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Measurement of the Neutron Electric FormFactor Gn
E in 2−→H(−→e , e′n)p Quasi-elasticScattering
Donal DayUniversity of Virginia
Charlottesville, VA 22904dbd@virginia.edu
March, 28, 2003
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003
Plan
1 IntroductionForm Factors
Interpretation
GnE Models
GnE Measurements
2−→H(−→e , e′n)p Technique
2 Experiment E93026Overview
Moller Polarimeter
Polarized Target
Neutron Detector
3 AnalysisOverview
Simulation
Neutron Identification
Asymmetries
Extracting GnE
4 Results and OutlookResult and Systematics
GnE World Data
Comparison to Models
Outlook
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 1
Nucleon Form Factors
dσ
dΩ= σMott
E′
E0
n(F1)
2+ τ
h2 (F1 + F2)
2tan
2(θe) + (F2)
2io
electron nucleonPSfrag replacements
E,
−→
k
E ′,
−→
k′ ER,
−→
PR
M
GE,M
γ
1
F p1 = 1 F n
1 = 0
F p2 = 1.79 F n
2 = −1.91
e scatt. angle: θe
pointlike target: σmott =α2 cos2(θe/2)
4E2 sin4(θe/2)
Kin. factor: τ = Q2/4M2
4-momentum transfer:
Q2 =
„−→k −
−→k′«2
−`E − E′
´2= 4EE′ sin2 (θe/2)
GE
“Q2”
= F1(Q2)− τF2
“Q2”
GM
“Q2”
= F1
“Q2”
+ F2
“Q2”
dσ
dΩ=
σMott
(1 + τ)
E′
E0
hG
2E + τ(1 + (1 + τ)2 tan
2(θ/2))G
2M
i
Q2 = 0 limit: GpE = 1 Gn
E = 0 GpM = 2.79 Gn
M = −1.91
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 2
GnE Interpretation
In the nonrelativistic limit Q2 = −→q 2 (Breit Frame) GE is Fourier Transform ofthe charge distribution ρ(r):
GnE
“q2”
=1
(2π)3
Zd3rρ(r)e(iq·r)
=
Zd3rρ (r)−
q2
6
Zd3rρ (r) r2 + ...
= 0−q2
6
Dr2ne
E+ ...
Anomalous magnetic moment of neutron and Yukawa theory of mesons gaverise to the idea of a separated charge distribution in the neutron. The chargeradius was expected to be negative.
Dr2ne
E= −6
dGE(0)
dQ2= −6
dF1(0)
dQ2+
3
2M2F2(0)
=D
r2in
E+D
r2Foldy
E
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 3
Charge radius, Foldy term
Dr
2ne
E= −6
dGnE(0)
dQ2= −6
dF n1 (0)
dQ2+
3
2M2F
n2 (0)
=D
r2in
E+D
r2Foldy
EFoldy term, 3µn
2mn= (−0.126)fm2, has nothing to do with the rest
frame charge distribution.˙r2
ne
¸is measured through neutron-electron scatteringDr
2ne
E=
3mea0
mn
bne = −0.113± 0.003± 0.004 fm2.
˙r2in
¸= −0.113 + 0.126 ≈ 0 suggesting that the spatial charge
extension seen in F1 is about 0 or very small.Recent studies have attempted to resolve this issue with theconclusion that Gn
E arises from the neutron’s rest frame chargedistribution.
N. Isgur Phys. Rev. Lett. 83, 272 (1999)
“Interpreting the Neutron’s Electric Form Factor. Rest Frame ChargeDistribution or Foldy Term?”
in relativistic expansion of the constituent quark model the Foldy termcancels against a contribution from F1.
M. Bawin & A.A. Coon Phys. Rev. C. 60, 025207 (1999)
“Neutron charge radius and the Dirac equation”explicit incorporation of the Dirac-Pauli form factors in Dirac equation.The Foldy term is canceled by a contribution from F1.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 4
Why is⟨r2in
⟩< 0?
r (fm)0 0.5 1 1.5 2 2.5 3
(r)
ρ2 rπ4
-0.05
0
0.05
0.1
0.15
Charge Distribution
r (fm)0 0.5 1 1.5 2 2.5 3
(r)
ρ2 rπ4
-0.05
0
0.05
0.1
0.15
Hadron Picturepπ− component in neutron wavefunctionπ− cloud on outside
n p n n D+ n
p- p-
CQMneutron = udd and spin–spin forces create a chargesegregation
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 5
Why measure GnE?
Fundamental quantity
• Test of QCD description of the nucleon
Symmetric quark model, with all valence quarks with samewavefunction, Gn
E ≡ 0→ details of the wavefunctions
0
0.025
0.05
0.075
0.1
0 0.25 0.5 0.75 1 1.25Q2(GeV/c)2
GEn
Galster
CI (valence)CI+DI (valence+sea)
Dong, Liu, Williams, PRD 58 074504
• More sensitive than otherform factors to sea quarkcontributions
• Soliton model Gorski 1992suggests that ρ(r) at large r
due to sea quarks
Necessary for study of nuclear structure.
