Precision measurements of the relative analyzing powers of five electron beam polarimeters, based
on Compton, Møller, and Mott scattering, have been performed using the CEBAF accelerator at the
Thomas Jefferson National Accelerator Facility (Jefferson Laboratory). A Wien filter in the 100 keV
beam line of the injector was used to vary the electron spin orientation exiting the injector. High
statistical precision measurements of the scattering asymmetry as a function of the spin orientation
were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of
polarization, these asymmetry measurements permit a high statistical precision comparison of the
relative analyzing powers of the five polarimeters. This is the first time a precise comparison of the
analyzing powers of Compton, Møller, and Mott scattering polarimeters has been made. Statistically
significant disagreements among the values of the beam polarization calculated from the asymmetry
measurements made with each polarimeter reveal either errors in the values of the analyzing power or
failure to correctly include all systematic effects. The measurements reported here represent a first step
toward understanding the systematic effects of these electron polarimeters. Such studies are necessary
to realize high absolute accuracy (ca. 1%) electron polarization measurements, as required for some
parity violation measurements planned at Jefferson Laboratory. Finally, a comparison of the value of
the spin orientation exiting the injector that provides maximum longitudinal polarization in each
experimental hall leads to an independent and very precise (better than 104) absolute measurement of
the final electron beam energy. |
