Summary of the NEEDS workshop

The purpose of the NEEDS workshop was to discuss accelerator data required for the interpretation of cosmic ray experiments. The physics of extensive air showers (EAS) is briefly outlined. The importance of data in the extreme forward direction is emphasized and an (inevitably personal) list of priorities is given. Progress in the field of cosmic rays above about 1 PeV will depend to a large extent on our reliable knowledge of high energy strong interactions in kinematic regions not explored up to now. This refers to the range of primary energies (which will require extrapolation by several orders of magnitude for any forseeable future) but also to the direct forward region (which is accessible in principle today but does not seem to find much interest at present). It is emphasized that the energy calibration of EAS depends entirely on simulations and hence on our knowledge of interaction cross sections at the relevant energies. This has direct bearing, e. g., on the question of the existence of the famous Greisen-Zatsepin-Kuzmin cut-off of the primary cosmic ray spectrum