1. Higher twist effects in polarized experiments
Nilanga Liyanage
University of Virginia
(Presented by J. P. Chen)
Introduction
Precision g2n measurements at x ~ 0.2: E97-103
A1n, A2n and d2n results at high x: E99-117
d2n and HT from moments-f2: GDH experiments
A2n in the resonance regions: Duality for A2?: E01-012

2. Quark-Gluon Correlations
In simple partonic picture g2(x)=0
Wandzura and Wilczek have shown that g2 can be written in two parts:
twist-2 contributions given by g1
the other originating from quark-gluon correlations (twist-3)

3. A Search for Higher Twist Effects
Jefferson Lab Hall A Experiment E97-103
Precision Measurement of the Neutron Spin Structure Function g2n(x,Q2):
A Search for Higher Twist Effects
T. Averett, W. Korsch (spokespersons) K. Kramer (Ph.D. student)
Precision g2n, 0.57 < Q2 < 1.34 GeV2, W > 2 GeV, at x ~ 0.2.
Direct comparison to twist-2 g2ww prediction using world g1n data.
Quantitative measurement of higher twist effects provides information on
nucleon structure beyond simple parton model (e.g. quark-gluon correlations).

4. Jefferson Lab Hall A Experimental Setup for inclusive polarized n (3He) Experiments

5. Hall A polarized 3He target
Both longitudinal
and transverse

6. E Results: g2n vs. x
Improved precision of g2n by an order of magnitude
Just submitted to nucl-ex , K. Kramer et al.

7. E results: g2n vs. Q2
Measured g2n consistently higher than g2ww

8. E results: g1n
Agree with NLO fit to world data, evolved to our Q2

9. Precision DIS A1n data at high x ;
JLab E Precision Measurement of A1n at Large x Spokespersons: J. P. Chen, Z. -E. Meziani, P. Souder, PhD Student: X. Zheng
Precision DIS A1n data at high x ;
2.7GeV2 < Q2 < 4.8 GeV2, W > 2 GeV
Significant improvement in HT extract from g1n
(Stamenov’s talk)
A2n at high x as a by-product
- Improved d2n by a factor of 2

10. E99-117 A1n Results Precision A1n at high x Comparison calculations
SU(6) symmetry
Valence quark models
pQCD (with HHC) predictions
Other models: Statistical model, Chiral Soliton model, PDF fits, …
Crucial input for pQCD fit to PDF
Crucial input for HT extraction
PRL 92, (2004)

11. A2n results from E99-117 Precision better than the world best results
Also g1n and g2n results
Improved d2n precision by a factor of 2:
d2n= ±
Can be directly compared with LQCD
PRC 70, (2004)

12. Precision g1n and g2n results from E99-117

13. Second Moment: d2n E94-010 (low Q2) (Meziani’s talk) E99-117+SLAC
(high Q2)
Twist-3 matrix element
Color polarizabilities
ChPT (low Q2) and MAID model;
Lattice QCD (high Q2)

14. HT Extraction and Color Polarizabilities: neutron
JLab + world n data,
HT effects extracted:
m4 = ( )M2
m6 = ( )M2
Twist-4 term
m4 = M2/9 (a2+4d2+4f2)
SLAC E155x: d2=0.0079(48)
+E99-117: d2=0.0062(28)
f2 = (total)
f2 = (stat.)
Color polarizabilities
cE =
cB =

15. HT extraction for proton
World data +
f2=
µ6/M4=
-0.043
EG1a data: R. Fatemi et al., PRL, (2003)
Osipenko et al. Phys. Lett. B 609, 258 (2005)

16. HT extraction with Bjorken Sum
eg1a + E data
A. Deur et al. PRL 93, (2004)
f2=-0.18±0.10
µ4/M2=-0.06±0.02
µ6/M4=0.09±0.03

17. Jefferson Lab E01-012
Measurement of neutron (3He) spin structure functions in the resonance region
Spokespersons: N. Liyanage, J. P. Chen, S. Choi; PhD student: P. Solvignon
Measured g1n, A1n, g2n, A2n in the resonance region for 1.0 < Q2 < 4.0 GeV2
Patricia Solvignon’s talk at this workshop

18. Duality in A2 ?
Comparison of A23He in the resonance region from E with DIS results.
A more strict DIS-Resonance comparison possible with JLab at 12 GeV

19. g23He in the resonance region from E01-012

20. JLab precision spin structure data for g2n and A1n, A2n
Summary
JLab precision spin structure data for g2n and A1n, A2n
High precision DIS g2n measurement at low Q2: E97-103
Clear deviation from the twist-2 contribution
Hints for quark-gluon correlations ?
High precision DIS A1n and A2n measurement at high x: E99-117
Best available DIS measurement at high x
Input for HT extract from g1n
Improved d2n precision by a factor of 2
Precision moments at low Q2: GDH experiments
d2n and HT extraction: Twist-4, f2
Resonance region A2n and g2n measurement at high x: E01-012
Duality for A2/g2 ?