A lead/proportional-tube electromagnetic calorimeter for direct photon detection

The fine-grained lead/proportional-tube electromagnetic calorimeter used in CERN experiment UA6 is described. Test-beam results demonstrate linear energy response over a wide dynamic range, position resolution for shower localization reaching 1.7 mm for 70 GeV electrons, and good electron/hadron differentiation. Electron shower transverse widths are measured to be less than 9.0 mm for energies between 3 and 70 GeV. This feature allows us to identify neutral-meson decays yielding two close photon showers that constitute the main background to single-photon detection.