The hadron calorimeter measures the energy of hadrons emerging from the electromagnetic calorimeter and assists in the identification of muons. The iron of the magnet return yoke provides 4 or more interaction lengths of absorber over a solid angle of 97% of 4-pi. The yoke is segmented into layers, with planes of detectors between each layer, and forms a cylindrical sampling calorimeter about one meter thick.
To acheive coverage in solid angle, the hadron calorimeter is constructed in three parts:
The muon detector is constructed as a barrel and two endcaps and covers the iron yoke almost completely. While muons penetrate to the muon detector and leave a single clean track, most hadrons are absorbed the yoke.
Information about the OPAL detector
Information about the electromagnetic calorimetry
Information about the luminosity monitors