Physics performance of the ALICE Zero Degree Calorimeter

ALICE is the dedicated heavy-ion experiment at the LHC collider. It will also collect proton-proton and proton-nucleus data as reference to study the onset of the transition to the Quark-Gluon Plasma state predicted by the Standard Model. The ALICE experimental setup essentially consists of a central barrel for particle tracking and identification, a forward spectrometer for muon detection and forward rapidity detectors to provide the triggers and to characterize the event. Among the forward detectors, the Zero Degree Calorimeter (ZDC) will measure the centrality in nucleus-nucleus and in proton-nucleus collisions. In A-A interactions the observable most directly correlated to the geometry of the collision is the energy carried forward by non interacting (spectator) nucleons. In p-A collisions the centrality evaluation relies instead on the detection of the so called 'slow' nucleons emitted by the nucleus. In both cases the simulation results show that the ZDC can be used to trigger on centrality with good accuracy over the whole centrality range. The ZDC will also provide an estimate of the beam luminosity in A-A collisions by measuring the rate of neutron emission in electromagnetic dissociation processes.