The inner part of the detector is composed of six equal modules, each containing an emulsion target 6 cm (2 radiation length) thick, a set of silicon trackers and a set of honeycomb tracker planes (Fig. 4). Each module provides an active mass of emulsion of 400 kg. The total length of a module is 1 m, thus providing sufficient space to perform pattern recognition with the tracking detectors and to determine the momentum and charge of particles. The six modules are followed by the electromagnetic calorimeter. Modules and calorimeter together are mounted inside the magnet.
The magnet is followed by a hadronic calorimeter and by two muon identification stations separated by an 80 cm iron absorber and composed of drift chambers.
The trigger uses a combination of signals from the silicon and wire chambers. The trigger requirement is based on combinations within one target module in order to ensure good homogeneity of the trigger efficiency.
Figure:
Schematic view of one target module with the emulsion and the tracking detectors.