Transverse Beam Spin Asymmetries Measured from Helium-4 and Hydrogen Targets

1. PAVI06 Transverse Beam Spin Asymmetries Measured from Helium-4 and Hydrogen Targets L. J. Kaufman University of Massachusetts on behalf of the HAPPEX collaboration • Thomas Jefferson National Accelerator Facility – Argonne National Laboratory – CSU, Los Angeles -William and Mary – Duke – DSM/DAPNIA/SPhN CEA Saclay - FIU – Harvard- INFN, Rome - INFN, Bari – IAE, Beijing – IPT Kharkov - Jozef Stefan Institute – Kent State - MIT – NPIRAS, St. Petersburg – ODU – Rutgers - Smith College – Syracuse– Temple – U. Blaise Pascal – U. of Illinois Urbana-Champaign – • UMass, Amherst– U. of Kentucky –U. of Virginia – UST, Heifei

2. PAVI06 World Data near Q2 ~0.1 GeV2 GMs = 0.28 +/- 0.20 GEs = -0.006 +/- 0.016 ~3% +/- 2.3% of proton magnetic moment ~0.2 +/- 0.5% of Electric distribution HAPPEX-only fit suggests something even smaller: GMs = 0.12 +/- 0.24 GEs = -0.002 +/- 0.017 Preliminary Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account

3. PAVI06 Transverse Beam Spin Asymmetries Beam normal asymmetries in elastic electron scattering Electron Beam is polarized transverse to the beam direction Interference between one- and two-photon exchange Effect suppressed by •  • Lorentz boost • forward angle

4. “inelastic” “elastic” SLAC Rosenbluth Data JLab Polarization Data What is interesting about AT? GE/GM is influenced by the real part of 2- amplitude – Speculation is that radiative corrections are missing from Rosenbluth data. AT is generated from the imaginary part of the 2- amplitude. Possible background to PV asymmetry Dominated by spectrum of hadronic intermediate states • Provides a clear and accessible window on the treatment of hadronic intermediate states in box diagrams.

5. PAVI06 Parity-Violation Experiments All PV experiments can, and do, measure these to control possible systematic errors PV experiments are optimized for small asymmetries: • High luminosity, low noise • Careful control of false asymmetries • Rapid helicity flip to cancel drifts, reduce noise • Symmetric configurations to cancel beam asymmetries Measurements are (or will be soon) available sampling a wide range of kinematics: • SAMPLE (200 MeV, back angle) • A4 (570 MeV, 855 MeV, large angle) • HAPPEX (3 GeV, forward angle) • G0 (3 GeV, forward angles) • E158 (45 GeV, very forward angle) • future back-angle A4, G0

6. PAVI06 Polarized e- Source Hall A Møller Polarimeter Target 400 W transverse flow 20 cm, LH2 20 cm, 200 psi 4He Jefferson Lab Hall A High Resolution Spectrometer S+QQDQ 5 mstr over 4o-8o

7. PAVI06 Hall A High Resolution Spectrometers

8. PAVI06 Focal Plane Detector

9. PAVI06 Vertical Polarization Setup L-R symmetry of Hall A requires out-of-plane transverse polarization -> Vertical polarization is not standard for Jefferson Lab Setup beam properties in the same way as for the PV measurement Achieved with Wien filter and unbalanced counter-wound solenoid Polarization measured with Mott polarimeter

10. PAVI06 Vertical Polarization Measurement Vertical polarization does not precess through the accelerator -> Møller provides measurement in Hall A to check against Mott. Tilted foil allows for sensitivity in the vertical plane Møller also provides a cross-check of the sign of the polarization

11. PAVI06 Raw Transverse Asymmetry 310 K pairs, total width ~610 ppm Araw correction ~ 0.14 ppm Hydrogen Preliminary Results Left HRS asymmetry (ppm) Helicity Window Pair Asymmetry # Pairs = 310 K RMS = 887 Slug # Right HRS Beam Corrected Detector Asymmetry (ppm) asymmetry (ppm) Q2 = 0.099 ± 0.0009 GeV2 Araw = -4.947 ppm  1.094 ppm (stat) Slug #

12. PAVI06 Left HRS Raw Transverse Asymmetry 935 K pairs, total width ~1040 ppm Araw correction ~ 0.11 ppm asymmetry (ppm) Helicity Window Pair Asymmetry # Pairs = 935 K RMS = 1480 Slug # Right HRS asymmetry (ppm) Slug # Helium Preliminary Results Beam Corrected Detector Asymmetry (ppm) Q2 = 0.0772 ± 0.0004 GeV2 Araw = -10.930 ppm  1.073 ppm (stat)

13. PAVI06 HAPPEX 2004 Hydrogen Transverse Ee = 3 GeV, CM ~16o, Q2 = 0.099 GeV2 AT = -6.58 ppm ± 1.47 ppm (stat) ± 0.24 ppm (syst) Total corrections ~200 ppb Afanasev Dominant systematic errors: • Polarimetry (190 ppb) • Beam asymmetry (100 ppb) • Al background dilution (70 ppb, assumed ATAl = 0) HAPPEX 2004 (preliminary)

14. PAVI06 HAPPEX 2005 Helium Transverse Ee = 2.75 GeV, lab ~6o, Q2 = 0.077 GeV2 AT = -13.51 ppm ± 1.34 ppm (stat) ± 0.37 ppm (syst) Dominant systematic errors: • Polarimetry (300 ppb) • Linearity (140 ppb) • Beam asymmetry (100 ppb) • Al background dilution (120 ppb) Afanasev Curve for Eb =3 GeV Without inelastic states, 10-9 HAPPEX 2005 (preliminary)

15. PAVI06 Conclusion Hydrogen: AT = -6.58 ppm ± 1.47 ppm (stat) ± 0.24 ppm (syst) Helium: AT = -13.51 ppm ± 1.34 ppm (stat) ± 0.37 ppm (syst) Measurement of AT from the proton First measurement of AT from a nucleus Asymmetries are 3-4 orders of magnitude larger than original predictions => hadronic intermediate states matter for the proton and nuclei AT for nuclei is non-negligible => AT will be an important measurement for upcoming experiments like PREX