Spin Structure: Longituinal and Transverse

1
Spin Structure Longituinal and Transverse

• J. P. Chen, Jefferson Lab
• JLab User Meeting, June 8, 2009

• Introduction
• Longitudinal and transverse spin
• Selected results from JLab
• Recently completed and planned measurements
• 12 GeV plan
• Thanks to my colleague from spin collaborations
  in Halls A, B, and C
• to allow me to use their slides freely.

2
Strong Interaction and QCD

• Strong interaction, running coupling 1
• -- QCD accepted theory for strong
  interaction
• -- asymptotic freedom (2004 Nobel)
• perturbation calculation works at
  high energy
• -- interaction significant at intermediate
  energy
• quark-gluon correlations
• -- interaction strong at low energy
  (nucleon size)
• confinement
• theoretical tools
• pQCD, OPE, Lattice QCD, ChPT,
• A major challenge in fundamental physics
• Understand QCD in strong interaction
  region
• ? Study and understand nucleon structure

as
E
3
Nucleon Structure and Sum Rules

• Global properties and structure
• Mass 99 of the visible mass in
  universe
• 1 GeV, but u/d quark mass
  only a few MeV each!
• Momentum quarks carry 50
• Spin ½, quarks contribution 30
  Spin Sum Rule
• Magnetic moment large part anomalous,
  gt150 GDH Sum Rule
• Axial charge
  Bjorken Sum Rule
• Angular momentum
  Jis Sum Rule
• Polarizabilities (Spin, Color)
• Tensor charge

4
Three Decades of Spin Structure Study

• 1980s EMC (CERN) early SLAC
• quark contribution to proton spin is very
  small
• DS (12-9-14) ! spin
  crisis
• (Ellis-Jaffe sum rule violated)
• 1990s SLAC, SMC (CERN), HERMES (DESY)
• DS 20-30
• the rest gluon and quark orbital angular
  momentum
• A0 (light-cone) gauge (½)DS Lq DG
  Lg1/2 (Jaffe)
• gauge invariant (½)DS
  Lq JG 1/2 (Ji)
• A new decomposition (X. Chen, et. al)
• Bjorken Sum Rule verified to lt10 level
• 2000s COMPASS (CERN), HERMES, RHIC-Spin, JLab,
  
• DS 30 DG probably small, orbital angular
  momentum probably significant
• Transversity, Transverse-Momentum Dependent
  Distributions
• Generalized Parton Distributions

5
Hall A polarized 3He target

• longitudinal,
• transverse and vertical
• Luminosity1036 (1/s)
• (highest in the world)
• High in-beam polarization
• gt 65
• Effective polarized
• neutron target
• 12 completed experiments
• 1 are currently running
• 6 approved with 12 GeV (A/C)

15 uA
6
Hall B/C Polarized proton/deuteron target

• Polarized NH3/ND3 targets
• Dynamical Nuclear Polarization
• In-beam average polarization
• 70-90 for p
• 30-40 for d
• Luminosity up to 1035 (Hall C)
• 1034 (Hall B)

7
JLab Spin Experiments

• Results
• Moments Spin Sum Rules and Polarizabilities
• Higher twists g2/d2
• Quark-Hadron duality
• Spin in the valence (high-x) region
• Just completed
• d2p (SANE) and d2n
• Transversity (n)
• Planned
• g2p at low Q2, CLAS6 with polarized HD target
• Future 12 GeV
• Inclusive A1/d2,
• Semi-Inclusive Transversity, TMDs,
  Flavor-decomposition
• Review Sebastian, Chen, Leader, arXiv0812.3535
  , PPNP 63 (2009) 1

8
Longitudinal Spin
Spin in Valence (high-x) Region Moments of Spin
Structure Functions Spin Sum Rules Spin
Polarizabilities Quark Hadron Duality
9
Valence (high-x) A1p and A1n results
Hall A E99-117, PRL 92, 012004 (2004)
PRC 70, 065207 (2004)
Hall B CLAS, Phys.Lett. B641 (2006) 11

