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Abstract:
The KASCADE Air-Shower experiment in Karlsruhe has by now
collected more than 160 Mio events with an energy threshold of
approx. 10^14 eV. A unique feature of KASCADE is the large
hadronic calorimeter opening a new window to the hadronic shower
core. Apart from its important aid in determining the chemical
composition of primary particles it gives access to a number of
observables used to test EAS predictions and thereby hadronic
interaction models. We present such kind of studies and
critically discuss limitations of the models. For the first
time, the 'knee' is observed simultaneously in electron, muon,
and hadron size distributions as well as in muon density
distributions at given distances to the shower core. The data
can consistently be described only, if an increasingly heavier
composition is assumed above the knee. These conclusions are
supported also by detailed event-by-event studies of the
muon/electron ratio. Such an analysis constitutes a great
advantage over traditional ones which were mostly based on
average numbers obtained from samples of events. Furthermore,
they proof the quality of EAS simulations and clearly show that
the primary spectrum is composed of several elemental groups.
Combined with other multivariate approaches the prelimary data
result in a knee position of 4-5 PeV and in primary indices of
-2.75 and -3.04 below and above the knee, respectively.
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