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Forbush effects caused by powerful X-class solar flares are studied using URAGAN muon hodoscope data for the period 2007–2019. The URAGAN muon hodoscope registers the cosmic ray muon flux on the Earth’s surface from different directions simultaneously. This allows study of the energy, angular, and space–time characteristics of variations in the cosmic ray muon flux during Forbush effects. The dependence of the measured Forbush effects on the parameters of heliospheric and geomagnetic disturbances is analyzed.

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.

An analysis is performed of the diurnal variation in cosmic-ray muons measured with the URAGAN muon hodoscope from 2007 to 2019. Characteristics are given of the yearly average diurnal variation in the count rate in several zenith-angle intervals. The results are compared to the diurnal variations in the count rate of neutrons from ten neutron monitors.

The existence of an excessive number of multimuon events observed in many experiments at ultrahigh EAS energies (above 1017 eV) relative to calculations cannot be explained using modern models of hadronic interactions. One way of solving the problem of muon excess is to study the energy characteristics of the EAS muon component. Results are presented from measurements of muon bundle energy characteristics over 7 years of observations. The experimental dependences are compared to results from simulation done with the CORSIKA software package.

Results of the study of variations of cosmic ray muon flux at the Earth surface during Forbush decreases registered in 2007–2018 by means of the muon hodoscope URAGAN are presented. The dynamics of the amplitude spectral index at different stages (the decrease, the minimum, and the recovery), which correspond to different phases of the influence of heliospheric disturbances on the flux of cosmic rays for the period 2012 to 2018, is considered. To investigate possible regularities in the behavior of the projection of the relative local anisotropy vector of the muon flux to the South and to the East (rS and rE) during 2007–2018, the distributions of these parameters for four phases (immediately before FD, decrease phase, minimum phase, recovery phase) were calculated.

Coronal mass ejections are among the most powerful disturbances of the interplanetary space. They can influence the state of the near-Earth space, including magnetosphere of the Earth. In addition, such disturbances modulate the flux of cosmic rays and penetrate both the heliosphere and the Earth’s magnetosphere. In order to find an early alert of such events, it is necessary to investigate the flux of particles arriving to the Earth and providing information about events in the heliosphere. The paper presents the results of investigation of the anisotropy of the cosmic ray muon flux by means of the muon hodoscope URAGAN in the period from 2007 to 2018.

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.

The influence of a high-speed solar wind on the state of magnetosphere, as well as on the cosmic ray flux registered on the Earth’s surface by the muon hodoscope URAGAN (MEPhI) is discussed. The results of the analysis of the parameters of muon flux local anisotropy in the periods of low solar activity (2008–2009 and 2017–2018) during geomagnetic disturbances caused by the high-speed solar wind are presented.

Energy characteristics of the muon component of extensive air showers (EASes) are investigated at the NEVOD experimental complex in order to solve the problem of a detected excess of muons in EASes at ultrahigh energies, relative to simulation results. The dependences of the energy deposit of muon bundles on the zenith angle and the local muon density are obtained for primary energies of 10–1000 PeV. The results from comparing the data to simulations performed with the CORSIKA program are presented.

The NEVOD experimental complex was created at MEPhI. It includes several facilities for studying the electron–photon, muon, and hadron components of the EAS in the energy range of 1 PeV to 1 EeV. This work presents the first results for two months of the joint operation of five facilities (NEVOD-EAS, CWD, CTS, PRISMA-32, and DECOR). The problems of synchronizing the facilities and selecting joint events are considered. The experimental data of these facilities are analyzed for different components of the EAS in overlapping energy ranges.

Continuous monitoring of the muon flux over wide ranges of zenith and azimuth angles with the URAGAN detector (Moscow, 55.7° N, 37.7° E, 173 m AMSL) allows detection of variations in its intensity and angular distribution. A way of locating domains of anisotropy in the muon angular distribution is described, and they are mapped in matrix form in the GSE coordinate system. The maximum depth (height) of deformation, the zenith and azimuth angles of the center in the local system, and its GSE longitude and latitude are determined for each observed domain. The GSE longitudes of the detected domains of anisotropy are available on the Internet as functions of time and can be used to monitor the heliosphere’s activity.

