How to reconcile GnM

Hampton University and Jefferson Lab Virginia, USA

Hall C User Meeting 2008, Jefferson Lab, August 4-5, 2008

Michael Kohl

2

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?

3

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”

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 AV

ed spin-parallel + perpendicular show sensitivity to Gn

M

PWIA:BLASTMC

BLASTMC

6

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

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 ~= 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

8

IncAs: e vs. Q2 and count rate

Kinematic coverage

9

IncAs: e vs. Q2 and count rate

Kinematic coverage Counts per day at 1034 / (cm2s)

and 6 msr solid angle

10

IncAs: * vs. Q2

d = 45o

Angle between target spinand momentum transfer

d = 75o

11

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

12

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

13

IncAs: Inclusive Asymmetries: d=45o

Error bars corresponding to 1 day / 6 msr / 1034 cm-2s-1 / PbPt=0.24

14

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

15

IncAs: A precision GMn measurement

2.4GeV/25o/5d@3.4e35/(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