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Hard scattering processes: Experiment

Hard scattering processes: Experiment

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Hard scattering processes: Experiment

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  1. Hard scattering processes: Experiment N.C.R. Makins *) University of Illinois at Urbana-Champaign SIR Workshop – Jefferson Lab, May 17-20, 2005 • Introduction • Semi-inclusive spin and azimuthal asymmetries and TMD distributions • Hard exclusive processes and GPDs • Conclusions *) in collaboration with H. Avakian

  2. Physics Motivation Orbital Angular Momentum (OAM) in the focus. Transverse momentum of quarks is a key to OAM. 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

  3. 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 ~ ~ TMD PDFs:fpu(x,kT),g1,f┴1T, h1,h┴1L GPDs: Hpu(x,x,t), Epu(x,x,t), H,E,… Measure momentum transfer to quark kT distributions also important for exclusive studies Measure momentum transfer to target Exclusive meson data important in understanding of SIDIS measurements x=0,t=0 dx d2kT PDFs fpu(x,kT),g1, h1 FFs F1pu(t),F2pu(t).. Some PDFs same in exclusive and semi-inclusive analysis Analysis of SIDIS and DVMP are complementary

  4. SIDIS kinematic plane and relevant variables

  5. Favored / disfavoredfragmentation functions: Quark Polarization from Semi-Inclusive DIS (SIDIS) In SIDIS, a hadron h is detected in coincidence with the scattered lepton: Flavor Tagging: Flavor content of observed hadron h is related to flavor of struck quarkq via the fragmentation functions D(z) scaling variable

  6. First 5-flavor fit to Δq(x) Final Δq Measurement from HERMES using all polarized data taken from 1996 - 2000 No evidence of anti-quark polarization, or flavor-asymmetry, Ds≈0 Sensitive to factorization more in talks by Zhu, Christova

  7. CLAS 5.7 GeV A1p-kinematic dependence for p+/-/0 A1p HERMES CLAS PRELIMINARY • No significant z-dependence of A1 in the range 0.3<z<0.7 • x dependence of CLAS A1p(A┴=0) consistent with HERMES data at 3 times higher Q2 and with LUND-MC (lines).

  8. SIDIS: factorization studies A1p++p- GRVS • A1 inclusive, from p+p- sum and p0 are consistent (in range 0.4<z<0.7 ) • A1pdependence can serve an important check of HT effects and applicability of simple partonic description. • There is an indication that A1p of p+ +p-is lower than inclusive at large z. more in talk by P.Bosted

  9. p0 in Semi-inclusive DIS as a test? advantages: • SIDIS p0 production is not contaminated by diffractive r • HT effects and exclusive p0 suppressed • Simple PID by p0-mass (no Kaon contamination) • Provides complementary to p+/- information on PDFs

  10. Collins AUT ~ Collins Effect Evidence of non 0 Collins effect First info on PT distribution undefined r contribution more details in talk by G. Schnell

  11. Sivers AUT ~ Sivers effect Evidence of non 0 Sivers effect For p+ consistent with increase with x,z,PT undefined r contribution

  12. Collins and Sivers Effects at COMPASS Collins AUT Sivers AUT No sizeable effect. Possible cancellations in isoscalar target (6LiD) undefined r contribution more details in talk by A.Bressan

  13. ‘SSA from HERMES/COMPASS‘ • check for consistency ‘‘Sivers function‘‘: hep-ph/0501196 consistent HERMES COMPASS more in A. Kotzinian’s talk

  14. sUL ~ KM Collins Effect and Kotzinian-Mulders Asymmetry Real part of interfe-rence of wave functions with L=0 and L=1 Efremov,Schweitzer (cQSM ) undefined r contribution Independent study the Collins fragmentation with longitudinally polarized target. Measure the twist-2 Mulders TMD (transversely pol. quarks in a longitudinally pol. proton) more in P.Bosted’s talk

  15. Beam SSA: ALU ssinfLU’~ 1/Q (Twist-3) “Sivers” effect by F.Yuan using h1┴ “Collins” effect by Schweitzer et al. using e(x) “Sivers ” effect Afanasev & Carlson, Metz & Schlegel more details in E.Avetisyan’s talk

  16. j2-p e- Q j1 e+ 2-h inclusive transverse momentum dependent Xsection: Collins Function In SIDIS Collins function always coupled with some(unknown) distribution function In e+e- only the Collins FF appears!

  17. Collins Function First direct measurement of the non 0 Collins function Rising behaviour vs. z more details in talk by A.Ogawa

  18. Transversity in double pion production h1 RT quark h2 The angular distribution of two hadrons is sensitive to the spin of the quark “Collinear” dihadron fragmentation described by two functions at leading twist: D1(z,cosqR,Mpp),H1R(z,cosqR,Mpp) The relative transverse momentum of the two hadrons replaces the PT in single-pion production No transverse momentum of the pair center of mass!