• Without GnE almost impossible to extract information in high Q2
few body structure functions
• Large source of error in extraction of strange quark form factorsfrom parity violating experiments
• Explains˙r2ch
¸of 48Ca as compared to 40Ca
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 6
Parametrizations of Nucleon Form Factors
The electric form factor, GpE(Q2) = 1
(2π)3
Rd3rρ(r)e(iq·r)
Dipole Parametrization: Good description of early GpE,M data
GD =
1 +
Q2
0.71(GeV/c)2
!−2
GpE = GD =
GpM
µp
=Gn
M
µn
GnE = −τµnGD ; τ =
Q2
4M2
'
&
$
%
GD =“1 + Q2
k2
”−2
implies an exponentialcharge distribution:
ρ (r) ∝ e−kr
Galster Parametrization: From e−D elastic scattering
GnE = −
τµn
1 + 5.6τGD
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 7
Models of Nucleon Form FactorsGround state QCD structure is strong coupling problem: currentlyunsolvable
Vector Meson Dominance
Target
phot onw,r,f
F (Q2) =P
i
CγViQ2+M2
Vi
FViN(Q2)
1Q2+M2
Vi
⇒ propagator of meson of mass MVi
CγVi⇒ photon-meson coupling strength
FViN(Q2) ⇒ meson-nucleon form factor.
VMD breaks down at large Q2: Can notreproduce the dipole form factor or reproducethe prediction of pQCD.
pQCDHigh Q2 helicity conservation by γ−quark interaction requiresthat Q2F1/F2 → constant as F2 helicity flip arises from secondorder corrections and are suppressed by an additional factor of1/Q. Furthermore for Q2 ΛQCD counting rules find F1 ∝αs(Q
2)/Q4. Thus F1 ∝ 1Q4 and F2 ∝ 1
Q6 ⇒ Q2F2F1
→constant. Contradicted by JLAB proton data which show thatQ
F2F1→ constant.
Hybrid ModelsFailure to follow the high Q2 behavior suggested by pQCD ledGK to incorporate pQCD at high Q2 with the low VMD behavior.Inclusion of φ by GK had significant effect on Gn
E. Lomon hasupdated with new fits to selected data.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 8
Lattice calculations of form form factors nascentFundamental but currently limited in statistical accuracyDong et al PRD58, 074504 (1998)
QCD based modesModels: try to capture aspects of QCDRCQM P.L. Chung and F. Coester, PR D44, 229 (1991), I.Z. Aznaurian, PL
B316, 39 (1993), M.R. Frank, B.K. Jennings, and G.A. Miller, PRC54, 920
(1996), M. Ivanov, M. Locher, and V. Lyubovitskij, Few Body Systems, 21, 131
(1996).
di-quark model P. Kroll, M.Schurmann, and W. Schweiger, Z. Phys. A432,
429 (1992).
QCD sum rules A.V. Radyushkin, Acta. Phys. Polon. B15, 403 (1984).
Cloudy bag model D.H. Lu, A.W. Thomas, and A.G. Williams, PR C57, 2628
(1998).
Helicity non-conservation shows up in the light front dynamicsanalysis of Miller and collaborators where in the imposition ofPoincare invariance analytic results that predicted Q
F2F1→ constant
and the violation of helicity conservation. Helicity non-conservationalso shows up in the pQCD model of Ralston and collaboratorswhich also predict that Q
F2F1
→ constant. Both models includequark orbital angular momentum.
