1. Thomas Jefferson National Accelerator Facility Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy The Department of Energy's Thomas Jefferson National Accelerator Facility, or Jefferson Lab (JLab), is a basic research laboratory built to probe the nucleus of the atom to learn more about the quark structure of matter. The Hall C Moller Polarimeter uses a superconducting Helmholtz coil (3 Tesla) to saturate the out-of-plane magnetization of an iron target foil oriented normal to the incident electron beam, resulting in a target polarization ~8%. The 90 degree center-of-mass Moller scattered pair (beam and target electron) are focussed, collimated, and detected in coincidence to form the experimental asymmetry. Only the longitudinal component of the beam polarization can be measured. However, no correction for in-plane (tilted target) magnetization measurement is necessary. The Mott polarimeter is located in the 5 MeV region of the CEBAF injector. The Mott scattering asymmetry results from the the spin-orbit coupling between the incident polarized electron beam and the target nuclear potential. Four scintillator detectors (E and dE) are spaced azimuthally and detect the elastically scattered electrons near the maximum in the Sherman function for gold (-173 deg). The polarimeter has been operated between 2 and 8 MeV with different high-Z targets (Au, Ag, Cu). Both transverse components of the beam polarization are measured. The Hall B Moller polarimeter operates at only a few nanoamps, typical of Hall B physics experiments. One of two 25 um permendur foils (49% Fe, 49% Co, 2%Va) oriented at 20 degrees (vertically) with respect to the incident beam is mounted in a weak 120 Gauss Helmholtz magnetic field. The Moller scattered electron pairs are detected in coincidence by two detectors downstream of a double quadrupole spectrometer. Both the longitudinal and vertical components of the beam polarization can be measured. The Hall A Compton polarimeter employs a Fabry-Perot optical cavity located at the center of a 4-dipole vertical chicane. A 1064 nm laser is locked to and pumps the optical cavity to more than 1400 Watts of circularly polarized (>99%) light. Compton backscattered photons from the incident polarized electron beam are detected by a PbWO4 calorimeter. The longitudinal component of the beam polarization can be measured. The Hall A Moller polarimeter consists of a polarized target, spectrometer (3 quadrupoles and 1 dipole), and a coincidence pair of lead glass and scintillator detectors. The target is an iron-alloy (supermendur) which makes the measurement invasive. Each of two target foils opposing one another at equal small vertical angles (20 degrees) to the incident electron beam direction are polarized by a weak 240 Gauss Helmholtz field. Both the longitudinal and horizontal components of the beam polarization are measured. Abstract A careful intercomparison of the relative analyzing powers of five electron beam polarimeters was performed with the CEBAF accelerator at Jefferson Lab 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 Moller 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 uncertainity better than 0.01% of the final electron beam energy. This work was supported by the U.S. DOE Contract No. DE-AC05-84-ER40150. Web address: www.jlab.org The Spin Dance 2000 Experiment J. Grames, Jefferson Lab, Newport News, VA