at an EIC Tanja Horn The 19 th Particles and Nuclei International - - PowerPoint PPT Presentation

Imaging Sea Quarks and Gluons at an EIC

Tanja Horn

The 19th Particles and Nuclei International Conference (PANIC 2011) Cambridge, MA, 28 July 2011

1 Tanja Horn, CUA Colloquium Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

Internal Landscape of the Nucleon

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

• Hadrons in QCD are relativistic

many-body systems

– Fluctuating number of elementary quark and gluon constituents – Rich structure of the wave function

• Components probed in ep scattering:

– JLab 12 GeV: valence region – EIC: probes sea quark and gluon components

• Key physical interests

– Transverse spatial distribution – Correlations: transverse, longitudinal, and nuclear modifications – Tests of reaction mechanism

valence quarks/gluons non-pert. sea quarks/gluons radiative gluons/sea

[Weiss 09]

x

Accessible range of energies and resolution, Q2, for probing components of the hadron wave function 2

Nucleon Structure through Exclusive Processes

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

• GPDs are a tool for transverse imaging of

the nucleon

– Encode information on correlations and distribution of partons in transverse space [Burkhardt 00]

– Moments, Form factor of local twist-2 spin-n

• perators: 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

allow access to Generalized Parton Distributions (GPDs)

– Factorization theorem: non-perturbative physics factorizes from perturbative QCD processes for longitudinal photons π, K, γ, etc.

hard

pointlike

GPD

ΔT

Q2 N N’ e e’

Q2>>R-2 Transverse Fourier x-x’

Transverse density correlations

q q

ξ=0 x<ξ

3

Imaging Example: DVCS

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

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)/F1(t)

t- dependence allows Fourier transform in ξ=0 limit ) ; , ( ~ ) Im( t x H DVCS   



  x t x H dx DVCS ) ; , ( ~ ) Re(

LT

4

Transverse Imaging through GPDs at EIC

• long. only

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

• Nucleon structure described by 4 GPDs:

– H, E (unpolarized), , (polarized)

H ~ E ~

pointlike?

• Mesons select definite charge, spin,

flavor component of GPD

Exclusive Reactions:

B M N   *  J/Ψ, φ

gluon

ρº, γ

gluon + singlet quark

ρ+, K*

non-singlet q

π, K, η

non-singlet Δq

J/Ψ, φ,

ρ, γ π, ρ, K, K*

ΔT

• DVCS (flavor blind) probes GPD H and

provides additional information on singlet quarks

EIC enables a comprehensive program of transverse imaging of gluons and sea quarks

5

Gluon Imaging with J/Ψ

• 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, PANIC 2011, Cambridge, MA

• 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]

6

[Weiss INT10-3 report]

Gluon Imaging: 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

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

• Experimentally need:

– Recoil detection for exclusivity, wide coverage in t with high resolution – Luminosity ~ 1034, electroproduction, 0< t <2 GeV2

Hyde, Weiss „09 7 valence-like gluons

• Transverse imaging of valence-like

gluons through:

N J N     / *

First gluon images of the nucleon at large x! √s~30 GeV

~100 days, ε=1.0, L=1034 s-1cm-2

[Weiss INT10-3 report]

Singlet Quark Imaging with DVCS

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

• DVCS cross section and beam charge

asymmetry allow accessing GPD H

– Additional information on singlet quarks

    

    d + d d d = ALU

• DVCS beam spin asymmetry linked to

imaginary part of Compton Form Factor H

– Complementary to unpolarized cross sections and beam charge asymmetry – Using L and T target asymmetries can also access other GPDs

Measurements of DVCS with different combinations of beam and target polarizations over a wide kinematic range with high precision/luminosity allows access to sea quark GPDs directly and indirectly to gluon GPDs

√s~140 GeV √s~140 GeV

~365 days, ε=1.0, L=1034 s-1cm-2 ~100 days, ε=0.5, L=1034 s-1cm-2 t (GeV2) dσ(ep→γp)/dt (nb/sr)

1.6E-3 < xB < 2.5E-3 3<Q2<6 GeV2

[Fazio 10+, INT report] [Geraud, Moutarde, Sabatie 10+, INT10-3 report]

8

Gluon vs. singlet quark size

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

• 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!  

) (g Area q q Area  

Detailed differential image of nucleon‟s partonic structure

√s=100 GeV

~30 days, ε=1.0, L=1034 s-1cm-2

[Sandacz, Hyde, Weiss 08+]

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Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

Imaging of non-singlet sea quarks

• 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

• New territory for collider!
• Lower and more symmetric energies

essential to ensure exclusivity

– t-distributions, Fourier transform

Imaging of strange sea quarks!