light front cloudy bag model Miller has extended the light frontdynamics to include the cloudy bag with a description of theneutron as a bare nucleon and a negative pion cloud with a longtail, giving rise to the negative charge radius.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 9
0
0.02
0.04
0.06
0.08
0.1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Q2(GeV/c)2
GEn
GalsterG-K (no F)G-K (with F)DipoleVMD - Hohler (fit 8.2)Bag Model - Lu (r=1.0 fm)Quark Model - Ivanov
Soliton→Holzwarth MMD→ Mergell, Meissner and DreschelGBECQM→ Wagenbrum and collaborators
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 10
GnE Measurements
No free neutron target =⇒ Use deuteron
• Inclusive cross section measurements on Deuterium:– Elastic e−D scattering at small angles:
depends on N-N potential, subtraction of proton contribution– Quasielastic e−D scattering
Rosenbluth separation, sensitive to deuteron structure
• Double Polarization measurementsasymmetry measurementdetection of neutron in coincidence→ less sensitive to deutron structure→ avoid Rosenbluth separation→ avoid subtraction of proton contribution2H(−→e , e′−→n )p, 2−→H (−→e , e′n)p, 3−→He(−→e , e′n)pp
Other methods
• 2H(e, e′n)p
• 2H(e, e′p)p (anticoincidence)
• Ratio techniquese,e′pe,e′n
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 11
e-D Elastic Scattering
Born approximation
dσ
dΩ= σNS
»A“
Q2”
+ B“
Q2”
tan2
„θe
2
«–
A(Q2) = G2c + 8
9ηG2Q + 2
3η2G2
M
B(Q2) = 43η(η + 1)G2
M
η = Q2
4M2D
small θe approximation
dσ
dΩ= · · · (Gp
e + GnE)
2hu(r)
2+ w(r)
2i
j0(qr
2)dr · · ·
1. AIA(Q2) deduced after corrections for relativistic effects andMEC
2. Subtract magnetic dipole using parametrization of data
3. S and D state functions to unfold nuclear structure for variouspotentials to get isoscalar form factor
4. Subtract proton form factor
5. Sensitive to deuteron wavefunction model and MEC
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 12
Early measurements of GnE and slope at Q2 = 0
Relativistic corrections and model dependence: Casper and Gross, PR 155, 1607 (1967)
(a) Partovi wave function
(b) Partovi and relativistic corrections
(c) Feshbach-Lomon and relativistic corrections
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 13
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 14
Elastic, ContinuedIn the case of 2H(e, e′)2
−→H components of the tensor polarization give useful
combinations of the form factors,
t20 =1
√2S
8
3τdGCGQ +
8
9τ
2dG
2Q +
1
3τd
h1 + 2(1 + τd) tan
2(θ/2)
iG
2M
ffallowing GQ(Q2) to be extracted. Exploiting the fact that GQ(Q2)suffersless from theoretical uncertainties than A(Q2), Gn
E can be extracted to largermomentum transfers.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 15
Quasielastic e− d Scattering
PWIA model (Durand and McGee): Cross section is incoherent sum of p and ncross section folded with deuteron structure.
σ =`σp + σn
´I (u, w)
=
(ε
»“G
pE
”2+`G
nE
´2–+
ν2
Q2
»“G
pM
”2+`G
nM
´2–)I (u, w)
= εRL + RT
ε =h1 + 2 (1 + τ) tan
2(θe/2)
i−1
• Extraction of GnE:
Rosenbluth Separation ⇒ RLSubtraction of proton contribution
• Problems:Unfavorable error propagationSensitivity to deuteron structure
SLAC: A. Lung et al, Phys. Rev. Lett. 70, 718 (1993)→Gn
E consistent with zero and Galster.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 16
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 2 3 4 5
Q2 (GeV/c) 2
(GE
n /
GD
)2
Galster
Lung et al.(1993)Hanson et al.(1973)
Open questions
GE
“Q2”
= F1(Q2)− τF2
“Q2”
GM
“Q2”
= F1
“Q2”
+ F2
“Q2”
If GnE is small at large Q2 then F n
1 must cancel τF n2 , begging the question, how
does F n1 evolve from 0 at Q2 = 0 to cancel τF n
2 at large Q2?
E133 data from SLAC shows the ratio of σn/σp falling with Q2, suggesting that
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 17
F n1 ' 0. This implies that Gn
E would dominate GnM at high Q2.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 18
Double polarization measurements
Akhiezer and Rekalo (1968), Dombey (1968)2H(~e, e′~n)p2−→H(~e, e′n)p, ~3He(~e, e′n)pp
Asymmetry measurements→ less sensitive to deuteron structure→ avoid Rosenbluth separation→ avoid subtraction of proton contribution (detect neutron)→ only relative charge measurement needed→ reduced dependence on detector acceptance→ radiative corrections reduced→ understand helicity dependent deadtime→ need absolute beam and target polarization
Target Type Q2(GeV/c)2 Reference2H (−→e , e′−→n ) 0.15 C. Herberg et al., Eur. Phys. J. A 5, 131 (1999)2−→H (−→e , e′n) 0.21 I. Passchier et al., Phys. Rev. Lett. 82, 4988 (1999)2H (−→e , e′−→n ) 0.252 T. Eden et al., Phys. Rev. C 50, R1749 (1994)
3−→He (−→e , e′n) 0.31 M. Meyerhoff et al., Phys. Lett. B 327, 201 (1994)2H (−→e , e′−→n ) 0.33 M. Ostrick et al., Phys. Rev. Lett. 83, 276 (1999)