10
pQCD with Quark Orbital Angular Momentum
F. Yuan, H. Avakian, S. Brodsky, and A. Deur,
arXiv0705.1553
Inclusive Hall A and B and Semi-Inclusive Hermes
BBS
BBSOAM
11
Projections for JLab at 11 GeV
A1p at 11 GeV
12
First Moment of g1p and g1n G1p and G1n
Test fundamental understanding
ChPT at low Q2, Twist expansion at high Q2,
Future Lattice QCD
G1n
G1p
EG1b, arXiv0802.2232 EG1a, PRL 91, 222002
(2003)
E94-010, from 3He, PRL 92 (2004) 022301
E97-110, from 3He, EG1a, from d-p
13
G1 of p-n
EG1b, PRD 78, 032001 (2008) E94-010 EG1a PRL
93 (2004) 212001
14
Effective Coupling Extracted from Bjorken Sum
A. Deur, V. Burkert, J. P. Chen and W. Korsch
PLB 650, 244 (2007) and PLB 665, 349 (2008)
as/p
15
Duality in Spin-Structure Hall A E01-012 Results
G1 resonance comparison with pdfs

• g1/g2 and A1/A2 (3He/n) in resonance region,
• 1 lt Q2 lt 4 GeV2
• Study quark-hadron duality in spin structure.
• ltResonancesgt ltDISgt ?
• PRL 101, 1825 02 (2008)

16
Higher Moments Generalized Spin Polarizabilities

• generalized forward spin polarizability g0
• generalized L-T spin polarizability dLT

17
Neutron Spin Polarizabilities

• dLT insensitive to D resonance
• RB ChPT calculation with resonance for g0 agree
  with data at Q20.1 GeV2
• Significant disagreement between data and both
  ChPT calculations for dLT
• Good agreement with MAID model predictions
• g0
  dLT

E94-010, PRL 93 (2004) 152301
Q2

Q2

18
CLAS Proton Spin Polarizability
g0p
g0p Q6

• EG1b, Prok et al.
• arXiv0802.2232
• Large discrepancies with ChPT!
• Only longitudinal data, model for transverse
  (g2)
• g0 sensitive to resonance

19
Summary of Comparison with cPT

• IAn G1P
  G1n G1p-n
  g0p g0n dLTn
• Q2 (GeV2) 0.1 0.1 0.05 0.1 0.05
  0.16 0.05 0.05 0.1 0.1
• HBcPT poor poor good poor good good
  good bad poor bad
• RBcPT/D good fair fair fair good
  poor fair bad good bad
• dLT puzzle dLT not sensitive to D, one of the
  best quantities to test cPT,
• it disagrees with neither
  calculations by several hundred !
• A challenge to cPT theorists.
• Very low Q2 data g1/g2 on n(3He) (E97-110)
• g1 on p and d
  available soon (EG4)
• Recently approved g2 on proton E08-027

20
New Experiment Proton g2 and ?LT
E08-027 A- rating by PAC33
K. Slifer, A. Camsonne, ,J. P. Chen

• Critical input to Hydrogen Hyperfine Calculations
• Violation of BC Sum Rule suggested at large Q2
• State-of-Art ?PT calcs fail dramatically for ?LT

Septa Magnets for low Q2 Transverse Polarized
Proton Target
n
?LT Spin Polarizability
BC Sum Rule
21
Transverse Spin (I) Inclusive
g2 Structure Function and Moments Burkhardt -
Cottingham Sum Rule Color Polarizability d2
22
g2 twist-3, q-g correlations

• experiments transversely polarized target
• SLAC E155x, (p/d)
• JLab Hall A (n), Hall C (p/d)
• g2 leading twist related to g1 by
  Wandzura-Wilczek relation

• g2 - g2WW a clean way to access twist-3
  contribution
• quantify q-g correlations
  

23
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)

24
BC Sum Rule (from K. Slifer)
0ltXlt1 Total Integral
P
Brawn SLAC E155x Red Hall C RSS Black Hall A
E94-010 Green Hall A E97-110 (preliminary) Blue
Hall A E01-012 (very preliminary)
N
BC Measlow_xElastic
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 (lt5)
25
BC Sum Rule
P
BC satisfied w/in errors for JLab Proton 2.8?
violation seen in SLAC data
N
BC satisfied w/in errors for Neutron
(But just barely in vicinity of Q21!)
3He
BC satisfied w/in errors for 3He
26
Color Polarizability d2 (twist-3)

