Spin Structure with JLab 6 and 12 GeV
J. P. Chen, Jefferson Lab
INT-12-49W: Workshop on Orbital Angular Momentum in QCD, Feb. 6, 2011
 Overview
 Selected Results from JLab 6 GeV
 A1 at High-x: Valence Quark Spin Distributions
 Moments
 g2 /d2: B-C Sum Rule, Color Lorentz Force (Polarizability)
 SIDIS: Transversity and Flavor Decomposition
 Planned experiments with JLab 12 GeV
Introduction
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Spin experiments provide fundamental information
as well as insights into QCD dynamics
Experiments: polarized beams(e, p), polarized targets (p, d, 3He/n)
longitudinal and transverse target polarization
A||, A|_  A1, A2
Ds||, Ds|_  Spin Structure Functions g1(x, Q2), g2(x, Q2)
Role of unpolarized PDFs/ R
Polarized PDFs Dq(x)
LO, NLO,…, QCD evolution,
Higher-twists
Moments, sum rules
High-x, low-x
World data (CERN, SLAC, HERMES, RHIC-spin, JLab, …)
JLab 6 GeV: high-x, low Q2, high-precision. ,
Future :12 GeV
Jefferson Lab Experimental Halls
6 GeV polarized
CW electron beam
Pol=85%, 200mA
HallA: two HRS’
Will be upgraded to
12 GeV by ~2014
Hall B:CLAS
Hall C: HMS+SOS
JLab Polarized
Proton/Deuteron Target
• Polarized NH3/ND3 targets
• Dynamical Nuclear Polarization
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In-beam average polarization
70-90% for p
30-50% for d
• Luminosity ~ 1035 (Hall C/A)
~ 1034 (Hall B)
JLab Polarized 3He Target
60%
15 uA
longitudinal,
transverse and vertical
Luminosity=1036 (1/s)
(highest in the world)
Record high pol ~ 60%
add Hall D
(and beam line)
6 GeV JLab
12
Upgrade magnets
and power supplies
CHL-2
Enhance equipment in
existing halls
Experimental Halls
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(new) Hall D: linear polarized photon beam, Selonoid detetcor
- GluoX collaboration: exotic meson spectroscopy
gluon-quark hybrid, confinement
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Hall B: CLAS12
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GPDs, TMDs, …
Hall C: Super HMS + existing HMS
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Form factors, structure functions (A1n/d2n), …
Hall A: Dedicated devices + existing spectrometers
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Super BigBite, SoLID, MOLLER
SIDIS (transversity/TMDs), PVDIS, …
JLab Spin Experiments
• Results: Published and Preliminary/Upcoming
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Spin in the valence (high-x) region
Spin (g1/g2) Moments: Spin Sum Rules, d2
SSA in SIDIS: Transversity (n)
SSA in Inclusive Reaction
• On-going
• g2p at low Q2
• Future: 12 GeV
• Inclusive: A1/d2,
• Semi-Inclusive: Transversity, Flavor-decomposition
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Reviews: S. Kuhn, J. P. Chen, E. Leader, Prog. Part. Nucl. Phys. 63, 1 (2009)
Valence Quark Spin Structure
A1 at high x and flavor decomposition
Why Are PDFs at High x Important?
• Valence quark dominance: simpler picture
-- direct comparison with nucleon structure models
SU(6) symmetry, broken SU(6), diquark
• x  1 region amenable to pQCD analysis
-- hadron helicity conservation?
role of quark orbit angular momentum?
• Clean connection with QCD, via lattice moments (d2)
• Input for search for new physics at high energy collider
-- evolution: high x at low Q2  low x at high Q2
-- small uncertainties amplified
-- example: HERA ‘anomaly’ (1998)
World data for A1
Proton
Neutron
JLab E99-117
Precision Measurement of A1n at Large x
Spokespersons: J. P. Chen, Z. Meziani, P. Souder; PhD Student: X. Zheng
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First precision A1n data at high x
Extracting valence quark spin
distributions
Test our fundamental understanding
of valence quark picture
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SU(6) symmetry
Valence quark models
pQCD (with HHC) predictions
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Quark orbital angular momentum
Crucial input for pQCD fit to PDF
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PRL 92, 012004 (2004)
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PRC 70, 065207 (2004)
Polarized Quark Distributions
• Combining A1n and A1p results
• Valence quark dominating at
high x
• u quark spin as expected
• d quark spin stays negative!
