University of Massachusetts Amherst Christine A. Aidala April 12, 2008 Peering into Hadronic Matter: The Electron-Ion Collider Winter Workshop on Nuclear

University of Massachusetts AmherstChristine A. Aidala

April 12, 2008

Peering into Hadronic Matter:The Electron-Ion Collider

Winter Workshop on Nuclear Dynamics

C. Aidala, WWND, April 12, 2008 2

The EIC: Communities Coming Together

• At RHIC, heavy ions and nucleon spin structure already meet, but in some sense by “chance”– Genuinely different physics

– Communities come from different backgrounds

– Bound by an accelerator that has capabilities relevant to both

• The proposed EIC a facility where HI and nucleon structure communities truly come together, peering into various forms of hadronic matter to uncover the secrets the QCD Lagrangian doesn’t reveal . . .


aaa

aQCD GGAqTqgqmiqL4

1)()(

QCD: Confounded Confinement!

– Salient features of QCD not evident from Lagrangian!• Asymptotic Freedom & Color Confinement

• Due largely to non-perturbative structure of QCD vacuum

– Gluons: mediator of the strong interactions• Determine essential features of strong interactions

• Dominate structure of QCD vacuum (fluctuations in gluon fields)

• Responsible for > 98% of the visible mass in universe(!)

QCD requires fundamental investigation

via experiment


Goals & Key Questions• Explore the new QCD frontier: strong color

fields in nuclei– How do the gluons contribute to the structure of the

nucleus? – What are the properties of high-density gluon matter?– How do fast quarks or gluons interact as they traverse

nuclear matter?

• Precisely image the sea quarks and gluons in the nucleon

– How do the gluons and sea quarks contribute to the spin structure of the nucleon?

– What is the spatial distribution of the gluons and sea quarks in the nucleon?

– How do hadronic final states form in QCD?

How do we understand the visible matter in our universe in terms of the fundamental quarks

and gluons of QCD?


Deep-Inelastic Scattering: A Tool of the Trade in Probing

the Partons within Nucleons/Nuclei

• Probe nucleon with an electron or muon beam• Interacts electromagnetically with (charged) quarks

and antiquarks• “Clean” process theoretically—quantum

electrodynamics well understood and easy to calculate!


DIS Kinematic Variables

Deep Inelastic Scattering:

e

ee

E

EEy

'

Measure of momentum fraction of struck quark

Measure of inelasticity

“Perfect” Tomography

Measure of resolution power:~1/wavelength2

222 )( kkqQ

pq

Qx

2

2

Inclusive DIS: Measure only energy and scattering angle of outgoing eSemi-inclusive DIS: Measure outgoing e & some final-state hadrons

Exclusive DIS: Measure entire final state

“Bjorken x”





nuclear matter?





Investigate using the tools of deep-inelastic scattering

at high energies:An Electron-Ion Collider





nuclear matter?






What Do We Know About Glue in Matter?

),(2

),(2

14

:DIS 22

22

2

4

2..

2

2

QxFy

QxFy

yxQdxdQ

dL

meeXep

Access the gluons in DIS via scaling violations:

dF2/dlnQ2 and linear DGLAP evolution in Q2

G(x,Q2)

Gluons dominate low-x wave function

)201( xG

)201( xS

vxu

vxd

!


Other Handles on the Gluon

Gluon distribution G(x,Q2)– Shown here:

• Scaling violation in F2: F2/lnQ2

• FL ~ s G(x,Q2)

– Other Methods:• 2+1 jet rates (needs jet algorithm and modeling of

hadronization for inelastic hadron final states)

• inelastic vector meson production (e.g. J/)

• diffractive vector meson production ~ [G(x,Q2)]2


Limitations of Linear Evolution in QCDEstablished models: • Linear DGLAP evolution

in Q2

• Linear BFKL evolution in x

Linear evolution in Q2 has a built-in high-energy “catastrophe”

• xG rapid rise for decreasing x and violation of unitary bound

must saturate– What’s the underlying

dynamics? Need new approach


Non-Linear QCD - Saturation• Linear BFKL evolution in x

– Explosion of color field as x0??

