OG 6.1.35 MULTIFRACTAL MOMENTS ANALYSIS OF THE CORE OF PeV AIR SHOWERS FOR AN ESTIMATE OF THE COSMIC RAY COMPOSITION

A system of large-area position-sensitive multiwire proportional chambers, installed in the bottom of the central detector of the KASCADE experiment is able to observe the density distributions of extensive air shower components in the shower core. Using the method of multifractal moments, a mass sensitive parametrisation of the density distributions is given. In combination with additionally measured parameters, such as the number of reconstructed muons in the core, an artiicial neural net analysis leads to an estimate of the abundance of the light primary component in cosmic rays in the energy region around the "knee". INTRODUCTION The KASCADE (KArlsruhe Shower Core and Array DEtector) experiment (Klages et al., 1997) aims at the determination of the chemical composition of cosmic rays in the energy region around the so-called "knee" by extensive air shower (EAS) observations. The structure of the shower core provides valuable information on the nature of the primary particle, thus supplementing shower parameters, which signal the longitudinal development of EAS and the total muon multiplicity, more precisely the N e =N-ratio. The sensitivity is due to diierences in the multiplicity and lateral density distribution, and in the energy spectra of particles in the shower center. The KASCADE central detector consists of an iron sampling calorimeter for studies of the hadron component, of an array of scintillators on top of the calorimeter for detecting the electron-photon component, of 456 fast scintillators in a layer of the calorimeter for triggering and for measurements of muon arrival times, and a setup of multiwire proportional chambers (MWPC), installed in the basement of the central detector. The MWPCs are arranged in double layers with a telescope eeect, improving the reconstruction quality of the particle hits and informing about the direction of incidence. The particles observed with the MWPCs are mainly muons with E 2 GeV, but also the "punch-through" of tails of hadron cascades in the shower core, penetrating the iron absorber (c. 1000 g/cm 2) above. Thanks to the spatial resolution of the MWPC setup the hit pattern in the shower core can be measured accurately, enabling a reasonable analysis of signatures for the mass of the EAS primary. For this purpose the observed patterns are parametrised in terms of multifractal moments, which prove to be informative for a mass discrimination (Haungs et al., 1996). This feature has been revealed on the basis of detailed analyses of simulated air showers. It is used …