• Disagree with pQCD model
calculations assuming HHC
(hadron helicity conservation)
• Quark orbital angular momentum
• Consistent with valence quark
models and pQCD PDF fits
without HHC constraint
pQCD with Quark Orbital Angular Momentum
H. Avakian, S. Brodsky, A. Deur, and F. Yuan, PRL 99, 082001 (2007)
Inclusive Hall A and B and Semi-Inclusive Hermes
BBS
BBS+OAM
Preliminary A1(p) Results, Hall C SANE
Spokespersons: S. Choi, M. Jones, Z. Meziani and O. Rondon
Courteous of
O. Rondon
Preliminary A1(3He) Results, Hall A E06-014
Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky
Courteous of
D. Flay
Spin-Structure in Resonance Region: E01-012
Spokesperson: N. Liyanage, J. P. Chen, S. Choi; PhD Student: P. Solvignon
PRL 101, 1825 02 (2008)
G1 resonance vs. pdfs
x Q2
A13He (resonance vs DIS)
x
Projections for JLab at 11 GeV
A1n
at 11 GeV
(Hall C/A)
A1p at 11 GeV
(CLAS12)
Du and Dd at JLab 11 GeV
Polarized Sea
JLab @11 GeV
p multiplicities in SIDIS
ep→e’pX
Hall-C
CLAS 6
DSS (Q2=2.5GeV2)
DSS (Q2=25GeV2)
Moments of Spin Structure Functions
Sum Rules, Polarizabilities
First Moment of g1p : G1p
Total Quark Contribution to Proton Spin (at high Q2)
Twist expansion at intermediate Q2, LQCD, ChPT at low Q2
G 1p
EG1b, arXiv:0802.2232
EG1a, PRL 91, 222002 (2003)
Spokespersons: V. Burkert,
D. Crabb, G. Dodge,
First Moment of g1n : G1n
G 1n
E94-010, PRL 92 (2004) 022301
E97-110, preliminary
EG1a, from d-p
G1 of p-n
EG1b, PRD 78, 032001 (2008)
E94-010 + EG1a: PRL 93 (2004) 212001
Second Spin Structure Function g2
Burkhardt - Cottingham Sum Rule
d2: Color Lorentz Force (Polarizability)
Spin Polarizabilities
Precision Measurement of g2n(x,Q2): Search for Higher Twist Effects
• Measure higher twist  quark-gluon correlations.
• Hall A Collaboration, K. Kramer et al., PRL 95, 142002 (2005)
BC Sum Rule
1
0<X<1 :Total Integral
P
N
Γ 2   g 2 ( x)dx  0
0
Brawn: SLAC E155x
Red: Hall C RSS
Black: Hall A E94-010
Green: Hall A E97-110 (preliminary)
Blue: Hall A E01-012 (spokespersons:
N. Liyanage, former student, JPC)
(preliminary)
BC = Meas+low_x+Elastic
“Meas”: Measured x-range
3He
“low-x”: refers to unmeasured low x part
of the integral.
Assume Leading Twist Behaviour
Elastic: From well know FFs (<5%)
BC Sum Rule
P
BC satisfied w/in errors for JLab Proton
2.8s violation seen in SLAC data
N
BC satisfied w/in errors for Neutron
(But just barely in vicinity of Q2=1!)
