imaging sea quarks and gluons at an eic

Imaging Sea Quarks and Gluons at an EIC

Tanja Horn

DIS2011, XIX International Workshop on Deep Inelastic Scattering

Newport News, VA, 14 April 2011

1Tanja Horn, CUA ColloquiumTanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

Nucleon Structure: landscapeNucleon Structure: landscape

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

• 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

• 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 processesNucleon Structure: exclusive processes

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

• 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]

• Tests of reaction mechanism– Model-independent features of small-size regime– Finite-size corrections

• Exclusive processes at sufficiently high Q2 should be understandable in terms of the “handbag” diagram

– The non-perturbative (soft) physics is represented by the GPDso Shown to factorize from QCD perturbative

processes for longitudinal photons [Collins, Frankfurt, Strikman 97]

π, K, γ, etc.

hardpointlike

GPD ΔT

Q2

N N’

ee’ Q2>>R-2

3

Transverse Fourier x-x’

ξ=0Transverse density correlationsqq

x<ξ

→ Talk by F. Yuan

Valence Quark Imaging Example: DVCSValence Quark Imaging Example: DVCS

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

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

xb (fm)|t| (GeV2)

H(x

=ξ,

t)/F

1(t

)

t- dependence allows Fourier transform in ξ=0 limit

4

DVCS: future facilitiesDVCS: future facilities

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA 5

2ppt

2pqs

• EIC: great opportunities for sea quarks and gluons

• JLab 12 GeV: Valence quark GPDs– Spin observables, p/D– Re DVCS from TCS with (and ?)

e

• COMPASS: DVCS at 0.01<x<0.1– Re DVCS from BSA with

[Stepanyan 09]

→Talk by H. Wollny

TCS kinematics projection at an EIC for 6 GeV electrons and 60 GeV protons

→ Talk by F.-X. Girod

[Stepanyan et al.]

Deep Virtual Meson Production (DVMP)Deep Virtual Meson Production (DVMP)

Nucleon GPDs: spin-flavorNucleon 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 Sea Quarks and Gluons at an EIC,

DIS 2011, Newport News, VA 6

• Nucleon structure described by 4 GPDs: – H, E (unpolarized), , (polarized)H

~E~

• Quantum numbers probe individual GPD components more selectively– Vector: ρº/ρ+/K* select H, E– Pseudoscalar: π,η,K select the polarized GPDs, and H

~ E~

pointlike?

Meson Reaction Mechanism: JLab 12 Meson Reaction Mechanism: JLab 12 GeVGeV

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

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

Q2 [GeV2]d

σ/d

t (t

=t m

in)

[nb

/Ge

V2 ]

“pole”

7

ρ˚ data

→ Talk by V. Kubarovsky

EIC: Quark Imaging through Meson EIC: Quark Imaging through Meson ProductionProduction

• Mesons select definite charge, spin, flavor component of GPD

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

valence quarks

Non-perturbative sea quarks

radiative sea

x

• Exclusive meson production

– Requires Q2, M2 >> hadronic scale, |t| small

BMN *

• Physics interest– Transverse imaging of

nonperturbative sea quarks and gluons

– Information about meson wave function: spin/flavor structure

8

EIC: Gluon Imaging with J/EIC: Gluon Imaging with J/ΨΨ

• Physics interest– Valence gluons, dynamical origin

– Chiral dynamics at b~1/Mπ

[Strikman, Weiss 03/09, Miller 07]

– Diffusion in QCD radiation

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

• Transverse spatial distributions from exclusive J/ψ, and φ at Q2>10 GeV2

– Transverse distribution directly from ΔT dependence

– Reaction mechanism, QCD description studied at HERA [H1, ZEUS]

• Existing data– Transverse area x<0.01 [HERA]

– Larger x poorly known [FNAL]

9

Gluon Imaging: Valence GluonsGluon Imaging: Valence 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

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

• 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

10

valence-like gluons

• Transverse imaging of valence gluons through: NJN /*

Gluon imaging: gluon vs. singlet Gluon imaging: gluon vs. singlet quark sizequark size

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

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!

)(gAreaqqArea

11

→ Talk by C. Weiss

[T. Horn, A. Bruell, C. Weiss]

• New territory for collider!

• Spatial structure of non-perturbative sea– Closely related to JLab 12 GeV

o Quark spin/flavor separationso Nucleon/meson structure

• Exclusive pion production– High luminosity for low rates– Differential measurements in x, t, Q2

– Kinematic reach in Q2 and x

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

EIC: Transverse sea quark imagingEIC: Transverse sea quark imaging

ep → e'π+n

12

Transverse spatial structure of non-perturbative sea quarks!

• Lower and more symmetric energies essential to ensure exclusivity

– t-distributions, Fourier transform

Pushes luminosity towards > 1034, also at lower energy

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

EIC: Transverse strange sea quark imaging

• 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

• 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 1034 with 5 on 50 GeV (s=1000 GeV2)

– Consistent with back-of-the-envelope scaling arguments

13

Imaging of strange sea quarks!

[T. Horn, D. 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 Q2>10 GeV2

– Transverse polarization natural for collider

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

[Horn, Weiss 09]

Transverse spin

x

slower

quarks move faster

x

Asy

mm

etry

14

Beyond transverse imaging

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

• 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

• 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

qq

→ Talks by F. Yuan and this session

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

Q2=10 GeV2, x=0.1, -t=0.1

4 on 2505 on 50

3 on 17

Δε~0.22

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

[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

• Needed where Q2 >> hadronic scale does not yet apply

L/T separation examples

EIC: Ee=5 GeV, Ep=50 GeV

Δε~0.22

stat: ΔσL/σL ~5%, syst: 6%/Δε

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.

Fπ,K

π, K, etc

φ

φ

Hard Scattering

GPD

• In exclusive reactions we can study both nucleon GPDs and meson form factors

s=1000 GeV2

100 days

Luminosity 1034

ep → e'π+n Pion form factorPion factorization

1/Q6

1/Q8

1/Q4

Q2 [GeV2]Q2 [GeV2]

17

Summary

• The EIC is an excellent tool to access nucleon structure

Tanja Horn, EIC@JLab - taking nucleon structure beyond the valence region, INT09-43W

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, DIS 2011, Newport News, VA

• 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

18