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Studies of transverse spin effects at JLab

Studies of transverse spin effects at JLab. Harut Avakian Jefferson Lab. Transversity 2005, Como, September 7-10, 2005. * In collaboration with P.Bosted, V.Burkert and L.Elouadrhiri. Outline. Physics motivation SIDIS studies at 6 GeV Factorization tests Spin azimuthal asymmetries

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Studies of transverse spin effects at JLab

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  1. Studies of transverse spin effects at JLab Harut Avakian Jefferson Lab Transversity 2005, Como, September 7-10, 2005 * In collaboration with P.Bosted, V.Burkert and L.Elouadrhiri

  2. Outline Physics motivation SIDIS studies at 6 GeV Factorization tests Spin azimuthal asymmetries Future plans Summary

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

  4. Polarized Semi-Inclusive DIS Cross section is a function of scale variables x,y,z n = E-E’ y = n /E x = Q2 /2Mn z = Eh /n Hadron-Parton transition: by distribution function f1u(x): probability to find a u-quark with a momentum fraction x Parton-Hadron transition: by fragmentation function Dp+(p-)(z): probability for a u-quark to produce a p+(p-)with momentum fraction z z 1u

  5. Transverse momentum of quarks • kT – led to introduction of kT dependent PDFs(TMDs) • kT – crucial for orbital momentum and spin structure studies • led to SSA in hard scattering processes • kT - important for cross section description • - PT distributions of hadrons in DIS • exclusive photon production (DVCS) • - hard exclusive vector meson cross section • - pp → p0X (E704,RHIC) cross sections Spin-Azimuthal Asymmetries: sensitive to kT To study orbital motion of quarks in semi-inclusive DIS measurements in a wide range of x,z,PT, f are required.

  6. Unpolarized target e p Longitudinally pol. target Transversely pol. target e p SIDIS (g*p→pX) cross section at leading twist (Ji et al.) e Boer-Mulders 1998 Kotzinian-Mulders 1996 Collins-1993 structure functions = pdf × fragm × hard × soft (all universal) Off diagonal PDFs related to interference between L=0 and L=1 light-cone wave functions. To observe the transverse polarization of quarks in SIDIS spin dependent fragmentation is required!

  7. y ST PT fC sT fS fh fS fS’ = p-fS fS’ sin(fh+fS) spin of quark flips wrt y-axis x FUU∞h1 ┴H1┴ ┴ sT(p×kT)↔ h1┴ (sTkT)(pSL)↔ h1L sinfC=sin(fh- fS’) y PT sT fC fh fS=fh ┴ cos(2fh) 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 fC fS= p/2+fh x sin(2fh) fS’ = p-fS= p-fh fS’ = p-fS= p/2-fh sin(2fh)

  8. Schafer-Teryaev sum rule Precise measurement of Collins asymmetries for different hadrons (p0 ,p+ +p-) would allow to test the Schafer-Teryaev sum rule

  9. High efficiency reconstruction of p0 r+,h opens a new avenue inSIDIS (HMP) SIDIS with neutral pions • SIDIS p0 production is not contaminated by diffractive r • p0 SSA sensitive to the unfavored polarized fragmentation • HT effects and exclusive p0 suppressed • Simple PID by p0-mass (no kaon contamination) • Provides information complementary to p+/- information on PDFs

  10. Fragmentationp+ p+ p0 HT and Semi-Exclusive Pion Production E. Berger, S. Brodsky 1979 (DY), E.Berger 1980, A.Brandenburg, V. Khoze, D. Muller 1995 A.Afanasev, C.Carlson, C. Wahlquist Phys.Lett.B398:393-399,1997 HT effects and exclusive p0 suppressed

  11. 50o 13o Experimental Setup (CLAS+IC) Polarized target • solid NH3 polarized target • proton polarization >75% • high lumi ~ 1.51034 s-1cm-2 IC Inner Calorimeter (424 PbWO4 crystals) for the detection of high energy photons at forward lab angles (increases p0 acceptance ~3 times at z~0.5).

