Description
Energetic particles, traditionally called Cosmic Rays, were
discovered nearly a hundred years ago, and their origin is
still uncertain. Their main constituents are normal nuclei
as in the standard cosmic abundances of matter; there are
also electrons, positrons and anti-protons, but no
anti-nuclei. Today we also have information on isotopic
abundances, which show some anomalies, as compared with the
interstellar medium. The cosmic ray all-particle spectrum
extends over energies from a few hundred MeV to 3x1020 eV
and shows few clear spectral signatures: There is a small
spectral break near 5x1015 eV, the "knee", where the
spectrum turns down; there is another spectral break near
3x1018 eV, the "ankle", where the spectrum turns up again.
Up to the ankle the cosmic rays are usually interpreted as
originating from Galactic sources; however, we do not know
what the origin of the knee is. The particles beyond the
ankle have to be extragalactic, but due to interaction with
the cosmic microwave background there is a strong cut-off
expected near 5x1019 eV, which is, however, not seen; The
measured high energy cosmic rays beyond this "GZK-cutoff"
(after its discoverers Greisen, Zatsepin and Kuzmin) are the
challenge to interpret.
High-energy primary cosmic rays above energies of about
1x1014 eV are investigated by observations of extensive air
showers (EAS) using large area ground based detector
installations for registering various components of the EAS
cascade development. In the present lecture different
experimental approaches deducing mass and energy sensitive
information from the most sophisticated EAS experiments and
their results are presented. In particular the
KASCADE-Grande experiment for measurements around the knee
and the Pierre Auger Observatory for detecting highest
energy cosmic rays will be discussed in detail. These
experiments involve measurements of secondary particle
distributions, as well as measurements of air Fluorescence
light and radio waves emitted during the EAS development.
The physical and astrophysical implications of the current
findings in various energy regions are briefly discussed and
prospects of the KASCADE-Grande and Pierre-Auger experiments
are presented.
Author
Dr
Andreas Haungs
(Forschungszentrum Karlsruhe)
