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Mott Electron Polarization Results

Mott Electron Polarization Results. Riad Suleiman July 10, 2013. Mott Scattering. Electron motion in nucleus electric field results in magnetic field in electron rest frame, , if is nucleus-electron separation, then and

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Mott Electron Polarization Results

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  1. Mott Electron PolarizationResults Riad Suleiman July 10, 2013

  2. Mott Scattering • Electron motion in nucleus electric field results in magnetic field in electron rest frame, , if is nucleus-electron separation, then and • Interaction of this magnetic field with electron (spin) magnetic moment introduces a term in the scattering potential, • Presence of spin-orbit term in scattering potential introduces spin dependence in scattering cross section which could be detected as a left/right count rate asymmetry

  3. V L L L L V r r Note: • Parity-conserving: Measure spin-momentum correlation of the type: Transverse (or Normal) Beam Asymmetry measured recently using the setup of parity-violating experiments at high energies (due to two-photon exchange) probes the same spin-momentum correlation as Mott Asymmetry at low energies (due to spin-orbit interaction of electron moving in a Coulomb field). • Parity-violating: Measure spin-momentum correlation of the type:

  4. Mott Cross Section and Sherman Function • Mott cross section: where, is the un-polarized cross section, and is the analyzing power (Single-Atom Sherman Function), • Sherman Function is largest for high-Z (Gold, Z=79) targets and low-energy electrons Non-spin-flip Amplitude Spin-flip Amplitude

  5. Theoretical Corrections • Radiative corrections • Screening by atomic electrons • Finite nuclear size

  6. Energy Sensitivity • For T=5.0 MeV, p=5.5 MeV/c. However, momentum was measured to be p=5.336 ± 0.023 MeV/c, or T=4.850 MeV • For δT/T=3%, δS/S(T=4.850)=0.09%

  7. Sherman Function and Target Thickness • Single-Atom Sherman Function must be corrected for plural scattering (a few large angle scattering) in the target: • SSA(d=0, T=5.0 MeV) = -0.5215, • Seff(d=1.0 μm, T=5.0) = -0.4006 • Systematic Error (∆S/S) = 2.8%

  8. Measuring Mott Asymmetry • How to measure the Mott Asymmetry ALR? • For one helicity state, measure the number of left and right detector events, and • Flip the electron polarization, measure the number of events again, and • Calculate the cross-ratio(r), • Then, the Mott Asymmetry: • Same for AUD • False Asymmetries: • Cancel to all orders: beam current, target thickness, solid angle, detector efficiency and dead time (due to slow DAQ common to all detectors) • Cancel to first order: differences in beam polarization between the two helicity states and misalignment errors resulting in detectors at different scattering angle

  9. 5 MeV Mott Beamline

  10. Detector Assembly Scattering Angle = 172.6° Solid Angle = 0.18 msr

  11. ΔE and E Detectors • H7415 (R6427) 1" PMT • 1 mm x 1" x 1" EJ-212 Plastic Scintillator • 0.125" x 1" x 2" Acrylic Light Guide • H6559 (R6091) 3" PMT • 3" diameter x 2.5" long EJ-200 • Plastic Scintillator painted with • EJ-510

  12. Old 5 MeV Mott DAQ • LeCroy CAMAC 4300B Fast Encoding and Readout ADC (FERA), 10 Bit • ORTEC CAMAC HM 413 HISTO-MEMORY

  13. Detectors Spectra • Beam Current = 1.0 μA • Gold Target 1.0 μm • Trigger Rate 1 kHz • 5 minutes of data

  14. E Detectors Spectra

  15. New5 MeV Mott DAQ Signals on Scope Mott Trigger Left E Left ∆E Signals in FADC Data

  16. Few FADC Events in LEFT Detector Calculate pedestal and Energy:

  17. Maximize Longitudinal Polarization on June 04, 2012 • By adjusting INJTWF, Px and Py were minimized and beam polarization was measured: • After minimization, new nominal Injector Two-Wien-Flipper (INJTWF) settings during PEPPo data taking are:

  18. Measure Longitudinal Polarization on June 10, 2012 • Beam polarization was changed to horizontal transverse (Px) with Horizontal Wien Angle changed from +86.70˚ to 0.00˚

  19. Polarization Precession in 5 MeV Dipole • Py is the same in Mott and Compton Polarimeters • Px and Pz polarization precession is: where ais electron anomalous magnetic moment, • Mott θbend = -12.5˚ • Compton θbend = +25.0˚ • Mott, T = 5.0 MeV, θspin = -0.16˚ • Compton, p = 8.25 MeV/c, θspin = +0.47˚ • Total polarization precession, θp= 0.63˚

  20. Polarization at Compton Polarimeter • At Mott: measurements on June 4 and June 10: • Px = -0.6%± 0.6% (stat) • Py = 1.2% ± 0.4% (stat) • Pz = 83.7% ± 0.6% (stat) • At Compton: • cos(0.63˚) = 1.000 • sin(0.63˚) = 0.011 • Px = 0.3%± 0.6% (stat) • Py = 1.2% ± 0.4% (stat) • Pz = 83.7% ± 0.6% (stat)

  21. Summary • The electron beam polarization during PEPPo experiment is: • Px= 0.3% ± 0.6% (stat) ± 2.8% (sys) • Py= 1.2% ± 0.4% (stat) ± 2.8% (sys) • Pz = 83.7% ± 0.6% (stat) ± 2.8% (sys) • More work this Fall to reduce the systematic error • New theoretical calculations • New target thickness extrapolation

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