A position sensitive highly radiation hard and fast hadron calorimeter for a lead ion experiment at CERN SPS

We present the performance of the Zero Degree Calorimeter (ZDC) built for the NA50 experiment at the CERN SPS. This detector measures the Cherenkov light produced in silica optical fibres embedded in tantalum and offers the double advantage of being highly radiation resistant (up to several Grad) and very fast (signal width of the order of 10 ns). It has an active volume of 5 × 5 × 65 cm3 with a fibre to tantalum volume ratio of 117; the fibres are positioned at an angle of 0° with respect to the beam direction and have a diameter of 365 μm. The measured energy resolution (σE) is 30% for protons at 205 GeV and 5% for lead ions at 160 GeV/nucleon. tector exhibits also very good localising properties since it can detect the impact point of the lead beam on its front face with a precision better than 0.4 mm rms.