Data of the NEVOD-DECOR experiment on investigations of inclined cosmic ray muon bundles for a long time period (May 2012 – March 2021) are presented. Their comparison with the results of calculations based on simulations of EAS muon component allows one to study the behavior of the energy spectrum and mass composition of primary cosmic rays and/or to check the validity of hadron interaction models in a wide energy range from about 10^16 to more than 10^18 eV. The analysis showed that the observed intensity of muon bundles at primary particle energies of about 10^18 eV and higher can be compatible with the expectation only under the assumption of an extremely heavy mass composition of cosmic rays. This conclusion is consistent with data of a number of other experiments investigating the muon component of air showers at ultra-high energies. On the contrary, measurements of the depth of the shower maximum in the atmosphere (Xmax) in the experiments using air fluorescence technique favor a light mass composition of primary cosmic rays at these energies. This contradiction (so-called “muon puzzle”) cannot be resolved without serious changes of the existing hadron interaction models.

Coronal mass ejections (CMEs) are the brightest manifestations of solar activity. During periods of higher solar activity, dozens of ejections are observed daily and affect cosmic ray fluxes in interplanetary space. Observation of CMEs is usually carried out by means of various satellite apparatuses. In this work, features of the investigation of coronal mass ejections that are detected in the muon flux by the ground-based URAGAN muon hodoscope operating as a part of the Experimental complex NEVOD at the Moscow Engineering Physics Institute are discussed. Results of studying the anisotropy of the cosmic ray muon flux during the CMEs of 2016 are presented.

A description of the detection and data-acquisition systems of the Cherenkov water calorimeter of the NEVOD Experimental Complex, which is a unique scientific facility located on the Earth’s surface, is presented. In the development of these systems, a solution is sought to the problem of measuring the energy of cascade showers initiated by single muons and the energy deposited by high-multiplicity muon bundles in a wide energy range.

Results are presented from analyzing experimental data on 0.1–10 TeV cascade showers generated by muons in the NEVOD Cherenkov water detector. The procedure for selecting and reconstructing the parameters of events with cascades in the detector volume is discussed. Results are presented from measurements of the zenith angle distribution of cascades for different energies. The measured distributions are compared to results from calculations.

A way of detecting local anisotropies of the muon flux using the matrix-form data of the URAGAN hodoscope (MEPhI) is proposed. Confidence intervals for estimating the matrix-data mathematical expectations in observations with reference and sliding data-sampling periods are selected, indicator functions are constructed, and a procedure for space–time filtering is developed. The results are presented from a search for local anisotropy in the muon flux recorded in the matrix-form data of the URAGAN hodoscope.

At the beginning of September 2017, the Sun was characterized by anomalously high solar activity (SA), which was unusual for the region of the minimum of the 11-year cycle. A great many powerful flares of the M- and X-classes were observed; these were accompanied by powerful coronal mass ejections (CMEs). These events caused strong magnetic storms on the Earth (the Kp index was as high as 8; the Dst index was

A way of eliminating diurnal variations in muon fluxes for matrix observations of the URAGAN hodoscope (MEPhI) is proposed, based on a matrix digital two-dimensional low-pass filter. Its structure is developed on the basis of matrix elementwise multiplications. Diurnal variations in the muon fluxes for the sequence of matrix observations of the Uragan hodoscope are eliminated.

Results are presented from an analysis of changes in the muon flux of cosmic rays during Forbush effects, recorded by the URAGAN muon hodoscope in the period 2012–2017 and the scintillation muon hodoscope in 2016–2017. Characteristics of the Forbush effects for this period are analyzed. The obtained characteristics of muon flux variations are compared to different parameters of the near heliosphere during the Forbush effects for the 11-year cycle of solar activity.

