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Harut Avakian

Transverse spin effects in SIDIS at 6 GeV with transversely polarized target using the CLAS Detector. Harut Avakian. PR-08-015 - Main objective: Study Spin-Orbit correlations in Semi-Inclusive DIS and Sivers distribution function. PAC33 JLab, January 15, 2006. and the CLAS collaboration.

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Harut Avakian

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  1. Transverse spin effects in SIDIS at 6 GeV with transversely polarized target using the CLAS Detector Harut Avakian PR-08-015 - Main objective: Study Spin-Orbit correlations in Semi-Inclusive DIS and Sivers distribution function PAC33 JLab, January 15, 2006 H. Avakian, PAC33, Jan 15

  2. and the CLAS collaboration H. Avakian, PAC33, Jan 15

  3. Outline Physics motivation TMD parton distributions and spin-orbit correlations Accessing TMDs in semi-inclusive DIS Observables with transversely polarized target CLAS configuration Projections for transverse SSAs at 6 GeV Hydrogen Deuteron Extraction of Sivers function Summary H. Avakian, PAC33, Jan 15

  4. RHIC Spin & SIDIS J q The Spin Structure of the Nucleon Describe the complex nucleon structure in terms of partonic degrees of freedom of QCD EMC at CERN (85):~20% from Deep Inelastic Scattering (DIS) ~0.6 from QCD-sum rule “spin crisis” Proton’s spin Understanding of the orbital motion of quarks crucial!!! H. Avakian, PAC33, Jan 15

  5. Wpu(k,rT) “Mother” Wigner distributions d2kT d2rT GPDs/IPDs TMD PDFs f1u(x,kT), .. h1u(x,kT) d2kT Structure of the Nucleon quark polarization PDFs f1u(x), .. h1u(x) • Gauge invariant definition (Belitsky,Ji,Yuan 2003) • Universality of kT-dependent PDFs (Collins,Metz 2003) • Factorization for small kT. (Ji,Ma,Yuan 2005) H. Avakian, PAC33, Jan 15

  6. Spin densities in transverse proton from Lattice G.Miller/”pretzelosity” (QCDSF/UKQCD) H. Avakian, PAC33, Jan 15

  7. - Sivers Effect Unpolarized quarks: Probability to find a quark with longitudinal momentum x and transverse momentum kT Correlation between the quark transverse momentum and transverse spin of the proton + FSI The shift ~ 0.3 fm related to anomalous magnetic moment of proton (Burkardt 2000) Collins (2002) Meissner, Metz & Goeke (2007) Calculation of moments of f1T┴requires knowledge of kT-dependence in a wide range H. Avakian, PAC33, Jan 15

  8. Beam polarization Target polarization SIDIS kinematical plane and observables Trento Conventions Phys.Rev. D70, 117504 (2004). PT U unpolarized L long.polarized T trans.polarized sin(f-fS) moment of the cross section for unpolarized beam and transverse target H. Avakian, PAC33, Jan 15

  9. QCD large-x limit, Brodsky & Yuan (2006) (perturbative limit) Longitudinally polarized quarks Transversely polarized quarks (Collins effect ) Transversity Pretzelosity Unpolarized quarks TMDs with transverse target H. Avakian, PAC33, Jan 15

  10. SIDIS transverse SSA proton deuteron Sivers Collins [4] Wakamatsu, PLB 509 (01) [5] Pasquini et al., PRD 72 (05) [6] Anselmino et al., PRD 75 (07) [1] Soffer et al. PRD 65 (02) [2] Korotkov et al. EPJC 18 (01) [3] Schweitzer et al., PRD 64 (01) • Transverse asymmetries measured at HERMES and COMPASS • Effects are largeat large x H. Avakian, PAC33, Jan 15

  11. SIDIS with CLAS and HD-Ice Scattering of polarized electrons off transversely polarized proton and deuteron HD target at -70cm ep→e’pX Polarized beam (PB=80%) HD-Ice Target located upstream ~70cm to increase the acceptance for p0 Mini torus shifted upstream ~50cm e Detection of multiparticle final states is crucial for understanding of background processes p- p+ • 25 days of H (H-75%,D-25%) H D H D (H D H D ) • 15 days of D (H-0%,D-40%) D D (eff. ~25 days with 40%) • 5 days H,D and empty target H. Avakian, PAC33, Jan 15

