Mechanical structure

The finer lateral segmentation can provide the better position resolution. The segmentation, however, is limited by front-end electronics. The detector is segmented into 32 in $\phi$ and 5 in $\theta$ for both the forward and backward cones. A three dimensional view of the crystal arrangement is shown in Fig. .

Figure: An isometric view of the BGO crystals of the forward and backward EFC detectors.

The schematic side view of the forward EFC is shown in Fig. . The distance between the front surface of the detector and the interaction point is 60 and 43.5 cm in the forward and backward EFCs, respectively. The inner bore radius of the detector is 6.5 cm.

Figure: Side view of the mounting of forward EFC.

The BGO crystals are housed in a bucket-shape container made of 1 mm-thick stainless steel, the inner bore of which is the beam pipe. The container is attached to the front surface of the compensation solenoids. Since the space allocated for EFC is limited, the radiation lengths of the forward and backward crystals are 12 and 11, respectively. Front-end circuits for photodiodes and preamps as well as miscellaneous instruments are installed in the space between the magnet surface and the backend of the BGO crystals which is 2.7 and 2.0 cm for the forward and backward EFC detectors, respectively.