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Overview of Nucleon Structure Study

Overview of Nucleon Structure Study . Jian -ping Chen ( 陈剑平 ), Jefferson Lab, Virginia, USA KITPC, Beijing,, China, July, 2012. Introduction: Recent Progress Jefferson Lab ( JLab ) Facility Examples: Nucleon Form Factors Nucleon Spin Structure

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Overview of Nucleon Structure Study

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  1. Overview of Nucleon Structure Study Jian-ping Chen (陈剑平), Jefferson Lab, Virginia, USA KITPC, Beijing,, China, July, 2012 • Introduction: • Recent Progress • Jefferson Lab (JLab) Facility • Examples: Nucleon Form Factors • Nucleon Spin Structure • 3-d Structure of the Nucleon • Near Term Future: JLab 12 GeV Energy Upgrade • Long Term Future : Electron Ion Collider

  2. Introduction Nucleon Structure and Strong Interaction (QCD)

  3. First (Indirect) Evidence of Proton Structure: Anomalous Magnetic Moment • 1933 Otto Stern Magnetic moment of the proton -- expected: mp=eћ/2mpc (since Sp=1/2) -- measured: mp=eћ/2mpc(1+kp)! first ‘spin crisis’ anomalous magnetic moment: kp= 1.5 +- 10% • 1943 Nobel Prize awarded to Stern for ‘development of the molecular beam method’ and ‘the discovery of the magnetic moment of protons’ now: kp=1.792847386 +- 0.000000063 and kn=-1.91304275 +- 0.00000045 GDH Sum Rule (1966) relates an integral of spin structure function to k2 Otto Stern Nobel Prize 1943

  4. Elastic Electron Scattering Discovery: Proton Has Internal Structure ~200 MeV Robert Hofstadter, Nobel Prize 1961 Differential cross section in cm2 / steradian Scattering off a spin-1/2 Dirac particle: The proton has an anomalous magnetic moment, and, hence, internal (spin) structure.

  5. Deep-Inelastic Electron Scattering 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.

  6. QCD Still Unsolved in Non-perturbative Region running coupling “constant” • Strong Interaction strength changes with energy scale  running coupling “constant” • 2004 Nobel prize for ``asymptotic freedom’’ • non-perturbative regime QCD ? confinement • One of the top 10 challenges for physics! • QCD: Important for discovering new physics beyond SM • Nucleon structure is one of the most active areas

  7. Nucleon Structure: A Universe Inside • Nucleon: proton =(uud) , neutron=(udd) + sea + gluons • Global properties and structure: full of surprises Mass: 99% of the visible mass in universe ~1 GeV, but u/d quark mass only a few MeV each! Lattice QCD: vacuum condensation (1 of top 10 discoveries in 2008) Charge and magnetic distributions: very different! Proton charge radius: muonic hydrogen Lamb shift result! (Nature 466, 213 (2010) ) Momentum: quarks carry ~ 50% Spin: ½, but total quarks contribution only ~30%! Spin Sum Rule Magnetic moment: large part is anomalous, >150%! GDH Sum Rule Axial charge Bjorken Sum Rule Tensor charge Orbital angular momentum Recent progress Transverve (3-d) structure: TMDs and GPDs …

  8. Electron Scattering and Nucleon Structure • Clean probe to study nucleon structure only electro-weak interaction, well understood • Elastic Electron Scattering: Form Factors  60s: established nucleon has structure (Nobel Prize) electrical and magnetic distributions • Resonance Excitations  internal structure, rich spectroscopy (new particle search) constituent quark models • Deep Inelastic Scattering  70s: established quark-parton picture (Nobel Prize) parton distribution functions (PDFs) polarized PDFs : Spin Structure Robert Hofstadter, Nobel Prize 1961 J.T. Friedman R. Taylor H.W. Kendall Nobel Prize 1990

  9. F2= 2xF1g2= 0

  10. 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

  11. Parton Distribution Functions (CTEQ6) JHEP 1001: 109 (2010)

  12. Polarized Structure functions

  13. Polarized Parton Distributions DSSV, PRL101, 072001 (2008)

  14. JLab Facility and 12 GeV Energy Upgrade 6 GeV CEBAF, Experimental Halls, Program 12 GeV Upgrade and Program

  15. Thomas Jefferson National Accelerator FacilityNewport News, Virginia, USA • One of two primary USA high-energy nuclear/hadronic physics laboratories • Construction 1984-1995 1st experiment in 1995 last 6 GeV experiment, 2012 • 6 GeV polarized CW electron beam (P = 85%, I = 200 mA) • 3 halls for fixed-target experiments

  16. Thomas Jefferson National Accelerator FacilityNewport News, Virginia, USA 6 GeV polarized CW electron beam Pol=85%, 200mA Will be upgraded to 12 GeV by ~2014 HallA: two HRS’ Hall B:CLAS Hall C: HMS+SOS

