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PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2. Paul Souder Syracuse University. Kent Paschke University of Massachusetts, Amherst. “global” experimental uncertainty. Recent Results for the Strange Vector FF.

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PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q 2

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  1. PR-05-109: A Measurement of the Strange Nucleon Form Factors at High Q2 Paul Souder Syracuse University Kent Paschke University of Massachusetts, Amherst

  2. “global” experimental uncertainty Recent Results for the Strange Vector FF G0 Results are big news: amplifies interesting low Q2 structure, strong constraint at Q2~0.2 GeV2, and significant non-zero result at higher Q2 h ~ Q2 • Deviation from APV(Gs=0) averages ~17% for Q2>0.4 GeV2 PR-05-109: HAPPEX High-Q2

  3. Focusing on High Q2 • In this range, background corrections are large, on order 40-60% of APV. • Combining data points reduces point-to-point uncertainty, correlated error dominates Q2 >0.35 GeV2: GsE + hGsM = 0.046 + 0.022 PR-05-109: HAPPEX High-Q2

  4. Proposal d(GEs + 0.48 GMs) = 0.0082 (experimental) at Q2 = 0.6 GeV2 • Very different experimental technique, with very low backgrounds • In the heart of the suggested positive contribution • Precise error bar needed to impact global fit Q2 = 0.63 Gev2 alone: 5.5s Q2= [0.4,1] GeV2: 4s PR-05-109: HAPPEX High-Q2

  5. HAPPEX High-Q2 Collaboration K.A. Aniol and D.J. Margaziotis - California State University, Los Angeles D.S. Armstrong, J.M. Finn, T. Holmstrom, B. Moffit, and V. Sulkosky - College of William and Mary F. Bataru, Z.-E. Meziani, B. Sawatzky, P. Solvignon, and H. Yao - Temple University H. Benaoum, R. Holmes, and P.A. Souder - Syracuse University R. Carlini, J.-P. Chen, R.J. Feuerbach, J. Grames, D.W. Higinbotham, C.W. de Jager, R. Michaels, B. Reitz, J. Roche, and A. Saha -TJNAF G.D. Cates, N. Liyanage, V. Nulyubin,J. Singh, R. Snyder, and W.A. Tobias - University of Virginia E. Cisbani, F. Cusanno, S. Fullani, F. Garibaldi, and G.M. Urciuoli - INFN Sezione Sanita P. Decowski - Smith College L.J. Kaufman, K.S. Kumar, and K.D. Paschke - University of Massachusetts, Amherst S. Kowalski - Massachusetts Institute of Technology L. Lagamba, R. De Leo, and S. Marrone - INFN Bari D. Lhuillier and C. Munoz-Camacho - CEA Saclay, DAPNIA/SPhN P. Markowitz - Florida International University P. Reimer and X. Zheng - Argonne National Laboratory R. Wilson - Harvard University PR-05-109: HAPPEX High-Q2

  6. HAPPEX PR-05-109: HAPPEX High-Q2

  7. Proposed Measurement: HAPPEX High-Q2 • Configuration: • 20 cm cryogenic Hydrogen Target • 100 mA • 80% polarization Kinematics: E = 3.42 GeV, q=13.7o, E’ = 3.1 GeV, Q2 = 0.6 GeV2 Rate: 1.1 MHz per arm (3700 ppm width per arm, 2600 ppm per pair) APV (assuming no strange vector FF): APVNS = -22.1 ppm ± 0.62 ppm (form factor/radiative correction) Anticipated results: dAPV= 0.55 ppm (stat) ± 0.33 ppm (syst) d(GsE + 0.48 GsM) = 0.0070 (stat) ± 0.0042 (syst) ± 0.0079 (FF) PR-05-109: HAPPEX High-Q2

  8. Improvements since HAPPEX-I • P2L (statistical power) • HAPPEX-I ran with 100 mA and 38% polarization, or 35 mA and 71% polarization • Now 100 mA at 75% polarization is routine. • Target thickness: 15cm -> 20cm • Precision polarimetry • HAPPEX-I: d(Pbeam) = 3.2% • Planned Compton upgrade: d(Pbeam) = 1% • Q2 determination • HAPPEX-I: d(Q2) = 1.2% • Nuclear Recoil method: d(Q2) = 0.5% PR-05-109: HAPPEX High-Q2

