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Study of Polarized Quark Fragmentation with CLAS and CLAS12

This workshop outlines the transverse structure of the nucleon and correlations between transverse spin and momentum. It discusses fragmentation of transversely polarized quarks, Collins effect, and the effects of different target polarizations. The workshop also covers twist-3 transverse momentum dependent distributions and the Collins effect in SSA measurements. It concludes with discussions on the Collins function, the CLAS transversely polarized HD-Ice target, and the kinematical coverage of CLAS12.

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Study of Polarized Quark Fragmentation with CLAS and CLAS12

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  1. Study of Polarized Quark Fragmentation with CLAS and CLAS12 Harut Avakian (JLab) CLAS12 European Workshop February 25-28, 2009- Genova, Italy CLAS12 workshop, Feb 26

  2. Outline Transverse structure of the nucleon and correlations between transverse spin and momentum. Introduction Fragmentation of transversely polarized quarks and Collins effect Unpolarized target Longitudinally polarized target Transversely polarized target Projections for 12 GeV Summary CLAS12 workshop, Feb 26

  3. SIDIS kinematical plane and observables z U unpolarized L long.polarized T trans.polarized sin2f moment of the cross section for unpolarized beam and longitudinal target Transverse spin effects are observable as correlations of transverse spin and transverse momentum of quarks. CLAS12 workshop, Feb 26

  4. Target fragmentation Current fragmentation h h h M GPD PDF xF 0 1 -1 Fracture Functions kT-dependent PDFs Generalized PDFs Single hadron production in hard scattering xF>0 (current fragmentation) h xF<0 (target fragmentation) xF- momentum in the CM frame Wide kinematic coverage of large acceptance detectors allows studies of hadronization both in the target and current fragmentation regions CLAS12 workshop, Feb 26

  5. Twist-3 Transverse Momentum Dependent (TMD) Distributions Quark polarization Twist-2 • kT – leads to 3D description with 8PDFs Real and imaginary parts of the DL≠0 interference contributions Nucleon polarization • Factorization of kT-dependent PDFs proven at low PT of hadrons (Ji et al) CLAS12 workshop, Feb 26

  6. ST Intial quark polarization fS fS’ = p-fS sin(fh+fS) spin of quark flips wrt y-axis y PT fS= p/2+fh fS fh x y PT fS=fh fh x fh y PT fS=p x Collins Effect: azimuthal modulation of the fragmentation function FUT∞h1H1┴ sT(q×PT)↔H1┴ y fC PT fC sT D(z,PT)=D1(z,PT)+H1┴(z,PT)sin(fh- fS’) fh hadronizing quark fS’ x fC sin(2fh) CLAS12 workshop, Feb 26

  7. p↑p→hX BRAHMS Observed SSA show strong dependence on the final state hadron Collins SSA measurements e+e-→hhX +(u,d) K+(u,s) • K+ and + asymmetries consistent within error bars • K- and - asymmetries may have opposite sign CLAS12 workshop, Feb 26

  8. kicked in the opposite to the leading pion(into the page) L Sub-leading pion opposite to leading (double kick into the page) Collins effect Simple string fragmentation (Artru model) p+ Leading pion out of page ( - direction ) z L p- Collins analyzing power may be indeed much bigger for unfavored fragmentation CLAS12 workshop, Feb 26

  9. hep-ph/9606390 Collins effect p+ leading pion out of page Simple string fragmentation for pions (Artru model) z L r production may produce an opposite sign AUT Leading r opposite to leading p(into page) z r L Fraction of direct kaons may be significantly higher than the fraction of direct pions. LUND-MC CLAS12 workshop, Feb 26

  10. The Collins function First calculation of the Collins function Bacchetta et al, Phys.Lett.B659:234-243,2008 HERMES/COMPASS/Belle spectator model Kaon Pion The Kaon Collins effect may be significant! CLAS12 workshop, Feb 26

  11. 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 CLAS12 workshop, Feb 26

  12. Collins sUT ~ Collins SSA at CLAS @5.7GeV fS’ = p-fS sin(fC)=sin(fh+fS) 25 days with HD-Ice CLAS with a transversely polarized target will allow simultaneous measurement of SIDIS asymmetries in current and target fragmentation regions and exclusive r,r+,w and g asymmetries CLAS12 workshop, Feb 26

  13. CLAS12 Wide detector and physics acceptance (current/target fragmentation) LTCC PCAL Lumi = 1035cm-2s-1 High beam polarization 80% High target polarization 85% NH3 (30 days) ND3 (50 days) EC HTCC FTOF Replace 2 sectors of LTCC with a proximity RICH detector to identify Kaons CLAS12 workshop, Feb 26

  14. CLAS12: Kinematical coverage epX SIDIS kinematics Q2>1GeV2 W2>4 GeV2(10) y<0.85 MX>2GeV Large Q2 accessible with CLAS12 are important for separation of HT contributions CLAS12 workshop, Feb 26

