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Published on October 12, 2007

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Spin Structure: Puzzles and Progress:  Spin Structure: Puzzles and Progress J. P. Chen, Jefferson Lab Hall A Collaboration Meeting, Jan. 4-5, 2007 Introduction: ‘Spin Crises’ or ‘Puzzles’ Spin Sum Rules: (Generalized) GDH, Bjorken, B-C, … Polarizabilities: Spin (dLT puzzle), Color (q-g correlations) Higher-twist Effects (q-g, q-q correlations) Duality in Spin Structure Polarized Parton Distributions at High-x New Vista: Transversity and TMDs Summary Nucleon Structure and QCD:  Nucleon Structure and QCD Success of the Standard Model electro-weak and QCD in high energy (short distance) region tested Major challenges: -- understand QCD in the strong interaction region (distance of the nucleon size) -- understand the nucleon structure Strong interaction, running coupling ~1 -- asymptotic freedom (2004 Nobel) perturbation calculation works at high energy -- interaction significant at intermediate energy quark-gluon correlations -- confinement interaction strong at low energy coherent hadron -- Chiral symmetry -- theoretical tools: pQCD, OPE, Lattice QCD, ChPT Spin Structure Study: new dimensions -- study QCD and nucleon structure -- very rich program: ‘crises’ and ‘puzzles’ Spin and Magnetic Moment (of electron):  Spin and Magnetic Moment (of electron) 1921 Otto Stern and Walther Gerlach Ag molecular-beam passing through inhomogeneous magnetic field split into two beams Ag atom has a magnetic moment Bohr magneton of the electron: me =eћ/2mec 1925 Uhlenbeck and Goudsmit spin: internal property, like angular momentum electron spin Se=1/2  two eigenstates +- 1/2 Dirac: relativistic effect: spin  magnetic moment electron is point-like particle (no internal structure observed so far) Anomalous Magnetic Moment (of Proton):  Anomalous Magnetic Moment (of Proton) 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 (a.m.m) 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 A.M.M and Its Implications:  A.M.M and Its Implications Anomalous magnetic moment is an evidence for an internal structure  finite size Finite size  Form factors Dirac form factor: normal relativistic effect Pauli form factor: relate to a.m.m. part Finite size   Excitation spectrum GDH Sum Rule relates a.m.m. to integral of excitation spectrum Theoretical Explanation of A.M.M.:  Theoretical Explanation of A.M.M. 1930s-1950s Pion cloud models kp/kn = -1/7 too small 1960s Quark models SU(3)color x SU(6)spin-flavor Symmetry kp/kn = -1.5 very close to experiment -1.46 small corrections due to orbital angular momentum 1990s Lattice QCD kp=1.85+-0.22, kn =-1.44+-0.11 2000s multi-dimension structure of nucleon A.M.M < -- > related to GPDs, TMDs through quark orbital angular momentum ‘Spin Crisis’ or ‘Spin Puzzle’:  ‘Spin Crisis’ or ‘Spin Puzzle’ 1980s: EMC (CERN) + early SLAC (E80/E130) quark contribution to proton spin is very small DS = (12+-9+-14)% ! ‘spin crisis’ (Ellis-Jaffe sum rule violated) 1990s: SLAC (E142/E143/E154/E155), SMC (CERN), HERMES (DESY) DS = 20-30% the rest: gluons (DG) and quark orbital angular momentum (L) (½)DS + DG + L =1/2 Bjorken Sum Rule verified to 5-10% level 2000s: COMPASS (CERN), RHIC-Spin, HERMES, JLab, … : DS ~ 30%; DG small, L is probably significant GDH and B-C sum rules, spin polarizabilities Higher-twist effects: q-g correlations Transverse spin Slide9:  F2 = 2xF1 g2 = 0 Unpolarized and Polarized Structure functions :  Unpolarized and Polarized Structure functions Unpolarized Parton Distributions (CTEQ6):  