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Imaging in Exclusive Processes

Imaging in Exclusive Processes. Tanja Horn. INT10-03 “Imaging QCD Matter”, Institute for Nuclear Theory, UW, Seattle. 12 November 2010. Tanja Horn, CUA Colloquium. Nucleon Structure: landscape. Hadrons in QCD are relativistic many-body systems

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Imaging in Exclusive Processes

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  1. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Imaging in Exclusive Processes Tanja Horn INT10-03 “Imaging QCD Matter”, Institute for Nuclear Theory, UW, Seattle 12 November 2010 Tanja Horn, CUA Colloquium

  2. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Nucleon Structure: landscape • Hadrons in QCD are relativistic many-body systems • Fluctuating number of elementary quark/gluon constituents • Rich structure of the wave function • Components probed in ep scattering: • JLab 12 GeV: valence region • EIC: sea quarks, gluons, Q2 dependence [Weiss 09] • Physical properties • Transverse imaging • Correlations: transverse, longitudinal, and nuclear modifications • Tests of reaction mechanism non-pert. sea quarks/gluons radiative gluons/sea valence quarks/gluons

  3. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Nucleon Structure: exclusive processes • Exclusive processes at sufficiently high Q2 should be understandable in terms of the “handbag” diagram • The non-perturbative (soft) physics is represented by the GPDs • Shown to factorize from QCD perturbative processes for longitudinal photons [Collins, Frankfurt, Strikman 97] e’ Q2>>R-2 e Q2 pointlike GPD ΔT N N’ • Physical interest in GPDs • Transverse spatial distribution of partons with longitudinal momentum x: transverse imaging of nucleon [Burkhardt 00] • Correlations in wave function • Moment xn-1 Form factor of local twist-2 spin-n operator: EM tensor, angular momentum • [Ji 96, Polyakov 02] Transverse Fourier x-x’ ξ=0 π, K, γ, etc. hard • Tests of reaction mechanism • Model-independent features of small-size regime • Finite-size corrections • [Frankfurt et al. 96, Kroll, Goloskokov >05]

  4. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Valence Quark Imaging Example: DVCS at JLab 12 GeV Interference with BH gives access to DVCS amplitude t- dependence allows Fourier transform in ξ=0 limit x=0.45 x=0.35 x=0.25 H(x=ξ,t)/F1(t) x b (fm) |t| (GeV2) Projected results for GPD H(ξ,x=ξ,t) extracted from beam spin asymmetry Transverse spatial image of proton obtained by Fourier transforming the measured GPD

  5. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle DVCS: future facilities • JLab 12 GeV: Valence quark GPDs • Spin observables, p/D • Re DVCS from TCS with (and ?) [Munoz 09] [Stepanyan et al. 09] • COMPASS: DVCS at 0.01<x<0.1 • Re DVCS from BCA with [Schoeffel 09] • EIC: great opportunities for sea quarks and gluons TCS kinematics projection at an EIC for 6 GeV electrons and 60 GeV protons [Stepanyan 09]

  6. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Nucleon GPDs: spin-flavor Deep Virtual Meson Production (DVMP) long. only • Nucleon structure described by 4 GPDs: • H, E (unpolarized), , (polarized) • Quantum numbers probe individual GPD components more selectively • Vector:ρº/ρ+/K* select H, E • Pseudoscalar: π,η,K select the polarized GPDs, and • Need good understanding of reaction mechanism • QCD factorization for mesons is complex (additional interaction of the produced meson)

  7. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Meson Reaction Mechanism: JLab 12 GeV Vector Mesons Pseudoscalar Mesons “pole” VGG GPD-based calculation p+ pole dσ/dt (t=tmin) [nb/GeV2] p° non-pole ρ˚ data π° has no pole contribution! Q2 [GeV2] • Understanding of reaction mechanism • Role of qqbar pair knockout • Finite-size corrections • Feature: pole term in GPD • Understand relative importance of “pole and “non-pole” contributions

  8. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle EIC: Quark Imaging through Meson Production • Physics interest • Transverse imaging of nonperturbative sea quarks and gluons • Information about meson wave function: spin/flavor structure x • Mesons select definite charge, spin, flavor component of GPD radiative sea Non-perturbative sea quarks valence quarks • Exclusive meson production • Requires Q2~10GeV2 for dominance of “pointlike” configurations pQCD

  9. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle EIC: Gluon Imaging with J/Ψ • Transverse spatial distributions from exclusive J/ψ, and φat Q2>10 GeV2 • Transverse distribution directly from ΔT dependence • Reaction mechanism, QCD description studied at HERA • Physics interest • Valence gluons, dynamical origin • Chiral dynamics at b~1/Mπ • [Strikman, Weiss 03/09, Miller 07] • Diffusion in QCD radiation • Existing data • Transverse area x<0.01 [HERA] • Larger x poorly known [FNAL]

  10. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Gluon Imaging: Valence Gluons • Transverse imaging of valence gluons through exclusive J/ψ, φ • Imaging requires • Full t-distribution for Fourier transform • Non-exponential? Power-like at |t|>1 GeV2? • Electroproduction with Q2>10 GeV2: test reaction mechanism, compare different channels, control systematics • Experimentally need: • Recoil detection for exclusivity, wide coverage in t with high resolution • Luminosity ~ 1034, electroproduction, high-t First gluon images of the nucleon at large x! Hyde, Weiss ‘09

