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Higher twist effects in polarized experiments

Higher twist effects in polarized experiments. Nilanga Liyanage University of Virginia (Presented by J. P. Chen) Introduction Precision g 2 n measurements at x ~ 0.2: E97-103 A 1 n , A 2 n and d 2 n results at high x: E99-117 d 2 n and HT from moments-f 2 : GDH experiments

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Higher twist effects in polarized experiments

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  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 < 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. 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 E99-117Precision 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 < 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, 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: d2n=0.0062 ± 0.0028 Can be directly compared with LQCD • PRC 70, 065207 (2004)

  12. Precision g1n and g2n results from E99-117

  13. 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) Second Moment: d2n

  14. 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 (a2+4d2+4f2) SLAC E155x: d2=0.0079(48) +E99-117: d2=0.0062(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

  15. HT extraction for proton World data + -0.043 EG1a data: R. Fatemi et al., PRL, 91 222002 (2003) f2=0.039+0.037 µ6/M4=0.011+ 0.017 - 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=-0.18±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 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 ?

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