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A Spin Manipulator for Electron Accelerators
We have designed and constructed a novel optical system capable of manipulating the orientation of the polarization direction. vector P, of a 100 keV beam of polarized electrons relative to the momentum vector, k, in an arbitrary manner. This spin manipulator is fully compatible with the UHV requirements of the photocathode sources that are typically used for accelerator-based experiments involving polarized electrons. We describe the design and operation of the system and its components, and document its performance
Physics with Positron Beams at Jefferson Lab 12 GeV
Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental program at the next generation of lepton accelerators. In the context of the Hadronic Physics program at the Jefferson Laboratory (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of the nucleon, in both the elastic and the deep-inelastic regimes. For instance, elastic scattering of (un)polarized electrons and positrons off the nucleon allows for a model independent determination of the electromagnetic form factors of the nucleon. Also, the deeply virtual Compton scattering of (un)polarized electrons and positrons allows us to separate unambiguously the different contributions to the cross section of the lepto-production of photons, enabling an accurate determination of the nucleon Generalized Parton Distributions (GPDs), and providing an access to its Gravitational Form Factors. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model through the search of a dark photon or the precise measurement of electroweak couplings. This letter proposes to develop an experimental positron program at JLab to perform unique high impact measurements with respect to the two-photon exchange problem, the determination of the proton and the neutron GPDs, and the search for the dark photon