Nuclear physics with a medium–energy EICC. Weiss (JLab), POETIC Workshop, Indiana University, Bloomington, 20–Aug–12

I) 3D structure of nucleon in QCD

Sea quark and gluon polarization

Spatial distributions, orbital motion

Multiparton correlations

II) Fundamental color fields in nuclei

Nuclear quark/gluon densities

Shadowing, coherent processes

Color transparency

III) Emergence of hadrons fromcolor charge

Color neutralization, hadron formation

Interaction of color charge with matter

• Overview of ep/eA physics with“generic” medium–energy EIC

√s = 20–70 GeV, L ∼ 1034cm−2s−1

Based on review article A. Accardi et al., EPJA48 (2012) 92.Input to JLab MEIC Concpetual Design Report (2012)

• Guiding principles

Focus on physical system,not formal descriptors:“What do we learn about dynamics?”

Unifying perspective low ↔ high energies

1

Science Requirements and Conceptual Design for a Polarized

Medium Energy Electron-Ion Collider at Jefferson Lab

S. Abeyratne12

, A. Accardi1,7

, S. Ahmed1, D. Barber

6, J. Bisognano

18, A. Bogacz

1, A.

Castilla13,17

, P. Chevtsov14

, S. Corneliussen1, J. Delayen

13, W. Deconinck

5, Ya. Derbenev

1, S.

DeSilva13

, D. Douglas1, V. Dudnikov

11, R. Ent

1, B. Erdelyi

12, Yu. Filatov

9,10, D. Gaskell

1, V.

Guzey1, T. Horn

4, A. Hutton

1, C. Hyde

13, R. Johnson

11, Y. Kim

8, F. Klein

4, A. Kondratenko

16,

M. Kondratenko16

, G. Krafft1,13

, R. Li1, F. Lin

1, S. Manikonda

2, F. Marhauser

11, R. McKeown

1,

V. Morozov1, P. Nadel-Turonski

1, E. Nissen

1, P. Ostroumov

2, M. Pivi

15, F. Pilat

1, M. Poelker

1,

A. Prokudin1, R. Rimmer

1, T. Satogata

1, M. Spata

1, H. Sayed

3, M. Sullivan

15, C. Tennant

1, B.

Terzić1, M. Tiefenback

1, H. Wang

1, S. Wang

1, C. Weiss

1, B. Yunn

1, Y. Zhang

1

1

Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, USA 2

Argonne National Laboratory, Argonne, IL 60439, USA 3

Brookhaven National Laboratory, Upton, NY 11973, USA 4

Catholic University of America, Washington, DC 20064, USA 5

College of William and Mary, Williamsburg, VA 23187, USA 6

Deutsches Elektronen-Synchrotron (DESY), 22607 Hamburg, Germany 7

Hampton University, Hampton, VA 23668

8 Idaho State University, Pocatello, ID 83209, USA

9 Joint Institute for Nuclear Research, Dubna, Russia

10 Moscow Institute of Physics and Technology, Dolgoprydny, Russia

11 Muons Inc., Batavia, IL 60510, USA

12 Northern Illinois University, De Kalb, IL 60115, USA

13 Old Dominion University, Norfolk, VA 23529, USA

14 Paul Scherrer Institute, 5232 Villigen PSI, Switzerland

15 SLAC National Accelerator Laboratory, Menlo Park, CA 94305, USA

16 Science and Technique Laboratory Zaryad, Novosibirsk, Russia

17 Universidad de Guanajuato, 36000 Guanajuato, Mexico

18 University of Wisconsin-Madison, Madison, WI 53706, USA

Editors: Y. Zhang and J. Bisognano

(August 10, 2012)

3D nucleon structure: Fields and particles

�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������

�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������

2Q e’

e

x,

interactions

wave function

• Hadrons in QCD

Relativity: Particle creation/annihilation,space–time picture frame dependent

Strong interactions: Vacuum structure,non–perturbative effects

Quantum mechanics: FluctuationsUniquely challenging dynamical system!