• New: BK/JIMWLK based models

– introduce non-linear effects saturation

– characterized by a scale Qs(x,A)

– arises naturally in the Color Glass Condensate (CGC) framework

proton

N partons new partons emitted as energy increasescould be emitted off any of the N partons

proton

N partons any 2 partons can recombine into one

Regimes of QCD Wave Function


Scattering of electrons off nuclei:

• Probes interact over distances L ~ (2mN x)-1

• For L > 2 RA ~ 2A1/3 probe cannot distinguish between nucleons in front or back of nucleus

• Probe interacts coherently with all nucleons

e+A: Studying Non-Linear Effects

Nuclear “Oomph” FactorPocket Formula: )(

1/320

2

x

AcQQ s

As

3.03.02

22 :dependence A

1~ : HERA

proton)for 1(

),(~

x

A ~ xG

xxG

R

QxxGQ A

A

sss

Enhancement of QS with A non-linear QCD regime reached at significantly lower energy in heavy nuclei than in proton


Nuclear “Oomph” Factor

More sophisticated analyses Oomph exceeds that of pocket formula (e.g. Armesto et al., PRL 94:022002, Kowalski, Teaney, PRD 68:114005)

)(

)(

:Note

222

222

ssss

sss

QQQ

QQQ


Universality & Geometric ScalingCrucial consequence of non-linear

evolution towards saturation:• Physics invariant along trajectories

parallel to saturation regime (lines of constant gluon occupancy)

• Scale with Q2/Q2s(x) instead of x and Q2

separately

Geometric Scaling• Consequence of saturation

x < 0.01


Qs : A Scale that Binds Them All

Freund et al., hep-ph/0210139

Nuclear shadowing Geometric scaling

Is the wave function of hadrons and nuclei universal at low x?

proton x 5

nuclei

)(/ 22 xQQ S


e+A Landscape and a New Electron-Ion Collider

• Well mapped in ℓ+p

• Not in ℓ+A!– Mostly small A– Low statistics

Much to be learned from an Electron-Ion Collider!

Terra incognita: small-x, Q Qs

high-x, large Q2


),(2

),(2

14 2

22

2

2

4

2

2

2

QxFy

QxFy

yxQdxdQ

dL

eXep

F2 : Sea Quarks Generated by Glue at Low x

F2 will be one of the first measurements at EIC

nDS, EKS, FGS:

pQCD-based models with different amounts of shadowing

Syst. studies of F2(A,x,Q2):• GA(x,Q2) with precision• distinguish among models


FL at EIC: Measuring the Glue Directly

),( 2QxGF sL

),(2

),(2

14 2

22

2

2

4

2

2

2

QxFy

QxFy

yxQdxdQ

dL

eXep

Access by making measurements at fixed x, Q2 for different y

y= Q2/xs

Scan in !

GA(x,Q2) with great precision

s


Connection to RHIC & LHC Physics

Matter at RHIC– Thermalizes fast ( ~ 0.6 fm/c)

– We don’t know why and how

– Initial conditions? G(x, Q2)

Role of saturation?– RHIC → forward region

– LHC → midrapidity

• bulk (low-pT matter) & semi-hard jets

Jet Quenching:– Need Reference: E-loss in cold matter

– No HERMES data for

• charm energy loss

• in LHC energy range

RHICLHC

EIC provides essential new input:• Precise handle on x, Q2

• Means to study exclusive effects

)(/)( xGxG DPb





nuclear matter?






gS

S

xS > xg ???

A low Q2 puzzle …

50% of Momentum Carried by Gluons … But Still Gluon Puzzles

If sea quarks come from gluon splitting, how can the gluon and sea distributions diverge as they appear to at low Q2??

EIC luminosity 100x > HERA Precision measurements!


Spin Structure of the NucleonQuark spin contribution to the proton spin:

“Spin Crisis”The rest from gluons and orbital angular momentum.

%30

qGLG 2

1

2

1

• Gluon spin contribution, G, still poorly constrained

• Only recent ideas on probing orbital angular momentum!

