Unique Electron Polarimeter Comparison and Spin–based Energy Measurement

A careful intercomparison of the relative analyzing power of five electron beam polarimeters was performed with the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility (JLab) during a dedicated two day machine development period. This is the first time such a high precision comparison between polarimeters of the Mott, Compton, and Møller type has been made. A Wien– style spin manipulator at the injector was used to vary the spin orientation of the electron beam. A series of polarization measurements as a function of spin orientation, determines the relative analyzing power between the five polarimeters. More importantly, the high statistical precision of the measurements reveal the relative differences between the polarimeters which are systematic in nature and may ultimately help realize high precision absolute electron polarimetry. In addition, a comparison of the value of the injector spin angle that provides precise longitudinal beam polarization at each experimental hall leads to an independent and potentially high precision measurement with relative uncertainty (better than 10−4) of the final electron beam energy.