  11. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Gluon imaging: gluon vs. singlet quark size • Do singlet quarks and gluons have the same transverse distribution? • Hints from HERA: • Dynamical models predict difference: pion cloud, constituent quark picture [Strikman, Weiss 09] • No difference assumed in present pp MC generators for LHC! • EIC: gluon size from J/ψ, singlet quark size from DVCS • x-dependence: quark vs. gluon diffusion in wave function • Detailed analysis: LO NLO [Mueller et al.] Detailed differential image of nucleon’s partonic structure

  12. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle EIC: Transverse sea quark imaging ep → e'π+n • New territory for collider! • Spatial structure of non-perturbative sea • Closely related to JLab 12 GeV • Quark spin/flavor separations • Nucleon/meson structure • Simulation for π+ production assuming 100 days at a luminosity of 1034 with 5 on 50 GeV (s=1000 GeV2) • V. Guzey, C. Weiss: Regge model • T. Horn: empirical π+ parameterization [Tanja Horn, Antje Bruell, Christian Weiss] Transverse spatial structure of non-perturbative sea quarks! • Lower and more symmetric energies essential to ensure exclusivity

  13. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle EIC: Transverse strange sea quark imaging [Tanja Horn, David Cooper] • Do strange and non-strange sea quarks have the same spatial distribution? • πN or KΛ components in nucleon • QCD vacuum fluctuations • Nucleon/meson structure ep → e‘K+n • Rate estimate for KΛ using an empirical fit to kaon electroproduction data from DESY and JLab assuming 100 days at a luminosity of 1034 with 5 on 50 GeV (s=1000 GeV2) • Consistent with back-of-the-envelope scaling arguments • Lower and more symmetric energies essential to ensure exclusivity Imaging of strange sea quarks! Pushes luminosity towards > 1034, also at lower energy

  14. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Transverse polarization example Transverse spin • Deformation of transverse distribution by transverse polarization of nucleon • Helicity flip GPD E, cf. Pauli ff slower x quarks move faster • EIC: exclusive ρ and φ production with transversely polarized beam • Excellent statistics at Q2>10 GeV2 • Transverse polarization natural for collider Asymmetry x [Horn, Weiss 09]

  15. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Beyond transverse imaging • Longitudinal correlations in nucleon • GPDs at x’≠x: correlated qqbar pairs in nucleon • QCD vacuum structure, relativistic nature of nucleon • EIC: reveal correlations through exclusive meson, γ at x>0.1, Q2 dependence …needs kinematic coverage way beyond JLab 12 GeV • Orbital motion of quarks/gluons • TMD and orbital motion from SIDIS • Major component of the EIC program • Connection with GPDs • Unintegrated distributions, Ji sum rule …should be discussed together

  16. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle L/T separations in exclusive K+/π+ production [Horn 08] Q2=10 GeV2, x=0.1, -t=0.1 • L/T separated cross sections require: • Data taken at different beam energies (Rosenbluth) • Sufficiently large Δε(to avoid magnification of the systematic uncertainty in the separation) 5 on 50 4 on 250 Δε~0.22 3 on 17 • Virtual photon polarization, ε, goes to unity at high √s Requires special low energies for at least one ε point

  17. L/T separation examples φ π, K, etc • In exclusive reactions we can study both nucleon GPDs and meson form factors φ Fπ,K GPD ep → e'π+n Pion form factor Pion factorization EIC: Ee=5 GeV, Ep=50 GeV stat: ΔσL/σL ~5%, syst: 6%/Δε s=1000 GeV2 100 days 1/Q6 Δε~0.22 Luminosity 1034 Hard Scattering 1/Q4 1/Q8 Q2 [GeV2] Q2 [GeV2] Horn, Huber, Bruell, Weiss [EICC 2008 HU] Excellent potential to study the QCD transition nearly over the whole range from the strong QCD regime to the hard QCD regime.

  18. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Deep Exclusive - meson kinematics 4 on 12 5 on 50 10 on 50 P (GeV/c) Q2>10GeV2 Moderate momentum over large angular range 4 on 250 10 on 250 Physics interest x>0.01: Non-perturbative sea quarks Lower-energy, and symmetric kinematics allow for wider π+ angular distribution:  Facilitates detection  Better angular and momentum resolution ep → e'π+n High momentum over full angular range [Tanja Horn]

  19. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Deep Exclusive – recoil baryon kinematics 4 on 12 5 on 50 10 on 50 DQ = 1.3 DQ = 1.3 DQ = 5 4 on 250 10 on 250 Want 0 < t < 1 GeV dt/t ~ t/Ep Wider recoil neutron distribution at lower Ep  Better t- resolution DQ = 0.3 DQ = 0.3 (Tanja Horn) ep → e'π+n [Tanja Horn] Exclusive processes at x>0.01: better prospect with lower-energy and more symmetric kinematics

  20. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Exclusive Meson Production Perspectives • Energies • More symmetric energies favorable, 5 on 50 seems to be a sweet spot for exclusive meson production • Lower energies essential for ε range in pseudoscalar L/T separations (pion form factor) • Kinematic reach • Need Q2>10 GeV2 (pointlike configurations) • x range between 0.001 and 0.1 overlapping with HERA and JLab12 GeV • s-range between 200 and 1000 GeV2 • Luminosity • Non-diffractive proceses (exclusive π and K production) require high luminosity for low rates, differential measurements in x, t, Q2 • Kaons push luminosity >1034 • Detection • Recoil detection for exclusivity, t-range

  21. Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Summary • The EIC is an excellent tool to access nucleon structure • JLab 12 GeV • Main focus: valence quark imaging with DVCS • Also initial deep exclusive meson production studies • EIC: gluon and sea quarks • Transverse gluon and sea quark imaging through deep exclusive meson production Tanja Horn, EIC@JLab - taking nucleon structure beyond the valence region, INT09-43W

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