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QCD Evolution and TMD/Spin Experiments

QCD Evolution and TMD/Spin Experiments. J. P. Chen, Jefferson Lab QCD Evolution Workshop, May 14-17, 2012. Introduction SIDIS Transverse Experiments: Transversity and TMDs Q 2 Dependence of the Moments of Spin Structure Functions Evolution and High-Twists.

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QCD Evolution and TMD/Spin Experiments

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  1. QCD Evolution and TMD/Spin Experiments J. P. Chen, Jefferson Lab QCD Evolution Workshop, May 14-17, 2012 • Introduction • SIDIS Transverse Experiments: Transversity and TMDs • Q2 Dependence of the Moments of Spin Structure Functions • Evolution and High-Twists

  2. Experiments < -- > Theory (QCD) • Quarks/Gluons are fundamental degrees of freedom in QCD but they are confined in hadrons experimental observables are on hadrons • Hard process (factorization) example: DIS at high Q2 simplify situation to allow extraction of information on quarks/gluons • Observable depending on probing scale: Q2 power dependence (twists) logarithmic dependence (evolution) • Initial exploration (discovery?) to precision study (full understanding?)

  3. Unpolarized DIS: Discovery of Quarks (Partons) Bjorken Scaling: J.T. Friedman R. Taylor H.W. Kendall Nobel Prize 1990 Callan-Gross relation: Point particles cannot be further resolved; their measurement does not depend on wavelength, hence Q2, Spin-1/2 quarks cannot absorb longitudinally polarized vector bosons and, conversely, spin-0 (scalar) quarks cannot absorb transversely polarized photons.

  4. Unpolarized Structure Function F2 • Bjorken Scaling • Scaling Violation • Gluon radiation – QCD evolution NLO: Next-to-Leading-Order • One of the best experimental tests of QCD

  5. Polarized DIS - Surprises with Spin EMC: J.Ashman et al, Nucl. Phys. B328 (1989) 1 The sum of Quark Spins contribute little to the proton spin, and strange quarks are negatively polarized.

  6. Polarized Structure functions

  7. HERMES Collins/Sivers asymmetry data

  8. COMPASS Sivers asymmetry 2010 data x > 0.032 region - comparison with HERMES results NEW NEW

  9. JLab 12 GeV Projections: Map Collins and Sivers asymmetries in 4-D (x, z, Q2, PT):

  10. Transverse Spin and TMDs SIDIS Experiments with a Transversely Polarized Target

  11. Nucleon Spin Quark Spin Leading-Twist TMD PDFs h1= Boer-Mulders f1 = h1L= Worm Gear Helicity g1 = h1= Transversity f1T= g1T= h1T= Sivers Worm Gear Pretzelosity : Survive trans. Momentum integration

  12. Leading-Twist TMD PDFs Nucleon Spin Quark Spin h1= Boer-Mulders f1 = h1L= Worm Gear Helicity g1 = h1= Transversity f1T= g1T= h1T= Sivers Worm Gear Pretzelosity : Probed with transversely pol target

  13. Status of Transverse Spin Study Large single spin asymmetry in pp->pX (Fermi Lab, RHIC-spin) Collins Asymmetries - sizable for the proton (HERMES and COMPASS) large at high x,p- and p+has opposite sign unfavored Collins fragmentation as large as favored (opposite sign)? - consistent with 0 for the deuteron (COMPASS) Sivers Asymmetries - non-zero for p+ from proton (HERMES), new COMPASS data - consistent with zero for p- from proton and for all channels from deuteron - large for K+? Collins Fragmentation from Belle Global Fits/models: Anselmino, Prokudin et al., Vogelsang/Yuan et al., Pasquini et al., Ma et al., Gamberg et al.… Very active theoretical and experimental efforts Many workshops/conferences to discuss TMDs with QCD, evolution, … RHIC-spin, JLab (6 GeV and 12 GeV), Belle, FAIR, J-PARC, EIC, … First neutron measurement from Hall A 6 GeV (E06-010) SoLID (and CLAS12, …) with polarized 3He/p at JLab 12 GeV Unprecedented precision with high luminosity and large acceptance

