Diamond Mott Polarimeter

Precise knowledge of electron beam polarization is crucial for the Nuclear Physics programs at Jefferson Lab and the future electron-ion collider. JLab’s CEBAF and the SOLID collaboration have a goal of 0.5% polarization uncertainty. The present topic calls for proposals to develop “advanced electron or positron beam polarimeters such as those that operate in the energy range of 10- 100 MeV, with average currents exceeding 200 uA, and with accuracies that are <1%.” Euclid Beamlabs, LLC proposes technologies for high accuracy advanced electron beam polarimetry, particularly by using diamond Mott polarimeter targets. Use of diamond targets will improve high-average-current performance and, in comparison with high-atomic-number (Z) (e.g., gold) targets and detailed modeling and simulation, will substantially reduce uncertainties associated with radiative corrections to the scattering asymmetry, thereby improving precision of existing Mott polarimetry. Diamond targets will also tolerate higher current beams, particularly when combined with water-cooled mounts and high-rate data acquisition systems. Finally, the 2+ excited state of 12C significantly enhances asymmetry and has recently been predicted not to fall off as a function of beam energy even at higher 100 MeV energies. We will provide detailed modelling and simulation of electron beam passage through a diamond target that include radiative corrections due to real-photon emission – previously unaccounted for in this process. Since we will be dealing with low-Z 12C target, the code MASCARAD previously developed for JLab experiments will be applied to evaluate internal radiative corrections and GEANT4 simulations for external radiative corrections. Euclid will also perform diamond target production and mounting. JLab will install at least 2-3 diamond targets in the existing CEBAF 5 MeV Mott target ladder, and will collect scattering asymmetry data at currents up to 100 uA from diamond. The potential market for precision polarimetry of spin-polarized electron beams encompasses all current and future accelerator facilities using spin-polarized electron beams. While this work is specifically intended to advance the state of the art at CEBAF (JLab), other possible machines requiring precision MeV polarimetry include the approved EIC (BNL), future ILC (Japan), future CERN (Europe), and future SUPERKEKB (Japan).