  12. 60 days of CLAS+IC (L=1.5.1034cm-2s-1) Factorization studies with pions A1 LUND-MC CLAS PRELIMINARY • Double spin asymmetries consistent with simple partonic picture • A1p inclusive and p0 (~30 times more data expected) an serve as an important check of HT effects and applicability of the simple partonic description.

  13. Azimuthal asymmetries at CLAS CLAS Q2=2.23-2.66 GeV2 x=0.28-0.32 z=0.16-0.19 pT=0.41-0.53 GeV Preliminary M.Osipenko • Unpolarized Semi-inclusive electroproduction of + measured. • Complete 5-dimensional cross sections were extracted. • Direct separation of different structure functions.

  14. SSA measurements at CLAS ep→e’pX W2>4 GeV2 CLAS PRELIMINARY p1sinf+p2sin2f Q2>1.1 GeV2 y<0.85 0.4<z<0.7 MX>1.4 GeV PT<1 GeV 0.12<x<0.48 p1= 0.059±0.010 p2=-0.041±0.010 p1=-0.042±0.015 p2=-0.052±0.016 p1=0.082±0.018 p2=0.012±0.019 • Significant SSA measured for pions with longitudinally polarized target • Complete azimuthal coverage crucial for separation of sinf, sin2f moments

  15. L Flavor decomposition of T-odd f┴ In jet SIDIS with massless quarks contributions from H1┴ vanish gauge link contribution With SSA measurements for p++p-and p0 on neutron and proton (p=p++p-) assuming Hfav=Hu→p+≈ -Hu→p-=-Hunfav With H1┴ (p0)≈0(or measured) target and beam HT SSAs can be a valuable source of info on HT T-odd distribution functions

  16. 60 days of CLAS+IC (L=1.5.1034cm-2s-1) Longitudinally polarized target SSA using CLAS+IC curves, cQSM from Efremov et al Hunf=-5Hfav Hunf=-1.2Hfav Hunf=0 • Provide measurement of SSA for all 3 pions, extract the Mulders TMD and study Collins fragmentation with longitudinally polarized target • Allows also measurements of 2-pion asymmetries

  17. CLAS12 High luminosity polarized (~80%) CW beam Wide physics acceptance (exclusive, semi-inclusive current and target fragmentation) Wide geometric acceptance 12GeV significantly increase the kinematic acceptance (x10 lumi)

  18. Collins sUT ~ Collins Effect • SSA in fragmentation • Subleading SSA has opposite sign • No effect in TFR Study the Collins fragmentation for all 3 pions with a transversely polarized target and measure the transversity distribution function. JLAB12 cover the valence region.

  19. Sivers sUT ~ Sivers effect • Asymmetry in distribution • Subleading SSA has same sign • Opposite sign effect in TFR Measure the Sivers effect for all 3 pions with a transversely polarized target in a wide kinematic range (TFR & CFR).

  20. CLAS12: Sivers effect projections Efremov et al (large xB behavior of f1T from GPD E) In large Nc limit: F1T=∑qeq2f1T┴q f1Tu = -f1Td CLAS12 projected CLAS12 projected Sivers function extraction from AUT (p0) does not require information on fragmentation function. It is free of HT and diffractive contributions. AUT (p0) on proton and neutron will allow flavor decomposition w/o info on FF.

  21. Summary • Current data are consistent with a partonic picture, and can be described by a variety of theoretical models. • Significantly higher statistics of JLab, in a wide kinematical range will provide a full set of data needed to constrain relevant distribution (transversity,Sivers,Collins,…) functions. • Experimental investigation of properties of 3D PDFs at JLab, complementary to planed studies at HERMES, COMPASS, RHIC, BELLE, GSI, would serve as an important check of our understanding of nucleon structure in terms of quark and gluon properties.

