He 2.1.1 the Status of the Extensive Air Shower Experiment Kascade

The extensive air shower (EAS) experiment KASCADE has been installed at the laboratory site of the Forschungszentrum Karlsruhe. It consists of an extended array of electron detectors and muon detectors as well as of a compact and complex central detector system. The latter contains a scintillator matrix, muon detectors, and a large hadron calorimeter. The main aim of the KASCADE project is the determination of the chemical composition in the ultra high energy (UHE) range around the "knee" in the primary cosmic ray spectrum. The main advantage of the new installation is the simultaneous measurement of a large number of observables for each individual event. This is achieved by the combination of various detection techniques for electrons, muons, and hadrons in air showers and by extensive simulation work on air shower properties and detector response. Data taking with a large part of the experiment has started in 1996. First results are reported on this conference. INTRODUCTION Since several decades one important topic of UHE cosmic ray studies has been the understanding of the "knee" in the primary spectrum. This distinct change in spectral index of the charged particle ux at observation level is generally believed to reeect a change in the energy spectrum of the primary cosmic rays near 510 15 eV. A variety of models for the sources, the acceleration schemes, and the transport of the cosmic rays have been proposed to produce such a change but are still under debate. The detailed knowledge of the chemical composition around the "knee" would be important for the understanding of these problems. On the other hand, all methods for the conversion of particle densities (measured at ground level) to primary energy rely on the validity of the interaction models used in extensive air shower simulations. These models are based on accelerator data and contain extrapolations in energy and rapidity which follow our present theoretical understanding of hadronic interactions. It is important, however, to test the model predictions experimentally. In the energy range above 10 14 eV direct measurements above the atmosphere are sparse and the data lack statistical accuracy due to the steeply decreasing ux and to limited detector area and exposure time. At ground level, the EAS are sampled with a typical detector coverage of less than 1%. The total thickness of the atmosphere corresponds to more than 10 hadronic interaction lengths. In addition, the intrinsic uctuations of the particle …