Imaging Sea Quarks and Gluons at an EIC

1. Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA Imaging Sea Quarks and Gluons at an EIC Tanja Horn DIS2011, XIX International Workshop on Deep Inelastic Scattering Newport News, VA, 14 April 2011 Tanja Horn, CUA Colloquium 1

2. Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 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 → Talk by F. Yuan 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 • Moments, Form factor of local twist-2 spin-n operators: EM tensor, angular momentum • [Ji 96, Polyakov 02] Transverse Fourier x-x’ π, K, γ, etc. hard • Tests of reaction mechanism • Model-independent features of small-size regime • Finite-size corrections ξ=0 x<ξ Transverse density correlations

4. Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA Valence Quark Imaging Example: DVCS 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA DVCS: future facilities • JLab 12 GeV: Valence quark GPDs • Spin observables, p/D • Re DVCS from TCS with (and ?) →Talk by F.-X. Girod [Stepanyan et al.] • COMPASS: DVCS at 0.01<x<0.1 • Re DVCS from BSA with →Talk by H. Wollny • 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA Nucleon GPDs: spin-flavor Deep Virtual Meson Production (DVMP) pointlike? 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 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 → Talk by V. Kubarovsky

8. Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 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, M2 >> hadronic scale, |t| small

9. Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 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 [H1, ZEUS] • 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA Gluon Imaging: Valence Gluons • Transverse imaging of valence gluons through: valence-like gluons • 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 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! → Talk by C. Weiss • 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 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 • Exclusive pion production • High luminosity for low rates • Differential measurements in x, t, Q2 • Kinematic reach in Q2 and x [T. Horn, A. Bruell, C. Weiss] • Lower and more symmetric energies essential to ensure exclusivity • t-distributions, Fourier transform Transverse spatial structure of non-perturbative sea quarks!

13. Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA EIC: Transverse strange sea quark imaging [T. Horn, D. Cooper] ep → e‘K+n • Do strange and non-strange sea quarks have the same spatial distribution? • πN or KΛ components in nucleon • QCD vacuum fluctuations • Nucleon/meson structure • 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA Beyond transverse imaging • Longitudinal correlations in nucleon • GPDs at x’≠x: correlated 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 → Talks by F. Yuan and this session …should be discussed together

16. Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA L/T separations in exclusive K+/π+ production [Horn 08] Q2=10 GeV2, x=0.1, -t=0.1 • Needed where Q2 >> hadronic scale does not yet apply 5 on 50 4 on 250 • 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) 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 08 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 Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 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