  22. support slides…

  23. Higher Twist SSAs Discussed as main sources of SSA due to the Collins fragmentation Target sinf SSA (Bacchetta et al. 0405154) In jet SIDIS only contributions ~ D1 survive Beam sinf SSA With H1┴ (p0)≈0(or measured) Target and Beam SSA can be a valuable source of info on HT T-odd distribution functions

  24. SIDIS: factorization studies P.Bosted JLab data at 6GeV are consistent with factorization and partonic description for variety of ratio observables

  25. p quark Collinear Fragmentation The only fragmentation function at leading twist for pions in eN→e’pX is D1(z) Ee =5.7 GeV No significant variation observed in z distributions of p+ for different x ranges (0.4<z<0.7, MX>1.5) and for A1p as a function of PT

  26. Collins AUT ~ CLAS12: Transversity projections 10-3 Simultaneous measurement of, exclusive r,r+,w with a transversely polarized target

  27. SSA: x-dependence PRELIMINARY 5.7 GeV HT–SSA significant for p + and p 0 (non-Collins?) AUL (p 0) ~ H1favore+H1unfavored • Study the Collins fragmentation mechanism with long. polarized target • For p - and p 0 SSA is sensitive to unfavored fragmentation

  28. SSA: kinematical dependence • Indicate a negative sin2f moment measured for p +. • Some indication of negative p- SSA (more data required for p - and p 0) • More data required to correct for exclusive 2p contribution.

  29. PT-dependence of beam SSA ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) In the perturbative limit 1/PT behavior expected (F.Yuan SIR-2005) 2.0 Perturbative region Non-perturbative TMD Asymmetries from kT-odd and kT-even (g1) distribution functions are expected to have a very different behavior (flat A1p(PT) observed at 5.7 GeV).

  30. Exclusive production background from PYTHIA Pions from string (direct) present the lower limit for current fragmentation events electron p0 sample “clean” at large z (non-string pions are mainly from semi-inclusive r+, w) Filled (open) symbols represent pions from exclusive (all) vector mesons.

  31. First glimpse of Twist-2 TMD h1L┴ For Collins fragmentation use chirally invariant Manohar-Georgi model(Bacchetta et al) Distribution functions from cQSM from Efremov et al PRELIMINARY CLAS-5.7GeV Systematic error only from unknown ratio of favored and unfavored Collins functions (R= H1d→p+/H1u→p+), band correspond to -2.5<R<0 • More data required with p- & p0 • Exclusive 2 pion background may be important p- and p0 SSA will also give access to h1Ld

  32. CLAS+Inner Calorimeter (IC) IC sE/E=0.0034/E+0.038/√E+0.022 CLAS+IC p0 CLAS Reconstruction efficiency of high energy p0 with IC increases ~ 3 times at large z due to small angle coverage (target in ~60cm from IC)

  33. Transversity Sub-leading pion opposite to leading (into page) Simple string fragmentation (Artru model) L=1 Leading r opposite to leading p(into page) r production may produce an opposite sign AUT r SIDIS @11 GeV: 2 pions r+ Understanding of 2 pion asymmetries will help to understand transversity measurements r0

  34. SIDIS: factorization studies GRVS HERMES • A1 inclusive, from p+p- sum and p0 are consistent (in range 0.4<z<0.7 ) • There is an indication that A1p of p+ +p-is lower than inclusive at large z. • More data required for 2 pion (r) final state studies

  35. 50o 13o GEANT simulation Maximum angle ~50o Minimum angle ~14o Angular acceptance for charged tracks for eg1+IC configuration (polarized target at -67 cm from IC)

  36. exclusive production background Pions from string present the lower limit for current fragmentation events Fraction of pions from non-diffractive vector mesons adds up to SIDIS sample Fraction of pions from exclusive rho-0(black squares) should have a special treatment

  37. exclusive production background Fraction of charged pions from rho-0 especially high for neutron target

  38. production background from exclusive events Non string pions are mainly from semi-inclusive rho+

  39. SSA: PT-dependence of sinf moment ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) ALUCLAS @4.3 GeV AUL(CLAS @5.7 GeV) AUTHERMES @27.5 GeV PRELIMINARY TMD pQCD Beam and target SSA for p+ are consistent with increase with PT In the perturbative limit is expected to behave as 1/PT

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