The Electron-Ion Collider at BNL

The Electron-Ion Collider at BNL:Capabilities and Physics Highlights

J.H. Lee Brookhaven National Laboratory

1Hadron 2011 Munich©

D. L

einw

eber

Outline• Why do we need

• electron-ion collider

• What can we do with

• e + (heavy) A

• high energy/luminosity polarized e + polarized p

• new opportunities for spectroscopy

• How can it be realized

• adding an electron accelerator at RHIC (or adding a hadron accelerator at CEBAF)

• design and status of eRHIC at BNL

2

QCD and Fundamental Structure of Matter

• QCD is THE theory of the strong interaction: Theory of the matter - quarks and gluons

• Hadronic constituent degree of freedom is governed by quarks, but gluons drive the baryonic structure (responsible for > 98% mass) and dominates the QCD vacuum structure

• “Mastering matter” requires the fundamental understanding of gluon dynamics beyond current knowledge: new frontier machine to deeply explore the regime where new degree of freedom emerges

3

Accessing gluonic structure

4

Probe interaction directly via gluons:Lacks the direct access to partonic kinematics

Indirect access to gluons (electro(-weak) structure function) :High precision and access to partonic kinematics (x, Q2)

Hadron-Hadron Lepton-Hadron (DIS)

Glue in Matter: What do we know

How to Measure Glue ?

Scaling violation: dF2/dlnQ2 and

linear DGLAP Evolution ! G(x,Q2)

4

HERA F 2

0

1

2

3

4

5

1 10 10 2

10 3

10 4

10 5

F 2

em

-log 10

(x)

Q 2 (GeV

2 )

ZEUS NLO QCD fit

H1 PDF 2000 fit

H1 94-00

H1 (prel.) 99/00

ZEUS 96/97

BCDMS

E665

NMC

x=6.32 10-5 x=0.000102

x=0.000161 x=0.000253

x=0.0004 x=0.0005

x=0.000632 x=0.0008

x=0.0013

x=0.0021

x=0.0032

x=0.005

x=0.008

x=0.013

x=0.021

x=0.032

x=0.05

x=0.08

x=0.13

x=0.18

x=0.25

x=0. 4

x=0.65

xf(

x,Q

2)

x

H1 PDF 2000

ZEUS-S PDF

CTEQ6.1

xuV

xg (!1/20)

xS (!1/20)

xdV

Q2 = 10 GeV

2

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

010

-410

-310

-210

-11

d2σep→eX

dxdQ2=

4πα2e.m.

xQ4

��1− y +

y2

2

�F2(x,Q2)− y2

2FL(x,Q2)

�.




4

HERA F 2

0

1

2

3

4

5

1 10 10 2

10 3

10 4

10 5

F 2

em

-log 10 (x

)

Q 2 (GeV

2 )

ZEUS NLO QCD fit

H1 PDF 2000 fit

H1 94-00

H1 (prel.) 99/00

ZEUS 96/97

BCDMS

E665

NMC

x=6.32 10-5 x=0.000102

x=0.000161 x=0.000253

x=0.0004 x=0.0005

x=0.000632 x=0.0008

x=0.0013

x=0.0021

x=0.0032

x=0.005

x=0.008

x=0.013

x=0.021

x=0.032

x=0.05

x=0.08

x=0.13

x=0.18

x=0.25

x=0. 4

x=0.65

xf(

x,Q

2)

x

H1 PDF 2000

ZEUS-S PDF

CTEQ6.1

xuV

xg (!1/20)

xS (!1/20)

xdV

Q2 = 10 GeV

2

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

010

-410

-310

-210

-11

d2σep→eX

dxdQ2=

4πα2e.m.

xQ4

��1− y +

y2

2

�F2(x,Q2)− y2

2FL(x,Q2)

�.