• Field–theoretical description

Imaginary time t → iτ , statistical mechanicsLattice QCD; analytic methods

• Particle–based description

Parton picture P → ∞: Wave functionFeynman, Gribov: Closed system. Alt: Light–front quantization

Components with different particle number

Many–body system: Constituents, interactions,spatial structure, orbital motion, . . .

High–energy process takes snapshotShort–distance interactions: Factorization

3D nucleon structure: Landscape

1

101

102

10-3 10-2 10-1 1

Q2

[GeV

2 ]

x

JLab 12 GeV

√s = 20 GeV

√s = 70 GeV

Theoretical coverage

10−3

10−2

10−1

1

saturationradiation non−pert.

interact.

radiative sea quarksgluonsgluons/sea

valence quarksgluons

QCD

EIC

.....

.

.

.. ...... ....... ...

.......

......

• Components probed predominantly

x > 0.1 Valence quarks: Source,quantum numbersAlso gluons at large x!Intrinsic sea ss̄, cc̄?

x ∼ 10−1 Sea quarks, gluons:−10−2 Quantum numbers

Generated by non–perturbativeQCD interactions!

x < 10−2 Gluons, singlet sea:Radiatively generatedSaturation at small x: New dyn. scale

Learn about interactions!

• Quantities measured

Particle number densities,incl. spin/flavor dependence PDFs

Transverse spatial distributions GPDs

Orbital motion, angul. momentum TMDs

Particle correlations MP distributions, GPDs

Densities with operator definition 〈N |QCD–Op |N〉Calculable with non–perturbative methodsScale dependence from RNG equation.

3D nucleon structure: Sea quark polarization

d−u,−−ss,

π, ΚSpin

Interactions?

x-410 -310 -210 -110 1

-0.2

-0.1

0

0.1

0.2

0.3 (x))d∆(x)-u∆x(

HERMES 5 Flavor

EIC 5 on 50

EIC 5 on 50 GeV100 days, 10^33Kinney, Seele 2008

• How are sea quarks polarizedin nucleon?

Non-perturbative QCD interactionsconnecting valence ↔ sea quarks

Role of mesonic degrees of freedom?

• Semi–inclusive scattering: Identifyparticles produced from struck quark

Flavor asymmetries poorly constrainedby present dataHERMES SIDISFirst constraints from RHIC W data

• EIC: Map sea quark distributionsand their spin dependence

High energy ensures independentfragmentation of struck quark

3D nucleon structure: Gluon polarization

Spin

Interactions?Q2

EIC stage-1 data

EIC 30×325

DSSV ∆χ2/χ2=2% bandx∆G

x

Q2 = 10 GeV2-0.1

0

0.1

0.2

0.3

10-5

10-4

10-3

10-2

10-1

1

M. Stratmann, INT Workshop 2010

• What is the polarized gluon distribution?

Origin of non-perturbative gluon fields?“Constituent quark” structure, quark correlations?

Gluon contribution to nucleon spin?Orbital angular momentum in wave function?

• ∆G(x) presently poorly constrained

Q2 dependence of g1(x,Q2)

EMC/SMC, SLAC, HERMES, COMPASS, JLab 6/12 GeV

Hard processes in ~p~p RHIC: Recent data

• EIC: Fully quantitative determinationGood results already with medium energy → Talk Stratmann

• Quark/gluon orbital angular momentum

Much progress in theoretical understandingINT Workshop Feb–12; many recent papers

Manifest in semi–inclusive spin asymmetriese.g. Sivers effect → Talk Prokudin

Challenge to separate OAM in wave functionfrom QCD final–state interactions→ Talk Burkardt

