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

Nucleon Structure: landscape Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle 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, Q 2 dependence Physical properties –Transverse imaging –Correlations: transverse, longitudinal, and nuclear modifications –Tests of reaction mechanism valence quarks/gluons non-pert. sea quarks/gluons radiative gluons/sea 2 [Weiss 09]

Nucleon Structure: exclusive processes Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Physical interest in GPDs –Transverse spatial distribution of partons with longitudinal momentum x: transverse imaging of nucleon [Burkhardt 00] –Correlations in wave function –Moment x n-1 Form factor of local twist-2 spin-n operator: EM tensor, angular momentum [Ji 96, Polyakov 02] Tests of reaction mechanism –Model-independent features of small-size regime –Finite-size corrections –[Frankfurt et al. 96, Kroll, Goloskokov >05] π, K, γ, etc. hard pointlike GPD ΔTΔT Q2Q2 NN’ e e’ Transverse Fourier x-x’ Exclusive processes at sufficiently high Q 2 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] Q 2 >>R -2 ξ=0 3

Valence Quark Imaging Example: DVCS at JLab 12 GeV Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Interference with BH gives access to DVCS amplitude Transverse spatial image of proton obtained by Fourier transforming the measured GPD Projected results for GPD H( ξ,x= ξ,t) extracted from beam spin asymmetry x=0.25 x=0.35 x=0.45 x b (fm) |t| (GeV2) H(x= ξ,t)/F 1 (t) t- dependence allows Fourier transform in ξ=0 limit 4

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

Deep Virtual Meson Production (DVMP) Deep Virtual Meson Production (DVMP) Nucleon GPDs: spin-flavor long. only Need good understanding of reaction mechanism –QCD factorization for mesons is complex (additional interaction of the produced meson) Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle 6 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

Meson Reaction Mechanism: JLab 12 GeV Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle non-pole ++ π ° has no pole contribution ! VGG GPD-based calculation pole °° 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 Vector Mesons Pseudoscalar Mesons Q 2 [GeV 2 ] d σ /dt (t=t min ) [nb/GeV 2 ] “pole” 7 ρ ˚ data

EIC: Quark Imaging through Meson Production Mesons select definite charge, spin, flavor component of GPD Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle valence quarks Non-perturbative sea quarks radiative sea x Exclusive meson production –Requires Q 2 ~10GeV 2 for dominance of “pointlike” configurations pQCD Physics interest –Transverse imaging of nonperturbative sea quarks and gluons –Information about meson wave function: spin/flavor structure 8

EIC: Gluon Imaging with J/Ψ Physics interest –Valence gluons, dynamical origin –Chiral dynamics at b~1/M π [ Strikman, Weiss 03/09, Miller 07 ] –Diffusion in QCD radiation Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Transverse spatial distributions from exclusive J/ ψ, and φ at Q 2 >10 GeV 2 –Transverse distribution directly from Δ T dependence –Reaction mechanism, QCD description studied at HERA Existing data –Transverse area x<0.01 [HERA] –Larger x poorly known [FNAL] 9

Gluon Imaging: Valence Gluons Imaging requires –Full t-distribution for Fourier transform –Non-exponential? Power-like at |t|>1 GeV 2 ? –Electroproduction with Q 2 >10 GeV 2 : test reaction mechanism, compare different channels, control systematics Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Transverse imaging of valence gluons through exclusive J/ ψ, φ Experimentally need: –Recoil detection for exclusivity, wide coverage in t with high resolution –Luminosity ~ 10 34, electroproduction, high-t First gluon images of the nucleon at large x! Hyde, Weiss ‘09 10

Gluon imaging: gluon vs. singlet quark size Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Detailed differential image of nucleon’s partonic structure 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.] 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! 11

[Tanja Horn, Antje Bruell, Christian Weiss] New territory for collider! Spatial structure of non-perturbative sea –Closely related to JLab 12 GeV o Quark spin/flavor separations o Nucleon/meson structure Simulation for π + production assuming 100 days at a luminosity of with 5 on 50 GeV (s=1000 GeV 2 ) –V. Guzey, C. Weiss: Regge model –T. Horn: empirical π + parameterization Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle EIC: Transverse sea quark imaging ep → e'π + n Lower and more symmetric energies essential to ensure exclusivity 12 Transverse spatial structure of non-perturbative sea quarks!

