The Forward hodoscope Wall (FW) was installed in 2007 and it was successfully used for tagging the spectator proton in the deuteron beam experiment in May 2007. The FW was placed at 7 m behind the target and it covers polar angles 0.33 < θ< 7.17 degree. The mechanical set-up of the detector consists of 287 scintillator modules read out by photomultipliers. 263 modules were operational during data taking in May 2007.
In order to achieve a reasonable angular and position resolution the size of the cells was selected in the following way: the innermost part was covered with cell sizes 4 x 4 cm2 (see Fig. 2, red squares), which increased to cell sizes of 8 x 8 cm2 (see Fig. 2, green squares) and the outer region was covered with 16 x 16 cm2 cells (see Fig. 2, blue squares). The scintillating material is BC408 (used also for the TOF detector). The thickness of the cells is 2.54 cm. Each cell is equipped with an individual PMT readout. The high voltage of each PMT is individually tuned in order to achieve overall high detection efficiency for protons. The estimated time resolution of the FW is about 500 ps; thus the estimated momentum resolution of the detected particles (protons) is about 11%.
Joint Institute of Nuclear Research, Dubna, Russia
Nuclear Physics Institute AS CR, Rez, Czech Republic