G. Mannocchi

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.

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.

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.

Status of the NEVOD-EAS experiment

The NEVOD-EAS setup is designed for independent estimation of the EAS parameters recorded in the NEVOD-DECOR experiment in the region of the energy spectrum knee. The setup’s recording system is based on the clusters of scintillation detectors for the EAS electron-photon component, located on the territory of MEPhI. Characteristics of the shower array recording system that ensure detection, data acquisition and primary processing, and the time synchronization of clusters are discussed, along with results of studying the nonuniformity of NEVOD-EAS scintillation detector responses.

Observation of UHECRs in horizontal flux

Preliminary results of muon bundle studies in of zenith angle range θ ≥ 60° and multiplicities by means of coordinate detector DECOR are discussed. Estimates of muon bundle characteristics at large zenith angles obtained with CORSIKA code demonstrate the ability of such not large detector as NEVOD-DECOR complex to perform cosmic ray studies in a very wide energy range from 1011 eV to more than 1017 eV.

Energy characteristics of multi-muon events in a wide range of zenith angles

Change of the energy characteristics of muon bundles with an increase of the primary cosmic ray particles energy can be a key to solving the problem of muon excess in the extensive air showers (EAS) observed in a number of experiments. In this work the data on the energy deposit of multi-muon events in a wide range of zenith angles (and as a consequence in a wide range of primary particles energies) obtained with NEVOD-DECOR setup over a long time period are presented. The experimental data are compared with the results of simulations of EAS muon component performed using CORSIKA code.

Investigating the energy characteristics of muon bundles in inclined EAS

The first results from studying the energy deposits of inclined muon bundles in a Cherenkov water detector on the Earth’s surface are presented. The general response of the NEVOD Cherenkov calorimeter’s PMT is used as a measure of the energy deposited (proportional to the muon energy losses in the detector’s matter), while the local muon density at the point of observation is estimated using data from the DECOR coordinate-tracking detector. It is found that the energy deposit normalized to the muon density depends largely on the zenith angle. A comparison of the experimental results and those from EAS muon component simulations using the CORSIKA package shows that the average energy of muons detected in the bundles grows rapidly as the zenith angle increases, reaching ∼500 GeV near the horizon.

Present status of muon diagnostics

Muon diagnostics is a technique of remote monitoring of various dynamic processes in the heliosphere, the magnetosphere and the atmosphere of the Earth based on the analysis of spatial-angular and temporal variations of muon flux simultaneously detected from all directions of the upper hemisphere. The developed approaches to data analysis and results of the study of various terrestrial and extra-terrestrial processes detected by means of a wide aperture URAGAN muon hodoscope are discussed.

Investigation of cosmic rays above the knee by means of muon bundles detected in a wide range of zenith angles

The results of investigation of muon bundles at the Earth’s surface in a wide range of zenith angles on the basis of the new phenomenological characteristic of extensive air showers—spectra of local muon density—have been investigated. Features of the local-density spectra are considered within a simple analytical model. The expected distributions of muon density in a wide range of zenith angles and primary energies, calculated on the basis of the CORSIKA code, are compared with the experimental data.

Investigation of the energy characteristics of EAS muon component with the NEVOD-DECOR setup

Investigations of the energy characteristics of muon component with the increase of the primary cosmic rays energy can be a key to solving muon puzzle - the problem of excess of EAS muons (observed in several experiments at high - ALEPH, DELPHI - and ultrahigh energies - DECOR, Pierre Auger Observatory) in comparison with the expected flux. The measurements results of the energy deposit of inclined muon bundles in water depending on the zenith angle and the local density of muons are presented. As a measure of the energy deposit, the total number of photoelectrons registered by PMTs of the Cherenkov water calorimeter NEVOD was used. The local density of muons, which gives an estimate of the energy of primary particles was obtained from the data of coordinate-tracking detector DECOR. The experimental data are compared with the results of calculations based on simulations of the muon component of EAS by means of the CORSIKA code.