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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In comparison with calculations, the excess of multimuon events found in many experiments at ultrahigh energies of extensive air showers (EASs) cannot be explained using modern models of hadron interactions. The existence of muon excess is called the muon puzzle. One of the ways to solve this problem is to study the energy characteristics of the EAS muon component. For this purpose, the energy deposit of cosmic ray muon bundles is measured in the NEVOD–DECOR experiment. Registration of muon bundles in a wide range of zenith angles allows one to explore a wide range of energies of the primary particles of cosmic rays (from 10 to 1000 PeV) within a single experiment. The results of measurements of the energy deposit of muon bundles over a long observation period are presented. [ABSTRACT FROM AUTHOR]

In 2018, the creation of the central part of the NEVOD-EAS cluster-type array aimed at detection of the electron-photon component of extensive air showers in the energy range from 1015 to 1017 eV was completed. At present, a continuous data taking is being performed at the array. The results of the reconstruction of registered extensive air showers using the methods developed within the framework of the cluster approach to experimental data analysis are presented. [ABSTRACT FROM AUTHOR]

The results of the long-term measurements of extensive air showers with the calibration telescope system of the Cherenkov water detector are presented for an energy range of 1014–1017 eV. We have used two independent methods for reconstruction of the charged particle local density spectrum: by the multiplicity of the hit counters and by their amplitude responses. By means of Geant4 calculations, we have shown how the structure of the building and the water tank affect the results of the spectrum reconstruction. We obtained two different exponents of charged particles' local density spectra for CTS top and bottom plane. The results are compared with CORSIKA calculations and data from other setups. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]