3He
BC satisfied w/in errors for 3He
Color Lorentz Force (Polarizability): d2
• 2nd moment of g2-g2WW
d2: twist-3 matrix element
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d 2 (Q )  3 x [ g 2 ( x, Q )  g 2
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2
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WW
( x, Q 2 )]dx
0
1
  x [2 g1 ( x, Q )  3g 2 ( x, Q )]dx
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d2 and g2-g2WW: clean access of higher twist (twist-3) effect: q-g correlations
Color polarizabilities cE,cB are linear combination of d2 and f2
Provide a benchmark test of Lattice QCD at high Q2
Avoid issue of low-x extrapolation
Relation to Sivers and other TMDs
d2(Q2)
E08-027 “g2p”
SANE
projected
6 GeV Experiments
Sane: new in Hall C
“g2p” in Hall A, 2011
“d2n” new in Hall A
Preliminary results on neutron from E01-012
Spokespersons: J. P. Chen, S. Choi, N. Liyanage, plots by P. Solvignon
Preliminary A2(p) Results, Hall C SANE
Spokespersons: S. Choi, M. Jones, Z. Meziani and O. Rondon
Courteous of
O. Rondon
Projection on d2p from Hall C SANE
Projection on Hall A E06-014 (d2n)
Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky
Courteous of
D. Flay
E08-027 : Proton g2 Structure Function
Fundamental spin observable has never been measured at low or moderate Q2
Spokespersons: A. Camsonne, J. P. Chen, D. Crabb, K. Slifer, 6 PhD students
BC Sum Rule : violation suggested for proton at large Q2, but found satisfied for the neutron & 3He.
Spin Polarizability : Major failure (>8s) of cPT for neutron dLT. Need g2 isospin separation to solve.
Hydrogen HyperFine Splitting : Lack of knowledge of g2 at low Q2 is one of the leading uncertainties.
Proton Charge Radius : also one of the leading uncertainties in extraction of <R p> from mH Lamb shift.
Spin Polarizability dLT
BC Sum Rule
Scheduled to run 2/2012-5/2012
Spin Polarizabilities
Preliminary E97-110 (and Published E94-010)
Spokesperson: J. P. Chen, A. Deur, F. Garibaldi, plots by V. Sulkosky
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Significant disagreement between data and both ChPT calculations for dLT
Good agreement with MAID model predictions
g0
dLT
Q2
Q2
Single Target-Spin Asymmetries in SIDIS
Transversity/Tensor Charge
Transversity
• Three twist-2 quark distributions:
• Momentum distributions: q(x,Q2) = q↑(x) + q↓(x)
• Longitudinal spin distributions: Δq(x,Q2) = q↑(x) - q↓(x)
• Transversity distributions: δq(x,Q2) = q┴(x) - q┬(x)
• It takes two chiral-odd objects to measure transversity
• Semi-inclusive DIS
Chiral-odd distributions function (transversity)
Chiral-odd fragmentation function (Collins function)
E06-010
3He
Target Single-Spin Asymmetry in SIDIS
Spokespersons: J. P. Chen, E. Cisbani, H. Gao, X. Jiang, J-C. Peng, 7 PhD students
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He-(e, e'h), h = p +, p -
X. Qian, et al. PRL (2011)
3He
Collins SSA small
Non-zero at highest x for p+
3He
Sivers SSA:
negative for π+,
Blue band: model (fitting) uncertainties
Red band: other systematic uncertainties
Results on Neutron
Collins
asymmetries are not
large, except at x=0.34
Sivers
p + (ud ) negative
Blue band: model (fitting) uncertainties
Red band: other systematic uncertainties
12 GeV: Mapping of Collins Asymmetries with SoLID
E12-10-006 3He(n), Spokespersons: J. P. Chen, H. Gao, X. Jiang, J-C. Peng, X. Qian
E12-11-007(p) , Spokespersons: K. Allda, J. P. Chen, H. Gao, X. Li, Z-E. Mezinai
• Both p+ and p• For one z bin
(0.4-0.45)
• Will obtain
many z bins
(0.3-0.7)
• Tensor charge
Summary
• Spin structure study full of surprises and puzzles
• A decade of experiments from JLab: exciting results
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valence spin structure
precision measurements of g2/d2: high-twist
spin sum rules and polarizabilities
first neutron transversity
• Bright future
• 12 GeV Upgrade will greatly enhance our capability
• Precision determination of the valence quark spin structure
flavor separation
• Precision measurements of g2/d2
• Precision extraction of transversity/tensor charge