3−→He (−→e , e′n) 0.36 J. Becker et al., Eur. Phys. J . A6, 329 (1999)2−→H (−→e , e′n) 0.5 H. Zhu et al., Phys. Rev. Lett. 87, 081801 (2001)3−→He (−→e , e′n) 0.67 D. Rohe et al., Phys. Rev. Lett. 83, 4257 (1999)2−→H (−→e , e′n) 0.5, 1.0 JLAB E93-026 preliminary 20012H (−→e , e′−→n ) 0.45, 1.15, 1.47 JLAB E93-038 preliminary 2001
3−→He (−→e , e′n) 0.67 Mainz 2003, Bermuth2H (−→e , e′−→n ) 0..3, 0.6, 0.8 Mainz data taking completed 2002
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 19
Polarized Electron on Polarized Free Neutron
qe
e
e'
(q, w)h = ±1
uynormal
ux
uz
polarization axis (q*, f*)
f*
q*
along qxz plane
Neutron Polarization P Beam Helicity h
Polarized Cross Section: σ = σ0 (1 + hPA)
A =a cos θ? (Gn
M)2+ b sin θ? cos Φ?Gn
EGnM
c`Gn
M
´2+ d
`Gn
E
´2θ
?= 90
Φ
?= 0
=⇒ A =
bGnEGn
M
c`Gn
M
´2+ d
`Gn
E
´2
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 20
Polarized Electron on Polarized Deuteron Target
Polarized Cross Section for quasielastic 2−→H(−→e , e′n)p:
σ(h, P ) = σ0
(1 + hAe + PAV
d + TATd + hPAV
ed + hTATed
)h: Beam HelicityP : Vector Target PolarizationT : Tensor Target Polarization T = 2−
√4− 3P 2
Deuteron supports a tensor polarization, T , in addition to the usual vector polarization,P – this can lead to both helicity dependent and helicity independent contributions
– ATed andAe vanish if symmetrically averaged
– AVd vanishes in the scattering plane
– ATd is suppressed by T ≈ 3%
Theoretical Calculations of electrodisintegration of the deuteron:H. Arenhövel, W. Leidemann, and E. L. Tomusiak, Z. Phys. A 331,123 (1988); 334, 363(E) (1989).H. Arenhövel, W. Leidemann, and E. L. Tomusiak, Phys. Rev. C46, 455 (1992).
AVed is sensitive to Gn
E
has low sensitivity to potential modelshas low sensitivity to subnuclear degrees of freedom(MEC, IC)
under certain kinematical conditions....
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 21
Sensitivity to GnE – Insensitivity to Reaction
-0.15
-0.1
-0.05
0
0.05
0.1
0 50 100 150 200 250 300 350
θnpcm (deg)
AedV
GEn=1.0×Galster
GEn=0.5×Galster
GEn=1.5×Galster
-0.15
-0.1
-0.05
0
0.05
0.1
100 120 140 160 180 200 220 240
θnpcm (deg)
AedV
BornNN+MECN+MEC+ICN+MEC+IC+REL
θcmnp : Angle between −→q and relative n-p momentum in cm system; 180 deg corresponds to
neutron in direction of −→q
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 22
Experimental Technique for 2−→H(−→e , e′n)p
How to access AVed?
Experiment measures counts for different orientationsof h and P :
NhP ∝ σ (h, P )
Beam-target Asymmetry:
ABT =N++ −N−+ + N−− −N+−
N++ + N−+ + N++ + N++
=hPAV
ed
1 + TATd
' hPAVed
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 23
E93026 Collaboration
112 collaborators from 18 institutions
Duke University, Florida International University,Hampton University, Jefferson Lab, Louisiana Tech University,
Mississippi State University, Norfolk State University,North Carolina A&T State University, Old Dominion University,
Ohio University, Southern University at New Orleans,Tel Aviv University, University of Basel,
University of Maryland at College Park, University of Virginia,Virginia Polytechnic Institute & State University,
Vrije Universiteit of Amsterdam, Yerevan Physics Institute
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 24
Experiment E93026
• Measured in Hall C at Thomas Jefferson National AcceleratorFacility (Jlab) in Newport News, Virginia, USA
• Measuring periods– Aug 1998 - Oct 1998– July 2001 - Dec 2001
• Kinematics:2.2× 106 neutrons at Q2 = 0.5 (GeV/c)2 (1998)6.5× 106 neutrons at Q2 = 0.5 (GeV/c)2 (2001).75× 106 neutrons at Q2 = 1.0 (GeV/c)2 (1998)1.4× 106 neutrons at Q2 = 1.0 (GeV/c)2 (2001)
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 25
Hall Schematic
• Polarized Target
• Chicane to compensate for beam deflection of ≈ 4 degrees
• Scattering Plane Tilted
• Protons deflected ≈ 17 deg at Q2 = 0.5
• Raster to distribute beam over 3 cm2 face of target
• Electrons detected in HMS (right)
• Neutrons and Protons detected in scintillator array (left)
• Beam Polarization measured in coincidence Möller polarimeter
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 26
Mic
row
ave
Inpu
tN
MR
Sign
al O
ut
Ref
riger
ator
Liqu
idH
eliu
m
Mag
net Ta
rget
(insi
de c
oil)
1° K
NM
R C
oil
To P
umps
7656
A14-
94
LN2
LN2
To P
umps
B 5T
e– Beam
Signal
Freq
uenc
y
Liqu
idH
eliu
mS
olid
Pol
ariz
edTa
rget
s•
froz
en(d
oped
)15N
D3
•4H
eev
apor
atio
nre
frig
erat
or
•5T
pola
rizin
gfie
ld
•re
mot
ely
mov
able
inse
rt
•dy
nam
icnu
clea
rpo
lariz
atio
n
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 27
Dynamic Nuclear Polarization
Pictorial Representation–Proton Enhancement
M m label
+1/2 +1/2 (c)
-1/2 +1/2 (a)
213 MHz
140 GHz
+1/2 -1/2 (d)
-1/2 -1/2 (b)
NMR
NMR
EPR
EPR
Forbidden
Forb
idde
n
Forbidden transitions (∆mj 6= ±1) allowed
Microwaves of 140Ghz - 213 MHz drive the b → c transition
Relaxation occurs through c → a transition
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 28
Target Stick
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 29
Deuteron NMR
