Cosmic rays in the knee energy range

Abstract

In the energy range of the so called 'knee' be- tween 100 TeV and 1 EeV one expects to identify the end of the galactic origin of cosmic rays. Only for the lowest energies a direct detection with instruments on high-altitude, long-flying balloons are possible. Measurements of the high- energy particles are performed indirectly via the detection of extensive air showers by extended arrays of particle or Cherenkov light sensitive detectors. Multidimensional anal- yses of the air shower data indicate a distinct knee in the energy spectra of light primary cosmic rays at few PeV and an increasing dominance of heavy ones towards higher ener- gies. This provides implications for discriminating astro- physical models of the origin of the knee and of the physics of the transition from galactic to extragalactic cosmic ray ori- gin. Where around 1 PeV many experiments were in oper- ation and have given valuable results in the last decade, at higher energies there was a lack of experimental efforts. To improve the reconstruction quality and statistics at energies from 10 to 1000 PeV, where the transition can be expected, presently several experiments are in operation or going to be in operation. First results of these experiments, as well as perspectives of future efforts in this energy range will be dis- cussed.