4

HERA F 2

0

1

2

3

4

5

1 10 10 2

10 3

10 4

10 5

F 2

em

-lo

g 10

(x)

Q 2 (GeV

2 )

ZEUS NLO QCD fit

H1 PDF 2000 fit

H1 94-00

H1 (prel.) 99/00

ZEUS 96/97

BCDMS

E665

NMC

x=6.32 10-5 x=0.000102

x=0.000161 x=0.000253

x=0.0004 x=0.0005

x=0.000632 x=0.0008

x=0.0013

x=0.0021

x=0.0032

x=0.005

x=0.008

x=0.013

x=0.021

x=0.032

x=0.05

x=0.08

x=0.13

x=0.18

x=0.25

x=0. 4

x=0.65

xf(

x,Q

2)

x

H1 PDF 2000

ZEUS-S PDF

CTEQ6.1

xuV

xg (!1/20)

xS (!1/20)

xdV

Q2 = 10 GeV

2

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

010

-410

-310

-210

-11

d2σep→eX

dxdQ2=

4πα2e.m.

xQ4

��1− y +

y2

2

�F2(x,Q2)− y2

2FL(x,Q2)

�.

5

• For smaller values of x, structure function F2 rises strongly with Q2: Simple quark-parton model Bjorken scaling breaks

• NLO QCD and the measurement “broadly similar”: limited success

• Gluons dominate at low-x, but the underlying dynamics and the evolution is not well established

How gluons grow

• Linear DGLAP evolution: requires “safety dynamics” to prevent unitarity violation

• Saturation regime arises naturally through non-linear BK/JIMWLK evolution

• in the Color Glass Condensate (CGC) framework

• characterized by saturation momentum QS(x,A)

• Experimental establishment on the “theoretical evidence” of saturation regime is fundamentally important for understanding of gluonic dynamics - strong interaction

5

Non-Linear QCD - Saturation

• BFKL Evolution in x– linear– explosion of color field?

• 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 any 2 partons can recombine into one

Regimes of QCD Wave Function

Monday, February 8, 2010

Gluon Density

H1

Col

labo

ratio

n

H1MRST 02 vs CTEQ 6

More work needed; MS– vs scheme-invariant evolution.

FL(x, Q2) could be decisive.

J. Blumlein RECAPP, Allahabad February 2009 – p.35

?

6

Estimating saturation scale• Gluonic saturation/recombination

• number of gluons per unit of transverse area: ρ~xG(x,Q2)/πR2

• cross-section for gluon recombination: σ~ αs/Q2

• saturation occurs when 1 < ρσ ⇒ Q2 < Qs2(x)

• saturation Qs varies

• Qs ∝ x1/3 (phenomenological “geometrical scaling” at HERA)

• Qs ∝ A1/3 (Gluons act coherently)

• Nuclear enhanced saturation scale

• To access saturation: increase energy (~1/x) or increase Qs (~A1/3)

7

Nuclear enhanced saturation

8

~x500

~x7

• With e+p, requiring Q2 lever arm need √s =1-2 TeV (HERA √s=320 GeV)

• x~10-3 in dAu at RHIC (approaching saturation)

• Saturation scale Qs increases with heavy-ion significantly: Well in reach with e+Au at RHIC

Probing Saturation regime

• HERA (ep) energy range higher, but G(x,Q2) in the very limited reach of the saturation regime

• eRHIC (eA) will probe deeply into the saturation region 13

Reach compared with previous facilities

Staged option: begins to reach into the saturation regime for heavy nuclei

Experience with nuclei have shown that we need to reach deeply into a new regime for assurance that the new regime has been reached

And, we need a safety margin (models can and have been wrong before)

9

e+p e+A

Two Concepts to Realize an Electron-Ion Collider (EIC)

10

eRHIC = RHIC + Electron Ring (ERL)

ELIC = CEBAF + Hadron Ring

Stage 1: 5+100 GeV/n e+Au (√s=45 GeV/n)Stage II: 30+130 GeV/n e+Au (√s=125 GeV/n)

Stage I: 11+40 GeV/n e+Au (√s=42 GeV/n)Stage II: 20+100 GeV/n e+Au (√s=89 GeV/n)

Both designs in 2 stages

Current design allows for:• more IP’s

• reusing infrastructure + detector components for STAR, PHENIX

• easier upgrade path from 5 GeV eRHIC-I

• minimal environmental impact concerns

• IR design to reach 1034 luminosity

eRHIC Design Under Active Consideration

RHIC: 325 GeV p or 130 GeV/u Au with DX

magnets removed

11

• All in-tunnel approach uses two energy recovery linacs and 6 recirculation passes to accelerate the electron beam• Staging: the electron energy will be increased in stages: 5-30 GeV by increasing the linac length

eRHIC: The complete QCD factory

• Versatile e↑+A, e↑+p↑, p↑+p,↑ A+A (up to U)

