The Forward Calorimeter (FCAL), Barrel Calorimeter (BCAL), and Rear Calorimeter (RCAL) sections of the ZEUS calorimeter are built in modules, running vertically in the case of FCAL and RCAL and longitudinally in the case of BCAL. Each module is segmented into towers, as depicted in figures 1 and 2. The layers of scintillator and depleted uranium making up calorimeter towers are divided into four different types of cells, depending on their position within the tower. Cells are either electromagnetic (EMC) or hadronic (HAC) and are classed as EMC, HAC0, HAC1, and HAC2.
The first interaction length in FCAL, BCAL, and RCAL consists of EMC cells, except for those near the edges of FCAL and RCAL, where the cells are shadowed from the interaction point by the BCAL. The EMC cells have a front area of 5cm by 20cm in the FCAL, 5cm by 23cm in the BCAL, and 10cm by 20cm in the RCAL. The BCAL EMC cells are the only projective cells in the calorimeter.
Certain FCAL and RCAL cells in the first interaction length are designated as HAC0 cells, and have 20cm by 20cm front faces. Particles from the interaction point passing through these cells first pass through BCAL EMCs. In the RCAL, twenty-four HAC0 cells are used as EMCs because the BCAL does not fully shadow them.
The subsequent three interaction lengths in FCAL and RCAL and two interaction
lengths in BCAL are HAC1 cells. The last 1.5 to 3 interaction lengths
(depending on radius from the beampipe) of FCAL and last 2 interaction
lengths of BCAL are HAC2 cells. HAC1 and HAC2 cells in the FCAL and RCAL have
20cm by 20cm front faces, while the BCAL HAC cells have front faces of 27cm
by 23cm for HAC1, and 35cm by 23cm for HAC2
. Figure 3 shows a typical trigger
tower (similar to FCAL at small 
or BCAL at
), with four EMC cells in front, followed by a HAC1 and a HAC2.