  19. 2p transvers spin SSA • Positive asymmetry observed for all invariant mass bins for proton • No evidence for a sign flip at the r-mass (Jaffe et al.) more details in talk by Kobayashi

  20. 2p transvers spin SSA • Asymmetry vs Minv, x, z consistent with 0. • Runs using p-target (NH3)

  21. Is the Sivers function “friend” of transversity? b - Impact parameter transversely polarized target quark flavor polarization lead to SSA shift defined by anomalous magnetic moment of proton (M.Burkardt) Or the “relative” of GPD E T In the polarized proton u quarks are shifted (~ 0.4 fmdefined by anomalous magnetic moment of proton) down and d quark up, giving rise to left-right asymmetries

  22. Sivers effect in the target fragmentation xF>0 (current fragmentation) xF<0 (target fragmentation) xF- momentum in the CM frame Wide kinematic coverage required for studies of hadronization in the target fragmentation region more details in A.Kotzinian’s talk

  23. Deeply Virtual Compton Scattering ep->e’p’g Polarized beam, unpolarized target: ~ DsLU~ sinfIm{F1H+ x(F1+F2)H+kF2E} Kinematically suppressed Unpolarized beam, longitudinal target: ~ DVCS DsUL~ sinfIm{F1H+x(F1+F2)(H+.. } BH Kinematically suppressed Unpolarized beam, transverse target: DsUT~ sinfIm{k(F2H – F1E) + …..} x = xB/(2-xB ),k = t/4M2 Kinematically suppressed GPD combinations accessible as azimuthal moments of the total cross section.

  24. CLAS at 4.3 GeV HERMES 27 GeV A(f) = asinf + bsin2f Pioneering DVCSExperiments SSA flips the sign from e+ to e-

  25. DVCS SSA: CLAS 5.7 GeV VGG 0.15<x<0.4 1.50 <Q2< 4.5 GeV2 -t<0.5 • Higher energy increases kinematics range. • Higher statistics allows binning of ALU in Q2, t, xB • More data available from ongoing experiments more details in talk by M.Garcon

  26. DVCS measurements at HERMES Beam Charge Asymmetry Longitudinal Target Spin Asymmetry ~ DsC ~cosfReH Ds~sinfIm{F1H+x(F1+F2)H...} With increased statistic asymmetries may constrain GPD models More in talk by F. Ellinghause

  27. Exclusive meson production GPD Different final state mesons filter out different combinations of unpolarized (H,E) and polarized (H,E) GPDs. ~ ~ Asymmetry depends linearly on the GPDE, which enters Ji’s sum rule. r0 production on transverse target Provide access to different combinations of GPD E and orbital momentum contributions Ju,Jd r0 -> 2Eu + Ed r+ -> Eu - Ed K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001 Studies needed to define on how far is the asymptotic regime and guide theory in describing HT.

  28. Conclusions • The new data are just the first trickle of a great wealth of upcoming information on 3D PDFs h1 h1 • Measurement of 3D PDFs requireglobal analysis of SSAs for exclusive and semi-inclusive final states measured in a wide range of kinematics at different facilities.

  29. Questions to address in SIDIS • How do we test the factorization and quantify its breakdown • Do we need the global analysis of exclusive and semi-inclusive processes? • How small the HT should be, to be interesting to measure? • What is the contribution to pion SIDIS observables from exclusive vector mesons • What we learn from PT-dependence of observables • What we learn from target fragmentation (xF<0) studies

  30. r+ pion SSA from r(p+p-/p+p0) (CLAS @5.7GeV) PYTHIA at 5.7 GeV r0 Larger fraction of p+ from r at low x and large z p+ SSA at large z may also have a significant (~20%) contribution from r Exclusiver (higher twist for SIDIS) crucial for pX and ppX studies

  31. 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 Better understanding of 2 pion asymmetries will help to understand transvers spin SSA mesurements

  32. PT-dependence of beam SSA ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) In the perturbative limit 1/PT behavior expected Perturbative region Nonperturbative 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).

  33. SSA: PT-dependence of sinf moment ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) CLAS @5.7 GeV CLAS @4.3 GeV Beam and target SSA for p+ (not sensitive to MX-cut) are consistent with increase with PT

  34. SIDIS: target and current fragmentation xF>0 (current fragmentation) xF- momentum in the CM frame xF<0 (target fragmentation, TFR) • – probability of finding a parton qwith momentum fraction xand a hadron hwith energy fraction z in the proton (Trentadue & Veneziano). Wide kinematic coverage of CLAS allows studies of hadronization in the target fragmentation region

  35. SSA in exclusive pion production Beam SSA ALU at 6GeV Target SSA at 27.5 GeV HERMES W2>4GeV2, Q2>1.5GeV2 CLAS PRELIMINARY - Beam SSA and Longitudinally pol. Target SSA provide information on HT ( 0 at leading order)

  36. Exclusive r measurements CLAS at 4.3 GeV W>1.75GeV HERMES at 27.5 GeV W>2GeV Regge GPDs(VGG) Decent description in pQCD framework already at moderate Q2

  37. e- p e-nr+ π+π0 Exclusive r+ production Exclusive r+n separated by invariant and missing masses. CLAS 5.7 GeV n r+ Provide access to different combinations of orbital momentum contributions Ju,Jd r0 -> 2Ju + Jd r+ -> Ju - Jd w -> 2Ju - Jd • Significant transverse target SSA predicted for exclusive r0, r+ • (Goeke et al hep-ph/0106012)

  38. Measuring the Q2 dependence of SSA ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) For fixed x, 1/Q behavior expected Wide kinematic coverage allows to check the higher twist nature of beam and longitudinal target SSAs