The Aleph pictorial electromagnetic calorimeter - A high granularity gaseous calorimeter operated in a high magnetic field

We outline briefly the general structure of the Aleph detector, to place in context conceptually and physically the electromagnetic calorimeter. The calorimeter is then described, emphasizing the read-out mechanical and electronic structure, which allows adequate granularity; three layers of towers 3 x 3 cm2, approximately 210.000 pieces of analog information. We discuss the basic properties of such apparatus with the results of tests performed on a prototype. We emphasize the peculiarities of operating such a wire gas calorimeter in a strong magnetic field parallel to the wires. (orig.)