Identification of mass composition of cosmic rays considering extensive air shower’s electron and muon component with highest energies


1 M.Sc. in Physics, Factuly of Physics, Shahid Bahonar University, Kerman, Iran

2 Professor, Factuly of Physics, Shahid Bahonar University, Kerman, Iran

3 Ph.D. Student of Physics, Factuly of Physics, Shahid Bahonar University, Kerman, Iran


The phenomena of Extensive Air Shower (EAS) are produced by the collision of primary cosmic rays (CR) with Energy more than eV with the atmospheric molecules. As a result the electron and muon components (cascades) of EAS develop through the air.
 The study of such cascades gives important information about the primary CR mass composition as well as its astrophysical origin models. One of the EAS detection methods is by the ground arrays of electron and muon detectors; the data of Yakutsk EAS array located in Russia have been used for primary CR with energy more than  eV. In the catalogue of world’s data, the EAS parameters such as  electron density,  muon density, R shower core distance, E primary energy and arrival directions (Zenith angel ѳ, Azimuth angle Φ) of each shower is given.
In this search the different parameters of EAS such as the age parameter, shower size () and total number of muons () are used as mass composition discriminators. The total number of muons and electrons in the shower have been calculated using the lateral distribution functions (LED) of electron and muon of Nishimura-Kamata-Griesen(NKG) formula.
The first sensitive parameter to use is   where its dependency on EAS energy is studied. It is expected that the ratio should increase from primary Gamma to proton and then in turn to heavy nucleus. The dependency of calculated  on energy shows an increase above  that could be due to LPM effect of Gamma primaries. At highest energies or the increase of Mass composition above this energy, which because of its high increase of  , heavier mass composition above  is suggested. The second parameter for investigating EAS mass composition is the EAS age parameter which is also calculated by using LDF of NKG formula. Higher age has flatter electron LDF or higher mass composition. Again it is observed that the age is increased (indicating higher mass) above.
The last main parameter to investigate mass composition is the dependency of  on . The calculated experimental results have been compared with the CORSIKA simulation work for Gamma, Proton(P) and iron(Fe) cosmic ray primaries. The results suggest a mixed P-Fe composition for energies above  and Fe primaries above. In conclusion the study of EAS age and  on E, also dependency of  on  and it,s comparison with the simulation work consistently show an increase of mass composition of cosmic ray above its primary energy .
Also because of the increased mass composition of CR (higher charge) it means more deflection of CR in the Galactic magnetic field. Therefore the particles of higher energies (above) are more confined to the galaxy than the lower energies so their sources may be of galactic than extragalactic origin.
The results of this search also give a light on the CR Astrophysical origin models named top-down models (10-50 percent of gamma primaries) and bottom-up models (less than 1 percent photons). (The low percent of Gamma primaries is not in the favor of top-down models scenario of no acceleration).