  17. add Hall D (and beam line) 12 Upgrade magnets and power supplies CHL-2 Enhance equipment in existing halls 6 GeV JLab

  18. Experimental Halls (new) Hall D: linear polarized photon beam, Selonoiddetetcor GluoX collaboration: exotic meson spectroscopy Hall B: CLAS12 GPDs, TMDs, … Hall C: Super HMS + existing HMS Form factors, structure functions, … Hall A: Dedicated devices + existing spectrometers Super BigBite,SoLID, MOLLER Spectrometer SIDIS (TMDs), PVDIS, …

  19. Nucleon Form Factors Charge and Magnetization Distributions Transverse Density

  20. JLab Data on EM Form Factors Testing Ground for Theories of Nucleon Structure Proton Neutron Electric Magnetic

  21. GEp: JLab Polarization-Transfer Data Using Focal Plane Polarimeter in Hall A • E93-027 PRL 84, 1398 (2000) • E99-007 PRL 88, 092301 (2002) • E04-108, PRL 104, 242301 (2010) Clear discrepancy between polarization transfer and Rosenbluth data • Investigate possible theoretical sources for discrepancy  two-photon contributions Information on the shape of the proton and the orbital angular momentum. Large relativistic effect Transverse density . NYT, May 6, 2003 12 GeV Plan

  22. GEn: 6 GeV Results and 12 GeV Plan • The dramatic turnover of the Argonne DSE model would be clearly visible. • If the turnover is seen, it would provide strong evidence for the importance of diquark degrees of freedom in the nucleon form factors.

  23. Nucleon Spin Structure Valence Quark Distributions Spin Polarizabilities/Color Polarizabilities

  24. Spin Milestones (I) • Nature: (www.nature.com/milestones/milespin) • 1896: Zeeman effect (milestone 1) • 1922: Stern-Gerlach experiment (2) • 1925: Spinning electron (Uhlenbeck/Goudsmit)(3) • 1928: Dirac equation (4) • 1935: Proton anomalous magnetic moment • 1940: Spin–statistics connection(7) • 1946: Nuclear magnetic resonance (NMR)(8) • 1950-51: NMR for chemical analysis (10) 1973: Magnetic resonance imaging(15) • 1975-76:NMR for protein structure determination (16) • 1980s: “Proton spin crisis or puzzle” • 1990: Functional MRI (19) • 1991: Magnetic resonance force microscopy (21) • 1997: Semiconductor spintronics (23) … • 2000s: “Nucleon transverse spin puzzle”?

  25. Three Decades of Nucleon Spin Structure Study • 1980s: EMC (CERN) + early SLAC quark contribution to proton spin is very small DS = (12+-9+-14)% !‘spin crisis’ • 1990s: SLAC, SMC (CERN), HERMES (DESY) DS = 20-30% the rest: gluon and quark orbital angular momentum spin sum rule: (½)DS + Lq + JG =1/2 (Ji) others: Jaffe, Chen et al., … Bjorken Sum Rule verified to <10% level • 2000s: COMPASS (CERN), HERMES, RHIC-Spin, JLab, … : • DS ~ 30%; DGprobably small,orbital angular momentum significant • Valence quark structure, Sum Rules/Polarizabilities • Transversity, Transverse-Momentum Dependent Distributions (TMDs) • Generalized Parton Distributions (GPDs)

  26. JLab Spin Experiments • Results: • Spin in the valence (high-x) region • SSA in SIDIS: Transversity (n)/ TMDs • g2/d2: Higher twists, B-C sum rule • Spin Moments: Spin Sum Rules and Polarizabilities • Quark-Hadron duality • Just completed: • g2pat low Q2 • Future: 12 GeV • Inclusive: A1, d2, • Semi-Inclusive: Transversity, TMDs, Flavor-decomposition • Exclusive: GPDs • Review: Sebastian, Chen, Leader, arXiv:0812.3535, PPNP 63 (2009) 1 J. P. Chen, Int. J. Mod. Phys. E 19, (2010) 1

  27. JLab E99117: Precision Measurement of A1n at High-xSpokespersons: Chen, Meziani, Souder , PhD Student, X. Zheng PRL 92, 012004 (2004) , PRC 70, 065207 (2004) Physics News Update, Science Now Science News, Physics Today Update

  28. pQCD with Quark Orbital Angular Momentum H. Avakian, S. Brodsky, A. Deur, and F. Yuan, PRL 99, 082001 (2007) Inclusive Hall A and B and Semi-Inclusive Hermes BBS BBS+OAM

  29. Planned JLab 12 GeV Experiments A1p at 11 GeV

  30. Spin PolarizabilitiesPreliminary E97-110 (and Published E94-010)Spokesperson: J. P. Chen, A. Deur, F. Garibaldi, plots by V. Sulkosky • Significant disagreement between data and both ChPT calculations for dLT • Good agreement with MAID model predictions g0dLT Q2 Q2