  15. - Unpolarized target: Boer-Mulders Effect CLAS12 2000h @ 11 GeV with 1035sec-1cm-2) Non-perturbative TMD Perturbative region • BM cos2f moment: the only leading twist azimuthal moment for unpolarized target • PT-dependence of BM asymmetry allows studies of transition from non-perturbative to perturbative description (Unified theory by Ji et al). CLAS12 workshop, Feb 26

  16. sUL ~ KM Collins fragmentation: Longitudinally polarized target Transversely polarized quarks in the long. polarized nucleon Kotzinian-Mulders Asymmetry curves, cQSM from Efremov et al • KM sin2f moment, sensitive to spin-orbit correlations: the only leading twist azimuthal moment for longitudinally polarized target • More info will be available from SIDIS (COMPASS,EIC) and DY (RHIC,GSI) CLAS12 workshop, Feb 26

  17. Collins sUT ~ Collins Effect Study the Collins fragmentation for all 3 pions with a transversely polarized target and measure the transversity distribution function. CLAS12 workshop, Feb 26

  18. Collins AUT ~ CLAS12: Transversity projections Simultaneous measurement of, exclusive r,r+,w with a transversely polarized target Collins function required to extract transversity from transverse target SSA measurements CLAS12 workshop, Feb 26

  19. Pretzelosity @ CLAS12: Exciting relation: (in bag & spectator model) helicity - transversity = ‘measure’ of relativistic effects • CLAS12 will provide first pretzelosity measurement in the valence region for Kaons and pions. B. Pasquini et al. arXiv:0806.2298 CLAS12 workshop, Feb 26

  20. Collins Effect: from asymmetries to distributions need Combined analysis of Collins fragmentation asymmetries from proton and deuteron may provide independent to e+e- (BELLE) Information on the underlying Collins function. CLAS12 workshop, Feb 26

  21. Sivers effect in the target fragmentation A.Kotzinian High statistics of CLAS12 will allow studies of kinematic dependences of the Sivers effect in target fragmentation region CLAS12 workshop, Feb 26

  22. L polarization in the target fragmentation L polarization in TFR provides information on contribution of strange sea to proton spin xF- momentum in the CM frame Study polarized diquark fracture functions sensitive to the correlations between struck quark transverse momentun and the diquark spin (Sivers) Wide kinematical coverage of CLAS12 allows studies of hadronization in the target fragmentation region CLAS12 workshop, Feb 26

  23. Summary • Probe the Collins polarized fragmentation function of pions and kaons for unpolarized, longitudinally polarized and transversely polarized targets • Provide precision measurements of the leading twist chiral-odd transverse spin distributions of valence quarks. • Study higher twist effects and test factorization in a wide range of Q2 • Measure polarization effects in the target fragmentation region. • Experiments confirm that Collins fragmentation function is large both for favored and unfavored hadron production. Large kinematical acceptance of CLAS12@ 11 GeV with L=1035cm-2sec-1 would allow us to : CLAS12 workshop, Feb 26

  24. Support slides…. CLAS12 workshop, Feb 26

  25. Collins fragmentation: Longitudinally polarized target Kotzinian-Mulders Asymmetry proton deuteron Pasquini et al. • Study the Collins function of kaons • Provides independent information on the RSMT TMD CLAS12 workshop, Feb 26

  26. ST fS fS fS’ = p-fS sin(fh+fS) spin of quark flips wrt y-axis FUU∞h1 ┴H1┴ sT(p×kT)↔ h1┴ ┴ (sTkT)(pSL)↔ h1L ┴ FUL∞h1L H1┴ Collins Effect: azimuthal modulation of the fragmentation function FUT∞h1H1┴ sT(q×PT)↔H1┴ y fC PT fC sT D(z,PT)=D1(z,PT)+H1┴(z,PT)sin(fh- fS’) fh fS’ x sin(fh+fS) y y PT fS= p/2+fh PT fS=fh fh fh cos(2fh) sin(2fh) fC x x sin(2fh) CLAS12 workshop, Feb 26

  27. CLAS12 - Electromagnetic Background Low energy electromagnetic processes, especially Møller scattering of beam electrons off atomic electrons are the main contributor to the background load in an open large acceptance spectrometer such as CLAS12. The full event and background load has been measured with CLAS, e.g. for DVCS process at 5.7 GeV. The GEANT simulation reproduces hit occupancy on tracking chambers. We used the calibrated simulation code to extrapolate to 11 GeV and simulate the same process at higher luminosity for CLAS12 situation. This background was also studied in a full Geant4 simulation. CLAS12 workshop, Feb 26

  28. Kaon distributions in ep  e’KX SIDIS kinematics LUND-MC Q2>1GeV2 W2>4 GeV2(10) y<0.85 MX>2GeV forward High energy kaons are at small angles (q<30o) More kaons at small x CLAS12 workshop, Feb 26

