Abstract :
The inclusive Deep-Inelastic-Scattering (DIS) of high energy leptons on free nucleons has been used from late 60s to measure the partonic distributions and, by using nuclear targets, to study the medium modification to these distributions. Semi-Inclusive DIS (SIDIS) of high energy leptons on free nucleons can be used to study another fundamental property of the quarks, the fragmentation function. This function can be also modified by the nuclear medium and can be revealed by performing SIDIS measurements on nuclear targets. These measurements have been recently performed by HERMES with a 27.5 GeV positron beam and at lower energy by CLAS. The possible interpretations in terms of medium modifications of the parton fragmentation function and the implications on the parton energy loss are discussed. Similar hadron quenching appeared from Au-Au central collisions at RHIC. Despite the two different regimes, both these observations have been interpreted in terms of in medium parton energy loss which depends on the density of the medium. A challenge in this research field, will be represented by the measurement of the jet quenching in a hot and dense medium like the Quark Gluon Plasma which is expected to be created at the LHC energy. For this purpose, an electromagnetic calorimeter to complement the excellent performance of the ALICE detector has been proposed.
