G. B. Khristiansen

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.

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.

Temporal structure of scintillation detector pulse in EAS

At the Moscow University EAS array the detector pulse shapes were observed with the help of two scintillation detectors of area 4 , each separated by 23 m. The pulse shapes were analysed in EAS with a particle density of more than 10 . 13 pulses were observed in the EAS with sizes at core distances R > 200 m. Some of the pulses have fine temporal structure with secondary peaks corresponding to tens of particles. Comparison of the individual experimental pulse shapes with the pulse shapes expected for the EAS particles arriving randomly due to the average time distribution indicates the non-statistical temporal structure of the pulses.

The EAS-1000 Array

The requirements for a newly constructed EAS array are summarized, and the EAS-1000 array now under construction is described. The array is depicted, and its accuracy in finding EAS parameters is shown. The expected statistics in observing EAS of different energies are presented for the most important scientific problems the array is supposed to solve.

The primary cosmic ray mass composition around the knee of the energy spectrum

Experimental muon number distributions in EAS obtained at Moscow State University are analysed to estimate the primary mass composition at energies before and after knee. The mass composition before the knee corresponds to the normal one (as at E 0 ∼10 12 eV), while experimental data after the knee are in agreement with the assumption that normal composition becomes enriched slowly by heavy nuclei, as also supported by contemporary diffusion models.

The necessity and reality of EAS-1000 construction

The main problems of superhigh energy cosmic ray physics are discussed. It is pointed out that the existing EAS arrays can not improve the level of experimental research in the near future and the arrays of a new generation are very much needed. The short description of the constructed EAS-1000 array and its first stage EAS-100 is given.

Calculations of characteristics of gamma ray and hadron families

The Monte-Carlo method is used to calculate the three-dimensional development of extensive air showers in the range of primary energy 3*1014-1016 eV for different observation levels: 60, 200 and 590 g cm-2. The data obtained are analysed from the viewpoint of the construction of gamma ray and hadron families. It is concluded that the fraction of families initiated in one collision alone (pure families) is rather low and that they are hardly separable from the others.

The EAS-1000 array and perspectives of the primary mass composition studies at ultra-high energies

The status of EAS:-1000 array is presented. Considering the possibility of data acquisition on EAS muons and Cherenkov light the problem of CR mass composition investigations is discussed.

Mass composition of the primary cosmic rays below and above the knee (1015 ÷ 1017 eV): a new approach using MSU data

Experimental data on muon number distributions at fixed shower size obtained with Moscow State University array are analyzed to derive primary mass composition at energies 1015 ÷ 1017 eV. Mass composition before the knee does not contradict to that measured by direct methods while mass composition after the knee is enriched by heavy nuclei in accordance with modern diffusion model.