  12. CLAS transversely polarized HD-Ice target HD-Ice target vs std nuclear targets Heat extraction is accomplished with thin aluminum wires running through the target (can operate at T~500-750mK) • Pros • Small field (∫Bdl~0.005-0.05Tm) • Small dilution (fraction of events from polarized material) • Less radiation length • Less nuclear background (no nuclear attenuation) • Wider acceptance • much better FOM, especially for deuteron • Cons • HD target is highly complex and there is a need for redundancy due to the very long polarizing times (months). • Need to demonstrate that the target can remain polarized for long periods with an electron beam with currents of order of 1-2 nA • Additional shielding of Moller electrons necessary (use minitorus) HD-Ice target at ~2nA ~ NH3 at 5 nA H. Avakian, PAC33, Jan 15

  13. 2 SIDIS with CLAS at 6 GeV Scattering of 5.7 GeV electrons off transversely polarized proton and deuteron epX (EG1) • DIS kinematics, Q2>1 GeV2, W2>4 GeV2, y<0.85 • 0.4>z>0.7, MX2>2 GeV2 Pt H. Avakian, PAC33, Jan 15

  14. Sivers effect: proton Vogelsang & Yuan Schweitzer et al • CLAS will provide a superior measurements of Sivers asymmetry at large x, where the effect is large and models unconstrained by previous measurements. • Measure also asymmetries in target fragmentation region and for exclusive r,r+,w channels (background) H. Avakian, PAC33, Jan 15

  15. Sivers effect: deuteron (~25 days) Vogelsang & Yuan Schweitzer et al • Neglecting the sea all 3 pions have on deuteron target the same AUT • AUT for deuteron doesn’t depend on fragmentation functions at large x • Difference in AUT for different pions will indicate large sea contribution • Deuteron measurement itself provides model independent combination of H. Avakian, PAC33, Jan 15

  16. this experiment Sivers asymmetry measurements on deuteron and proton target allow model independent extraction of Sivers function for u and d quarks at large x p++p-or p0 AUT for proton doesn’t depend on fragmentation functions Sivers effect on p0: extracting the Sivers function ed→e’p0X ep→e’p0X up down H. Avakian, PAC33, Jan 15

  17. d d Collins SSA at CLAS @5.7GeV d u u L=1 sin(fC)=sin(fh+fS) • L/R SSA generated in fragmentation • Hadrons from struck quark have opposite sign SSA Anselmino et al CLAS with a transversely polarized target will allow simultaneous measurement of SIDIS asymmetries in current and target fragmentation regions and exclusive r,r+,w asymmetries (background) H. Avakian, PAC33, Jan 15

  18. Summary Precision measurement of azimuthal moments in semi-inclusive DIS with transversely polarized hydrogen and deuterium targets with CLAS will allow to study partonic spin and transverse momentum correlations • Perform statistically significant measurement of the Sivers leading twist transverse momentum dependent PDF. • Provide important information on the Collins Fragmentation and in particular on transversity distribution function • Study transversely and longitudinally polarized quarks in transversely polarized nucleons • + inclusive, hyperons, higher twists…. Beam Request: E>5.7 GeV , PB=80% for 45 days 25 days (PH=75% PD=25%) +15 days (PH=0% PD=40%) unpolarized H and D and empty target 5 days H. Avakian, PAC33, Jan 15

  19. Support slides…. H. Avakian, PAC33, Jan 15

  20. Sivers effect: PT-dependence Model calculations Yuan & Vogelsang, Schweizer & Efremov PT-dependence at large PT crucial (not accessible at Hall-A/C). H. Avakian, PAC33, Jan 15

  21. CLAS vs CLAS12? • Data is available for Spin-Orbit correlation studies with unpolarized targets and experiment is approved at 6 GeV to run in 2009 with longitudinal target. Transverse target measurements will provide a complete set of data at 6 GeV (also important for longitudinal data analysis). • Provide input to develop global analysis of 3D parton distributions, TMDs GPDs and Wigner distributions. • Study the Q2 dependence of different SSA at fixed Bjorken-x will require measurements with different beam energies, including 6 GeV. • Enables early understanding of higher order corrections and higher twist contributions. • CLAS data at 6 GeV will be important to analyze future CLAS12 data (different systematics). • Reaction asymmetries from events ray traced back to vertex gives tomographic decomposition of target polarization vs e running time. -> essential to optimize plans for 12 GeV experiments H. Avakian, PAC33, Jan 15