Unpolarized Parton Distributions (CTEQ6) After 40 years DIS experiments, unpolarized structure of the nucleon reasonably well understood. High x  valence quark dominating NLO Polarized Parton Distributions (AAC06):  NLO Polarized Parton Distributions (AAC06) JLab Spin Structure Experiments :  JLab Spin Structure Experiments Inclusive, Low-Intermediate Q2 : JLab Hall A: neutron/3He, longitudinal and transverse Generalized GDH, E94-110, Q2 range 0.1 - 1 GeV2 Small Angle GDH, E97-110, Q2 range 0.02 – 0.3 GeV2 E97-113: g2n at Q2 of 0.5-1.5 GeV2, higher-twist E99-117: A1n at high x, Spin Duality (E01-012): Q2 from 1-4 GeV2 JLab Hall B : proton/deuteron, longitudinal EG1a/EG1b, Q2 range 0.05 - 4 GeV2 EG4: Q2 range 0.015 – 0.5 GeV2 JLab Hall C: proton/deuteron, longitudinal and transverse RSS: <Q2> = 1.3 GeV2 Semi-inclusive: transversity, flavor decomposition,…. Slide14:  Jefferson Lab Experimental Halls HallA: two HRS’ Hall B:CLAS Hall C: HMS+SOS 6 GeV pol. e beam Pol=85%, 100mA Slide15:  Hall A polarized 3He target Both longitudinal, transverse and vertical Luminosity=1036 (1/s) (best in the world) High in-beam polarization > 50% Effective polarized neutron target 7 completed experiments 5 approved with 6 GeV JLab 3 approved with 12 GeV (A/C) Hall B/C Polarized proton/deuteron target:  Hall B/C Polarized proton/deuteron target Polarized NH3/ND3 targets Dynamical Nuclear Polarization In-beam average polarization 70-80% for p 20-40% for d Luminosity up to ~ 1035 (Hall C) ~ 1034 (Hall B) Slide17:  Spin Sum Rules and Polarizabilities Moments of Spin Structure Functions Gerasimov-Drell-Hearn Sum Rule Circularly polarized photon on longitudinally polarized nucleon :  Gerasimov-Drell-Hearn Sum Rule Circularly polarized photon on longitudinally polarized nucleon A fundamental relation between the nucleon spin structure and its anomalous magnetic moment Based on general physics principles Lorentz invariance, gauge invariance  low energy theorem unitarity  optical theorem casuality  unsubtracted dispersion relation applied to forward Compton amplitude First measurement on proton up to 800 MeV (Mainz) and up to 3 GeV (Bonn) agree with GDH with assumptions for contributions from un-measured regions Generalized GDH Sum Rule:  Generalized GDH Sum Rule Many approaches: Anselmino, Ioffe, Burkert, Drechsel, … Ji and Osborne, a rigorous generalization Forward Virtual-Virtual Compton Scattering Amplitudes: S1(Q2,n), S2(Q2, n) (or alternatively, gTT(Q2,n), gLT(Q2,n)) Same assumptions: no-subtraction dispersion relation optical theorem (low energy theorem) Generalized GDH Sum Rule For v=0 Connecting GDH with Bjorken Sum Rules:  Connecting GDH with Bjorken Sum Rules Q2-evolution of GDH Sum Rule provides a bridge linking strong QCD to pQCD Bjorken and GDH sum rules are two limiting cases High Q2, Operator Product Expansion : S1(p-n) ~ gA  Bjorken Q2  0, Low Energy Theorem: S1 ~ k2  GDH Operator Product Expansion of higher twists: > ~1 GeV2 Intermediate region: Lattice QCD calculations Chiral Perturbation Theory: < ~0.1 GeV2? Calculations: Bernard, Hemmert, Meissner, RBcPT with D; Ji, Kao, Osborne; Kao, Spitzenberg, Vanderhaeghen, HBcPT Sum Rules and Polarizabilities:  Sum Rules and Polarizabilities Drechsel, Pasquini, Vanderhaeghen, Phys. Rep. 378,99 (2003) Drechsel, Tiator, Annu. Rev. Nucl. Part. Sci. 54, 69 (2004) Chen, Deur, Meziani, Mod. Phy. Lett. A 20, 2745 (2005) Consider Forward Spin-flip VVCS Amplitude (or ) low energy expansion dispersion relation expand RHS, term-by-term  GDH sum, polarizability, … JLab E94-010 Neutron spin structure moments and sum rules at Low Q2 Spokespersons: G. Cates, J. P. Chen, Z.