Detailed study on lateral density distribution of electro-magnetic component of air showers observed with highly packed array of Grapes III

The air shower array of the GRAPES III consist of 217 scintillation detectors (each 1 m 2 ) and detectors are arranged with 8m separation. Using this highly packed ar- ray of GRAPES III, detailed analysis on the lateral struc- ture of electro-magnetic component in air showers has been conducted for shower size between 5 10 3 to 10 6 . About 3 10 8 air showers are analyzed. These results are com- pared with the expectations from Monte Carlo simulations (Corsika s QGS Jet model). Their characteristics were exam- ined carefully and are compared with other group s results. The meaning of the age parameter of NKG function are in- vestigated thoroughly and correlation between longitudinal development and lateral density distribution are discussed. Also presented is the mass dependency of lateral structure of the electro-magnetic component and possible usage of the age parameter together with muon size to identify the nature of primary particles. The observed electron size distribution is discussed.