NUCLEAR ATTENUATION IN SIDIS

摘要

After the first studies of SLAC and EMC, the recent and precise HERMES results in SIDIS on N and Kr nuclei have shown a significant nuclear attenuation for fast hadrons in a new region of the kinematic plane. In addition, for the first time, different medium effects have been observed for different hadron types. In particular while the effect for the pion do not depend on the charge, a sizable difference has been observed between K~+ and K~- and between p and p. The so called Cronin effect in the pt broadening of the leading hadron has also been observed in SIDIS. These results have been interpreted in terms of medium modification of fragmentation functions due to gluon bremsstrahluug and re-scattering of the struck quark while traveling in the medium. However the data on Kr suggested the importance of the additional hadron re-interaction in the nucleus. The SIDIS results provide important informations on the parton energy loss and on the hadron formation time which are basic ingredients for other hadronic reactions and in particular for the heavy-ion interactions at high energies, which are currently studied to provide hints for the Quark Gluon Plasma formation.