-E. Meziani PhD Students: A. Deur, P. Djawotho, S. Jensen, I. Kominis, K. Slifer:  JLab E94-010 Neutron spin structure moments and sum rules at Low Q2 Spokespersons: G. Cates, J. P. Chen, Z.-E. Meziani PhD Students: A. Deur, P. Djawotho, S. Jensen, I. Kominis, K. Slifer Q2 evolution of spin structure moments and sum rules (generalized GDH, Bjorken and B-C sum rules) transition from quark-gluon to hadron Check cPT calculations Results published in five PRL/PLB New results on 3He GDH integral on neutron PRL 89 (2002) 242301 Q2 New Hall A 3He Results (preliminary):  New Hall A 3He Results (preliminary) GDH integral IA G1 2 Q2 evolution of moments of 3He spin structure functions Test Chiral Perturbation Theory predictions at low Q2 need cPT calculations for 3He Slide24:  G2: 1st moment of g2 for 3He and neutron Q2 evolution of G23He and G2n B-C sum rule satisfied within uncertainties E94-010, PRL 92 (2004) 022301 G23He G2n E94-010, preliminary Hall B EG1b Preliminary Results: G1p Plots from G. Dodge spokespersons: V. Burkert, D. Crabb, G. Dodge, S. Kuhn, R. Minehart, M. Taiuti:  Hall B EG1b Preliminary Results: G1p Plots from G. Dodge spokespersons: V. Burkert, D. Crabb, G. Dodge, S. Kuhn, R. Minehart, M. Taiuti EG1b preliminary and EG1a, PRL 91: 222002 (2003) G1p Moments of neuton and p-n plots from A. Deur:  Moments of neuton and p-n plots from A. Deur Hall B EG1b preliminary and Hall A E94-010 PRL 92 (2004) 022301 EG1b preliminary and Hall A + Hall B EG1a: PRL 93 (2004) 212001 p-n neutron Generalized Spin Polarizabilities:  Generalized Spin Polarizabilities Consider Spin-flip VVCS amplitudes: gTT(Q2,n), gLT(Q2,n) Low-energy expansion, the O(n3)term gives generalized forward spin polarizability, g0 , and generalized longitudinal-tranverse spin polarizability, dLT Neutron Spin Polarizabilities:  Neutron Spin Polarizabilities ChPT expected to work at low Q2 (up to ~ 0.1 GeV2?) g0 sensitive to resonance, dLT insensitive to D resonance E94-010 results: PRL 93 (2004) 152301 RB ChPT calculation with resonance for g0 agree with data at Q2=0.1 GeV2 Significant disagreement between data and both ChPT calculations for dLT Good agreement with MAID model predictions g0 dLT Q2 Q2 Summary of Comparison with cPT:  Summary of Comparison with cPT IAn G1P G1n G1p-n g0n dLTn Q2 (GeV2) 0.1 0.1 0.05 0.1 0.05 0.16 0.05 0.1 0.1 HBcPT (NL) poor poor good poor good good good poor bad RBcPT(NL)/D good fair fair fair good poor fair good bad Q2 ~0.1 GeV2 is too high for HBcPT? 0.05 is good? RBcPT(NL) with D reasonable to Q2 ~ 0.1? dLT puzzle: dLT not sensitive to D, one of the best quantities to test cPT, it disagrees with neither calculations by several hundred %! Very low Q2 data on n(3He), p and d available soon (E97-110, EG4) Need NNL O(P5)? Kao et al. are working on that. A challenge to cPT theorists. JLab E97-110 GDH Sum Rule and Spin Structure of 3He and Neutron with Nearly Real Photons Spokespersons: J. P. Chen, A. Deur, F. Garibaldi; PhD Students: J. Singh, V. Sulkosky, J. Yuan:  JLab E97-110 GDH Sum Rule and Spin Structure of 3He and Neutron with Nearly Real Photons Spokespersons: J. P. Chen, A. Deur, F. Garibaldi; PhD Students: J. Singh, V. Sulkosky, J. Yuan Measured generalized GDH at Q2 near zero for 3He and neutron Slope at Q2 ~ 0 Benchmark test of ChPT Data taken in 2003 Analysis underway Preliminary asymmetries and cross sections available See J. Singh’s talk Hall B EG4 Projected Results Spokespersons: M. Battaglieri, R. De Vita, A. Deur, M. Ripani:  Hall B EG4 Projected Results Spokespersons: