Commissioning and calibration of the Zero Degree Calorimeters for the ALICE experiment

The Zero Degree Calorimeters (ZDCs) for the ALICE experiment will measure the energy of the spectator nucleons in heavy ion collisions at the CERN LHC. Since all the spectator nucleons have the same energy, the calorimeter response is proportional to their umber providing a direct information on the centrality of the collision. Two sets of ZDCs are located at opposite sides with respect to the interaction point (I), 116 m away from it Each set consists of a neutron (ZN) calorimeter, placed between the two beam pipes, an a proton (ZP) calorimeter, positioned externally to the outgoing beam pipe. The ZDCs spaghetti calorimeters, which detect the Cherenkov light produced by the shower particle in silica optical fibers embedded in a dense absorber. In summer 2007 the ZN and ZP calorimeters have been placed on a movable platform and then installed in the LHC tunnel. The results of the commissioning studies and in particular the solutions adopted to control the stability of the PMTs response will be shown: light injection with a laser diode and cosmic rays. The foreseen calibration with e.m. dissociation event in Pb-Pb collisions will also be discussed. Finally the first measurements carried out during the commissioning in the LHC tunnel will be presented.