Test beam results on the Proton Zero Degree Calorimeter for the ALICE experiment

The proton Zero Degree Calorimeter (ZP) for the ALICE experiment will measure the energy of the spectator protons in heavy ion collisions at the CERN LHC. Since all the spectator protons have the same energy, the calorimeter's response is proportional to their number, providing a direct information on the centrality of the collision. The ZP is a spaghetti calorimeter, which collects and measures the Cherenkov light produced by the shower particles in silica optical fibers embedded in a brass absorber. The details of its construction will be shown. The calorimeter was tested at the CERN SPS using pion and electron beams with momenta ranging from 50 to 200 GeV/c. The response of the calorimeter and its energy resolution have been studied as a function of the beam energy. Also, the signal uniformity and a comparison between the transverse profile of the hadronic and electromagnetic shower are presented. Moreover, the differences between the calorimeter's responses to protons and pions of the same energy have been investigated, exploiting the proton contamination in the positive pion beams.