MegaScience projects are unique scientific experiments and facilities of a large scale that were initiated to allow to go beyond modern knowledge in the field of fundamental sciences and open up new opportunities in the technological development. The implementation of such complex projects requires the combined efforts of many scientists and institutions at national and multinational level. The paper presents an analysis of new trends in the training of researchers in the field of elementary particle physics, high energy physics and cosmophysics for research projects and experiments at MegaScience facilities. The authors consider the vast experience of extensive training of MEPhI students for fundamental science and analyzed new approaches to organizing the individual training of researchers at the university. The result of this work was presented and discussed within the proceedings of the Third Conference “Personnel training and legal support for the implementation of scientific projects of the Mega-science class” organized by National Research Nuclear University MEPhI and Kutafin Moscow State Law University on 17 June 2021.

Multiwire drift chambers designed for the neutrino experiment at the IHEP U-70 accelerator have found a new application in the MEPhI experiment focused on the detection of ultrahigh-energy cosmic rays. Their high durability and fine spatial and angular characteristics make these chambers perfectly suitable for such studies. The drift chambers were tested at MEPhI and used in constructing the CTUDC coordinatetracking setup, which operated together with the NEVOD water Cherenkov detector and the DECOR detector. The results of the studies of the parameters of drift chambers in the cosmic-ray flux at test benches and in the CTUDC setup are presented.

As part of an in-depth investigation of the muon excess observed in ultrahigh-energy cosmic rays, one needs to measure the energy characteristics of muon component of extensive air showers (EAS). The mean muon energy can be estimated from the energy deposited in the detector by the muon bundles. In the NEVOD–DECOR experiment, the local muon density and the shower-arrival direction are measured with a track-coordinate detector, and the deposited energy is measured in the Cherenkov calorimeter. The results of the measurements carried out in 17400 h of detector operation are compared with those of the simulation based on the CORSIKA package.

The design for the TAIGA-HiSCORE array, a part of the TAIGA Gamma Ray Observatory, is considered. The observatory is being constructed in the Tunka Valley, 50 km from Lake Baikal. Preliminary results obtained using the first 28 optical stations of the array are presented.

Coronal mass ejections are the brightest manifestations of solar activity. Dozens of coronal mass ejections are observed daily during periods of higher solar activity. They directly affect cosmic ray fluxes that carry information on plasma clouds, including clouds moving toward the Earth. Several aspects of geoeffective and non-geoeffective coronal mass ejections, observed with the ground-based URAGAN muon hodoscope operated as part of the NEVOD experimental complex at MEPhI, are discussed. The anisotropy of cosmic ray muon fluxes recorded during coronal mass ejections in 2014 and 2015 is investigated.

Cosmic ray muons are formed in the upper layers of the atmosphere under the effect of primary cosmic radiation, and their flux is sensitive to variation in atmospheric parameters. Thunderstorms are a pronounced manifestation of nonstationary processes in the atmosphere, and they are good material for developing and testing the main approaches to investigating such processes according to muon flux variations detected on the Earth’s surface. In this work, spatial and angular parameters of the muon flux detected by the URAGAN muon hodoscope during thunderstorms in the Moscow area in 2014 and 2015 are presented along with the results from analysis. Thunderstorms are identified and their development is followed using information obtained by the DMRL-C Doppler weather radar (Russian Federal Service for Hydrometeorology and Environmental Monitoring).

A cluster type NEVOD-EAS setup is being constructed by the National Research Nuclear University MEPhI on the basis of the Unique Scientific Facility “Experimental Complex NEVOD”. The NEVODEAS setup is intended for the detection of extensive air showers (EASs) with energies in the region of the knee in the energy spectrum of primary cosmic rays (1015–1017 eV). The key elements of the setup are 192 particle detectors for EAS electron–photon and muon components. These detectors are composed of NE102A organic scintillators and Philips XP3462 photomultiplier tubes enclosed in pyramidal steel cases. The techniques used to investigate the characteristics of scintillator plates, photomultiplier tubes, and NEVOD-EAS detectors, as well as the results of this investigation, are discussed. All measurements have been taken using special testing facilities and the precision URAGAN muon hodoscope, with which it is possible to comprehensively investigate the nonuniformity of light collection in the detector (the dependence of the detector response on the location of the passage of a charged particle through its operating volume).

