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E166 Status and Plans: (polarized e+ at SLAC) proposed experiment has been approved in June

Undulator-Based Production of Polarized Positrons. E166 Status and Plans: (polarized e+ at SLAC) proposed experiment has been approved in June - subject to demonstration of acceptable background conditions data taking run (6 weeks) expected in 2005.

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E166 Status and Plans: (polarized e+ at SLAC) proposed experiment has been approved in June

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  1. Undulator-Based Production of Polarized Positrons E166 Status and Plans: (polarized e+ at SLAC) • proposed experiment has been approved in June - subject to demonstration of acceptable background conditions • data taking run (6 weeks) expected in 2005

  2. Undulator-Based Production of Polarized Positrons E-166 Collaboration 45 Collaborators from 15 Institutions Brunel, CERN, Cornell, DESY, Durham, Thomas Jefferson Lab., Humboldt, KEK, Princeton, South Carolina, SLAC, Tel Aviv, Tokyo Metropolitan, Tennessee, Waseda

  3. E-166 Experiment E-166 is a demonstration of undulator-based polarized positron production for linear colliders - E-166 uses the 50 GeV SLAC beam in conjunction with 1 m-long, helical undulator to make polarized photons in the FFTB. - These photons are converted in a ~0.5 rad. len. thick target into polarized positrons (and electrons). - The polarization of the positrons and photons will be measured.

  4. Physics Motivation: An Example Separation of the selectron pair in with longitudinally polarized beams to test association of chiral quantum numbers to scalar fermions in SUSY transformations

  5. E-166 Beamline Schematic 50 GeV, low emittance electron beam 2.4 mm period, K=0.17 helical undulator 0-10 MeV polarized photons 0.5 rad. len. converter target 51%-54% positron polarization

  6. E-166 Helical Undulator Design, l=2.4 mm, K=0.17 PULSED HELICAL UNDULATOR FOR TEST AT SLAC THE POLARIZED POSITRON PRODUCTION SCHEME. BASIC DESCRIPTION. Alexander A. Mikhailichenko CBN 02-10, LCC-106

  7. Photon Intensity, Angular Dist., Number, Polarization Spectrum

  8. Polarized Positrons from Polarized g’s Circular polarization of photon transfers to the longitudinal polarization of the positron. Positron polarization varies with the energy transferred to the positron. (Olsen & Maximon, 1959)

  9. Polarized Positron Production in the FFTB Polarized photons pair produce polarized positrons in a 0.5 r.l. thick target of Ti-alloy with a yield of about 0.5%. Longitudinal polarization of the positrons is 54%, averaged over the full spectrum Note: for 0.5 r.l. W converter, the yield is about 1% and the average polarization is 51%.

  10. Polarimeter Overview 1 x 1010 e-  4 x 109 4 x 109 4 x 107 4 x 109  2 x 107 e+ 4 x 105 e+  1 x 103  2 x 107 e+  4 x 105 e+

  11. Transmission Polarimetry of (monochromatic) Photons M. Goldhaber et al. Phys. Rev. 106 (1957) 826. all unpolarized contributions cancel in the transmission asymmetry  (monochromatic case)

  12. Transmission PolarimetryofPositrons 2-step Process: • re-convert e+   via brems/annihilation process • polarization transfer from e+ to  proceeds in well-known manner • measure polarization of re-converted photons with the photon transmission methods • infer the polarization of the parent positrons from the measured photon polarization Experimental Challenges: • large angular distribution of the positrons at the production target: • e+ spectrometer collection & transport efficiency • background rejection issues • angular distribution of the re-converted photons • detected signal includes large fraction of Compton scattered photons • requires simulations to determine the effective Analyzing Power Formal Procedure: Fronsdahl & Überall; Olson & Maximon; Page; McMaster

  13. Spin-Dependent Compton Scattering Simulation with modified GEANT3 (implemented by V. Gharibyan) • standard GEANT is unpolarized • ad-hoc solution: - substitute unpolarized Compton subroutines with two spin-dependent versions (+1 and -1) and run these in sequence for the same same beam statistics - then determine analyzing power from this data

  14. Analyzer Magnets g‘ = 1.919  0.002 for pure iron, Scott (1962) Error in e- polarization is dominated by knowledge in effective magnetization M along the photon trajectory: active volume Photon Analyzer Magnet: 50 mm dia. x 150 mm long Positron Analyzer Magnet: 50 mm dia. x 75 mm long

  15. Positron Polarimeter Layout

  16. Positron Transport System e+ transmission (%) through spectrometer photon background fraction reaching CsI-detector

  17. Expected Positron Polarimeter Performance I Simulation based on modified GEANT code, which correctly describes the spin-dependence of the Compton process Number- & Energy-Weighted Analyzing Power vs. Energy Photon Spectrum & Angular Distr. 10 Million simulated e+ per point & polarity on the re-conversion target

  18. Expected Positron Polarimeter Performance II Table 13

  19. Polarimetry Summary • Transmission polarimetry is well-suited for photon and positron beam measurements in E166 • Analyzing power determined from simulations is sufficiently large and robust • Measurements will be very fast with negligible statistical errors • Expect systematic errors of ΔP/P ~ 0.05 from magnetization of iron

  20. E-166 Beam Request 6 weeks of activity in the SLAC FFTB: • 2 weeks of installation and check-out • 1 week of check-out with beam • 3 weeks of data taking: roughly 1/3 of time on photon measurements, 2/3 of time on positron measurements.

  21. E-166 Institutional Responsibilities

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