A new method for studying cosmic ray anisotropy by means of muon bundle detection at the Earth’s surface is described. An important advantage of this method is a simple way to compensate the atmospheric effects in the counting rate of muon bundles. Seasonal and diurnal variations of the muon bundle counting rate are almost completely eliminated by using only one atmospheric parameter. For the first time, the muon multiplicity in the detected bundles was used to estimate the dependence of the anisotropy amplitude on the primary energy. Parameters of the cosmic ray dipole anisotropy were obtained for two average logarithmic values of primary energies of 1 and 5 PeV.

From 2012 to 2023, the PRISMA-32 array operated at the Experimental Complex NEVOD (MEPhI, Moscow). The purpose of the array was to study extensive air showers detecting their neutron and electron-photon components using unshielded neutron detectors. To expand the capabilities of this facility, including the study of cosmic and geophysical phenomena with a neutron flux, its upgrade was carried out. In this upgrade, a measurement channel to study the variations of the neutron background and the processes affecting them was added. To achieve this, the photomultipliers, the integrating amplifiers, the digitalizing electronics and the high-voltage power supply system were replaced. The paper describes the structure of the upgraded array, which was named PRISMA-36, and presents the results of studying the characteristics of the main elements of its "variation" channel. A method for identifying signals caused by neutron capture and the determined criteria for their selection are discussed. An example of a Forbush decrease, caused by a X1.1-class flare and recorded with the variation channel of the PRISMA-36 array, is given.

At NRNU MEPhI, the world’s largest coordinate detector TREK is being created using drift chambers to study cosmic ray muons. The basis of the installation is multiwire drift chambers (DC), previously used in the neutrino detector at the Institute of High Energy Physics (Protvino, Moscow oblast) at the U-70 accelerator. To study the characteristics of DCs before installation in the TREK and the projected MDM detector, a stand was created that makes it possible to determine their efficiency, coordinate and angular accuracy, and zone characteristics. The article presents the design of the stand and the results of testing 394 DCs for the TREK and MDM installations.

The authors describe a way of calibrating the URAN array with thin scintillation detectors using joint events of registration of extensive air showers with the NEVOD-EAS array. Results are presented from reconstructing parameters of extensive air showers based on data from the URAN array with allowance for coefficients of calibration.

A new algorithm for selecting signals caused by the detection of neutrons is described. The estimates of its effectiveness for the PRISMA-32 and URAN arrays are presented. Using this algorithm, for various air-shower sizes the number of neutrons was reconstructed, the time distributions of neutrons and their lateral distribution functions were obtained.

A comparison of the reconstruction accuracy of the shower size and coordinates of the axes of extensive air showers based on the response of the NEVOD-EAS array are presented. The reconstruction is based on various functions of the lateral distribution of particles. A comparison of the lateral distribution of EAS particles according to modeled and experimental data is given.

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.

In this paper, we describe the quasi-spherical optical module QSM-6M to detect Cherenkov radiation in water. The module is based on six photomultiplier tubes (PMTs) with flat photocathodes Hamamatsu R877. We discuss the results of the photomultiplier testing, as well as the choice of the high-voltage divider providing the PMT dynamic range from 1 to 105 photoelectrons. The techniques for studying QSM-6M characteristics, as well as the results of the underwater testing of the module for an 18-month period are presented. We also present the results of the analysis of the QSM-6M response to single-muon and multiparticle events detected by the installations of the Experimental Complex NEVOD.

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.

In this paper we discuss the calibration of the NEVOD-EAS array which is a part of the Experimental Complex NEVOD, as well as the results of studying the response features of its scintillation detectors. We present the results of the detectors energy calibration, performed by comparing their response to different types of particles obtained experimentally and simulated with the Geant4 software package, as well as of the measurements of their timing resolution. We also discuss the results of studies of the light collection non-uniformity of the NEVOD-EAS detectors and of the accuracy of air-shower arrival direction reconstruction, which have been performed using other facilities of the Experimental Complex NEVOD: the muon hodoscope URAGAN and the muon tracking detector DECOR.

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.