M. Battaglieri, R. De Vita, A. Deur, M. Ripani Extend to very low Q2 of 0.015 GeV2 longitudinal polarization  g1p, g1d Benchmark test of cPT Data taking in 2006. dLT Puzzle:  dLT Puzzle Possible reasons for dLT puzzle: discussions with theorists B. Holstein: A real challenge to (cPT) theorists! Ulf-G. Meissner: Don’t know now. Need to work on it. T. Hemmert: Speculation: Short range effects beyond pN? Kochelev/Vanderhaegen: t-channel axial vector meson exchange? Isoscalar in nature? C. Weiss: An efffect of QCD vacuum structure? To solve the puzzle and to understand the nature of the problem, need isospin separation  need measurement on proton Does the discrepancy also exists for proton? New proposal to measure dLT on proton (K. Slifer’s talk) Hall C RSS Preliminary Results on G1p and G2p from K. Slifer (Spokesperons: M. Jones, O. Rondon) :  Hall C RSS Preliminary Results on G1p and G2p from K. Slifer (Spokesperons: M. Jones, O. Rondon) Q2=1.3 GeV2, G1p consistent with Hall B results G2p = 0, satisfy B-C sum rule G1p G2p Hall A E01-012 Preliminary Results: G1n:  Hall A E01-012 Preliminary Results: G1n Spokesperson: N. Liyanage, J. P. Chen, S. Choi, PhD Student: P. Solvignon g1/g2 and A1/A2 (3He/n) in resonance region, 1 < Q2 < 4 GeV2 Study quark-hadron duality in spin structure. P. Solvignon’s talk G1n G1n resonance comparison with pdfs Q2 Q2 Slide35:  g2, d2 and f2: Higher Twists Quark-gluon Correlations and Color Polarizabilities Nucleon Structure Beyond Simple Parton Models:  Nucleon Structure Beyond Simple Parton Models Interaction important at intermediate to low Q2 quantify the interaction 1st step beyond parton models: quark-gluon correlations how to measure q-g correlations? In QCD framework: Operator Product Expansion  1/Q expansion (twist expansion) twist t is related to (mass dimension – spin) mt contains twist-t matrix elements Twist-2 and Twist-3:  Twist-2 and Twist-3 -- twist-2: parton (quark, gluon) distributions -- no interactions -- twist-3: quark-gluon correlations -- one gluon one additional 1/Q g2: twist-3, q-g correlations:  g2: twist-3, q-g correlations experiments: transversely polarized target SLAC E155x, (p/d) JLab Hall A (n), C (p/d) g2 leading twist related to g1 by Wandzura-Wilczek relation g2 - g2WW: a clean way to access twist-3 contribution quantify q-g correlations Slide39:  Jefferson Lab Hall A E97-103 Precision Measurement of g2n(x,Q2): Search for Higher Twist Effects T. Averett, W. Korsch (spokespersons) K. Kramer (Ph.D. student) Improve g2n precision by an order of magnitude. Measure higher twist  quark-gluon correlations. JLab Hall A Collaboration, K. Kramer et al., PRL (2006) E97-103 results: g2n vs. Q2:  E97-103 results: g2n vs. Q2 measured g2n consistently higher than g2ww: positive twist-3 higher twist effects significant below Q2=1 GeV2 Models (color curves) predict small or negative twist-3 Bag Model Soliton Models Color Polarizability: d2 (twist-3):  Color Polarizability: d2 (twist-3) 2nd moment of g2-g2WW d2: twist-3 matrix element Color polarizabilities cE,cB are linear combination of d2 and f2 q-g correlations Provide a benchmark test of Lattice QCD at high Q2 cPT and Model (MAID) at low Q2 Avoid issue of low-x extrapolation Measurement on proton: d2p (Hall C and SLAC):  Measurement on proton: d2p (Hall C and SLAC) d2p Q2 Measurements on neutron: d2n (Hall A and SLAC):  Measurements on neutron: d2n (Hall A and SLAC) Planned d2n with JLab 6 GeV and 12 GeV (from B. Sawatzky):  Planned d2n with JLab 6 GeV and 12 GeV (from B. Sawatzky) Projections with planned 6 GeV and 12 GeV experiments