Transcript n n: d2 and A1 Recent Results and Outlook Diana Parno CENPA, University of Washington 2013 Users’ Group Meeting, Jefferson Lab.

n
n:
d2 and A1 Recent
Results and Outlook
Diana Parno
CENPA, University of Washington
2013 Users’ Group Meeting, Jefferson Lab
Outline
• Deep inelastic scattering and structure functions
• d2 and A1 for the neutron
• E06-014 in Hall A at 6 GeV
• Outlook at 12 GeV
Diana Parno - May 29, 2013
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Deep Inelastic Scattering
k’
k
Incident
electron
Scattered
electron
q
Incident
nucleon
p
Virtual
photon
• Start with a polarized
electron and a polarized
nucleon
• They exchange a virtual
photon
• Virtual photon-nucleon
vertex contains nucleon
structure information
• Inclusive measurement:
only detect scattered
electrons
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Nucleon Structure Functions
• Scattering from a point particle is straightforward:
k’
k
θ
• To describe scattering from a complex structure – like a
nucleon – you need structure functions:
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Polarized Structure Functions
• Now add relative spin orientations to the picture
ù
d 2s ¯Ý d 2s ­Ý 4a 2 E ' é E + E 'cosq
Q2
2
2
= 2 ê
g1 ( x,Q ) g x,Q )ú
2 2(
dWdE ' dWdE ' Q E ë
Mn
Mn
û
• F1(x, Q2) and g1(x, Q2) have simple meanings in the
quark-parton model:
1
F1 (x,Q ) = åei2 éëq-i (x,Q 2 ) + q¯i (x,Q 2 )ùû
2 i
2
1
g1 (x,Q ) = å ei2 éëq-i (x,Q 2 ) - q¯i (x,Q 2 )ùû
2 i
2
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d2
• From g1 and g2, we form the quantity d2 for the nucleon:
d2 (Q ) =
2
ò x ( 2g (x,Q ) + 3g (x,Q ))dx
1
0
2
2
1
2
2
Bag Model
We need precise data at large x
QCD Sum Lattice Chiral Data
Rules
QCD Soliton
• Clean probe of twist-3 physics
(quark-gluon correlations)
• 2σ discrepancy between
lattice prediction and
measurement of neutron d2
d2
Proton
Neutron
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Predictions and Data
6
A1
• Picture the polarizations at the hadron vertex:
Photon spin Nucleon spin
Photon spin Nucleon spin
q
p
q
Opposite helicities: s1/ 2
Same helicities:
s3/2
s1/ 2 - s 3 / 2
A1( x,Q ) º
=
s1/ 2 + s 3 / 2
2
p
g1 (x,Q 2 ) -
Q2
n
2
g2 (x,Q 2 )
F1 (x,Q )
2
»
g1 ( x,Q 2 )
F1 ( x,Q 2 )
• Flavor decomposition of spin structure from A1n and A1p
combined
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More Neutron DIS Data Needed
• ... at Q2 ≈ 5 GeV2 and
large x.
• ... at large x. pQCD predicts
lim A1 (x,Q ) =1
n
2
x®1
d2
A1n
n
x
Q2 (GeV2)
Leader, Sidorov and Stamenov,
PRD 75: 074027 (2007)
Avakian et al, PRL 99: 082001 (2007)
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Outline
• Deep inelastic scattering and structure functions
• d2 and A1 for the neutron
• E06-014 in Hall A at 6 GeV
• Outlook at 12 GeV
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E06-014 in Hall A
•
•
•
•
Feb-Mar 2009
Ee = 4.7 and 5.9 GeV
Inclusive asymmetries
Inclusive cross
Compton
Polarimeter
sections
BigBite
spectrometer
Beam direction
Left high-resolution
Polarized electron
spectrometer
beam
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Polarized 3He
target
10
He Target
~90%
•
•
Polarized 3He Target
~2%
~8%
• 87% of the time, the neutron
carries the 3He nuclear spin
• Polarized 3He target ≈
polarized neutron target
• Hybrid spin-exchange optical pumping
~10 atm 3He cell with trace
of K,
amounts
1.
Polarize
RbRb
via optical pumping
Polarization achieved
2.
