How to reconcile G n M
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Transcript of How to reconcile G n M
How to reconcile GnM
Hampton University and Jefferson Lab Virginia, USA
Hall C User Meeting 2008, Jefferson Lab, August 4-5, 2008
Michael Kohl
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Pre-polarization era
GnM world data from
unpolarized experiments
Cross section ratio
quasielastic
+ CLAS preliminary
Polarization era
GnM world data + 3He
Neutron Magnetic Form Factor GnM
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 Q2 ~ 0.6-0.9 (GeV/c)2
Uncertainties >0.9 (GeV/c)2?
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The BLAST Detector
Left-right symmetric
Large acceptance:0.1 < Q2/(GeV/c)2 < 0.820o < < 80o, -15o < < 15o
COILS Bmax = 3.8 kG
DRIFT CHAMBERSTracking, PID (charge)p/p=3%, = 0.5o
CERENKOV COUNTERSe/ separation
SCINTILLATORSTrigger, ToF, PID (/p)
NEUTRON COUNTERSNeutron tracking (ToF)
DRIFT CHAMBERS
CERENKOVCOUNTERS
SCINTILLATORS
NEUTRON COUNTERS
TARGET
BEAM
BEAM
COILS
4NC
TOFCC
WC
NC
LADSL20
L15
upstream downstream
1 m
Target Spin Orientation
Freedom of in-plane spin angle
32o (2004) / 47o (2005)
32o
e- left → * 90o
“spin-perpendicular”
e- right → * 0o
“spin-parallel”
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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 AV
ed spin-parallel + perpendicular show sensitivity to Gn
M
PWIA:BLASTMC
BLASTMC
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Extraction of GnM
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
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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 ~= 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
How to reconcile GnM around 1 (GeV/c)2
e’: HMS, 25o-60o
e’: Bigcal, 25o-60oD-Spin: ~45o
e-: E=(0.85), 1.2, 2.4 GeV
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IncAs: e vs. Q2 and count rate
Kinematic coverage
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IncAs: e vs. Q2 and count rate
Kinematic coverage Counts per day at 1034 / (cm2s)
and 6 msr solid angle
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IncAs: * vs. Q2
d = 45o
Angle between target spinand momentum transfer
d = 75o
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IncAs: Inclusive Asymmetries: d=45o
App+Ann p+n
A =
Error bars corresponding to 1 day / 6 msr / 1034 cm-2s-1 / PbPt=0.24
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IncAs: Inclusive Asymmetries: d=45o
App+Ann p+n
A =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
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IncAs: Inclusive Asymmetries: d=45o
Error bars corresponding to 1 day / 6 msr / 1034 cm-2s-1 / PbPt=0.24
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IncAs: Inclusive Asymmetries: d=45o
50% variation in GMn 50% variation in R
Error bars corresponding to 1 day / 6 msr / 1034 cm-2s-1 / PbPt=0.24
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IncAs: A precision GMn measurement
2.4GeV/25o/[email protected]/(cm2s)
1.2GeV/50o
3% statistics:
6msr – HMS (right)
60msr – Bigcal (left)
Dilution = 0.25PbPt = 0.8*0.33I = 100 nAL=3.4x1035/(cm2s)
5 days per point
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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 CRelevance for determining target polarization in g1d
from asymmetriesSqueeze it in (?) … or submit Loi/Proposal to PAC34
for consideration after 12 GeV upgrade