N. S. Barbashina

A Coordinate Detector for Studying Horizontal Fluxes of Cosmic Rays

A DECOR coordinate detector is a multilayer system of plastic streamer tube chambers located around a NEVOD Cerenkov water calorimeter. The basic characteristics of the detector are as follows: the area is ∼100 m2, the angular resolution is ∼1°, and the space resolution is ∼1 cm. The structure of the detector, data acquisition and trigger systems, and results obtained during the operation of a pilot assembly (8 chamber layers and a working area of 8.4 m2) are given.

The URAGAN wide-aperture large-area muon hodoscope

The URAGAN wide-aperture large-area multilayer muon hodoscope is developed for the NEVOD experimental complex of the Moscow Engineering Physics Institute. The hodoscope will be used to study atmospheric and heliospheric processes responsible for variations in the muon flux at the Earth’s surface. The structures of the detector and its system of data acquisition and processing are described. The data obtained during continuous sets of measurements in 2005–2006 using the first two supermodules of the setup are analyzed, and preliminary results of this analysis are discussed.

Ultra-high energy cosmic ray investigations by means of EAS muon density measurements

A new approach to investigations of ultra-high energy cosmic rays based on the ground-level measurements of the spectra of local density of EAS muons at various zenith angles is considered. Basic features of the local muon density phenomenology are illustrated using a simple semi-analytical model. It is shown that muon density spectra are sensitive to the spectrum slope, primary composition, and to the features of hadronic interaction. New experimental data on muon bundles at zenith angles from 30° to horizon obtained with the coordinate detector DECOR are compared with CORSIKA-based simulations. It is found that measurements of muon density spectra in inclined EAS give possibility to study characteristics of primary cosmic ray flux in a very wide energy range from 10 15 to 10 19 eV.

Long-term variations in the muon flux angular distribution

The intensity of the atmospheric muon flux depends on many factors: the energy spectrum of primary cosmic rays and the state of the Earth’s heliosphere, magnetosphere, and atmosphere. The wide-aperture URAGAN muon hodoscope (Moscow, Russia, 55.7° N, 37.7° E, 173 m a.s.l.) makes it possible to investigate not only variations in the muon flux intensity but also temporal changes in the parameters of its angular distribution. These changes are analyzed using the vector of local anisotropy and its projections, which have different sensitivities to the parameters of modulation of both primary cosmic rays in the heliosphere and the Earth’s magnetosphere and secondary cosmic rays as they pass through the Earth’s atmosphere. The vector of local anisotropy is the sum of unit vectors (directions of the reconstructed muon tracks) normalized to the number of tracks. The results of an analysis of long-term variations in mean hourly projections of the vector of local anisotropy obtained from the 2007–2011 URAGAN hodoscope data are presented.

Observation of heliospheric disturbances in the muon component of cosmic rays

The possibilities of using ground-based muon hodoscopes to study heliospheric disturbances are discussed. Mapping of the matrices of muon flux angular distributions recorded at the ground level in geocentric solar ecliptic coordinates with allowance for the asymptotic directions of primary protons of galactic cosmic rays makes it possible to observe the dynamics of heliospheric disturbances in the near-Earth space. Variations in some other characteristics of muon flux angular distributions are also analyzed.

Energy spectrum of cascade showers generated in water by near-horizontal muons

We discuss measuring cascade shower energy using the NEVOD Cherenkov water detector with a spatial lattice of quasi-spherical modules (QSMs). Dense QSM spacing makes it possible to reconstruct a number of cascade particles along the shower axis from the PMT response amplitude. Our cascade curve reconstruction technique is applied to showers generated by near-horizontal high-energy muons selected using the DECOR coordinate detector deployed around NEVOD. The first results from cascade energy spectrum measurements are reported.

NEVOD-DECOR experiment: results and future

Russian-Italian NEVOD-DECOR experiment on the measurements of the local muon density spectra (LMDS) at various zenith angles gave possibility to obtain information on primary cosmic ray flux and interaction characteristics in a record wide energy range from 1015 to more than 1018 eV. Comparison of the measurement results with CORSIKA-based simulations showed the increase of LMDS slope at PeV energies of primaries (corresponding to the first knee); a trend to a heavier primary mass composition above the knee; indication for a second knee (a further increase of the spectrum slope near 1017 eV). At large zenith angles and high muon densities (corresponding to primary energies around 1018 eV) a considerable excess of muon bundle events in comparison with the expectation based on independent estimates of the primary spectrum and widely used hadron interaction models has been found. In 2011, a new phase of measurements of the energy spectrum of cascade showers initiated by high-energy muons in water and of the energy deposit of muon bundles at various zenith angles and muon multiplicities started. Further plans include the deployment of a traditional EAS array around the NEVOD-DECOR complex.

Specific features of studying Forbush decreases in the muon flux

The variations in the cosmic ray (CR) muon flux during the Forbush decreases (FDs), registered by the DECOR muon detector and the URAGAN muon hodoscope during the periods of their operation from 2004 to 2006, are analyzed. The unified method for determining the parameters of variations in the CR flux during FDs has been developed, and the dependences of the FD characteristics on the rigidity of primary CRs and information about the spatial-angular dynamics of the muon flux during FDs have been obtained.

A proposed NEVOD-EAS installation for the detection of extensive air showers

A new installation is dedicated to the independent evaluation of extensive air shower (EAS) energies detected in the NEVOD-DECOR experiment in the knee region of the energy spectrum. The design for the measuring system of the shower installation is based on clusters of scintillation detectors that are located on the roofs of laboratory buildings at MEPhI (Moscow) and will detect the electromagnetic (for near-vertical showers) and muon (for large zenith angles) EAS components. Features of the measuring system, the system for data acquisition and processing, and the results from investigating the characteristics of a single detector are discussed, along with the algorithm for event formation by the data of separate clusters.

Application of the URAGAN muon hodoscope to calibrate charged particle detectors

Independent calibration of the charged particle detectors is often required in developing different devices for elementary particle physics. The use of the URAGAN muon hodoscope, created at MEPhI’s NEVOD Scientific and Educational Center, is described. The high accuracy of muon track reconstruction allows calibration and precision study of the sensitive working volume of such detectors.