• 2nd moment of g2-g2WW
• d2 twist-3 matrix element

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?
27
d2(Q2)
BRAND NEW DATA!
Very Preliminary
Proton MAID Model
RED RSS. (Hall C, NH3,ND3)
BLUE E01-012. (Hall A, 3He)
Neutron
GREEN E97-110. (Hall A, 3He)
stat only
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d2(Q2)
E08-027 g2p
SANE
6 GeV Experiments Sane just completed in Hall
C g2p in Hall A, 2011
projected
d2n just completed in Hall A
29
Transverse Spin (II) Single Spin Asymmetries in
SIDIS
Transversity and TMDs
30
Transversity

• Three twist-2 quark distributions
• Momentum distributions q(x,Q2) q?(x) q?(x)
• Longitudinal spin distributions ?q(x,Q2) q?(x)
  - q?(x)
• Transversity distributions dq(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)
• TMDs (without integrating over PT)
• Distribution functions depends on x, k- and Q2
  dq, f1T- (x,k- ,Q2),
• Fragmentation functions depends on z, p- and Q2
  D, H1(x,p- ,Q2)
• Measured asymmetries depends on x, z, P- and Q2
  Collins, Sivers,
• (k-, p- and P- are related)

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Leading-Twist TMD Quark Distributions
Nucleon
Unpol.
Trans.
Long.
Quark
Unpol.
Long.
Trans.
32
E06-010 Single Target-Spin Asymmetry in
Semi-Inclusive n?(e,e'p/-) Reaction on a
Transversely Polarized 3He Target
First neutron measurement 7 PhD Students
Completed data taking 10/08-2/09 exceeded PAC
approved goal
Collins
Sivers
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Hall-A Transversity
en?epX
en?eKX
Polarized 3He effective polarized neutron
target World highest polarized luminosity
1036 New record in polarization gt70 without
beam 65 in beam and with spin-flip (proposal
42)
HRSL for hadrons (p- and K-), new RICH
commissioned BigBite for electrons, 64 msr,
detectors performing well
34
A1 PT-dependence in SIDIS (CLAS6) (Harut Avagyan)
M.Anselmino et al hep-ph/0608048
m020.25GeV2 mD20.2GeV2
0.4ltzlt0.7
x10 fore data is already accumulated in 2009!

• PT-dependence of A1 provides access to
  kT-distributions and widths of f1 and (m0) and
  g1(m2 )
• Data shows slight preference for m0lt m2

35
Measurement of Sivers function and GPD-E at CLAS 6
CLAS6 (25 days-2011)
(DVCS)
(SIDIS)
GPD-E0
DVCS Transverse asymmetry (function of momentum
transfer to proton) is large and has strong
sensitivity to GPD-E
CLAS will provide a measurements of Sivers
asymmetry at large x, where the effect is large
and models unconstrained by previous
measurements.
Meissner, Metz Goeke (2007)
36
3-D Mapping of Collins/Siver Asymmetries at JLab
12 GeVWith A Large Acceptance Solenoid Detector

• Both p and p-
• For one z bin
• (0.5-0.6)
• Will obtain 4
• z bins (0.3-0.7)
• Upgraded PID for K and K-

37
Summary

• Spin structure study full of surprises and
  puzzles
• A decade of experiments from JLab exciting
  results
• valence spin structure, quark-hadron duality
• spin sum rules and polarizabilities
• test cPT calculations, ? dLT puzzle
• precision measurements of g2/d2 high-twist
• first neutron transversity measurement
• JLab played a major role in recent experimental
  efforts
• shed light on our understanding of STRONG QCD
• lead to breakthrough?
• Bright future
• complete a chapter in spin structure study with 6
  GeV JLab
• 12 GeV Upgrade will greatly enhance our
  capability
• Goal a full understanding of nucleon structure
  and strong interaction

38
Measurements on neutron d2n (Hall A and SLAC)
39
Planned d2n with JLab 12 GeV

• Projections with 12 GeV experiments
• Improved Lattice Calculation (QCDSF,
  hep-lat/0506017)

40
Flavor decomposition with SIDIS
Du and Dd at JLab 11 GeV
Polarized Sea