Rb-Koptical
interactions
polarize K
pumping
through
and 2-step spin exchange
3. K-3He interactions polarize 3He
» K → Rb
» Rb → 3He
● April 14, 2013
25
Ameya Kolarkar, PhD thesis, 2008
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E06-014 Kinematics
DIS region
Resonance
region
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Preliminary E06-014 Results
• What you will see accounted for:
– Beam polarization
– Target polarization
– N2 dilution in target cell
– Dilution from e+/e- pairs produced in π0 decay
– Basic nuclear corrections (effective polarization model)
• What you won’t see accounted for:
– Radiative corrections (nearly complete)
– Asymmetries from e+/e- pairs
– Some systematics (cut selection, kinematics)
– More sophisticated nuclear corrections
Deconvolution method in progress – Melnitchouk et al.
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x2g1n (d2n integrand)
• Lacks radiative /
pair-production
corrections
• Systematic error
bars will grow
• Preliminary
nuclear-correction
method
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x2g2n (d2n integrand)
• Lacks radiative /
pair-production
corrections
• Systematic error
bars will grow
• Preliminary
nuclear-correction
method
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A1He-3
DIS
Resonance
E06014 (Ee = 5.89 GeV)
E06014 (Ee = 4.74 GeV)
E142
• Lacks radiative /
pair-production
corrections
• Systematic error
bars will grow
• No nuclear
correction yet
E99-117
E01-012 (resonance)
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Outline
• Deep inelastic scattering and structure functions
• d2 and A1 for the neutron
• E06-014 in Hall A at 6 GeV
• Outlook at 12 GeV
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E12-06-121: d2n at 12 GeV
• Ee=11 GeV, upgraded 3He target
• SHMS: large x range at nearly constant Q2
• HMS: fill in gaps at low x
SHMS
HMS
E06-014 kinematics
Diana Parno - May 29, 2013
Approved with A- rating
29 days in Hall C
• Measure d2n at 4
constant Q2 values
• Error at each point
will be comparable
to E06-014
Spokespeople:
T. Averett
W. Korsch
Z.-E. Meziani
B. Sawatzky
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Kinematic coverage of A n1 measurement using HMS and SHMS with a 11 GeV
e higher (lower) Q2 settings correspond to a scattering angle of 30◦ (12.5◦ ).
ch angle setting, the solid (open) markers are for the lower (higher) momentum
Kinematic points with overlapping x and Q2 bins are shifted horizontally for
he error bars are proportional to the expected statistical uncertainties on A n1 .
3
y to match ∆ A n1 (stat.) at the two different Q2 values.
At highest x settings
e
), the smaller angle acceptance of the SHMS is compensated by its large ytar g
e, hence error bars from the SHMS is about the same as those from the HMS.
uncertainties combining the two spectrometers and different kinematics are
ection 4.
E12-06-110: A1n at 12 GeV
• E =11 GeV, upgraded He target
• Simultaneous HMS, SHMS
measurements improve statistics
30°
Approved with A rating
36 days in Hall C
• Precise DIS A1n
measurements from
0.25 ≤ x ≤ 0.77
12.5°
Push to high x
Spokespeople:
G. Cates
J.-P. Chen
Z.-E. Meziani
X. Zheng
Explore Q2 dependence
16
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E12-06-122: A1n at 12 GeV
• Ee=6.6, 8.8 GeV; upgraded
target
• BigBite: Primary measurement
• Left HRS: Cross-check (lower statistics)
3He
Approved with A- rating
23 days in Hall A
• Third set of Q2 values
for interpolation
• Test of open-geometry
measurement
technique
Spokespeople:
T. Averett
G. Cates
N. Liyanage
G. Rosner
B. Wojtsekhowski
X. Zheng
