers detected by the facilities of the NEVOD Experimental Complex are analyzed and compared with events simulated. The calibration and energy threshold of the NEVOD-EAS ...detector are discussed, as well as the results of retrieval of the axis directions from the NEVOD-EAS and DECOR data. An example of the event detected by all facilities of the complex is given.
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