A coordinate tracking unit based on drift chambers (CTUDC) for registering single muons and muon bundles at large zenith angles is created at the MEPhI. The unit consists of multi-wire drift chambers (DCs) with large drift gaps. These DCs were used earlier for the neutrino channel on the U-70 accelerator. The CTUDC consists of two coordinate planes with 8 drift chambers in each, assembled on the opposite sides of the NEVOD Cherenkov water detector (CWD). The effective area of the unit is 29.6 m2. The CWD trigger system and DECOR coordinate-tracking detector provide timestamps for the drift chambers. The first results from the registration of single muons and muon bundles by the unit in combination with other detectors of the NEVOD experimental complex are presented.

The URAN array is designed to study primary cosmic rays in the region of the knee by detecting neutrons produced as a result of interaction between EAS particles and nuclei in the atmosphere or matter near the installation. It consists of 72 detectors mounted on the roofs of experimental buildings and combined into cluster structures of 12 detectors. The registering element is scintillator based on natural boron. The area of each detector is 0.36 m2.

The NEVOD-EAS array is now being installed at MEPhI to determine the sizes, directions of arrival, and positions of the axes of extensive air showers (EAS), different components of which are recorded by the detectors of the NEVOD experimental complex. The central part of the NEVOD-EAS array, which contains four clusters of scintillation detector stations designed to record a shower’s electron–photon component, was created and put into operation in 2015. A description of the shower array measuring system and the results from reconstructing extensive air showers recorded in the first 49-day series of experiments are presented.

Experimental data on the energy deposits of muon bundles in inclined extensive air showers (EASes), obtained at the NEVOD–DECOR installation over a long period of time, are presented. The experimental data are compared to calculations based on simulating an EAS’s muon component using the CORSIKA code.

Coronal holes generate a high speed solar wind. This wind is the cause of magnetic storms on the Earth during the years of low solar activity. Also a high speed solar wind creates disturbances in the interplanetary magnetic field. The disturbance may reflect cosmic rays hitting them in the direction of the Earth. As a result, it is possible to observe a change in the flux of cosmic rays on the Earth before the arrival of the disturbance. The paper identifies a criterion for early detection of cosmic ray flux increasing by the muon hodoscope URAGAN (MEPhI, Moscow) to coronal holes in years of decreased solar activity (2009-2010, 2018-2019). It was found that increases of cosmic ray intensity are visible before the main sequence of areas of increasing and decreasing cosmic ray intensities in GSE maps in 60% of the cases.

The experimental data on thermal neutron flux registered by the “Neutron” setup (MEPhI, Moscow) on the Earth's surface for the period from May 2015 to February 2019 were analyzed. The effects of Forbush decrease (FD) and the lunar cycles were studied. The comparison with the results of FD studies in data of two other setups: the Moscow neutron monitor (MNM) and the muon hodoscope URAGAN (MEPhI, Moscow) was made. Comparison showed that the FD amplitudes of “Neutron” are comparable with those of MNM (on average, less by about 30%), and about 1.5 times more than for MH URAGAN. The counting rate recovery of “Neutron” detectors is much faster than for MNM and MH URAGAN.

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.

Modern nuclear physics is impossible without the implementation of projects of the megascience class, for the creation of which the efforts of many organizations and countries are consolidated. The level and complexity of experiments carried out with the use of such facilities is provided by scientific researchers with a wide range of competencies. The education of such researchers is an important task for scientific and educational organizations. These issues were discussed at the 2nd conference “Personnel training and legal support for the implementation of scientific projects of the Mega-science class” organized by National Research Nuclear University MEPhI and Kutafin Moscow State Law University on June 25, 2020. The aim of the Conference was to discuss the policy management issues of implementation of the Mega-science class research projects.

