The Hadron Calorimeter (HC) is positioned behind the IE. The calorimeters detects energy released by hadrons, including neutral hadrons. The HC is constructed of alternating layers of steel and plastic scintillator tiles. The scintillators are arranged in pads within each layer; multiple layers are optically combined to form towers. The entire calorimeter is 300 cm (H) by 200 cm (W). The depth is 209 cm or 7.8 hadronic interaction lengths.
The tiles are arranged with small (20 cm square) tiles in the center and larger (40 cm and 50 cm square) tiles at the outer edges for a total of 66 tiles per layer. There are 28 layers of 4.4 cm thick13 steel which alternate with 28 layers of scintillator. The first nine layers are combined to form the towers in the first section, the next 15 layers form the second section, and the last 4 layers form the towers in the final section. This arrangement is illustrated in spec:hc_front. This scheme allows for a small number (192) of channels of readout, but still allows a measurement of energy deposition as a function of depth by using the super-layers. Also, the last super-layer can be used to provide rudimentary muon identification which is helpful for very low energy muons. The HC is more fully described in References Bonomi:1997qg and Boca:1998zp.
|[Front view] [Side view] spec:hc_front|
HC Energy Trigger The signals from the PMT dynodes in the HC are summed, integrated and discriminated to form a hadronic energy trigger. The efficiency of this energy trigger as a function of the energy is shown in spec:hc_eff. The HC energy forms an important component of the FOCUS trigger, as described in spec:trigger.