Pushes luminosity towards > 10 34, also at lower energy Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle EIC: Transverse strange sea quark imaging Do strange and non-strange sea quarks have the same spatial distribution? – π N or K Λ components in nucleon –QCD vacuum fluctuations –Nucleon/meson structure ep → e‘K + n Lower and more symmetric energies essential to ensure exclusivity Rate estimate for KΛ using an empirical fit to kaon electroproduction data from DESY and JLab assuming 100 days at a luminosity of with 5 on 50 GeV (s=1000 GeV 2 ) –Consistent with back-of-the-envelope scaling arguments 13 Imaging of strange sea quarks! [Tanja Horn, David Cooper]

Transverse polarization example Deformation of transverse distribution by transverse polarization of nucleon –Helicity flip GPD E, cf. Pauli ff EIC: exclusive ρ and φ production with transversely polarized beam –Excellent statistics at Q 2 >10 GeV 2 –Transverse polarization natural for collider Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle [Horn, Weiss 09] Transverse spin x slower quarks move faster x Asymmetry 14

Beyond transverse imaging Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle 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, Q 2 dependence 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 …needs kinematic coverage way beyond JLab 12 GeV …should be discussed together 15

L/T separations in exclusive K + / π + production Virtual photon polarization, ε, goes to unity at high √ s Requires special low energies for at least one ε point Q 2 =10 GeV 2, x=0.1, -t=0.1 4 on 2505 on 50 3 on 17 Δε~0.22 Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle [Horn 08] 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) 16

L/T separation examples EIC: E e =5 GeV, E p =50 GeV Δε~0.22 stat: Δσ L /σ L ~5%, syst: 6%/Δε 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. F π,K π, K, etc φ φ Hard Scattering GPD In exclusive reactions we can study both nucleon GPDs and meson form factors s=1000 GeV days Luminosity ep → e'π + n Pion form factor Pion factorization 1/Q 6 1/Q 8 1/Q 4 Q 2 [GeV 2 ] 17

Lower-energy, and symmetric kinematics allow for wider π + angular distribution:  Facilitates detection  Better angular and momentum resolution 4 on on 250 Deep Exclusive - meson kinematics [Tanja Horn] Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle P (GeV/c) 5 on 5010 on 50 4 on 250 Q 2 >10GeV 2 High momentum over full angular range Moderate momentum over large angular range Physics interest x>0.01: Non-perturbative sea quarks ep → e'π + n 18

 = 5  = 1.3  = 0.3  t/t ~ t/E p  Wider recoil neutron distribution at lower E p  Better t- resolution (Tanja Horn) Want 0 < t < 1 Ge V 4 on 125 on 5010 on 50 4 on on 250 Deep Exclusive – recoil baryon kinematics [Tanja Horn] ep → e'π + n Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Exclusive processes at x>0.01: better prospect with lower-energy and more symmetric kinematics 19

Exclusive Meson Production Perspectives Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle Luminosity –Non-diffractive proceses (exclusive π and K production) require high luminosity for low rates, differential measurements in x, t, Q 2 –Kaons push luminosity >10 34 Kinematic reach –Need Q 2 >10 GeV 2 (pointlike configurations) –x range between and 0.1 overlapping with HERA and JLab12 GeV –s-range between 200 and 1000 GeV 2 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) Detection –Recoil detection for exclusivity, t-range 20

Summary The EIC is an excellent tool to access nucleon structure Tanja Horn, - taking nucleon structure beyond the valence region, INT09-43W Tanja Horn, Imaging in Exclusive Processes, INT10-3, Seattle 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 21