Simulation studies and implementation of Linsley's EAS time structure method for the primary cosmic ray spectrum

Abstract A compact extensive air shower (EAS) array of eight plastic scintillators viewed by HAMAMATSU H7195 photomultiplier tubes covering a total area of 2 m 2 is built in the rooftop of the Faculty of Technology building, Okayama University of Science, and operated since April 2006. We have installed a shift register system in our EAS array to record EAS particle arrival time within 5 μ s . We have also performed detector simulations based on the database obtained from the AIRES simulator and developed the procedures to estimate the primary cosmic ray energy from Linsley's method. Applying this method to our EAS data and the simulation result, we derived the energy spectrum from 10 16 to 10 19.5 eV . Consequently, we obtained the power-law index of − 3.2 ( + 0.46 − 0.8 ) in the primary energy range of 10 16 to 10 18.5 eV , and obtained that a change around 10 18 eV appeared if not taking account of the zenith angle distribution of primary cosmic rays. We also showed the improvement of energy resolution by applying the restriction of zenith angle of primary cosmic rays in our simulation, as well as the potential of Linsley's method with a mini array.