  9. Hall A Polarimeters Cherenkov cones Compton Moller PMT Target Spectrometer: QQDQ PR-05-109: HAPPEX High-Q2

  10. Hydrogen elastic distribution, Q2=0.1 GeV2 PMT Cherenkov cones 12 m dispersion sweeps away inelastic events PMT Overlap the elastic line above the focal plane and integrate the flux Very clean separation of elastic events by HRS optics  High Resolution Spectrometers Large dispersion and heavy shielding reduce backgrounds at the focal plane: typically Sfi < 1.5% Standard detector package used to track individual electrons to measure kinematics, study background, in dedicated low-current studies. PR-05-109: HAPPEX High-Q2

  11. False Asymmetries Araw = Adet - AQ + E+ ixi HAPPEX-H (2004 results): APV = -1.14  0.24 (stat)  0.06 (syst) ppm Systematic error due to helicity correlated beam dynamics controlled below the level required for HAPPEX-High Q2 (60 ppb). It is requested the machine be optimized for longitudinal polarization to Hall A, to minimize the transverse spin asymmetry. PR-05-109: HAPPEX High-Q2

  12. Background G0: typical dilution factor at high Q2 ~ 20% The probability of rescattering inside the spectrometer as measured by a dipole field scan • Measured using: • Dedicated runs at very low current using track reconstruction of the HRS • Dedicated integrating runs PR-05-109: HAPPEX High-Q2

  13. Q2 measured using standard HRS tracking package, with reduced beam current Goal: Measuring Q2 • Central scattering angle must be measured to dq< 0.25% • Asymmetry distribution must be averaged over finite acceptance Nuclear recoil, using water cell optics target:dp between elastic and excited state peaks reduces systematic error from spectrometer calibration. At Q2~0.1 GeV2 (6o) in 2004: Achieved dq~ 0.3% PR-05-109: HAPPEX High-Q2

  14. Compton Polarimeter Upgrade Upgrade required for E05-007 (PV-DIS) and E03-011 (PREx) Goal of the upgrade: 1-2% at 850 MeV. 1% at 3.4 GeV is expected. New Electron Detector High resolution silicon microstrips Integrating Photon Detector Electronics Improve systematic uncertainties 3kW Green Fabry-Perot Cavity Twice the Analyzing power of present IR cavity Twice the luminosity PR-05-109: HAPPEX High-Q2

  15. Compton Upgrade Status • Optics • Green Laser, Optics, HF mirrors procured • Low power optics commissioning completed • Prototype FP Cavity built and tested • Photon Detector • Prototype integrating data acquisition electronics installed • Commissioning in progress during HAPPEX-2005 • Electron detector • Design completed Project completion target: Spring 2007 PR-05-109: HAPPEX High-Q2

  16. Error Budget PR-05-109: HAPPEX High-Q2

  17. Electromagnetic FF Axial FF (GAZ) Extraction of SVFF from APV Including radiative corrections, APV from hydrogen is: Axial FF: d(APV) = 0.33 ppm EMFF: dominated by GnM, d(APV) = 0.53 ppm Total: d(APV) =0.62 ppm, 2.8% PR-05-109: HAPPEX High-Q2

  18. d(GAZ) ~ 0.14 Axial Form Factor Axial Form Factor: Uncertainty dominated by “anapole moment” Assume dipole FF, with MA = 1.001 GeV d(GAZ) ~ 0.12, d(APV) = 0.33 ppm Compatible with Phys. Rev. C 69, 065501 (2004) [Zhu et al , 2000] [Maekawa et al , 2000] E04-115 G0 Backward Angle PR-05-109: HAPPEX High-Q2

  19. EM Form Factors But: 2-photon effects can complicate this picture at 2-4% level Experimental constraint: E04-116 in Hall B (approved): precision comparison of elastic positron-proton and electron-proton scattering, with very good coverage at this Q2 PR-05-109: HAPPEX High-Q2

  20. Estimated Precision PR-05-109: HAPPEX High-Q2

  21. Beam Request • 30 Days • includes 3 days commissioning/study • Proposed at 100 mA, 80% polarization, 20 cm LH2 target • adjust runtime based on P2I • Special scheduling requirements: • optimized for longitudinal polarization • control of source parameters for “parity-quality” • sufficient ESR power or CHL supplement for cryotarget • No major, non-standard equipment or specialized installation required. • APPROVED, at “A-” rating! Conditionality now removed (Q2=0.63GeV2). Possible run 2008 (2007, depending on 6GeV Hall A experiments) PR-05-109: HAPPEX High-Q2

  22. HAPPEX-III d(GEs + 0.48 GMs) = 0.0082 (experimental) ± 0.0079 (FF) • Very different experimental technique, with very low backgrounds • 4-sigma measurement in the middle of the suggested positive contribution • No major new technology or special equipment PR-05-109: HAPPEX High-Q2

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