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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.

The TAIGA observatory addresses ground-based gamma-ray astronomy at energies from a few TeV to several PeV, as well as cosmic ray physics from 100 TeV to several EeV and astroparticle physics. The TAIGA experiment current status, recent results and development prospects are presented.

The scintillation experiment of the TAIGA astrophysical complex comprises two systems: Tunka-Grande and Taiga-Muon. The main objective of these systems is to study the energy spectrum and mass composition of cosmic rays in the energy range of eV, as well as to search for gamma radiation in the same energy range. An additional task of the experiments is to search for a signal from gamma quanta in the sub-PeV energy range in conjunction with wide angle Cherenkov detectors TAIGA-HiSCORE and Tunka-133. The report presents the objectives and status of the facility and a description of the design of scintillation counters and clusters. The results of the study of EAS with an unusual spatiotemporal structure are presented together with the results of a study of the joint operation of the Tunka-Grande and TAIGA-HiSCORE setups in order to search for sub-PeV gamma quanta. Estimates are made of the expected number of registered gamma quanta from the Crab Nebula.

A trigger system of the Experimental Complex NEVOD (EC NEVOD) unique scientific facility is described. Detectors and setups that differ in area, physical principles of detection, and background counting rate are included in the EC NEVOD to detect various components of cosmic rays. Each detector is equipped with its own original data-acquisition and trigger system and is able to operate independently. In addition, the detectors are all combined by a single system of data triggering and synchronization. Features of the individual detector systems, their main characteristics and methods of their initialization and integration are presented.

This paper proposes a method for separation the light component of cosmic rays in the energy range of 200 TeV–20 PeV (the knee region in the PCR spectrum) from hybrid events detected by two Cherenkov setups IACT + HiSCORE in TAIGA experiment. The possibility of such separation is demonstrated using Monte Carlo calculations and the first experimental estimates are made.

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.

An analysis is performed of the spectrum of gamma rays from the Crab Nebula in the 4–100 TeV range of energies, obtained using data from two Atmospheric Cherenkov Telescopes that are part of the TAIGA complex. A way of selecting and restoring the energy of gamma rays is described that includes a procedure for restoring the energy spectrum.

The more correct recalculation from the measured Cherenkov light fluxes at distances of 200 (Q200) and 100 (Q100) m from the Extensive Air Shower (EAS) core to the energy of the primary particle has been developed using the results of M-C simulation by the CORSIKA code, assuming a light primary composition of cosmic rays. Using the new conversion expressions, a differential energy spectrum was obtained according to the data of the Tunka-133 array for 7 years of operation and the TAIGA-HiSCORE array for 2 years of operation.

— The paper is devoted to the modeling and analysis of data detected by the TAIGA-IACT installation in the stereo mode. Five Imaging Atmospheric Cherenkov Telescopes (IACT) with a viewing angle of 9.6° are expected to be included in the installation. Today there are three telescopes spaced far apart (from 320 to 500 m) in the installation. The effective area of the installation is as large as 0.6 km 2 ; therefore, it is possible to conduct statistically significant measurements of weak γ-ray sources in the energy range above 10 TeV over a reasonable observation time (300–400 h). The Monte Carlo procedure for simulating the hadrons and γ-rays detected by the telescopes is described as is the procedure for reconstructing the parameters of extensive air showers, such as the arrival direction of an event, the axis position, the depth of the maximum of shower development ( X max ), and the primary-particle energy. In order to solve the problem of γ-hadron separation, the criteria for selecting γ-rays detected in the stereo mode have been optimized and the effective area of the installation has been calculated.

Results are presented from measuring the energy characteristics of muon bundles in inclined extensive air showers in the NEVOD-DECOR experiment. Estimates of the average energy of muons in the bundles are obtained in the 10 to 1000 PeV range of primary particle energies and compared to values calculated under different assumptions about the composition of cosmic radiation and models of hadronic interactions. An excess of experimental values of the average muon energy relative to calculations is found for high local densities corresponding to primary particle energies above 100 PeV.