The CPLEAR Electromagnetic Calorimeter

Abstract A large-acceptance lead/gas sampling electromagnetic calorimeter (ECAL) was constructed for the CPLEAR experiment to detect photons from decays of π 0 s with momentum p π 0 ≤ 800 MeV/ c . The main purpose of the ECAL is to determine the decay vertex of neutral-kaon decays K 0 → π 0 π 0 → 4γ and K 0 → π 0 π 0 π 0 → 6γ. This requires a position-sensitive photon detector with high spatial granularity in r −, ϕ −, and z −coordinates. The ECAL - a barrel without end-caps located inside a magnetic field of 0.44 T - consists of 18 identical concentric layers. Each layer of 1 3 radiation length ( X 0 ) contains a converter plate followed by small cross-section high-gain tubes of 2640 mm active length which are sandwiched by passive pick-up strip plates. The ECAL, with a total of 6 X 0 has an energy resolution of α(E) E ≈ 13% (E( GeV ) and a position resolution of 4.5 mm for the shower foot. The shower topology allows separation of electrons from pions. The design, construction, read-out electronics, and performance of the detector are described.