Improved Lattice Calculation (QCDSF, hep-lat/0506017) JLab 12 GeV Projection for x2g2n:  JLab 12 GeV Projection for x2g2n Solenoid (100 hours) SHMS+HMS (500 hours) (W. Korsch) d2n with JLab 12 GeV:  d2n with JLab 12 GeV Projection with Solenoid, Statistical only Improved Lattice Calculation (QCDSF, hep-lat/0506017) Twist-4 Extraction and Color Polarizabilities:  Twist-4 Extraction and Color Polarizabilities JLab + world neutron data, higher-twist 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) f2 = 0.034+-0.043 (total) or f2 = 0.033+-0.005 (stat.) Color polarizabilities cE = 0.033+-0.029 cB = -0.001+-0.016 p and p-n (eg1 + E94-010) f2= -0.160+-0.179 (p) -0.136+-0.109 (p-n) f2 can be accessed through parity violating spin structure function g3 Slide48:  Valence Quark Spin Structure A1 at high x and flavor decomposition Slide49:  JLab E99-117 Precision Measurement of A1n at Large x Spokespersons: J. P. Chen, Z. -E. Meziani, P. Souder, PhD Student: X. Zheng First precision A1n data at high x Extracting valence quark spin distributions Test our fundamental understanding of valence quark picture SU(6) symmetry Valence quark models pQCD (with HHC) predictions Quark orbital angular momentum Crucial input for pQCD fit to PDF PRL 92, 012004 (2004) PRC 70, 065207 (2004) Polarized Quark Distributions:  Polarized Quark Distributions Combining A1n and A1p results Valence quark dominating at high x u quark spin as expected d quark spin stays negative! Disagree with pQCD model calculations assuming HHC (hadron helicity conservation) Quark orbital angular momentum Consistent with valence quark models and pQCD PDF fits without HHC constraint Slide51:  BigBite (8.8 GeV) HMS+SHMS (11 GeV) 1800 hours (X. Zheng) Solenoid, 200 hours Slide52:  Semi-inclusive Deep Inelastic Scattering Transversity and TMDs Leading-Twist Quark Distributions:  Leading-Twist Quark Distributions No K┴ dependence K┴ - dependent, T-odd K┴ - dependent, T-even ( A total of eight distributions) Transversity:  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) Slide55:  AUTsin() from transv. pol. H target Simultaneous fit to sin( + s) and sin( - s) `Collins‘ moments Non-zero Collins asymmetry Assume dq(x) from model, then H1_unfav ~ -H1_fav Need independent H1 (BELLE) `Sivers‘ moments Sivers function nonzero (p+) orbital angular momentum of quarks Regular flagmentation functions Current Status:  Current Status Collins Asymmetries - sizable for proton (HERMES) large at high x, large for p- p- and p+ has opposite sign unfavored Collins fragmentation as large as favored (opposite sign)? - consistent with 0 for deuteron (COMPASS) Sivers Asymmetries - non-zero for p+ from proton - consistent with zero for p- from proton and for all channels from deuteron - large for K+ Very active theoretical and experimental study RHIC-spin (PHENIX, STAR, BRAHMS), JLab (Hall A 6 GeV, CLAS12, …), KEK (Belle), GSI FAIR (PAX) Fits/models by Anselmino et al., Yuan et al. and other groups Solenoid with polarized 3He at JLab 12 GeV Unprecedented precision with high luminosity and large acceptance E06-010/06-011 Single Target-Spin Asymmetry in Semi-Inclusive n↑(e,e′π+/-) Reaction on a Transversely Polarized 3He Target:  E06-010/06-011 Single Target-Spin Asymmetry in Semi-Inclusive n↑(e,e′π+/-) Reaction on a Transversely Polarized 3He Target Collins Sivers Spokespersons: Xiaodong Jiang, Jian-ping Chen, Evaristo Cisbani, Haiyan Gao, Jen-Chieh Peng Students: K. Allada, C. Dutta, X. Qian, M. Shabestari, One from UIUC. See K. Allada and C. Dutta’ talks Collins and Sivers Asymmetries at 12 GeV :  