L. I. Dushkin

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.

Investigating the energy, angular, and temporal characteristics of forbush effects registered by the URAGAN muon hodoscope

The results from analyzing variations in the flux of cosmic ray muons during Forbush effects (FEs) registered by the URAGAN muon hodoscope over the period 2005–2009 are presented. The dependences of the amplitudes for reductions in the intensity of the cosmic ray muon flux on the energy of primary particles in energy ranges higher than 10 GeV were obtained. Their changes upon different phases of Forbush effect development were investigated. The local anisotropy vectors were calculated on the basis of spatial-angular variations in the muon flux. Correlations between the parameters of physical properties in the near heloiosphere related to the Forbush effects and the characteristics of muon flux variations were analyzed.

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.

Status of a development of the large scale coordinate-tracking setup based on the drift chambers

The large-scale coordinate detector for registration of near-horizontal muon flux of ultrahigh energy cosmic rays is being developed in MEPhI. Detector is based on the drift chambers from the neutrino experiment at the IHEP accelerator U-70, their key advantages are the large effective area (1.85 m2), good coordinate and angular resolution with a small number of measuring channels. Detector will be operated as a part of the experimental complex NEVOD, in particular, jointly with Cherenkov water detector with volume of 2000 m3. The current status of the project and results of studies of drift chamber characteristics are discussed.

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.

Energy release of inclined muon groups in the nevod water Cherenkov detector

The results of the analysis of the first experimental data on the energy release of inclined muon groups of cosmic rays in the water Cherenkov detector, obtained at the NEVOD-DECOR complex, are presented. It was found that the average specific energy release in the Cherenkov calorimeter (normalized to the muon densitymeasured by the data of the coordinate detector)weakly depends on the muon density; however, the significant dependence on the zenith angle is observed, which indicates an increase in the average muon energy in groups with an increase in the zenith angle.

Study of cascade showers generated by near-horizontal muons in the water Cherenkov detector with a dense array of optical modules

The method for reconstructing the cascade curve by the Cherenkov radiation in water of the NEVOD detector with a dense spatial array of optical modules is discussed. Cascades are generated by near-horizontal muons which are separated by the DECOR coordinate detector. The cascade curves and the cascade energy spectrum measured in an ∼8000-hour measurement series are presented.

A coordinate-tracking setup based on drift chambers for investigating ultrahigh energy cosmic rays

A large-scale coordinate-tracking setup for registering the near-horizontal muon flux from ultrahigh energy cosmic rays is under development at the MEPhI. The setup is based on drift chambers from the neutrino detector at the Institute of High Energy Physics’ U-70 accelerator, which have a large sensitive area (1.85 m2) and good angular and spatial resolution with a relatively low number of measuring channels.

Measuring the energy deposited by muon bundles of inclined EAS in the NEVOD–DECOR experiment

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.