C. Aidala, WWND, April 12, 2008 24An EIC makes it possible!Region of existing g1p data

World Data on g1pWorld Data on F2

p

Not enough range in x, Q2 to access G via scaling violations


L

R

Observed LargeSingle-Spin Asymmetry

Now confirmed at much higher energies at RHICFermilab E704:

p p X at 400 GeV

Must be due to spin-orbit effects in the proton itself and/or in the fragmentation

process

Spin-Orbit Effects and Transverse Spin

STAR

TkpS

Also access orbital angular momentum and spatial distribution of partons within nucleon via measurements of

Generalized Parton Distributions (GPD’s)- Exclusive measurements

- Possible due to high luminosities, large detector coverage


EIC Status: White Papers 2007• The Electron Ion Collider

White Paper• The GPD/DVCS White

Paper• Position Paper: e+A Physics

at an Electron Ion Collider• The eRHIC machine:

Accelerator Position Paper• ELIC ZDR Draft

Available at:• NSAC LRP2007 home page• Rutgers Town Meeting page• http://www.bnl.gov/eic


The EIC Working Group17C. Aidala, 28E. Aschenauer, 10J. Annand, 1J. Arrington, 26R. Averbeck, 3M. Baker, 26K. Boyle, 28W. Brooks, 28A. Bruell, 19A. Caldwell, 28J.P. Chen, 2R. Choudhury, 10E. Christy, 8B. Cole, 4D. De Florian, 3R. Debbe, 26,24-1A. Deshpande*, 18K. Dow, 26A. Drees, 3J. Dunlop, 2D. Dutta, 7F. Ellinghaus, 28R. Ent, 18R. Fatemi, 18W. Franklin, 28D. Gaskell, 16G. Garvey, 12,24-1M. Grosse-Perdekamp, 1K. Hafidi, 18D. Hasell, 26T. Hemmick, 1R. Holt, 8E. Hughes, 22C. Hyde-Wright, 5G. Igo, 14K. Imai, 10D. Ireland, 26B. Jacak, 15P. Jacobs, 28M. Jones, 10R. Kaiser, 17D. Kawall, 11C. Keppel, 7E. Kinney, 18M. Kohl, 9H. Kowalski, 17K. Kumar, 2V. Kumar, 21G. Kyle, 13J. Lajoie, 16M. Leitch, 27A. Levy, 27J. Lichtenstadt, 10K. Livingstone, 20W. Lorenzon, 145. Matis, 12N. Makins, 6G. Mallot, 18M. Miller, 18R. Milner*, 2A. Mohanty, 3D. Morrison, 26Y. Ning, 15G. Odyniec, 13C. Ogilvie, 2L. Pant, 26V. Pantuyev, 21S. Pate, 26P. Paul, 12J.-C. Peng, 18R. Redwine, 1P. Reimer, 15H.-G. Ritter, 10G. Rosner, 25A. Sandacz, 7J. Seele, 12R. Seidl, 10B. Seitz, 2P. Shukla, 15E. Sichtermann, 18F. Simon, 3P. Sorensen, 3P. Steinberg, 24M. Stratmann, 22M. Strikman, 18B. Surrow, 18E. Tsentalovich, 11V. Tvaskis, 3T. Ullrich, 3R. Venugopalan, 3W. Vogelsang, 28C. Weiss, 15H. Wieman,15N. Xu,3Z. Xu, 8W. Zajc.

1Argonne National Laboratory, Argonne, IL; 2Bhabha Atomic Research Centre, Mumbai, India; 3Brookhaven National Laboratory, Upton, NY; 4University of Buenos Aires, Argentina; 5University of California, Los Angeles, CA; 6CERN, Geneva, Switzerland; 7University of Colorado, Boulder,CO; 8Columbia University, New York, NY; 9DESY, Hamburg, Germany; 10University of Glasgow, Scotland, United Kingdom; 11Hampton University, Hampton, VA; 12University of Illinois, Urbana-Champaign, IL; 13Iowa State University, Ames, IA; 14University of Kyoto, Japan; 15Lawrence Berkeley National Laboratory, Berkeley, CA; 16Los Alamos National Laboratory, Los Alamos, NM; 17University of Massachusetts, Amherst, MA; 18MIT, Cambridge, MA; 19Max Planck Institüt für Physik, Munich, Germany; 20University of Michigan Ann Arbor, MI; 21New Mexico State University, Las Cruces, NM; 22Old Dominion University, Norfolk, VA; 23Penn State University, PA; 24RIKEN, Wako, Japan; 24-1RIKEN-BNL Research Center, BNL, Upton, NY; 25Soltan Institute for Nuclear Studies, Warsaw, Poland; 26SUNY, Stony Brook, NY; 27Tel Aviv University, Israel; 28Thomas Jefferson National Accelerator Facility, Newport News, VA