• Sweep RF frequency-measure absorptive part of response withtuned phase sensitive circuit
• Polarization proportional to signal area
• Fix scale by measuring polarization in thermal equilibrium (TE)
@ (5 Tesla, 1.5 K)
PTE =4tanh(µB/2kT )
3 + tanh2(µB/2kT )≈ 0.07%
Typically can achieve 3 to 5% systematic error (relative)
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
32.4 32.6 32.8 33
TE
w(MHz)
Volta
ge(A
rb U
nits
)
0
20
40
60
80
100
120
140
32.4 32.6 32.8 33
Enhanced
w(MHz)
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 30
Gen Target Performance, 10Sep01
0 200 400 600 800 10000
10
20
30
40
50
Time (min)
Deu
tero
n Po
lariz
atio
n (%
)
Average polarization ' 25%
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 31
Neutron Detector• Highly segmented scintillator
• Rates: 50 - 200 kHz per detector
• Pb shielding in front to reducebackground
• 2 thin planes for particle ID (VETO)
• 6 thick conversion planes forneutron detection
• 142 elements total, >280 channels
• Extended front section forsymmetric proton coverage
• PMTs on both ends of scintillator
• Spatial resolution ' 10 cm
• Time resolution ' 400 ps
• Provides 3 space coordinates, timeand energy
Protons
BeamHeight
Neutrons
1.0 cm11cm
(length:160cm)10 cm
10 cm
1998 2001
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 32
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 33
Analysis
• Event Reconstruction
– HMS standard reconstruction + target magnet + raster– NDET tracking: Particle Identification
⇒ cut variables: W, Ypos, coincidence-time , θnq
• Event Selection and Normalization→ Normalized yields: N↑, N↓
• Experimental asymmetries:
ε = N↑−N↓
N↑+N↓= PB · PT · f · AV
ed⇒`AV
ed
´meas
Dilution factor f =Npolarized
N from 12C
• Radiative corrections, Accidental background subtraction
⇒ measured deuteron asymmetry AVed binned in four variables
• Theoretical calculations of AVed (for different Gn
E = α×Galster)from Arenhövel for a kinematical grid
• Average theoretical AVed over experimental acceptance using
MC and compare with measured`AV
ed
´meas
⇒ GnE
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 34
Timing
Coincidence Time (ns)
0
200
400
600
800
1000
1200
1400
-30 -20 -10 0 10 20 30
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 35
Particle Identification
• Neutrons No paddle hits along trajectory to target
• Veto inefficiency from 2/3 using first bar layer 3% per plane
• Target Field helps, θnq < 0.1 rad
• Protons bent ≈ 17 deg (0.3 rad)
0200400600800
10001200140016001800
0 0.1 0.2 0.3 0.4
MCData
qnq (radian)
0
500
1000
1500
2000
2500
3000
3500
0 0.2 0.4 0.6qpq (radian)
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 36
Particle Identification
Not typical–most protons above the bulk of the bars
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 37
Fired but failed the MT cut.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 38
Experimental Asymmetries
-0.1
-0.05
0
0.05
0.1
std W θnpcm E’ ypos θpq
lab special
Burger Plot v4
neutron-stdneutron-altproton-stdproton-alt
-0.15
-0.1
-0.05
0
0.05
0.1
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3std tbig
Burger Plot v12 -- bins in ntrk_dx (vertical slope)
n - stdn - alt
proton - stdgood p
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 39
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
std ytar x’tar y’tar xfp yfp x’fp y’fp W
Burger Plot v8 -- Electron Kinematics
n-std neutron-alt
proton-stdproton-alt
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 40
Dilution factor
Solution: Monte Carlo and experimental data
E, (GeV)
0200400600800
1000120014001600
2.35 2.4 2.45 2.5 2.55
ypos (cm)
0100200300400500600700800900
-50 0 50
θnq (radian)
0200400600800
1000120014001600
0 0.1 0.2 0.3 0.4
θnpcm (degree)
0
200
400
600
800
1000
1200
125 150 175 200 225
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 41
Structure of AVed
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 42
Extracting GnE
0.5 0.80.91.0
1.11.31.5
data
E¢, MeV
Aed
V
ypos, cm
Aed
V
qnq, radian
Aed
V
qnpcm, deg
Aed
V
Q2, (GeV/c)2
Aed
V
0
0.025
0.05
0.075
0.1
2050 2100 21500
0.025
0.05
0.075
0.1
-20 0 20 40
0
0.025
0.05
0.075
0.1
0 0.025 0.05 0.075 0.10
0.025
0.05
0.075
0.1
170 180 190
0
0.025
0.05
0.075
0.1
0.45 0.5 0.55 0.6Scale Factor (¥ Galster)
c2
E¢yposqnqqnp
cm
s=6.5%0
10
20
30
40
50
60
70
0.6 0.8 1 1.2 1.4
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 43
Extracting GnE
Scale Factor (× Galster)
χ2
E′ ypos θnq θnpcm
2σ
0
10
20
30
40
50
60
70
80
0.6 0.8 1 1.2 1.4
8.68.8
99.29.4
0.90.95 1
E′: Energy of the scattered electron
Ypos: Horizontal coordinate of the hadron track in the neutrondetector
θnq: Angle between 3-momentum transfer (−→q ) and hadron track
θcmnp: Angle between neutron and (−→q ) in cm
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 44
CEX and multi step processes
Not all good neutrons are generated by quasielastic scattering.Data and asymmetry get contaminated, in the following way.
