PROTOTYPE DESIGN, CONSTRUCTION AND TEST OF A PB/SCINTILLATOR SAMPLING CALORIMETER WITH WAVELENGTH SHIFTER FIBER OPTIC READOUT

A prototype for the new DELPHI luminosity monitor has been built and tested. The scope of this prototype was to measure the response of the proposed calorimeter in the region which is most critical for the luminosity measurement, i.e. at the inner edge of the acceptance. The aim of the new luminosity monitor is to measure the LEP luminosity with per mill systematic uncertainty: this requires experimental biases at the level of 50 mum or less in the definition of the fiducial volume. Even though we plan to use a tungsten mask to define the inner edge of the acceptance, the calorimeter was designed to match intrinsically this kind of accuracy. A relatively good energy resolution is a must to be able to reject the accidental Bhabha coincidences due to off momentum electrons in LEP. A cut at 80% of the beam energy should reduce this background to less than 1 parts per thousand. The technique used ensures good energy resolution and high spatial uniformity. With the prototype we have already achieved better than 2% uniformity in response and an energy resolution of 3% at 45 GeV.