~100 Scientists, 30 Institutions, 9 countries*Contact People


Electron Ion Collider Concepts

• eRHIC (BNL): Add Energy Recovery Linac to RHIC

PHENIX

STAR

e-cooling (RHIC

II)

Four e-beam passes

Main ERL (2 GeV per pass)

Electron Cooling

Snake

Snake

IR

IReRHIC(Linac-Ring)

ELIC

• ELIC (JLAB): Add hadron beam facility to CEBAF


Main detector: Top view

Hadronic calorimete

rAdditional detector:

Emphasize low-x, low-Q2

diffractive physics (Abt, Caldwell, Liu, Sutiak, hep-ex/0407053)

Main detector:

Emphasize high-luminosity,

full physics program(Pasukonis, Surrow,

physics/0608290)

Si tracking stations

EM calorimete

r

e

p/ADetector Design

Learn from experience at HERA!


EIC Timeline & Status• NSAC Long Range Plan 2007

– Recommendation: $6M/year for 5 years for machine and detector R&D

• Goal for Next Long Range Plan 2012– High-level recommendation for construction

• EIC Roadmap (Technology Driven)– Finalize Detector Requirements from Physics 2008– Revised/Initial Cost Estimates for eRHIC/ELIC 2008– Investigate Potential Cost Reductions 2009– Establish process for EIC design decision 2010– Conceptual detector designs 2010– R&D to guide EIC design decision 2011– EIC design decision 2011– “MOU’s” with foreign countries? 2012


Summary

• What is the role of gluons and gluon self-interactions in nucleons and nuclei?

– Explore non-linear QCD

– Existence of universal saturation regime?

• What is the internal spin, flavor, and space-time structure of the nucleon?

An Electron-Ion Collider would offer unprecedented opportunities to explore the next

QCD frontier

New collaborators and ideas welcome!



Extra Slides


• Peak luminosity 2.6 x 1033 cm-2s-1 in electron-hadron collisions• Electron beam polarization not affected by energy• +- 5 meter “element-free” straight section for detectors• Ion beams up to U• Ability to take full advantage of electron cooling of the hadron

beams• Can run hadron-hadron collisions in RHIC simultaneously

PHENIX

STAR

e-cooling (RHIC II)

Four e-beam passes

Main ERL (2 GeV per pass)

eRHIC at BNL

Add energy-recovery linac to RHIC

24-250 GeV protons30-100 GeV/n ions

3-10 (20) GeV electrons


Electron Cooling

Snake

Snake

3-9 GeV electrons

30-225 GeV protons30-100 GeV/n ions

IR

IR

Visionary green-field design:• Peak luminosity up to ~8 x 1034 cm-2s-1 through short ion bunches• “Figure-8” lepton and ion rings• +- 3m “element-free” straight sections• Ion beams up to Au• Superconducting RF ion linac concept for all ions• 12 GeV CEBAF accelerator serves as injector to electron ring

ELIC at JLab

Add hadron beam facility to CEBAF


eRHIC vs. ELIC• eRHIC could potentially go up to higher electron

energy of 20 GeV, compared to 9 for ELIC.

• eRHIC can run hadron-hadron collisions simultaneously

• Successful R&D for ELIC could lead to luminosities ~10-50 times higher than eRHIC

• ELIC costs higher

• ELIC timeline longer


LHeC: L = 1.1x1033 cm-

2s-1 Ecm = 1.4 TeV

EIC: L > 1x1033 cm-2s-1

Ecm = 20-100+ GeV

• Add 70-100 GeV electron ring to interact with LHC ion beam• Use LHC-B interaction region• High luminosity mainly due to large ’s (= E/m) of beams

• Variable energy range• Polarized and heavy ion beams• High luminosity in energy region of interest for nuclear scienceNuclear science goals:• Explore the new QCD frontier: strong color fields in nuclei• Precisely image the sea-quarks and gluons to determine the spin, flavor and spatial structure of the nucleon.