An experiment on the measurements of the energy deposit of inclined cosmic ray muon bundles is being conducted at the experimental complex NEVOD (MEPhI). The complex includes the Cherenkov water calorimeter with a volume of 2000 m3 and the coordinate-tracking detector DECOR with a total area of 70 m2. The DECOR data are used to determine the local muon densities in the bundle events and their arrival directions, while the energy deposits (and hence the average muon energy loss) are evaluated from the Cherenkov calorimeter response. Average energy loss carries information about the mean muon energy in the bundles. The detection of the bundles in a wide range of muon multiplicities and zenith angles gives the opportunity to explore the energy range of primary cosmic ray particles from about 10 to 1000 PeV in the frame of a single experiment with a relatively small compact setup. Experimental results on the dependence of the muon bundle energy deposit on the zenith angle and the local muon density are presented and compared with expectations based on simulations of the EAS muon component with the CORSIKA code.

The Experimental complex (EC) NEVOD includes a number of unique experimental facilities for studies of main components of cosmic rays on the Earth's surface. The complex is used for basic research of CR flux characteristics and their interactions in the energy range 1015 – 1019 eV. To extend the experimental capabilities nowadays new large-scale detectors are being deployed around the EC NEVOD: an array for the EAS registration (NEVOD-EAS), a detector of atmospheric neutrons (URAN) and a large-area coordinate-tracking detector (TREK). The description of experimental capabilities of the complex is given, and first results of simultaneous detection of various EAS components are discussed.

A new method for the analysis of spatial and angular characteristics of the cosmic ray muon flux registered in the hodoscopic mode using a single setup – the muon hodoscope – is presented. Various parameters of the muon flux anisotropy and methods of calculation of these parameters are discussed. It is shown that the horizontal projection of the muon flux relative anisotropy vector which characterizes lateral (horizontal) displacement of the muon flux angular distribution is the sensitive parameter to a variety of nonstationary processes in the heliosphere. The experimental data on the variation of the muon flux anisotropy during the passage of various irregularities in the solar wind and interplanetary magnetic field in the Earth’s vicinity are presented.

The most powerful coronal mass ejection of the 24th solar cycle took place on the opposite side of the Sun on July 23, 2012 and had no geomagnetic consequences. Nevertheless, as a result of passing of the ejection through the heliosphere, variations of galactic cosmic rays flux were observed on the Earth. These variations were registered by the muon hodoscope URAGAN (MEPhI, Moscow). Muon flux angular distributions on the Earth’s surface are reported and analyzed.

Muon hodoscope URAGAN continuously detects the angular distribution of muons in a wide range of zenith angles and allows to obtain information about the variations both in the intensity and angular characteristics of the muon flux related with active processes in the heliosphere, the magnetosphere and atmosphere of the Earth. This paper describes the procedure of organizing of real-time URAGAN data presented in the Internet.

The temperature effect of high mountain muon detectors, which exceeds the theoretically expected one, is investigated. The inverse instrument problem for experimental determination of the density of the temperature coefficient is solved. Results provided by the mddb database created for muon detectors are used as observational data and briefly described.

Simulations of how secondary components of cosmic rays are generated and pass through the atmosphere are performed using the CORSIKA software package. The relationship between the vertical projection of the local anisotropy vector A Z and the index of primary particle spectrum γ is calculated. The time series of A Z for 2007–2015 are obtained using data from the URAGAN muon hodoscope. Matrix data corrected for barometric and temperature effects are used to estimate A Z . Using the A Z time series, the average annual daily variations Δγ are estimated. Annual and daily variations in the slope of the energy spectrum of primary protons are observed.

In passing through the heliosphere, the cosmic ray flux changes its properties (energy and angular distribution) due to the influence of interplanetary medium. As a consequence, the muon flux generated by primary cosmic rays in the Earth’s atmosphere changes its properties as well. Muons detected on the Earth’s surface are mostly generated by primary protons and helium nuclei with energies of 10 GeV to TeV. The interplanetary magnetic field has a great impact on the trajectories of these particles in the heliosphere. Constructing the back trajectories of the particles from the detector on the Earth’s surface to the region of the heliosphere allows us to evaluate the relationship between trajectories of muons and primary particles. This work presents calculated trajectories of muons, parental protons, and helium nuclei with different energies for positive and negative Sun polarity. It is shown that changing the Sun’s polarity leads to qualitative changes in the regions of the heliosphere through which primary particles pass.