• in the lead shielding in front of the neutron detector:– d(e,e’p) followed by Pb(p, n)– d(e,e’p) followed by Pb(p, π0) and π0 → γ + γ
• the 15ND3 target
– d(e,e’p) followed by 15N(p,n)
First estimates of Pb(p,n) revealed that this effect is not neglible.
• A simulation was written using the measured protondistribution in the detector; Pb(p,n) cross section from chargeexchange studies for Gn
M .
• The net contamination in asymmetry due to Pb(p,n) is−3.44± 1.02% for Q2 = 0.5. The error dominated by theuncertainty in the cross section.
• For Q2 = 1 the simulation has not been run. Estimate ofcontamination is −3± 3%.
• The 15N(p,n) contamination is small and is estimated to be−0.3%± 0.3% for Q2 = 0.5 and Q2 = 1.
• Photon contamination is neglible for Q2 = 0.5 and about oneorder of magnitude smaller than from Pb(p,n) for Q2 = 1
based on total cross section of proton induced π0 production.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 45
Preliminary Results
0
0.05
0.1
0.15
0 1 2Q2 (GeV2/c2)
GEn
Sick (01)Bermuth (03)
Ostrik (99)Herberg (99)
Golak (01)
Passchier (99)Zhu (01)Gen01 - Preliminary
Galster
Result for 1998 Q2 = 0.5 (GeV/c)2:
GnE = 0.04632± 0.00616stat ± 0.00341syst
? PRL 87 (2001) 081801
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 46
Preliminary Results and Systematics
Final (98)? Q2 = 0.5 (GeV/c)2 GnE = 0.04632± 0.0070
Preliminary (2001) Q2 = 0.5 (GeV/c)2 GnE =' Galster± ' 7.5%(stat.)
Preliminary (2001) Q2 = 1.0 (GeV/c)2 GnE =& Galster± ' 14%(stat.)
Systematics 98 01 (predicted)Target Polarization 5.8% 3-5%
Dilution Factor 3.9% 3%Cut Dependence 2.4% 2%
Kinematics 2.2% 2%Gn
M 1.7% 1.7%Beam Polarization 1.0% 1-3%
Other 1.0% 1%Sum 8.0% 6-8%
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 47
Comparison to Models
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 48
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 49
Comparison to Models
0.6
0.8
1
1.2
10-1
1 10Q2 [ GeV2 ]
GM
p/µ
GD
0
0.5
1
1.5
0 2 4 6 8
Q2 [ GeV2 ]µG
Ep/G
Mp
0.8
1
1.2
10-1
1Q2 [ GeV2 ]
GM
n/µ
GD
0
0.025
0.05
0.075
0 0.5 1 1.5 2
Q2 [ GeV2 ]
GE
n
VMD-pQCD(2002)VMD-pQCD(2001)
Point Form - CQM (2001)
Soliton (2002)Light Front - CQM (2002)
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 50
Future GnE Results/ Measurements
Under Analysis
• Jefferson Lab: 2−→H(~e, e′n)p at Q2 = 0.5 and 1.0(GeV/c)2 (E93026)
• Jefferson Lab: D(~e, e′~n)p at Q2 = 0.45, 1.1 and 1.45(GeV/c)2 (E93038)
• Mainz: D(~e, e′~n)p at Q2 =' 0.3, 0.6 and 0.8(GeV/c)2
Future measurements
• Jefferson Lab: 3−→He(~e, e′n)pp up to at Q2 = 3.4(GeV/c)2
• Bates: 2−→H(~e, e′n)p and 3−→He(~e, e′n)pp precisionmeasurements up to Q2 ' 1 (GeV/c)2 with internaltargets and BLAST.