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Conclusions
• DIS measurements of d2n and A1n at large x will
– test Lattice QCD and pQCD
– probe higher-twist effects
– explore nucleon spin structure
• E06-014 data will address these questions
– Stay tuned for final results
• The 12-GeV program will improve the picture even further
– Push to higher x
– Explore Q2 evolution
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The E06-014 Collaboration (Hall A)
K. Allada
W. Armstrong
T. Averett
F. Benmokhtar
W. Bertozzi
A. Camsonne
M. Canan
G. D. Cates
C. Chen
J.-P. Chen
S. Choi
E. Chudakov
F. Cusanno
M. M. Dalton
W. Deconinck
C. W. de Jager
X. Deng
A. Deur
C. Dutta
L. El Fassi
D. Flay
G. B. Franklin
M. Friend
H. Gao
F. Garibaldi
S. Gilad
R. Gilman
O. Glamazdin
S. Golge
J. Gomez
L. Guo
O. Hansen
D. W. Higinbotham
T. Holmstrom
J. Huang
C. Hyde
H. F. Ibrahim
X. Jiang
G. Jin
J. Katich
A. Kelleher
A. Kolarkar
Co-spokesperson
W. Korsch
G. Kumbartzki
J. J. LeRose
R. Lindgren
N. Liyanage
E. Long
A. Lukhanin
V. Mamyan
D. McNulty
Z.-E. Meziani
R. Michaels
M. Mihovilovič
B. Moffit
N. Muangma
S. Nanda
A. Narayan
V. Nelyubin
B. Norum
Nuruzzaman
Y. Oh
D. S. Parno
PhD (in progress)
J. C. Peng
M. Posik
X. Qian
Y. Qiang
A. Rakhman
R. D. Ransome
S. Riordan
A. Saha
B. Sawatzky
M. H. Shabestari
A. Shahinyan
S. Širca
P. Solvignon
R. Subedi
V. Sulkosky
A. Tobias
W. Troth
D. Wang
Y. Wang
B. Wojtsekhowski
X. Yan
H. Yao
Y. Ye
Z. Ye
L. Yuan
X. Zhan
Y. Zhang
Y.-W. Zhang
B. Zhao
X. Zheng
PhD (complete)
Further Acknowledgments
• The DOE Office of Science
• The Accelerator Division
• The “Big Family” collaboration for setup help
• The Transversity
collaboration for many of the
pictures used in this talk
Thank you!
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Backup Slides
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DIS Vocabulary
k’
k
θ
• Let’s define some useful variables in the lab frame
(nucleon rest frame)
Q2 º -q2 = 2EE '(1- cosq )
p×q
nº
= E - E'
M
Q2
Q2
xº
=
2 p × q 2Mn
Four-momentum transfer
Electron energy loss (lab frame)
Bjorken x (momentum fraction)
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Polarized Structure Functions
k’
• Longitudinally polarized beam and target
k
θ
2
ù
d 2s ¯Ý d 2s ­Ý 4a 2 E ' é E + E 'cosq
Q
2
2
= 2 ê
g1 ( x,Q ) g x,Q )ú
2 2(
dWdE ' dWdE ' Q E ë
Mn
Mn
û
• Longitudinally polarized beam and transversely polarized target
é g ( x,Q 2 ) 2Eg ( x,Q 2 ) ù
ds
ds
4a E '
1
2
ê
ú
=
sin
q
cos
f
dWdE ' dWdE '
Q2 E
Mn 2
êë Mn
úû
2
¯Þ
2
­Þ
2
2
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Polarized Electron Beam
• The electrons on target are longitudinally
polarized…but how well polarized are they?
N- - N¯
Pe = N + N¯
• Two measurement methods for E06-014:
• Møller scattering (e-e-
e- e- )
• Destructive measurement
e-γ)
•
Non-destructive measurement
• Circularly polarized photons
• Longitudinally polarized electrons
Diana Parno - May 29, 2013
From Hall A Møller Group
Asymmetry
• Compton scattering
(e-γ
Photon energy
27
BigBite
• 3 multiwire drift chambers
– Tracking
– Momentum
Scattered
particles
Adapted from Xin Qian, PhD thesis, 2010
• Gas Čerenkov
– Exclude pions from
trigger
• 2 lead-glass calorimeters
– Energy
– Particle identification
• Scintillator plane
– Timing
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5.9-GeV Cross Sections
s raw
s Ne-,dil
2
s Ne+,dil
2
s e+
• Radiative
corrections have
not been applied
s corr
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4.7-GeV Cross Sections
s raw
s Ne-,dil
2
s Ne+,dil
2
s e+
• Radiative
corrections have
not been applied
s corr
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