3D nucleon structure: Spatial distributions

x

x

q−

gluons

q +

changes with

���������� ����������

������������

������������

/ψJ

������������������������

������������������������

2

GPD

Q

t

hard

10-7

10-6

10-5

10-4

0 0.5 1 1.5 2

dσT (

ep

→ e

’p J

/ψ)

/ dx

dQ2 d

t [

µb /

GeV

4 ]

-t [GeV2]

sep = 1000 GeV2, L = 1034 cm-2 s-1, 16 weeks

J/ψ electroproduction

Weiss INT 10

5 < Q2 < 10 GeV2

power-like?

x = 0.05

0.1

0.2

40 < W2 < 60 GeV2

80 < W2 < 100 GeV2

160 < W2 < 200 GeV2

• How are quarks/gluons distributedin transverse space?

Fundamental size and “shape”of nucleon in QCD

Distributions change with x:Diffusion, chiral dynamics

Input for saturation models,multiparton interactions in pp@LHC

• Exclusive processes γ∗+N → J/ψ+N

Gluonic form factor of nucleon:Generalized parton distribution

Other channels γ, ρ0, π,Ksensitive to quarks → Talks Hasch, Liuti, Fazio

• EIC: “Gluon imaging” of nucleon

Luminosity for low rates,differential measurements

Color fields in nuclei: Physics

�����������������������������������

�����������������������������������

����������������������������������������

����������������������������������������

����������������������������������������

����������������������������������������

structuremodified

effectscollective

l coh

Q2

• What are the fundamental color fieldsin nuclei?

Modification of nucleon structure

Collective effects A 6= ∑N

Non–nucleonic degrees of freedom

→ QCD origin of NN interaction at different energies→ Approach to black–disk/saturation regime

• Interaction with high–energy probe

Transverse resolution r ∼ 1/Q

Coherence length lcoh ∼ ν/Q2 × factor

Final states: Inclusive, identified spectators,exclusive, . . .

Color fields in nuclei: Landscape

1

10

100

1 10 100 1000

Q2

[GeV

2 ]

lcoh [fm]

JLab 12

√s = 20 GeV

√s = 70 GeV

Theoretical coverage

cohl

Q2

RA

EIC

• Fields probed in eA

lcoh ≪ RA: Modified nucleon structure,short–range correlationsJLab 12 GeV: EMC effect for valence quarksEMC effect for gluons, antiquarks?

lcoh & RA: Collective effectsNew regime accessible with medium–energy EIC!

• QCD phenomena

Shadowing: QM interference inscattering from multiple nucleonsIs it different for gluon and quark fields?

Color transparency: Disappearance ofinteraction for small probes σ ∝ r2

Fundamental prediction of QCD as gauge theory

Coherent scattering: Quark/gluon fieldsof entire nucleus Nuclear GPDs, quark/gluon size

Quantum fluctuations: Diffraction

Saturation: Strong gluon fields,black disk regime in hard interactionsNew dynamical scale Qs

Color fields in nuclei: Gluon density

0.20.40.60.81.01.21.4

0.20.40.60.81.01.21.4

10-4

10-3

10-2

10-1

10.00.20.40.60.81.01.21.4

10-4

10-3

10-2

10-1

10-4

10-3

10-2

10-10.0

0.20.40.60.81.01.21.4

Q2=100 GeV

2

Q2=1.69 GeV

2

EPS09NLO

C C C(

,2 =

100

GeV

2 )C

(,

2 =1.

