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Hard scattering studies at JLab

Hard scattering studies at JLab. Harut Avakian Jefferson Lab. XI Workshop on High Energy Spin Physics , Dubna, September 2005. * Talk presented by A.Kotzinian. Outline. Physics motivation SIDIS studies at 6 GeV Hard exclusive processes Future plans Summary. Physics Motivation.

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Hard scattering studies at JLab

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  1. Hard scattering studies at JLab Harut Avakian Jefferson Lab XI Workshop on High Energy Spin Physics , Dubna, September 2005 * Talk presented by A.Kotzinian

  2. Outline Physics motivation SIDIS studies at 6 GeV Hard exclusive processes Future plans Summary

  3. Physics Motivation Orbital Angular Momentum (OAM) in the focus. ~20-30% ½ = ½ (Du+Dd+Ds) + Lq + Jg Proton’s spin Parton Distribution Functions generalized to contain information not only on longitudinal, but also on the transverse distribution of partons: Complementary sets of non-perturbative functions sensitive to different aspects of transverse distributions • Generalized Parton Distributions (GPD) H, E ... • Transverse-momentum dependent (TMD) parton distributions

  4. Probability to find a quark u in a nucleon P with a certain polarization in a position r and momentum k Wpu(x,k,r) “Parent” Wigner distributions d3r d2kT (FT) GPD TMD GPDs Hpu(x,x,t).. TMD PDFs fpu(x,kT), dx d2kT x=0,t=0 Measure momentum transfer to quark Measure momentum transfer to target PDFs fpu(x,kT),g1, h1 FFs F1pu(t),F2pu(t).. kT-integrated PDFs same in exclusive and semi-inclusive analysis Analysis of SIDIS and DVMP are complementary

  5. 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

  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. Semi-Inclusive Pion Electroproduction with a Polarized Beam and Longitudinally Polarized Target at 6 GeV JLab experiment P-05-113 and the CLAS collaboration

  8. 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).

  9. 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.

  10. High efficiency reconstruction of p0 r+,h opens a new avenue inSIDIS (DVMP) 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

  11. 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

  12. 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.

  13. Target 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

  14. SSA: x-dependence PRELIMINARY 5.7 GeV HT SSA from Collins mechanism AUL (p 0) ~ H1favore+H1unfavored With H1┴ (p0)≈0(or measured) target and beam HT SSAs can be a valuable source of info on HT T-odd distribution functions f┴ ,g┴ L

  15. 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

  16. long. only Hard Exclusive Processes and GPDs DVMP DVCS hard gluon hard vertices DVCS – for different polarizations of beam and target provide access to different combinations of GPDs H, H, E DVMP for different mesons is sensitive to flavor contributions (r0/r+ select H, E, for u/d flavors, p, h, K select H, E)

  17. d4 ~ |TDVCS + TBH|2 dQ2dxBdtd Deeply Virtual Compton Scattering ep->e’p’g DVCS BH GPD TBH: given by elastic form factors TDVCS: determined by GPDs Polarized beam, unpolarized target: ~ DVCS DsLU~ sinfIm{F1H+ x(F1+F2)H+kF2E} Kinematically suppressed BH Unpolarized beam, longitudinal target: ~ DsUL~ sinfIm{F1H+x(F1+F2)(H+.. } x = xB/(2-xB ),k = t/4M2 Kinematically suppressed • GPD combinations accessible as azimuthal moments of the total cross section.

  18. Target Spin Asymmetry: t- Dependence Higher efficiency photon detection will also improve significantly DVCS target SSA measurements.

  19. 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

  20. 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).

  21. 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.

  22. sUL ~ KM Collins Effect and Kotzinian-Mulders Asymmetry Study the Collins fragmentation with longitudinally polarized target. Measure the twist-2 Mulders TMD (real part of interference of L=0 and L=1 wave functions)

  23. 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).

  24. 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.

  25. Sivers effect in the target fragmentation A.Kotzinian High statistics of CLAS12 will allow studies of Q2 dependence of the Sivers effect in target fragmentation region

  26. e 1 Λ p 2 L polarization in the target fragmentation e’ L polarization in TFR provides information on contribution of strange sea to proton spin xF- momentum in the CM frame J.Ellis, D.Kharzeev, A. Kotzinian ‘96 W.Melnitchouk and A.W.Thomas ‘96 Wide kinematical coverage of CLAS12 allows studies of hadronization in the target fragmentation region

  27. CLAS12- DVCS/BH Beam Asymmetry e p epg DsLU~sinfIm{F1H+..}df Sensitive to GPDH L = 1x1035 T = 2000 hrs ALU E=4.3 GeV S. Stepanyan et al. Phys. Rev. Lett. 87 (2001)

  28. CLAS12-DVCS/BH Target Asymmetry L = 2x1035 cm-2s-1 T = 1000 hrs DQ2 = 1GeV2 Dx = 0.05 e p epg E = 11 GeV 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

  29. Q2=3.5 GeV2 bval=bsea=1 MRST02 NNLO distribution • Other kinematics measured concurrently GPDs H from expected DVCS ALUdata p

  30. Q2=5 GeV2 Exclusiver0 production on transverse target 2D (Im(AB*))/p T AUT = - |A|2(1-x2) - |B|2(x2+t/4m2) - Re(AB*)2x2 A~ 2Hu + Hd B~ 2Eu + Ed r0 A~ Hu - Hd B ~ Eu - Ed r+ Eu, Edneeded for angular momentum sum rule. r0 K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001 Asymmetry is a more appropriate observable for GPD studies at 12 GeV as possible corrections to the cross section are expected to cancel

  31. 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 3D distribution functions (TMDs,GPDs) • 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.

  32. support slides…

  33. 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

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

  35. 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

  36. 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.

  37. 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

  38. 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

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

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

  41. 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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