Yu. A. Fomin

Nuclear composition of primary cosmic rays in the `knee' region according MSU EAS array data

Experimental data on the EAS muon number fluctuations obtained with the Moscow State University EAS array are analysed to derive the primary mass composition at energies before and after the knee. The mass composition before the knee ( eV) corresponds to that measured by direct methods, while the mass composition after the knee ( eV) is enriched by heavy nuclei.

Primary cosmic ray mass composition at energies 1015–1017 eV as measured by the MSU EAS array

Abstract Experimental muon number distributions in Extensive Air Showers obtained at Moscow State University with enlarged statistics and improved procedure for muon number determination are analysed in the framework of an updated quark-gluon string model. The primary mass composition at energies before and after the kink in the primary energy spectrum is estimated. Mass composition before the kink is close to a normal one, and after the kink experimental data agree with the assumption that normal composition becomes enriched slowly by heavy nuclei according to the Peters-Zatsepin model.

Estimate of the fraction of primary photons in the cosmic-ray flux at energies ∼1017 eV from the EAS-MSU experiment data

We reanalyze archival EAS-MSU data in order to search for events with an anomalously low content of muons with energies Eμ > 10 GeV in extensive air showers with the number of particles Ne ≳ 2 × 107. We confirm the first evidence for a nonzero flux of primary cosmic gamma rays at energies E ∼ 1017 eV. The estimated fraction of primary gamma rays in the flux of cosmic particles with energies E ≳ 5.4 × 1016 eV is εγ = (0.43−0.11+0.12)%, which corresponds to the intensity Iγ = (1.2−0.3+0.4) × 10−16 cm−2 s−1 sr−1. The study of arrival directions does not favor any particular mechanism of the origin of the photon-like events.

Estimates of the cosmic gamma-ray flux at PeV to EeV energies from the EAS-MSU experiment data

Archival EAS-MSU data are searched for anomalous muonless events which may be caused by primary gamma rays with energies between 1015 and 1018 eV. We consider a refined sample of high-quality data and confirm the previously reported detection of a nonzero gamma-ray flux at ∼5 × 1016 eV with a similar flux value but at somewhat lower statistical significance, corresponding to a depletion of the sample. We present upper limits on the flux below and above these energies, including the first constraints in the range 1016.5–1017.5 eV never studied by any other experiment.

Primary cosmic ray composition at energies from 1017 to 1018 eV according to the EAS MSU array data

EAS MSU array data on the composition of primary cosmic rays at energies above 1017 eV are analyzed. The problem of existence of a cosmic ray component that is not related to the conventional mechanism of formation of galactic cosmic rays is considered and the fraction of γ rays in primary cosmic rays is estimated.

Simulation of the Tunka-133 scintillation experiment

The project of the scintillation complex of the upgraded Tunka-133 detector is described. Software for simulation of recording and processing of events by the future scintillation part of the Tunka-133 detector is presented. Highlights of the simulation are given. Results of the simulation of extensive air showers using Aires software are listed.

Estimating the fraction of gamma quanta in the primary cosmic ray flux with energies of ∼1017 eV from the MSU EAS array data

Using data from the MSU EAS array and model calculations, we search for events with abnormally small fractions of muons with energies above 10 GeV in showers with particle numbers of >2 × 107 and zenith angles of <30 degrees. We confirm with good statistical accuracy that the content of gamma quanta in the primary cosmic ray flux can be as high as 2% at energies of ∼1017 eV.

Study of the longitudinal development of individual EAS inferred from the Cherenkov light pulse shape: method and results

Abstract The method of Cherenkov pulse shape for the study of longitudinal development of extensive air showers (EAS) is considered. Some results obtained with this method are described: the dependence of the depth of the EAS maxima on the primary energy, evaluation of the inelastic p- 14 N cross section, and individual EAS cascade curves.

Results and perspectives of cosmic ray mass composition studies with EAS arrays in the Tunka Valley

The study of the cosmic ray mass composition in the energy range 1016 - 1018 eV is one of the main aims of Tunka-133. This EAS Cherenkov array started data acquisition in the Tunka Valley (50 km from Lake Baikal) in autumn 2009. Tunka-133 provides a measurement of the EAS maximum depth (Xmax) with an accuracy of about 30 g/cm2 . Further mass composition analyses at the highest energies (1017 - 1018 eV) will be based on the comparison of primary energy measured by the radio method and the densities of charged particles measured by shielded and unshielded detectors. The high duty cycle of the common operation of the new scintillation array (Tunka-Grande) and the radio extension of the experiment (Tunka-REX) will provide a high statistics of events.

On the choice of the lateral distribution function for EAS charged particles

Knowledge of the lateral distribution function (LDF) of charged particles in extensive air showers (EASs) is necessary for adequate determination of both the total number Ne of particles and other parameters used to classify the showers selected for analysis. Many researchers continue to actively use the Nishimura-Kamata-Greisen LDF despite that fact that it was obtained theoretically within a fairly rough approximation of electromagnetic cascade theory. In this study, the dependence of the shape of the EAS spectrum over the number of particles on the type of LDF used to treat experimental data is investigated. The Nishimura-Kamata-Greisen function and the scaling function are analyzed [5]. Major attention is given to the data obtained at the Moscow State University EAS array.