√s~30 GeV

[Horn et al. 08+, INT10-3 report]

ep → e'K+Λ ep → e'π+n

~100 days, ε=1.0, L=1034 s-1cm-2 10

Beyond transverse imaging

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

• 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

• Orbital motion of quarks/gluons

– Transverse spin asymmetry AUT in f, J/Y production – Constrain gluon helicity flip GPD Eg – Transverse Momentum Distributions (TMDs) and orbital motion from SIDIS

– Imaging in momentum space, major component of EIC program

– Connection with GPDs

– Unintegrated distributions, Ji sum rule

11

• L/T separated cross sections in non-perturbative regime (non-diff.)

– Data taken at different beam energies (Rosenbluth) – Sufficiently large Δε (to control systematic uncertainty in the separation)

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, PANIC 2011, Cambridge, MA

[Horn, Weiss 09]

Transverse spin

x

slower quarks move faster

x Asymmetry

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Image the Transverse Momentum of the Quarks

The difference between the p+, p–, and K+ asymmetries reveals that quarks and anti-quarks of different flavor are orbiting in different ways within the proton.

Swing to the left, swing to the right: A surprise of transverse-spin experiments dh ~ Seq

2q(x) df Df h(z)

13 Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

Sivers distribution

[NSAC LRP07]

EIC: π+ projections with proton target

~30 days, ε=0.5, L=1034 s-1cm-2

√s~140 GeV √s~50 GeV √s~15 GeV

[Huang 10+] 14 Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

Only a small subset of the (x,Q2) landscape has been mapped here:

terra incognita

Gray band: present “knowledge” Red band: EIC (1) (dark gray band: EIC (2))

Image the Transverse Momentum of the Quarks

Exact kT distribution presently unknown! “Knowledge” of kT distribution at large kT is artificial!

(but also perturbative calculable limit at large kT) [Prokudin, Qian, Huang] [Prokudin] 15 Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

An EIC with good luminosity & high transverse polarization is the

• ptimal tool to to study this!

Mesons from SIDIS

16 Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA [Horn 08+] Lab Scattering angle (rad) Momentum (GeV/c)

Q2 > 1 GeV2 0.01 < y < 0.95 0.1 < z < 0.9

Momentum (GeV/c) Momentum (GeV/c)

Non-exclusive processes, e.g., SIDIS, produce high- momentum mesons at small angles

Q2 ~ xys

10 deg 5 deg Large concentraction of pions in the first 5-10 degrees

√s=31.6 GeV √s=100 GeV √s=44.7 GeV

[Aschenauer et al., INT10-3 report]

Events of interest:

1 10 1 10 1 10

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA 17

Mesons from Exclusive Production

√s=31.6 GeV √s=44.7 GeV √s=100GeV

Momentum (GeV/c) Momentum (GeV/c) Momentum (GeV/c) Lab Scattering angle (rad) Lab Scattering angle (rad) Lab Scattering angle (rad)

Q2 > 10 GeV2 → events of interest for imaging studies

• Momentum distributions at lower center of mass energies (up to √s ~45 GeV,) have more

central scattering angles and cover lower momenta

• At even higher CM energies angular spread reduces significantly (narrow forward cone)

− Momentum distribution in this cone is very large forward cone approaches beam energy

Exclusive measurements at very high CM energy require detection of high energy mesons over a very small angular range Best momentum resolution for symmetric or nearly symmetric collisions

[Horn 08+, INT10-3 report]

Nuclear Science: Map t between tmin and 1 (2) GeV2  Must cover between 1 and 5 degrees  Should cover between 0.5 and 5 degrees  Like to cover between 0.2 and 7 degrees t ~ Ep

2Q2  Angle recoil baryons = t½/Ep

18 Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

Recoil Baryons from Exclusive Reactions

Ep = 250 GeV Ep = 30 GeV

Δθ=1-2˚

Better t-resolution with lower proton energy and more symmetric kinematics

Δθ<0.3˚

Q2 > 10 GeV2

[Horn 08+, INT10-3 report]

Towards the internal landscape of the nucleon

p m

x

TMD

Exact kT distribution presently unknown – EIC can do this well

• 19

Tanja Horn, Imaging Sea Quarks and Gluons at an EIC, PANIC 2011, Cambridge, MA

EIC enables a comprehensive program of transverse imaging of gluons and sea quarks EIC: Transverse momentum distribution derived directly from SIDIS, plus large gain in our knowledge of transverse momentum effects as function of x.

J/Ψ, φ

gluon

ρº, γ

gluon + singlet quark

ρ+, K*

non-singlet q

π, K, η

non-singlet Δq

GPD GPD Transverse Momentum Imaging Transverse Spatial Imaging and beyond, e.g.,

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, PANIC 2011, Cambridge, MA

• JLab 12 GeV

– Main focus: valence quark imaging with DVCS – Also initial deep exclusive production studies

• EIC enables a comprehensive program of transverse imaging of

gluons and sea quarks – Imaging through deep exclusive reactions

20