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How to reconcile G n M

Hall C User Meeting 2008, Jefferson Lab, August 4-5, 2008. How to reconcile G n M. Michael Kohl. Hampton University and Jefferson Lab Virginia, USA. d(e,e’n). d(e,e’p). No pol. data >0.6 (GeV/c) 2 Discrepancy of several s at Q 2 ~ 0.6-0.9 (GeV/c) 2 Uncertainties >0.9 (GeV/c) 2 ?.

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How to reconcile G n M

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  1. Hall C User Meeting 2008, Jefferson Lab, August 4-5, 2008 How to reconcile GnM Michael Kohl Hampton University and Jefferson Lab Virginia, USA

  2. d(e,e’n) d(e,e’p) • No pol. data >0.6 (GeV/c)2 • Discrepancy of several s at Q2 ~ 0.6-0.9 (GeV/c)2 • Uncertainties >0.9 (GeV/c)2? Neutron Magnetic Form Factor GnM • Pre-polarization era • GnM world data fromunpolarized experiments • Cross section ratioquasielastic • + CLAS preliminary • Polarization era • GnM world data + 3He + BLAST preliminary PRELIMINARY *Ph.D. work of N. Meitanis (MIT) and B. O’Neill (ASU)

  3. The BLAST Detector BEAM DRIFT CHAMBERS TARGET COILS CERENKOV COUNTERS BEAM NEUTRON COUNTERS SCINTILLATORS • Left-right symmetric • Large acceptance:0.1 < Q2/(GeV/c)2 < 0.820o < q< 80o, -15o <  < 15o • COILS Bmax = 3.8 kG • DRIFT CHAMBERSTracking, PID (charge)dp/p=3%, dq = 0.5o • CERENKOV COUNTERSe/p separation • SCINTILLATORSTrigger, ToF, PID (p/p) • NEUTRONCOUNTERSNeutron tracking (ToF)

  4. Target Spin Orientation NC 1 m upstream downstream WC CC TOF L20 L15 LADS NC Freedom of in-plane spin angle 32o (2004) / 47o (2005) e- left → q*  90o “spin-perpendicular” 32o e- right → q*  0o “spin-parallel”

  5. Extraction of GnM • Quasielastic 2H(e,e’) inclusive • Full Montecarlo simulation of the BLAST experiment • Deuteron electrodisintegrationby H. Arenhövel • Accounted for FSI,MEC,RC,IC • Beam-target vector asymmetry AVed spin-parallel + perpendicular show sensitivity to GnM • PWIA: BLASTMC BLASTMC

  6. * Extraction of GnM BLASTMC Enhanced sensitivity in super ratio Independent of polarization 50% variation in GMn  20% variation in R *Ph.D. work of N. Meitanis (MIT) and B. O’Neill (ASU)

  7. How to reconcile GnM around 1 (GeV/c)2 • IncAs: Simultaneous measurement of inclusive beam-vector asymmetries in quasifree kinematics with 2 target spin orientations relative to momentum transfer • Polarized deuterium target (UVA), qd ~= 45o (left)Pb*Pt = 0.8*0.3 = 0.24, L=1034 / (cm2s) • HMS (right) + Bigcal (left) / use solid angle 6msrsingle-arm (e,e’) left and right at symmetric angle D-Spin: ~45o e’: Bigcal, 25o-60o e-: E=(0.85), 1.2,2.4 GeV e’: HMS, 25o-60o

  8. IncAs: qe vs. Q2 and count rate • Kinematic coverage

  9. IncAs: qe vs. Q2 and count rate • Kinematic coverage • Counts per day at 1034 / (cm2s)and 6 msr solid angle

  10. IncAs: q* vs. Q2 Angle between target spin and momentum transfer qd = 45o qd = 75o

  11. Apsp+Ansn sp+sn A = IncAs: Inclusive Asymmetries: qd=45o Error bars corresponding to 1 day / 6 msr / 1034 cm-2s-1 / PbPt=0.24

  12. Apsp+Ansn sp+sn A = IncAs: Inclusive Asymmetries: qd=45o Effect of GMn opposite in left and right sectors 50% variation of GMn Error bars corresponding to 1 day / 6 msr / 1034 cm-2s-1 / PbPt=0.24

  13. IncAs: Inclusive Asymmetries: qd=45o Error bars corresponding to 1 day / 6 msr / 1034 cm-2s-1 / PbPt=0.24

  14. IncAs: Inclusive Asymmetries: qd=45o 50% variation in GMn  50% variation in R Error bars corresponding to 1 day / 6 msr / 1034 cm-2s-1 / PbPt=0.24

  15. IncAs: A precision GMn measurement 3% statistics: • 6msr – HMS (right) • 60msr – Bigcal (left) • Dilution = 0.25PbPt = 0.8*0.33I = 100 nAL=3.4x1035/(cm2s) • 5 days per point 2.4GeV/25o/5d@3.4e35/(cm2s) 1.2GeV/50o

  16. IncAs: Inclusive Asymmetries • Inclusive asymmetries powerful tool for high precisionmeasurement of GMn • Excellent control of systematic uncertaintiesthrough cancellations (eff., lumin., pol., …) • Super ratio method with enhanced sensitivity to GMn – no precise knowledge of polarization required • For perp/par kinematics, dR/R ~= dGMn/GMn • IncAs = Polarization method beyond He-3 • SANE and g1d to use polarized deuterium in Hall C • Relevance for determining target polarization in g1d from asymmetries • Squeeze it in (?) … or submit Loi/Proposal to PAC34for consideration after 12 GeV upgrade

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