Electron Spectrometer and Detection System

The HMS in Hall C or the HRS in Hall A have the necessary combination of momentum acceptance, resolution, and solid angle for this experiment. Only modest energy resolution on the electron side is necessary as the neutron arm dominates the overall determination of the missing energy. The large vertical acceptance of these spectrometers is an advantage when considering the deflection of the electrons in the target field. For the present experiment, we will use the HMS in the reverse-quad mode, which offers a larger solid angle (10 msr). The tradeoff of horizontal for vertical acceptance is also desirable as it allows to maintain the condition of perpendicular to the target polarization over a larger acceptance.

The detection package will consist of drift chambers for reconstruction of the electron angles and momenta; for particle identification, a gas Cerenkov counter and lead glass shower counters; and plastic scintillator hodoscopes for timing and to help with muon rejection in the shower counter. The needs of this experiment are well within the capabilities of the standard detection system planned for the CEBAF electron spectrometers. In fact, the low rates we anticipate will not pose a problem to their rate handling capabilities.