Experimental Complex NEVOD (MEPhI, Moscow) includes several detectors and installations for measuring different components of extensive air showers (EAS). For the development of multicomponent EAS studies with the implementation of a complementary approach to the analysis of experimental information of the scientific facilities of the complex, a specialized hardware and software system is being created. This system will speed up the obtaining of new physical results by simplification of development and implementation of both traditional approaches and modern methods for data processing, including neural networks and algorithms for analyzing large amounts of data. The hardware and software architecture of the system, its features and prospects of the further development are discussed.

The Experimental complex NEVOD includes several different setups for studying various components of extensive air showers (EAS) in the energy range from 10 10 to 10 18 eV. The NEVOD-EAS array for detection of the EAS electron-photon component began its data taking in 2018. It is a distributed system of scintillation detectors installed over an area of about 10 4 m 2 . A distinctive feature of this array is its cluster organization with different-altitude layout of the detecting elements. The main goal of the NEVOD-EAS array is to obtain an estimation of the primary particle energy for events measured by various detectors of the Experimental complex NEVOD. This paper describes the design, operation principles and data processing of the NEVOD-EAS array. The criteria for the event selection and the accuracy of the EAS parameters reconstruction obtained on the simulated events are discussed. The results of the preliminary analysis of experimental data obtained during a half-year operation are presented.

The paper presents a comparison of three neutrons identifying methods in scintillators based on ZnS with 6Li and 10B: charge integration method, pulse gradient analysis, and simplified digital charge collection. A quality factor is used for comparison. It is calculated by the distribution of distances from the event position to the discrimination curve. It is shown that the charge integration method is observed to provide the best discrimination performance in this research.

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 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.

The URAN array operates as part of the NEVOD experimental complex for studying the hadron component of extensive air showers by recording the neutrons that accompany a shower. The first results are presented from studying characteristics of the neutron component of extensive air showers (i.e., the lateral distribution and dependence of the number of neutrons on the size of a shower). The characteristics were recorded by the URAN array in 2019.

The Experimental Complex (EC) NEVOD includes a number of detectors used to carry out basic research of cosmic rays (CR) and their interactions in the energy range 1011–1019 eV and applied research of the heliosphere, magnetosphere and atmosphere of the Earth by the muonography method which is based on the analysis of spatial-angular variations of the muon flux generated by primary CR particles with energies of 10^9–10^11 eV. The EC NEVOD is being constantly developed. Nowadays, it consists of three basic groups of experimental facilities unique in the world: the major facilities (Cherenkov water detector NEVOD, calibration telescope system — CTS, coordinate-tracking detector DECOR), the peripheral facilities (extensive air shower array NEVOD-EAS, distributed thermal neutron detector systems PRISMA and URAN), the muon hodoscopes for cosmophysical and geophysical investigations (TEMP and URAGAN). All detectors and installations of the first two groups are combined by a multilevel triggering system and the time synchronization system ensuring timestamping of registered multicomponent events. Today, the Experimental Complex NEVOD is the only facility capable of studying such a wide set of fundamental and applied scientific problems in the field of cosmic rays and solar-terrestrial physics.

The method for studying characteristics of the response of optical modules of neutrino telescopes to various classes of events registered in the volume of the Cherenkov water detector NEVODis discussed. Results of testing of an optical module with Hamamatsu R877 photomultiplier in single muon events and in events with high energy deposit are presented.

Abstract The paper is devoted to the development of a new summator-multiplexor (SM) for the block of electronics of the cluster of detector stations (BECDS) of the NEVOD-EAS air-shower array. The new summator-multiplexor is designed to replace the currently used SMs based on CAEN N169 units. The developed basic circuit diagram and the operation principle of the new SM are described. The results of testing of a prototype of the new summator-multiplexor for the BECDS of the NEVOD-EAS array are discussed.

The URAN array was created in the Scientific and Educational Centre NEVOD (MEPhI). The URAN facility was designed to register neutrons that accompany EAS at the energies of the primary cosmic rays around and above the “knee”. It includes 72 detectors based on a thin inorganic scintillator for registration of the charged and neutron components of the EAS. The total area of the facility is about 10 3 m 2 . For the correct interpretation of the experimental data of the URAN, the response of the URAN facility to the passage of EAS was simulated using the CORSIKA7.6900 program and Geant4.10.5 software package. It gave a possibility to study neutron generation in the experimental complex building. Experimental data were processed and analyzed. Results of simulation and experimental data are presented.