How to reconcile G n M Hampton University and Jefferson Lab Virginia, USA Hall C User Meeting 2008, Jefferson Lab, August 4-5, 2008 Michael Kohl

2 Pre-polarization era G n M world data from unpolarized experiments Cross section ratio quasielastic + CLAS preliminary Polarization era G n M world data + 3 He Neutron Magnetic Form Factor G n M d(e,e’n) d(e,e’p) + BLAST preliminary *Ph.D. work of N. Meitanis (MIT) and B. O’Neill (ASU) PRELIMINARY  No pol. data >0.6 (GeV/c) 2  Discrepancy of several  at Q 2 ~ (GeV/c) 2  Uncertainties >0.9 (GeV/c) 2 ?

3 The BLAST Detector Left-right symmetric Large acceptance: 0.1 < Q 2 /(GeV/c) 2 < o <  < 80 o, -15 o <  < 15 o COILS B max = 3.8 kG DRIFT CHAMBERS Tracking, PID (charge)  p/p=3%,  = 0.5 o CERENKOV COUNTERS e/  separation SCINTILLATORS Trigger, ToF, PID (  /p) NEUTRON COUNTERS Neutron tracking (ToF) DRIFT CHAMBERS CERENKOV COUNTERS SCINTILLATORS NEUTRON COUNTERS TARGET BEAM COILS

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

5 Extraction of G n M Quasielastic 2 H(e,e’) inclusive Full Montecarlo simulation of the BLAST experiment Deuteron electrodisintegration by H. Arenhövel Accounted for FSI,MEC,RC,IC Beam-target vector asymmetry A V ed spin-parallel + perpendicular show sensitivity to G n M PWIA: BLASTMC

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

7 IncAs: Simultaneous measurement of inclusive beam- vector asymmetries in quasifree kinematics with 2 target spin orientations relative to momentum transfer Polarized deuterium target (UVA),  d ~= 45 o (left) P b *P t = 0.8*0.3 = 0.24, L=10 34 / (cm 2 s) HMS (right) + Bigcal (left) / use solid angle 6msr single-arm (e,e’) left and right at symmetric angle How to reconcile G n M around 1 (GeV/c) 2 e’: HMS, 25 o -60 o e’: Bigcal, 25 o -60 o D-Spin: ~45 o e - : E=(0.85), 1.2, 2.4 GeV

8 IncAs:  e vs. Q 2 and count rate  Kinematic coverage

9 IncAs:  e vs. Q 2 and count rate  Kinematic coverage  Counts per day at / (cm 2 s) and 6 msr solid angle

10 IncAs:  * vs. Q 2  d = 45 o Angle between target spin and momentum transfer  d = 75 o

11 IncAs: Inclusive Asymmetries:  d =45 o A p  p +A n  n  p +  n A = Error bars corresponding to 1 day / 6 msr / cm -2 s -1 / P b P t =0.24

12 IncAs: Inclusive Asymmetries:  d =45 o A p  p +A n  n  p +  n A = Effect of GMn opposite in left and right sectors 50% variation of GMn Error bars corresponding to 1 day / 6 msr / cm -2 s -1 / P b P t =0.24

13 IncAs: Inclusive Asymmetries:  d =45 o Error bars corresponding to 1 day / 6 msr / cm -2 s -1 / P b P t =0.24

14 IncAs: Inclusive Asymmetries:  d =45 o 50% variation in GMn  50% variation in R Error bars corresponding to 1 day / 6 msr / cm -2 s -1 / P b P t =0.24

15 IncAs: A precision GMn measurement 2.4GeV/25 o 2 s) 1.2GeV/50 o 3% statistics:  6msr – HMS (right)  60msr – Bigcal (left)  Dilution = 0.25 P b P t = 0.8*0.33 I = 100 nA L=3.4x10 35 /(cm 2 s)  5 days per point

16 IncAs: Inclusive Asymmetries  Inclusive asymmetries powerful tool for high precision measurement of GMn  Excellent control of systematic uncertainties through 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 PAC34 for consideration after 12 GeV upgrade