Higher twist effects in polarized experiments

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
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 lt Q2 lt 1.34 GeV2, W gt 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
E97-103 Results g2n vs. x

• Improved precision of g2n by an order of
  magnitude
• Just submitted to nucl-ex 0506005, K. Kramer et
  al.

7
E97-103 results g2n vs. Q2

• Measured g2n consistently higher than g2ww

8
E97-103 results g1n

• Agree with NLO fit to world data, evolved to our
  Q2

9
JLab E99-117 Precision Measurement of A1n at
Large xSpokespersons J. P. Chen, Z. -E.
Meziani, P. Souder, PhD Student X. Zheng

• Precision DIS A1n data at high x
• 2.7GeV2 lt Q2 lt 4.8 GeV2, W gt 2 GeV
• Significant improvement in HT extract from g1n
• (Stamenovs 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, 012004 (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
• d2n0.0062 0.0028
• Can be directly compared with LQCD
• PRC 70, 065207 (2004)

12
Precision g1n and g2n results from E99-117

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Second Moment d2n

• E94-010 (low Q2) (Mezianis talk)
• E99-117SLAC
• (high Q2)
• Twist-3 matrix element
• Color polarizabilities
• ChPT (low Q2) and MAID model
• Lattice QCD (high Q2)

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HT Extraction and Color Polarizabilities neutron

• JLab world n data,
• HT effects extracted
• m4 (0.019-0.024)M2
• m6 (-0.019-0.017)M2
• Twist-4 term
• m4 M2/9 (a24d24f2)
• SLAC E155x d20.0079(48)
• E99-117 d20.0062(28)
• f2 0.034-0.043 (total)
• f2 0.033-0.005 (stat.)
• Color polarizabilities
• cE 0.033-0.029
• cB -0.001-0.016

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HT extraction for proton

• f20.0390.037
• µ6/M40.011 0.017

World data
-0.043
EG1a data R. Fatemi et al., PRL, 91 222002 (2003)
- 0.013
Osipenko et al. Phys. Lett. B 609, 258 (2005)
16
HT extraction with Bjorken Sum

eg1a E94-010 data A. Deur et al. PRL 93, 212001
(2004)
f2-0.180.10 µ4/M2-0.060.02 µ6/M40.090.03
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 lt Q2 lt 4.0 GeV2
• Patricia Solvignons talk at this workshop

18
Duality in A2 ?

• Comparison of A23He in the resonance region from
  E01-012 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
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 ?