  14. Separation of Collins, Sivers and pretzelocity effects through angular dependence

  15. E06‑010 ExperimentSpokespersons: Chen/Evaristo/Gao/Jiang/Peng Luminosity Monitor • First measurement on n (3He) • Polarized 3He Target • Polarized Electron Beam, 5.9 GeV • ~80% Polarization • Fast Flipping at 30Hz • BigBite at 30º as Electron Arm • Pe = 0.7 ~ 2.2 GeV/c • HRSL at 16º as Hadron Arm • Ph = 2.35 GeV/c • Excellent PID for p/K/p • 7 PhD Thesis Students (All graduated) Beam Polarimetry (Møller + Compton)

  16. E06-010 3He Target Single-Spin Asymmetry in SIDIS X. Qian, et al. PRL (2011) 107:072003 (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

  17. Neutron Results with Polarized 3He from JLab X. Qian at al., PRL 107:072003(2011) Collins asymmetries are not large, except at x=0.34 Sivers negative Blue band: model (fitting) uncertainties Red band: other systematic uncertainties

  18. Asymmetry ALT Result J. Huang et al., PRL. 108, 052001 (2012). • 3He ALT : Positive for p- To leading twist:

  19. Neutron ALT Extraction • Corrected for proton dilution, fp • Predicted proton asymmetry contribution < 1.5% (π+), 0.6% (π-) • Dominated by L=0 (S) and L=1 (P) interference • Consist w/ model in signs, suggest larger asymmetry Trans-helictiy

  20. JLab 12 GeV Era: Precision Study of TMDs From exploration to precision study with 12 GeV JLab Transversity: fundamental PDFs, tensor charge TMDs: 3-d momentum structure of the nucleon  Quark orbital angular momentum Multi-dimensional mapping of TMDs 4-d (x,z,P┴,Q2) Multi-facilities, global effort Precision  high statistics high luminosity and large acceptance

  21. SIDIS with SoLID

  22. 12 GeV: Mapping of Collins/Siver Asymmetries with SoLID E12-10-006 3He(n), Spokespersons: J. P. Chen, H. Gao, X. Jiang, J-C. Peng, X. QianE12-11-007(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

  23. Map Collins and Sivers asymmetries in 4-D (x, z, Q2, PT)

  24. Expected Improvement: Sivers Function f1T= • Significant Improvement in the valence quark (high-x) region • Illustrated in a model fit (from A. Prokudin)

  25. E12-11-107: Worm-gear functions (“A’ rating: ) Spokespersons: Chen/Huang/Qiang/Yan • Dominated by real part ofinterference between L=0 (S) and L=1 (P) states • No GPD correspondence • Lattice QCD -> Dipole Shift in mom. space. • Model Calculations -> h1L =? -g1T. h1L= Longi-transversity Trans-helicity Center of points: g1T=

  26. Discussion Unprecedented precision 4-d mapping of SSA Collins and Sivers p+, p- and K+, K- New proposal polarized proton with SoLID Study factorization with x and z-dependences Study PT dependence Combining with the world data extract transversity and fragmentation functions for both u and d quarks determine tensor charge study TMDs for both valence and sea quarks study quark orbital angular momentum study Q2 evolution Global efforts (experimentalists and theorists), global analysis much better understanding of multi-d nucleon structure and QCD Long-term future: EIC to map sea and gluon SSAs

  27. Moments of Spin Structure Functions Q2 Dependence, Evolution and Higher-Twists

  28. Higher-Twist Extraction from Data LSS, polarized PDF (NLO) H-T coefficients MRST, unpolarized PDF H-T coefficients

  29. First Moment of g1p/g1n: G1p /G1n Total quark contribution to nucleon spin (at high Q2) Twist expansion at intermediate Q2, LQCD, ChPT at low Q2 G1p G1n E94-010, PRL 92 (2004) 022301 E97-110, preliminary, EG1a, from d-p EG1b, arXiv:0802.2232 EG1a, PRL 91, 222002 (2003)