69G

eV2 )

C

Eskola et al. 09

valence quarks sea quarks gluons

ShadowingEMC

• Nuclear quark/gluon densitiesx > 0.1 “EMC effect:” Modification of

free nucleon structure:

x ∼ 0.1 Antishadowing: Poorly understood

x ≪ 0.1 “Shadowing:” QM interference

• Gluon poorly constrained

Q2 dependence of nuclearstructure function F2A(x,Q

2)

x-410 -310 -210 -110 1

]2 [

GeV

2Q

1

10

210

310

410 EIC Stage IIEIC Stage I

= 0.5c2Q = 1.5c

2Q1/3Pb = 0.5Ac

2Q1/3Pb = 1.5Ac

2Q

MEIC NNPDF analysis Accardi, Dupre INT 10

• Medium–energy EIC: Precise determinationof nuclear quark/gluon densities

Wide coverage in x,Q2

• Inportant for understanding approachto saturation at small xShadowing affects nuclear enhancement of Qs

Color fields in nuclei: New probes with EIC

tagged

transparency

coherent

V,γ

• Spectator tagging

Bound nucleon structure: EMC effect

Neutron structure from D(e, e′p)XJLab BONUS experiment

Requires forward p/n detection

• Coherent nuclear processes A(e, e′M)A

Fundamental quark/gluon radii of light nucleiKowalski, Caldwell 09: Heavy nuclei, very challeging

Impact parameter dependent shadowing

• Color transparency in meson production

Fundamental prediction of QCD

Complement to saturation experiments:“Disappearance” at high Q2

Hadrons from color charge: Fragmentation

?e−e+

??"hole"

spinx,

ep

����������N

x

z

xF

Current

Target

fragmentation

fragmentation

Correlations

• How do hadrons emergefrom QCD color charge?

Conversion energy → matterCosmic ray physics, early universe

Dynamical mechanisms: QCD radiation,pair creation by soft fieldsVacuum structure, qq̄ condensate

• Fragmentation functions from e+e−

Many puzzles: ss̄, kaons, baryonsEssential input to SIDIS

• EIC: New possibilities

Fragmentation functions from ep:Favored ↔ unfavored, test universality

Target fragmentation: How does nucleonwith “color hole” materialize?x, spin dependence

Correlations current–target regions:Multiparton correlationsNew field of study: pp at LHCNew possibilities for nucleon structure

Qualtiatively new! Many applications! Unique for EIC

Hadrons from color charge: Matter

A

m a t t e r

+

q

h

q

−

e e

cold QCD

A A A

q

hot QCDm a t t e r

0

tCN

Ft

t h

??

Z0 0.2 0.4 0.6 0.8 10.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4 HERMES data+π+K

EIC error bars is arbitrary)h

A(Rs = 200 GeV^2

< 30 GeVν20 < +π+K

D Meson

< 70 GeVν50 < +π+K

D Meson

Multiplicity Ratio Accardi, Dupre INT 10

2Q1 10 210

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

HERMES data+π

EIC error bars is arbitrary)A

h(R

)2 (s=200 GeV+π &&2 (s=1000 GeV+π

< 130 GeV)ν100 <

2Ratio Vs Q

• How does fast color charge interactwith hadronic matter?

Energy loss, attenutation

Time scales for color neutralization tN ,hadron formation tF

Cold vs. hot matter? eA/γA ↔ jets in AA

• EIC: Comprehensive studies

Wide range of energy ν = 10 − 100 GeV:Move hadronization inside/outside nucleus,distinguish energy loss and attenuationFixed–target: Correlations ν–Q2

Wide range of Q2: QCD evolution offragmentation functions and medium effects

Hadronization of charm, bottom:Clean probes, QCD predictions

High luminosity: Multidimensional binning

√s > 30GeV: Study jets and

their substructure in eA

Summary

• Unique nuclear physics program with medium-energy EIC√s = 20-70 GeV

Three–dimensional structure of nucleon in QCD

Fundamental color fields in nuclei

Emergence of hadrons from color charge

Natural organization . . . could be sharpened further!

• Focus on what we learn about the dynamical system

Many questions addressed by more than one measurement:Orbital angular momentum — inclusive ∆G, semi–inclusive asymmetries;Quark correlations — exclusive and semi–inclusive processes

• Qualitatively new probes available in eA

Spectator tagging, coherent processes: Should be developed further!

ep better formalized, but eA completely new