Experimental Complex NEVOD Research Articles

A quasi-spherical optical module QSM-6M based on the Hamamatsu R877 PMT for the detection of Cherenkov radiation in water

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.

Calibration of the NEVOD-EAS array for detection of extensive air showers

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.

Multicomponent Studies of Extensive Air Showers at Facilities of the NEVOD Experimental Complex

Multicomponent Studies of Extensive Air Showers at Facilities of the NEVOD Experimental Complex

Multicomponent extensive air showers studies at the installations of the experimental complex NEVOD

Results of the analysis of the parameters of extensive air showers detected by the installations of the Experimental Complex NEVOD, as well as the results of their comparison with simulated events are presented. The calibration and energy threshold of the NEVOD-EAS air-shower array, as well as the results of reconstructing the axes direction according to the data the NEVOD-EAS and DECOR installations are discussed. An example of the event detected by all installations of the complex is given.

Cosmic-Ray Anisotropy Study by Means of Detection of Muon Bundles

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.

The NEVOD-EAS air-shower array

The Experimental complex NEVOD includes several different setups for studying various components of extensive air showers (EAS) in the energy range from 1010 to 1018eV. 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 104 m2. 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.

NEVOD — An experimental complex for multi-component investigations of cosmic rays and their interactions in the energy range 1–1010 GeV

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.

NEVOD: A unique scientific facility of Megascience class

The term “Megascience” appeared relatively not long time ago and has no distinct definition. Intuitively, this term is understood as something big and certainly expensive, i.e. a concept of “Megascience” is replaced by a concept of “Megamoney”. In this paper, the unique scientific facility “NEVOD Experimental complex” (USF NEVOD), which satisfies all requirements to Megascience facilities, is described. USF NEVOD provides conduction of basic and applied investigations of cosmic rays in the record energy interval 109 − 1019 eV. Obtained scientific results are considered, and their comparison with other, larger scale detectors is discussed. This comparison shows the advantage of original approach used in the NEVOD complex compared to traditional methods of investigations. Taking into account the location of USF NEVOD in the University, the Scientific and Educational Center was organized on its bases. This allows solve two important tasks: to provide permanent operation of USF NEVOD by envolving students and to ensure their training in frame of real scientific experimental investigations. Some other questions of development and functioning of unique scientific facilities are considered, too.

Status of the Russian-Italian experiment NEVOD-EAS

The NEVOD-EAS air shower array is currently under construction in MEPhI, within the Russian-Italian NEVOD-DECOR partnership. The goal of the array is to provide an independent measurement of the size, of the core location and of the arrival direction of the extensive air showers (EAS) detected with the other facilities of the Experimental complex NEVOD. These measurements will provide a calibration of a novel perspective technique developed in the Experimental complex NEVOD for studying inclined muon bundles – the method of local muon density spectra. The array will also extend the opportunities of the Experimental complex NEVOD in carrying out multi-component studies of extensive air showers. The present status of the NEVOD-EAS air-shower array is described and the future perspectives are discussed.

Investigation of the Energy Loss of Muon Bundles in the Cherenkov Water Calorimeter

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.

Investigation of muon bundles generated by UHECR by means of the new coordinate-tracking detector

The new coordinate-tracking detector based on drift chambers (CTUDC) is created in MEPhI. The detector represents two planes with total area of 30 m2 placed on the opposite sides of Cherenkov water detector of 2000 m3 volume. Each plane consists of 8 large multiwire drift chambers (4000x508x112 mm3). The key advantages of these chambers are a large effective area (1.85 m2) and a good coordinate and angular resolution with a small number of measuring channels. From the beginning of 2017, CTUDC operates as a part of the experimental complex NEVOD. The detector is designed for measuring of high density muon bundles (up to 10 particles per m2) at zenith angles in the range from 30° to 90°. The results of the CTUDC operation during the last year are given, the first distributions of the events in zenith angle, muon bundle multiplicity and density obtained from the detector data are discussed.

Comparing EAS registered with PRISMA-32 array and CWC NEVOD

Results of comparing events detected with two detectors of the Experimental complex NEVOD: PRISMA-32 array and Cherenkov water calorimeter (CWC) NEVOD – are presented. The PRISMA-32 is an array for simultaneous registration of the EAS electron-photon and neutron components. It consists of 32 en-detectors deployed over the area of about 500 m2, along the perimeter of the CWC NEVOD. The CWC NEVOD is a detector of a calorimetric type with a volume of 2000 cubic meters in which the registration system of 91 quasispherical modules (546 FEU-200 photomultipliers) is placed. CWC provides measurement of the intensity of Cherenkov radiation from any direction with practically the same efficiency.

A cluster approach to the analysis of experimental data of the NEVOD-EAS shower array

The NEVOD-EAS array for the detection of extensive air showers in the energy range 1015–1017 eV is being created in MEPhI on the basis of the Experimental complex NEVOD. The array will allow independent estimations of the size, axis position and arrival direction of EAS registered by the detectors of the experimental complex. The NEVOD-EAS registering system is organized in a cluster principle, and data analysis is performed using a newly developed cluster approach. The features of this approach to the NEVOD-EAS experimental data analysis are discussed.

Dependence of the Energy Deposit of Muon Bundles on Local Muon Density and Zenith Angle

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.

Anisotropy in the Directions of Arrival of Muon Bundles Detected at the NEVOD Experimental Complex

Anisotropy in the Directions of Arrival of Muon Bundles Detected at the NEVOD Experimental Complex

Multicomponent Registration of the EAS

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.

Anisotropy of the high energy cosmic ray flux measured by means of muon bundles in the Experimental complex NEVOD

The work is devoted to the study of the anisotropy of the high energy cosmic ray flux by means of muon bundles registered during 2012-2018 with the coordinate-tracking detector DECOR, which is a part of the Unique Scientific Facility «Experimental complex NEVOD». We have analyzed data for two event samples corresponding to E > 1015 eV and E > 1016 eV energy ranges of primary particles. The method of data processing is described and estimates of the dipole anisotropy parameters (the amplitude and the phase) are presented.

Energy loss measurements of inclined muon bundles in the Cherenkov water detector

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.

Studying the Anisotropy of the Muon Flux during Nongeoeffective Coronal Mass Ejections of 2016

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.

Investigation of Ultrahigh-Energy Cosmic-Ray Anisotropy Using the Data on Muon Bundles Recorded with the DECOR Coordinate-Tracking Detector

Results of investigation of the high-energy cosmic-ray flux anisotropy using data on muon bundles are presented. The events were recorded in the period of 2013–2017 with the DECOR coordinate-tracking detector, which is a part of the unique scientific setup of the Experimental complex NEVOD. Methods for experimental data processing and taking atmospheric effects into account are described. Results of the analysis of two types of muon bundle events, which correspond to different ranges of primary particle energies (E > 1015 eV and E > 1016 eV) are discussed. Upper limits of the anisotropy amplitude for the two types of events are obtained.