Collins and Sivers Asymmetries at 12 GeV Projections with MADII (1200 hours) for neutron by L. Zhu Summed over two other variables (z, PT) Similar precision with SHMS/HMS Hall B 12GeV (p), better precision, still summed over Need much higher precision data to study 3-d (x, z and PT) dependence High luminosity AND large acceptance 12 GeV baseline equipment will have either high luminosity (Hall C/A) or large acceptance (Hall B) p- p+ Collins Sivers Solenoid detector for SIDIS:  3He target Solenoid detector for SIDIS GEMs Gas Cerenkov Calorimeter GEMs Spin Structure with the Solenoid at JLab 12 GeV:  Spin Structure with the Solenoid at JLab 12 GeV DIS-PV needs Solenoid (luminosity: 5x1038 , acceptance ~ 300 msr) Test SM, study hadronic physics: Charge Symmetry, Higher-Twist, d/u at high-x Neutron spin structure with polarized 3He and solenoid highest polarized luminosity: 1036 A solenoid with detector package (GEM, Shower counter+ gas Cherenkov) large acceptance: ~700 msr for polarized  high luminosity and large acceptance Inclusive DIS: improve by a factor of 10-100 A1 at high-x: 200 hours, high precision d2 at high Q2: 100 hours, very high precision parity violating spin structure g3/g5 : first significant measurement SIDIS: improve by a factor of 100-1000 transversity and TMDs, spin-flavor decomposition (~2 orders improvement) Solenoid Projection vs PT and x for p+ (60 days):  Solenoid Projection vs PT and x for p+ (60 days) For one z bin (0.5-0.6) Will obtain 4 z bins (0.3-0.7) Also p- at same time With upgraded PID for K+ and K- Summary:  Summary Spin structure study full of surprises and puzzles A generation of experiments from JLab: exciting results Spin sum rules and polarizabilities: test cPT calculations Reasonable to 0.05 for HBcPT and to 0.1 for RBcPT/D?  ‘dLT puzzle’ New data and experiments help solve the puzzle g2, d2: higher-twist effects and q-g correlations, LQCD Spin-duality: transition and link between hadrons and quark-gluons A1 at high-x: valence structure, flavor decomposition Bright future Complete a chapter in inclusive spin structure study (A1, d2 ,…) Transversity and TMDs: new dimensions New tools (12 GeV, Solenoid) greatly enhance our capability 3-D Projections for Collins and Sivers Asymmetry (p+):  3-D Projections for Collins and Sivers Asymmetry (p+) 14.3 degree:  14.3 degree SIDIS Kinematical with the Solenoid (10o-17o):  SIDIS Kinematical with the Solenoid (10o-17o) Q2 vs x PT vs x W vs x z vs x DIS cuts: W > 2.3 GeV W’ > 1.6 GeV Q2 > 1.0 GeV2 0.3 < z < 0.7 Slide66:  Hep-ex/0610068 COMPASS leading hadron results A1n and Du/u, Dd/d results in the news :  A1n and Du/u, Dd/d results in the news Physics News Update, 12/18/2003 ‘Bringing the Nucleon into Sharper Focus’ Science Now , 12/23/2003 ‘Quarks in a Surprising Spin’ Science News, 1/3/2004 ‘Topsy Turvy’ Physics Today Update, 2/2004 ‘Spinning the Nucleon into Sharper Focus’ APS-DNP current research topic, 5/5/2004 ’The Spin Structure of the Nucleon in the Valence Quark Region’ Preliminary CLAS (Hall B) A1p results: W>2 from S. Kuhn:  Preliminary CLAS (Hall B) A1p results: W>2 from S. Kuhn Projection with MAD 2000 hours (X. Jiang) comparison with HERMES:  Projection with MAD 2000 hours (X. Jiang) comparison with HERMES Solenoid improves precision by 2 orders of magnitude. Flavor Decomposition with SIDIS

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Spin Structure: Puzzles and Progress J. P. Chen, Jefferson Lab Hall A Collaboration Meeting, Jan. 4-5, 2007 Introduction: ‘Spin Crises’ or ‘Puzzles’
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