The CPLEAR electromagnetic calorimeter

A large-acceptance lead/gas sampling electromagnetic calorimeter (ECAL) was constructed for the CPLEAR experiment to detect photons from decays of π ⁰s with momentum p_π⁰ ≤ 800 MeV/ c. The main purpose of the ECAL is to determine the decay vertex of neutral-kaon decays K ⁰ → π ⁰π ⁰ → 4γ and K ⁰ → π ⁰π ⁰π 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 ( X₀) 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 X₀ 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.