  30. Bjorken Sum: G1 of p-n EG1b, PRD 78, 032001 (2008) E94-010 + EG1a: PRL 93 (2004) 212001

  31. Higher Twist (Twist-4 f2) Extraction Color Polarizabilities/Lorentz Force PLB 93 (2004) 212001 • JLab + world neutron data, • m4 = (0.019+-0.024)M2 • Twist-4 term • m4 = (a2+4d2+4f2)M2/9 • extracted from m4 term f2 = 0.034+-0.005+-0.043 • Color polarizabilities/Lorentz force cE = 0.033+-0.029 • cB = -0.001+-0.016 • Proton and p-n (A. Deur) f2= -0.160+-0.028+-0.109 (p), -0.101+-0.027+-0.067 (p-n)

  32. 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

  33. Duality in Spin-Structure: Hall A E01-012 Results G1 resonance comparison with pdfs partial moments • g1/g2 and A1/A2 (3He/n) in resonance region, 1 < Q2 < 4 GeV2 • Study quark-hadron duality in spin structure. <Resonances> = <DIS> ? • PRL 101, 1825 02 (2008)

  34. Second Spin Structure Function g2 d2: Color Polarizability/Lorentz Force Burkhardt - Cottingham Sum Rule

  35. 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)

  36. Color Polarizability /Lorentz Force: d2 • 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

  37. d2 on neutron E01-012

  38. d2(Q2) E08-027 “g2p” SANE 6 GeV Experiments Sane: new in Hall C “g2p” in Hall A, running now projected “d2n” new in Hall A

  39. Burkhardt - Cottingham Sum Rule 0<X<1 :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 (preliminary) N 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 very prelim Elastic: From well know FFs (<5%)

  40. 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 Q2=1!) 3He very prelim BC satisfied w/in errors for 3He

  41. Results on G2n : E01-012 and E94-010

  42. Higher-Twist Extraction and Comparison Extract Higher-Twist part of G2DIS Compare with higher-twist estimated from E97-103 data

  43. E08-027 : Proton g2 Structure Function Fundamental spin observable has never been measured at low or moderate Q2 Spokespersons: Camsonne, Chen, Crabb, Slifer(contact), 6 PhD students, 3 postdocs • BC Sum Rule : violation suggested for proton at large Q2,but found satisfied for the neutron & 3He. • Spin Polarizability: Major failure (>8s) of PT for neutron dLT. Need g2 isospinseparation 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 <Rp> from m-H Lamb shift. Running until 5/18/2012 BC Sum Rule Spin Polarizability LT

  44. Summary • Study quark-gluon structure of nucleon depends on probing scale Q2 Q2dependence provides valuable information on QCD dynamics • TMD study from exploration to precision: Q2 evolution critical • Q2dependence of moments of spin structure g1/g2: • study higher-twists • precision measurements of g2and d2: twist-3 • Extraction of f2: twist-4 d2/f2 cE, cB : Color polarizabilities/Lorentz forces

  45. Announcements • End-of-run (g2p experiment in Hall A) party this afternoon 3-5 pm at CEBAF Center Atrium • KITPC (Kavli Institute for Theoretical Physics China ) Program on Nucleon structure (QCD and Hadron Physics) July 2- 20, 2012, Beijing, China http://kitpc.itp.ac.cn/program.jsp?id=PF20120611 The last week (7/16-7/20) will be for The 4th Workshop on Hadron Physics in China and Opportunities in US http://www.ciae.ac.cn/eng/hadron2012/index.htm • The 7th International Workshop on Chiral Dynamics August 6-10, 2012, JLab http://www.jlab.org/conferences/CD12/

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