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

A prototype for the new DELPHI luminosity monitor has been built and t ested. The scope of this prototype was to measure the response of the proposed calorimeter in the region which is most critical for the lumi nosity measurement, i.e. at the inner edge of the acceptance. The aim of the new luminosity monitor is to measure the LEP luminosity with pe r mill systematic uncertainty: this requires experimental biases at th e level of 50 mum or less in the definition of the fiducial volume. Ev en though we plan to use a tungsten mask to define the inner edge of t he acceptance, the calorimeter was designed to match intrinsically thi s kind of accuracy. A relatively good energy resolution is a must to b e able to reject the accidental Bhabha coincidences due to off momentu m 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 ensu res good energy resolution and high spatial uniformity. With the proto type we have already achieved better than 2% uniformity in response an d an energy resolution of 3% at 45 GeV.