PR : A Measurement of the Strange Nucleon Form Factors at High Q 2 Kent Paschke University of Massachusetts, Amherst Paul Souder Syracuse University

PR : HAPPEX High-Q 2 Recent Results for the Strange Vector FF Deviation from A PV (G s =0) averages ~17% for Q 2 >0.4 GeV 2 G0 Results are big news: amplifies interesting low Q 2 structure, strong constraint at Q 2 ~0.2 GeV 2, and significant non-zero result at higher Q 2  ~ Q 2 “global” experimental uncertainty

PR : HAPPEX High-Q 2 Focusing on High Q 2 In this range, background corrections are large, on order 40-60% of A PV. Combining data points reduces point-to-point uncertainty, correlated error dominates Q 2 >0.35 GeV 2 : G s E +  G s M =

PR : HAPPEX High-Q 2 Proposal  (G E s G M s ) = (experimental) at Q 2 = 0.6 GeV 2 Very different experimental technique, with very low backgrounds In the heart of the suggested positive contribution Precise error bar needed to impact global fit Q  = 0.63 Gev 2 alone: 5.5  Q   = [0.4,1] GeV 2 : 4 

PR : HAPPEX High-Q 2 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 HAPPEX High-Q 2 Collaboration

PR : HAPPEX High-Q 2 HAPPEX targetQ 2 [GeV 2 ] A PV G s = 0 (ppm) Stat. Error (ppm) Syst. Error (ppm) sensitivity 1H1H (6%) 0.56 (3%) G s E G s M = ± (exp) ± (FF) 1H1H (5.7%) 0.04 (2.9%)  (G s E G s M ) = He (2.2%) 0.18 (2.1%)  (G s E ) = 0.015

PR : HAPPEX High-Q 2 Proposed Measurement: HAPPEX High-Q 2 Configuration: 20 cm cryogenic Hydrogen Target 100  A 80% polarization Kinematics: E = 3.42 GeV,  =13.7 o, E’ = 3.1 GeV, Q 2 = 0.6 GeV 2 Rate: 1.1 MHz per arm (3700 ppm width per arm, 2600 ppm per pair) A PV (assuming no strange vector FF): A PV NS = ppm ± 0.62 ppm (form factor/radiative correction) Anticipated results:  A PV = 0.55 ppm (stat) ± 0.33 ppm (syst)  ( G s E G s M ) = (stat) ± (syst) ± (FF)

PR : HAPPEX High-Q 2 Improvements since HAPPEX-I P 2 L (statistical power) HAPPEX-I ran with 100  A and 38% polarization, or 35  A and 71% polarization Now 100  A at 75% polarization is routine. Target thickness: 15cm -> 20cm Precision polarimetry HAPPEX-I:  (P beam ) = 3.2% Planned Compton upgrade:  (P beam ) = 1% Q 2 determination HAPPEX-I:  (Q 2 ) = 1.2% Nuclear Recoil method:  (Q 2 ) = 0.5%

PR : HAPPEX High-Q 2 Target Spectrometer: QQDQ Hall A Cherenkov cones PMT Compton Moller Polarimeters

PR : HAPPEX High-Q 2 Cherenkov cones PMT High Resolution Spectrometers Very clean separation of elastic events by HRS optics Overlap the elastic line above the focal plane and integrate the flux  Large dispersion and heavy shielding reduce backgrounds at the focal plane: typically  f i < 1.5% Standard detector package used to track individual electrons to measure kinematics, study background, in dedicated low-current studies. 12 m dispersion sweeps away inelastic events Hydrogen elastic distribution, Q 2 =0.1 GeV 2

PR : HAPPEX High-Q 2 False Asymmetries It is requested the machine be optimized for longitudinal polarization to Hall A, to minimize the transverse spin asymmetry. A raw = A det - A Q +  E +  i  x i HAPPEX-H (2004 results): A PV =  0.24 (stat)  0.06 (syst) ppm Systematic error due to helicity correlated beam dynamics controlled below the level required for HAPPEX-High Q 2 (60 ppb).

PR : HAPPEX High-Q 2 Background Measured using: Dedicated runs at very low current using track reconstruction of the HRS Dedicated integrating runs The probability of rescattering inside the spectrometer as measured by a dipole field scan Al Quasi- elastic Spectrometer Rescatter HAPPEX-I (0.48 GeV 2 ) fraction1.4%0.2%  (A PV )/A PV 0.3%0.1% This proposal (0.6 GeV 2 ) fraction1.4%0.4%  (A PV )/A PV 0.3%0.1% G0: typical dilution factor at high Q 2 ~ 20%

PR : HAPPEX High-Q 2 Measuring Q 2 Nuclear recoil, using water cell optics target:  p between elastic and excited state peaks reduces systematic error from spectrometer calibration. At Q 2 ~0.1 GeV 2 (6 o ) in 2004: Achieved  ~ 0.3% Goal: Q 2 measured using standard HRS tracking package, with reduced beam current Central scattering angle must be measured to   < 0.25% Asymmetry distribution must be averaged over finite acceptance

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

PR : HAPPEX High-Q 2 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 : HAPPEX High-Q 2  A PV / A PV  (G E s +  G M s ) Polarization1.0% Q 2 Measurement0.8% Backgrounds0.3% Linearity0.6% Finite Acceptance0.3% False Asymmetries0.3% Total Systematic1.5% Statistics2.5% Total Experimental2.9% Error Budget

PR : HAPPEX High-Q 2 Extraction of SVFF from A PV Electromagnetic FF Axial FF (G A Z ) Including radiative corrections, A PV from hydrogen is: Axial FF:  (A PV ) = 0.33 ppm EMFF: dominated by G n M,  (A PV ) = 0.53 ppm Total:  (A PV ) = 0.62 ppm, 2.8%

PR : HAPPEX High-Q 2 Axial Form Factor Axial Form Factor: Uncertainty dominated by “anapole moment” [Zhu et al, 2000] Assume dipole FF, with M A = GeV  (G A Z ) ~ 0.12, E G0 Backward Angle  (G A Z ) ~ 0.14 Compatible with Phys. Rev. C 69, (2004) [Maekawa et al, 2000]  (A PV ) = 0.33 ppm

PR : HAPPEX High-Q 2 EM Form Factors uncertainty  (A PV )/A PV GpMGpM 2%negligible GpEGpE 1.5%0.24 ppm GnEGnE 8%0.26 ppm GnMGnM 2%0.44 ppm Total 0.53 ppm But: 2-photon effects can complicate this picture at 2-4% level Experimental constraint: E in Hall B (approved): precision comparison of elastic positron-proton and electron-proton scattering, with very good coverage at this Q 2

PR : HAPPEX High-Q 2  A PV / A PV  (G E s +  G M s ) Total Systematic1.5% Statistics2.5% Total Experimental2.9% Axial FF1.5% EM FF2.4% Total FF2.8% TOTAL:4.0%0.011 Estimated Precision

PR : HAPPEX High-Q 2 Beam Request 30 Days includes 3 days commissioning/study Proposed at 100  A, 80% polarization, 20 cm LH 2 target adjust runtime based on P 2 I 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 (Q 2 =0.63GeV 2 ). Possible run 2008 (2007, depending on 6GeV Hall A experiments)

PR : HAPPEX High-Q 2 HAPPEX-III  (G E s G M s ) = (experimental) 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 ± (FF)