  31. E08-027 : Proton g2 Structure Function Fundamental spin observable has never been measured at low or moderate Q2 Spokespersons: Camsonne, Chen, Crabb, Slifer(contact), 7 PhD students, Completed Data Taking 5/2012 BC Sum Rule Spin Polarizability LT

  32. Jlab 6 GeV Results on Color Polarizbilityd2 E08-027 “g2p” SANE 6 GeV Experiments Sane: completedin Hall C “g2p” in Hall A, Just completed projected “d2n”completedin Hall A

  33. Color Polarizability d2n with JLab 12 GeV Projections with 12 GeV experiments Improved Lattice Calculation (QCDSF, hep-lat/0506017)

  34. 3-D Structure Generalized Parton Distributions Transverse Momentum-Dependent Distributions

  35. Unified View of Nucleon Structure d2kT drz d3r TMD PDFs f1u(x,kT), .. h1u(x,kT)‏ GPDs/IPDs 6D Dist. Wpu(x,kT,r ) Wigner distributions (X. Ji ) 3D imaging dx & Fourier Transformation d2kT d2rT Form Factors GE(Q2), GM(Q2)‏ PDFs f1u(x), .. h1u(x)‏ 1D

  36. 3-D Imaging - Two Approaches TMDs GPDs 2+1 D picture in momentum space 2+1 D picture in impact-parameter space Bacchetta, Conti, Radici QCDSF collaboration • collinear but long. momentum transfer • indicator of OAM; access to Ji’s total Jq,g • existing factorization proofs • DVCS, exclusive vector-meson production • intrinsic transverse motion • spin-orbit correlations- relate to OAM • non-trivial factorization • accessible in SIDIS (and Drell-Yan)

  37. b - Impact parameter T uX(x,b ) u(x,b ) dX(x,b ) d(x,b ) T T T T quark flavor polarization Needs: Hu Eu Ed Hd 3D Images of the Proton’s Quark Content M. Burkardt PRD 66, 114005 (2002) transverse polarized target Accessed in Single Spin Asymmetries.

  38. Quark distribution q(x) Accessed by beam/target spin asymmetry -q(-x) Accessed by cross sections t=0 Access GPDs through DVCS x-section & asymmetries DIS measures at x=0

  39. L = 2x1035 cm-2s-1 T = 1000 hrs DQ2 = 1GeV2 Dx = 0.05 e p epg E = 11 GeV CLAS12-DVCS/BH Target Asymmetry Longitudinally polarized target ~ Ds~sinfIm{F1H+x(F1+F2)H...}df CLAS preliminary AUL E=5.75 GeV <Q2> = 2.0GeV2 <x> = 0.2 <-t> = 0.25GeV2

  40. Transverse Spin: Transversity • Three twist-2 quark distributions: • Momentum distributions: q(x,Q2) = q↑(x) + q↓(x) • Longitudinal spin distributions: Δq(x,Q2) = q↑(x) - q↓(x) • Transversity distributions: δq(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 : δq, 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)

  41. 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

  42. Spokespersons: Chen, Cisbana, Gao, Jiang, Peng;7 Ph D students X. Qian at al., PRL 107:072003(2011) Exploration: Neutron Results with Polarized 3He from 6 GeV JLab Collins asymmetries are not large, except at x=0.34 Sivers negative Blue band: model (fitting) uncertainties Red band: other systematic uncertainties

  43. Neutron Trans-Helicity(Worm-Gear)Study Quark Orbital Angular Momentum • J. Huang et al. PRL (2012) • Dominated by L=0 (S) and L=1 (P) interference • Consist w/ model in signs, suggest larger asymmetry Trans-helictiy Preliminary

  44. SoLID for SIDIS/PVDIS with 12 GeVJLab • Five approved experiments: • three SIDIS “A rated”, one PVDIS “A rated”, one J/Psy “A- rated” • International collaboration: eight countries and 50+ institutions • Strong Chinese participation, USTC, CIAE, Lanzhou, IMP, Tsinghua, Peking, Huangshan, Shandong, HZUST • GEMs: Chinese groups, • UVa. • MRPC: Tsinghua

  45. E12-10-006/E12-11-108, Both Approved with “A” Rating Mapping of Collins(Sivers) Asymmetries with SoLIDSpokespersons: Chen/Gao/Jiang/Peng/Qian (Neutron/3He)Allada/Chen/Gao/Li(CIAE)/Meziani (Proton) • Both p+ and p- • Precision Map in region x(0.05-0.65) z(0.3-0.7) Q2(1-8) PT(0-1.6) • <10% d quark tensor charge Collins Asymmetry

  46. E12-11-107: Worm-gear Functions (“A’ rating: ) Spokespersons: Chen/Huang/Qiang/Yan(USTC) • 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=

  47. 12 GeV Parity Violation Program

  48. 12 GeV PVDIS Sensitivity: C1 and C2 Plots World’s data 6 GeV PVDIS Precision Data PVDIS Qweak Cs

  49. Electron Ion Collider Future QCD Facility: Study QCD Sea and Gluons

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