  22. Acceptance corrections for AUT Esimated acceptance corrections for CLAS using HERMES analysis chain (GMCtrans) H. Avakian, PAC33, Jan 15

  23. Sivers from HERMES Disagreement in shape and magnitude of PT-dependences Need precision measurements of PT-dependences on proton and deuteron H. Avakian, PAC33, Jan 15

  24. H. Avakian, PAC33, Jan 15

  25. First calculations of “pretzelosity” P.Schweitzer, diquark model F.Yuan, Bag model H. Avakian, PAC33, Jan 15

  26. Tests of partonic picture CTEQ5M PDFs + Binnewies FF X=0.3, Q2=2.5 GeV2, W=2.5 GeV A1 GRSV2000 E00-108 at JLAB JLab data on x-sections and asymmetries is consistent with partonic description (0.4<z<0.7, MX>1.5) H. Avakian, PAC33, Jan 15

  27. Factorization studies Both ratios agree with PDF models for z<0.7 (Mx>1.4 GeV) H. Avakian, PAC33, Jan 15

  28. D-/D+ from Deuteron p+ to p- ratio Unfavored to favored ratio consistent with HERMES and EMC for z=0.55 H. Avakian, PAC33, Jan 15

  29. CLAS12: Kinematical coverage epX SIDIS kinematics Q2>1GeV2 W2>4 GeV2(10) y<0.85 MX>2GeV x=0.3 → Q2=~2 GeV2 (CLAS), ~5 GeV2 (HERMES) ~15 GeV2 (COMPASS) Large Q2 accessible with CLAS12 are important for separation of HT contributions H. Avakian, PAC33, Jan 15

  30. A1 PT-dependence in SIDIS M.Anselmino et al hep-ph/0608048 m02=0.25GeV2 mD2=0.2GeV2 p+ ALL can be explained in terms of broader kT distributions for f1 compared to g1 p- ALL may require non-Gaussian PT-dependence for different helicities and flavors H. Avakian, PAC33, Jan 15

  31. CLAS: Target and minitorus shifted upstream 70cm. H. Avakian, PAC33, Jan 15

  32. SIDIS transverse SSA H. Avakian, PAC33, Jan 15

  33. H. Avakian, PAC33, Jan 15

  34. Transverse target: p+ yield ratios to deuteron Multiple scattering and attenuation in nuclear environment introduces additional PT-dependence for hadrons H. Avakian, PAC33, Jan 15

  35. Burkardt (2007) TMDs: QCD based predictions Large-x limit Brodsky & Yuan (2006) Large-Nc limit (Pobilitsa) Do not change sign (isoscalar) All others change sign u→d (isovector) H. Avakian, PAC33, Jan 15

  36. H. Avakian, PAC33, Jan 15

  37. Partonic description of hard scattering p,g,.. Main focus: MX • transverse structure of nucleon (orbital motion of quarks ) • parton distributions (separate valence, sea) X.Ji • Where is the region I/II boundary? • Can useful information come from Region II? H. Avakian, PAC33, Jan 15

  38. Spin-Azimuthal Asymmetries Spin asymmetries + azimuthal dependence → new class of measurementsSpin-Azimuthal Asymmetries: Significant progress made recently in studies of Single-Spin Azimuthal Asymmetries (SSA) with longitudinally and transversely polarized targets in in electroproduction (HERMES, SMC,COMPASS, and CLAS), pp scattering (RHIC), and e+e- (BELLE) . • SSA are sensitive to the orbital momentum of quarks, enable measurements of GPDs and kT-dependend PDFs (TMDs) • provide a window to the physics of partonic final and initial state interactions • model calculations indicate that SSA are not affected significantly by a wide range of corrections. • Good agreement in SSAs measured in a wide energy range in electroproduction and pp scattering. H. Avakian, PAC33, Jan 15

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