• out to 14 (GeV/c)2 with an upgraded CLAS and the12 GeV upgrade.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 51
Summary
• GnE is related to the charge distribution of the
neutron.
• GnE remains the poorest known of the four nucleon
form factors.
• GnE is a fundamental quantity of continued interest.
• We extracted GnE from beam-target asymmetry
measurements.
• GnE can be described by the Galster parametrization
(surprisingly) and data under analysis is of sufficientquality to test QCD inspired models.
• Future progress likely with new experiments andbetter theory.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 52
Reaction Mechanism Dependence
-0.15
-0.1
-0.05
0
0.05
0.1
100 120 140 160 180 200 220 240
θnpcm (deg)
AedV
BornNN+MECN+MEC+ICN+MEC+IC+REL
Experimental acceptance: 160 deg < θcmnp < 180 deg
Difference between full Calculation andBorn + REL: '8%
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 53
From ε to GnE in Detail
The polarized beam and target electron deuteron cross section can beexpressed in the form:
S(h, Pd1 , P
d2 ) = S0
»1 + hAe + P
d1 A
Vd + P
d2 A
Td
+ h(Pd1 A
Ved + P
d2 A
Ted)
–,
where Ae, AVd , AT
d , AVed, AT
ed are electron asymmetry, vector and tensortarget asymmetries, and electron-deuteron vector and tensor asymmetries.
Comparing with the cross section expression, one can obtain expressions forthe five asymmetries:
Ae =1
2hS0[S(h, 0, 0)− S(−h, 0, 0)] ,
AVd =
1
2P d1 S0
hS(0, P
d1 , P
d2 )− S(0,−P
d1 , P
d2 )i
,
ATd =
1
2P d2 S0
hS(0, P
d1 , P
d2 )− S(0,−P
d1 , P
d2 )− 2S0
i,
AV,Ted
=1
4hP d1/2
S0
(hS(h, P
d1 , P
d2 )− S(−h, P
d1 , P
d2 )i
∓hS(h,−P
d1 , P
d2 )− S(−h,−P
d1 , P
d2 )i)
.
Note that S0 is in the denominator and we never measure S0.
S(+h) + S(−h) 6= S0
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 54
.
ε =(L+ − R+)− (L− − R−)
(L+ + R+) + (L− + R−).
L+ = Φ+nDS(h, P d1 , P d
2 )
L− = Φ−nDS(h,−P d1 , P d
2 )
R+ = Φ+nDS(−h, P d1 , P d
2 )
R− = Φ−nDS(−h,−P d1 , P d
2 )
ε =hh(1− β)Ae + (1 + αβ)P d
1 AVed + (1− βγ)P d
2 ATed
i(1 + β) + (1− αβ)P d
1 AVd
+ (1 + βγ)P d2 AT
d
,
α = −P1−P1+
β =Φ−Φ+
γ =P2(P1−)
P2(P1+)
P d2 = 2−
h4− 3(P d
1 )2i1/2
AVed =
1
h(1 + αβ)P d1
(εh(1 + β) + (1− αβ)P
d1 A
Vd + (1 + βγ)P
d2 A
Td
i
−hh(1− β)Ae + (1− βγ)P
d2 A
Ted
i).
With full φ acceptance Ae, AVd and AT
ed have zero contributions.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 55
ATd remains. For P d
1 = 20%, P d2 ' 3%
with ATd ≈ 10−2AT
d can be ignored
AVed =
ε(1 + β)
h(1 + αβ)P d1
.
With the dilution factor
AVed =
ε(1 + β)
h(1 + αβ)P d1 f
.