High-Energy physics goals:• Parton dynamics at the TeV scale - physics beyond the

Standard Model - physics of high parton

densities (low x)

Important cross fertilization of ideas:• Significant European interest in an EIC• EIC collaborators on LHeC Science Advisory Committee

(with Research Directors of CERN, FNAL, DESY)

The EIC and the LHeC


A Truly Universal Regime?

A.H. Mueller, hep-ph/0301109

Small x QCD evolution predicts:

• QS approaches universal behavior for all hadrons and nuclei

Not only functional form f(Qs) universal but even Qs becomes the same

?

• Radical View: – Nuclei and all hadrons have a component of their

wave function with the same behavior– This is a conjecture! Needs to be tested


Nuclear Modification of Structure Functions


Diffractive Structure Function F2D at EIC

- Distinguish between linear evolution and saturation models

- Insight into the nature of pomeron - Search for exotic objects (Odderon)

xIP = momentum fraction of the pomeron w.r.t the hadron

Curves: Kugeratski, Goncalves, Navarra, EPJ C46, 413

= x/xIP

d4 eh eXh

dxdQ2ddt

4 e.m.2

2Q41 y

y 2

2

F2

D y 2

2FL

D


Connection to p+A Physics– e+A and p+A provide excellent

information on properties of gluons in the nuclear wave functions

– Both are complementary and offer the opportunity to perform stringent checks of factorization/universality

– Issue:

• p+A lacks the direct access to x, Q2

F. Schilling, hex-ex/0209001

Breakdown of factorization (e+p HERA versus p+p TeVatron) seen for diffractive final states.


• Experimentally can be determined directly IF VARIABLE ENERGIES!• Highly sensitive to effects of gluon

+ 12-GeV data+ EIC alone

(includes systematic uncertainties)

Longitudinal Structure Function FL


at small x

Superb sensitivity to g

at small x!

Gluon Contribution to the Proton Spin150 GeV x 7 GeV, 5 fb-1


G Via Open Charm and Dijet Production

HERMES, COMPASS, SMC


Projected data on g/g with an EIC, via + p D0 + X

K- + +

RHIC-Spin

Advantage: measurements directly at single Q2 ~ 10 GeV2 scale!

• Uncertainties in xg smaller than 0.01 • Measure 90% of G (@ Q2 = 10 GeV2)

g

/g

G Via Open Charm and Dijets at EIC

g

Dijets


RHIC-Spin region

Spin-Flavor Decomposition of the Light Quark Sea

| p = + + + …>u

u

d

u

u

u

u

d

u

u

dd

dMany

models predict

u > 0, d < 0

Precisely Image the Sea Quark Polarization

C. Aidala, WWND, April 12, 2008 47gives transverse position of quark (parton) with longitud. mom. fraction x

Fourier transform in momentum transfer

x = 0.01 x = 0.40 x = 0.70

Wigner function: Probability to find a u(x) quark with a certain polarization at position r and with momentum k

Wu(x,k,r)

GPDu(x,,t) Hu, Eu, Hu, Eu

~~

p

m

BGPD

d2k

T

u(x)u, u

F1u(t)

F2u,GA

u,GPu

f1(x)g1, h1

PartonDistributions

Form Factors

d2k

T

dx

= 0, t = 0

Link to Orbital

Momentum

Towards a 3D spin-flavor landscape

Link to Orbital

Momentum

p

m

xTMD

d3 r

TMDu(x,kT) f1,g1,f1T ,g1T

h1, h1T ,h1L ,h1


Detector Design

But: - low-field region around central tracker- better particle identification- forward-angle detectors- auxiliary detectors for exclusive events- auxiliary detectors for normalization

Main detector: Learn from ZEUS + H1

at HERA

Documents

University of Massachusetts Amherst Christine A. Aidala April 12, 2008 Peering into Hadronic Matter: The Electron-Ion Collider Winter Workshop on Nuclear