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A Precision Measurement of G E p /G M p with BLAST

A Precision Measurement of G E p /G M p with BLAST. Chris Crawford MIT Laboratory for Nuclear Science for the BLAST collaboration. Introduction. G E ,G M fundamental quantities describing charge/magnetization in the nucleon Test of QCD based calculations and models

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A Precision Measurement of G E p /G M p with BLAST

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  1. A Precision Measurement of GEp/GMp with BLAST Chris Crawford MIT Laboratory for Nuclear Science for the BLAST collaboration

  2. Introduction • GE,GM fundamental quantities describing charge/magnetization in the nucleon • Test of QCD based calculations and models • Provide basis for understanding more complex systems in terms of quarks and gluons • QED Lamb shift

  3. World Data • Unpolarized Data • CEA, Bonn, DESY, SLAC • Christy et al. (JLab 2004) • Arrington et al. (JLab ) • Polarization Transfer • Milbrath et al. (BATES) 1999 • Jones et al. (JLab), 2000 • Dieterich et al. (MAMI), 2001 • Gayou et al. (JLab), 2002 • Theory • quark orbital momentum • 2g effects

  4. World Data • Unpolarized Data • CEA, Bonn, DESY, SLAC • Christy et al. (JLab 2004) • Arrington et al. (JLab ) • Polarization Transfer • Milbrath et al. (BATES) 1999 • Jones et al. (JLab), 2000 • Dieterich et al. (MAMI), 2001 • Gayou et al. (JLab), 2002 • Theory • quark orbital momentum • 2g effects

  5. World Data • Unpolarized Data • CEA, Bonn, DESY, SLAC • Christy et al. (JLab 2004) • Arrington et al. (JLab ) • Polarization Transfer • Milbrath et al. (BATES) 1999 • Jones et al. (JLab), 2000 • Dieterich et al. (MAMI), 2001 • Gayou et al. (JLab), 2002 • Theory • quark orbital momentum • 2g effects

  6. MIT-Bates Exp. 01-01 Spokespersons: H. Gao, J. Calarco, H. Kolster • new technique • precision test of theories at low Q2 • meson cloud structure

  7. Form Factor Ratio @ BATES • Exploits unique features of BLAST • internal target: low dilution, fast spin reversal • large acceptance: simultaneously measure all Q2 points • symmetric detector: ratio measurement • Different systematics • also insensitive to Pb and Pt • no spin transport • Q2 = 0.1 – 0.8 (GeV/c) 2 • overlap with JLab data

  8. Asymmetry Super-ratio Method • Helicity Asymmetry • Super-ratio • b = 45±

  9. Storage Ring E = 850 MeV Iinj=175 mA Pb = 0.65 Internal ABS Target 40 cm storage cell t = 2.71013 cm-2 Pt = 0.40 Polarized Beam and Target • isotopically pure internal target • high polarization, fast spin reversal • L = 1.6  1031 cm-2s-1

  10. BLAST Coils Backward-Angle TOF TOF Scintillators Drift Chambers Čerenkov Detectors Neutron Detectors LADS Detectors Detector Package

  11. BLAST

  12. Data Sets • 1H run 1, December 2003 • reversed BLAST field – electrons out-bending • 20 kC beam (3.4 pb-1) Pz=.45 480k elastic events • 1H run 2, April 2004 • nominal BLAST field – electrons in-bending • 57 kC beam (9.6 pb-1) Pz=.40 950k elastic events • 2D run, May – October 2004 • 450 kC beam (76 pb-1) Pz=.75 • 1H run 3, November 2004 • ~250 kC (42 pb-1) planned

  13. TOF Scintillator Cuts TOF paddle, proton TOF paddle, electron

  14. Resolution and Yields preliminary TOF paddle #

  15. Experimental Spin Asymmetry

  16. GE/GM by Super-ratio Method

  17. GE/GM by Fit Method • fit for: • take advantage of large acceptance • optional: also fit for b (spin angle) • super-ratio method: • in each Q2 bin • redundant measurement of polarization

  18. Preliminary Results • combineddatasets(77 kC) • preliminary results based on ¼ of the projected data

  19. Preliminary Results • combineddatasets(77 kC) • preliminary results based on ¼ of the projected data

  20. Conclusion • new precision measurement of GEp/GMp • exploits unique capabilities of BLAST • 2 – 4% projected errors at low Q2

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