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 56
Gen01 Collaboration
A. Aghalaryan, A. Ahmidouch, R. Asaturyan, I. Ben-Dayan, F. Bloch, W. Boeglin, B. Boillat,H. Breuer, J. Brower, C. Carasco, M. Carl, R. Carlini, J. Cha, N. Chant, E. Christy, L. Cole,
L. Coman, M. Coman, D. Crabb, S. Danagoulian, D. Day, K. Duek, J. Dunne, M. Elaasar, R. Ent,J. Farrell, R. Fatemi, D. Fawcett, H. Fenker, T. Forest, K. Garrow, A. Gasparian, I. Goussev,
R. Grima, P. Gueye, M. Harvey, M. Hauger, R. Herrera, B. Hu, I. Jaegle, J. Jourdan, C. Keith,J. Kelly, C. Keppel, M. Khandaker, A. Klein, A. Klimenko, L. Kramer, B. Krusche, S. Kuhn,M. Jones, Y. Liang, J. Lichtenstadt, R. Lindgren, J. Liu, A. Lung, D. Mack, G. Maclachlan,
P. Markowitz, P. McKee, D. McNulty, D. Meekins, J. Mitchell, H. Mkrtchyan, R. Nasseripour,I. Niculescu, K. Normand, B. Norum, A. Opper, E. Piasetzky, J. Pierce, M. Pitt, Y. Prok, B. Raue,
J. Reinhold, J. Roche, D. Rohe, O. Rondon, D. Sacker, N. Savvinov, B. Sawatzky, M. Seely,I. Sick, N. Simicevic, C. Smith, G. Smith, M. Steinacher, S. Stepanyan, J. Stout, V. Tadevosyan,
S. Tajima, L. Tang, G. Testa, R. Trojer, B. Vlahovic, B. Vulcan, K. Wang, G. Warren, S. Wells,F.R. Wesselmann, H. Woehrle, S. Wood, C. Yan, Y. Yanay, L. Yuan, J. Yun, M. Zeier, H. Zhu,
B. ZihlmannDuke University, Florida International University, Hampton University, Jefferson Lab,
Louisiana Tech University, Mississippi State University, Norfolk State University,North Carolina A&T State University, Old Dominion University, Ohio University,Southern University at New Orleans, Tel Aviv University, University of Basel,
University of Maryland at College Park, University of Virginia,Virginia Polytechnic Institute & State University, Vrije Universiteit of Amsterdam,
Yerevan Physics Institute
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 57
Impact of GnM
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
0 0.2 0.4 0.6 0.8 1
Q2(GeV/c)2
GMn
/µn G
D
Mainz(1998)
Mainz(2002)
Jlab(2000)
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 58
Dynamic Nuclear Polarization
Pictorial Representation–Deuteron
+1/2 -1 (f)
+1/2 0 (e)
-1/2 0 (b)
-1/2 +1 (a)
32.7 MHz
140 GHz
M m label
lb
l
-1/2 -1 (c)
+1/2 +1 (d)
NMR
NMR
NMR
NMR
EPR
EPR
EPR
For positive enhancement drive the c → e or b → d transition. Relaxationoccurs through e → b and d → a transition
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 59
NMR system
Magnetic susceptibility is a function of the frequency
χ(ω) = χ′(ω) + iχ′′(ω) consisting of a dispersive part (χ′) and an absorptivepart (χ′′)
P = 2µ0π~γ2NJ
R∞0 χ′′dω
L(ω) = L0[1 + 4πηχ(ω)]
Measure the impedance of coil to get at χ′′
L
C
RCC
RD RA
l/2 Cable
BRM PhaseOut
MagnitudeOut
LengthAdjust
Ref
OutIn
Liverpool Q Meter
RFGenerator
Room TempCryogenic
Target Cavity
50W
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 60
Deposited Energy-ADCs
0
5000
10000
15000
0 2000 4000 60000
5000
10000
15000
20000
0 2000 4000 6000
0
2500
5000
7500
10000
0 2000 4000 60000
2500
5000
7500
10000
0 2000 4000 6000
0
500
1000
1500
0 2000 4000 60000
500
1000
1500
0 2000 4000 6000
Neutrons do not have definite energy deposit due to conversion mechanism.12-14 MeVee
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 61
Dilution Factor and Packing Fraction
df =Rpolarized
Rpolarized + RunpolarizedPf =
VND3
Vcell
Material Source Ni/ND
Nitrogen ND3 0.333Helium (1− Pf) 0.240Helium external 0.080Aluminum Cell in/out 0.015Copper NMR Coil 0.003Nickel NMR Coil 0.001∗∗Carbon Calibration 0.286∗∗Helium Calibration 0.560
ρi ∗ thickness/Ai
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 62
Current Asymmetry
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 63
Cut Optimization
θnq (radian)
0
1000
2000
3000
4000
5000
6000
7000
x 10 2
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
SumDNHeAl
Invariant Mass (MeV/c2)
0
200
400
600
800
1000
1200
x 10 3
750 800 850 900 950 1000 1050 1100 1150 1200 1250
SumDNHeAl
Balancing count rate and dilution factor
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 64
Accidental Background
proton cointime
0
200
400
600
800
1000
1200
x 10 2
-5 0 5 10
neutron cointime
0
2000
4000
6000
8000
10000
-5 0 5 10
• Shape of background is determined by fact that TDC acceptsonly one hit– Randoms/Reals ≈ 4% for neutrons– Acts like dilution for unpolarized randoms
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 65
MC vs Data ND 3
Neutron
ypos (cm)
DataMC
xpos (cm)
E′ (MeV) W (MeV)
θnq (radian) θnpcm (degree)
0
1000
2000
3000
4000
-50 0 500
2000
4000
-50 0 50 100
0
1000
2000
3000
2000 2050 2100 21500
2000
4000
800 900 1000 1100
0
2000
4000
6000
0 0.1 0.2 0.30
1000
2000
3000
160 170 180 190 200
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 66
Proton
ypos (cm)
DataMC
x (cm)
E¢ (MeV) W (MeV)
05000
1000015000200002500030000
-50 0 500
500010000150002000025000300003500040000
-200 -100 0 100
05000
1000015000200002500030000
2000 2050 2100 21500
100002000030000400005000060000
800 900 1000 1100
Florida International/JLAB Workshop on the Deuteron, March 27–29, 2003 67
Recommended