  29. CLAS12 Background at L=1035cm-2s-1, T = 150ns Electrons Photons Photons One Event One Event Shielding 5 T Magnetic Field and Shielding CLAS12 workshop, Feb 26

  30. Rpd- Both ratios agree with PDF models for z<0.7 (Mx>1.4 GeV) CLAS12 workshop, Feb 26

  31. D-/D+ from Deuteron p+ to p- ratio Unfavored to favored ratio consistent with HERMES and EMC for z=0.55 CLAS12 workshop, Feb 26

  32. p multiplicities in SIDIS ep→e’pX M.Aghasyan Hall-C DSS (Q2=2.5GeV2) DSS (Q2=25GeV2) p+/- multiplicities at large z diverge from SIDIS predictions p0 multiplicities less affected by higher twists 0.4<z<0.7 kinematical range, where higher twists are expected to be small CLAS12 workshop, Feb 26

  33. Collins Effect: from asymmetries to distributions need Combined analysis of Collins fragmentation asymmetries from proton and deuteron may provide independent to e+e- (BELLE) Information on the underlying Collins function. CLAS12 workshop, Feb 26

  34. Higher Twist SSAs and Quark-Gluon Correlations Discussed as main sources of SSA due to the Collins fragmentation Target sinf SSA (Bacchetta et al. 0405154) In jet SIDIS only contributions ~ D1 (Sivers type) Transversely polarized quarks With H1┴ (p0)≈0(or measured) Target and Beam SSA can be a valuable source of info on HT T-odd distribution functions CLAS12 workshop, Feb 26

  35. SSA with unpolarized target quark polarization CLAS12 workshop, Feb 26

  36. SSA with unpolarized target quark polarization CLAS12 workshop, Feb 26

  37. SSA with long. polarized target quark polarization CLAS12 workshop, Feb 26

  38. SSA with long. polarized target quark polarization CLAS12 workshop, Feb 26

  39. CLAS: Fraction from baryonic decays in SIDIS Significant fraction from target fragmentation at pion momenta below 2 GeV CLAS12 workshop, Feb 26

  40. Dilution factor in SIDIS Fraction of events from polarized hydrogen in NH3 Nu,Np -total counts from NH3 and carbon normalized by lumi ru, rp -total areal thickness of hydrogen (in NH3), and carbon target Cn=Nitr/Carbon ratio (~0.98) Diff. symbols for diff x-bins p- Multiple scattering and attenuation in nuclear environment introduces additional PT-dependence for hadrons CLAS12 workshop, Feb 26

  41. CLAS12: Acceptance deformation due to incomplete azimuthal coverage Lab No significant effect seen from limited f coverage by RICH CLAS12 workshop, Feb 26

  42. Inbendin/outbending configurations Different polarities increase the acceptance of positive and negative hadrons. CLAS12 workshop, Feb 26

  43. Kinematic dependence of K/ ratios Critical for separation moment range 2<PK<5 and q<25 degree CLAS12 workshop, Feb 26

  44. Kaon distributions in ep  e’KX Q2>1GeV2 W2>4 GeV2(10) y<0.85 MX>2GeV SIDIS kinematics High energy kaons are at small angles CLAS12 workshop, Feb 26

  45. 4s K-p separation at 5 GeV/c 80 % kaon eff. with 1:1000 p rejection 95 % kaon eff. with 1:100 p rejection Already with 2 sectors gain of factor ~3 in the relevant z region of interest Contalbrigo Marco PAC34 27 January 2009 A Rich detector for CLAS12 MC simulation:  3 cm thick C5F12 radiator 80 cm CH4 proximity gap  1 cm pixel pad size  5 o-30 o radiator polar angle CLAS12 workshop, Feb 26

  46. Transverse Momentum Dependent (TMD) Distributions Quark polarization • kT – leads to 3D description with 8PDFs Nucleon polarization Real and imaginary parts of the L=0 and L=1 interference contribution Related to transversity by Lorentz Invariant relations. In constituent quark model (Pasquini et al). CLAS12 workshop, Feb 26

  47. Compare SIDIS experiments COMPASS/HERMES/CLAS cover different Q2 for the same x-range x=0.3 → Q2=~2 GeV2 (CLAS), ~7 GeV2(HERMES) ~30 GeV2(COMPASS) CLAS12 workshop, Feb 26

  48. HERMES: Diffractive corrections to DIS CLAS12 workshop, Feb 26

  49. Brodsky & Yuan (2006) Collins Effect: from asymmetries to distributions need CLAS12 Combined analysis of Collins fragmentation asymmetries from SIDIS and e+e- (BELLE) would allow separation of transverse spin distributions (Anselmino et al., arXiv:0707.1197 ) CLAS12 workshop, Feb 26

  50. BBS/LSS with OAM JLab@12GeV: Inclusive DIS BBS/LSS no OAM PDF measurements at large x provide additional information on OAM CLAS12 workshop, Feb 26

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