CONSTRUCTION AND TEST OF A FINE-GRAINED LIQUID ARGON PRESHOWER PROTOTYPE

A separate liquid argon preshower detector consisting of two layers fe aturing a fine granularity of 2.5 x 10(-3) was studied by the RD3 coll aboration. A prototype covering approximately 0.8 in pseudo-rapidity a nd 9 degrees in azimuth was built and tested at CERN in July 94. CMOS and GaAs VLSI preamplifiers were designed and tested for this occasion . The combined response of this detector and an accordion electromagne tic calorimeter prototype to muons, electrons and photons is presented . For minimum ionizing tracks a signal-to-noise ratio of 4.5 per presh ower layer was measured. Above 150 GeV the space resolution for electr ons is better than 250 mu m in both directions. The precision on the e lectromagnetic shower direction, determined together with the calorime ter, is better than 4 mrad above 50 GeV. It is concluded that the pres hower detector would adequately fulfil its role for future operation a t CERN Large Hadron Collider.