Author/Authors :
Alexander، نويسنده , , G. and Barley، نويسنده , , J. and Batygin، نويسنده , , Y. and Berridge، نويسنده , , William S. and Bharadwaj، نويسنده , , V. and Bower، نويسنده , , G. and Bugg، نويسنده , , W. and Decker، نويسنده , , Anja Dollan، نويسنده , , R. and Efremenko، نويسنده , , Y. and Flِttmann، نويسنده , , K. and Gharibyan، نويسنده , , V. and Hast، نويسنده , , C. and Iverson، نويسنده , , R. and Kolanoski، نويسنده , , H. and Kovermann، نويسنده , , J.W. and Laihem، نويسنده , , K. and Lohse، نويسنده , , T. and McDonald، نويسنده , , K.T. and Mikhailichenko، نويسنده , , A.A. and Moortgat-Pick، نويسنده , , G.A. and Pahl، نويسنده , , P. and Pitthan، نويسنده , , R. and Pِschl، نويسنده , , R. and Reinherz-Aronis، نويسنده , , Brandon E. and Riemann، نويسنده , , S. and Schنlicke، نويسنده , , A. J. Schuler، نويسنده , , K.P. and Schweizer، نويسنده , , T. and Scott، نويسنده , , D. and Sheppard، نويسنده , , J.C. and Stahl، نويسنده , , A. and Szalata، نويسنده , , Z. and Walz، نويسنده , , D.R. and Weidemann، نويسنده , , A.، نويسنده ,
Abstract :
Full exploitation of the physics potential of a future International Linear Collider will require the use of polarized electron and positron beams. Experiment E166 at the Stanford Linear Accelerator Center (SLAC) has demonstrated a scheme in which an electron beam passes through a helical undulator to generate photons (whose first-harmonic spectrum extended to 7.9 MeV) with circular polarization, which are then converted in a thin target to generate longitudinally polarized positrons and electrons. The experiment was carried out with a 1-m-long, 400-period, pulsed helical undulator in the Final Focus Test Beam (FFTB) operated at 46.6 GeV. Measurements of the positron polarization have been performed at five positron energies from 4.5 to 7.5 MeV. In addition, the electron polarization has been determined at 6.7 MeV, and the effect of operating the undulator with a ferrofluid was also investigated. To compare the measurements with expectations, detailed simulations were made with an upgraded version of Geant4 that includes the dominant polarization-dependent interactions of electrons, positrons, and photons with matter. The measurements agree with calculations, corresponding to 80% polarization for positrons near 6 MeV and 90% for electrons near 7 MeV.