• High luminosity: L (e+p) = 1.5x1034 cm-2s-1 (HERA L =5x1031)

• Electron Accelerator

• Unpolarized and polarized (80%) e-,e+ 5-30 GeV

• RHIC

• Unpolarized and polarized (70%) protons 50 - 250 (325) GeV

• Light Ions (d, Si, Cu), Heavy Ions (Au,U) 50-100 (130) GeV/u

• Polarized light ions (He3) 215 GeV/u

12

Key measurements for characterizing glue in matter in high energy electron-Ion collisions

• Precisely mapping momentum and space-time distribution of gluons in nuclei in wide kinematic range including saturation regime through:

• Inclusive measurements of structure functions (F2,FL): eA→eX, eA→eX+gap

• Semi-inclusive and correlation measurements of final state distributions: eA→e{π,K,Φ,D,J/Ψ...}X

• Exclusive final states: eA→e{ρ,Φ,J/Ψ,γ}A

• Multiple controls: x, Q2, t, MX2 for light and heavy nuclei

13

eRHIC: 10 GeV + 100 GeV/n - estimate for 10 fb-1

Example of the key measurements:Gluon distribution from FL

Example of Key Measurement: FL

11

HKM and FGS are "standard" shadowing parameterizations that are evolved with DGLAP

FL ~ !s G(x,Q2)

requires "s scan, Q2/xs = y

Here:

#Ldt = 4/A fb-1 (10+100) GeV

= 4/A fb-1 (10+50) GeV = 2/A fb-1 (5+50) GeV

statistical error only

Syst. studies of FL(A,x,Q2): • G(x,Q2) with great precision • Distinguish between models

x

GP

b(x)

/Gd(

x)

Statistical errors for

∫Ldt = 10 fb-1 ≈ 2 year running

〈Q2〉: 1.3 2.4 3.8 5.7 9.5 17 34 89

Color Glass CondensateHKM

FGS

RHICLHC

10-110-210-30.2

0.4

0.6

0.8

1

1.2

d2σep→eX

dxdQ2=

4πα2e.m.

xQ4

��1− y +

y2

2

�F2(x,Q2)− y2

2FL(x,Q2)

�.

Example of Key Measurement: FL

11

HKM and FGS are "standard" shadowing parameterizations that are evolved with DGLAP

FL ~ !s G(x,Q2)

requires "s scan, Q2/xs = y

Here:

#Ldt = 4/A fb-1 (10+100) GeV

= 4/A fb-1 (10+50) GeV = 2/A fb-1 (5+50) GeV

statistical error only

Syst. studies of FL(A,x,Q2): • G(x,Q2) with great precision • Distinguish between models

x

GP

b(x)

/Gd(

x)

Statistical errors for

∫Ldt = 10 fb-1 ≈ 2 year running

〈Q2〉: 1.3 2.4 3.8 5.7 9.5 17 34 89

Color Glass CondensateHKM

FGS

RHICLHC

10-110-210-30.2

0.4

0.6

0.8

1

1.2

d2σep→eX

dxdQ2=

4πα2e.m.

xQ4

��1− y +

y2

2

�F2(x,Q2)− y2

2FL(x,Q2)

�.

• FL ~ αSG(x,Q2)

• Systematic studies of FL

(A,x,Q2)

• G(x,Q2) with great precision

• Distinguish between models

• Utilize wide range of √s of eRHIC

14

Example of the key measurements: Imbalance in di-hadron correlations

15

Di-hadron correlations in e+A

Dominguez, Xiao and Yuan (2010) at small x, multi-gluon distributions are as important as single-gluon distributions, they contribute to

such di-hadron correlations

never been measured, we expect to see the same effect in e+A vs e+p

Q2 = 4 GeV22 < pT1 < 3 GeV1 < pT2 < 2 GeV

• Suppression of away side peak and increase of width (decorrelation at ΔΦ=π) at large Q2 in eA due to multiple interactions between partons and dense nuclear matter in the CGC frame work

Q2 q

q

e

A

jet-1

jet-2p

Au

Au x 18.5

Example of the key measurements: Characterizing saturation regime through exclusive diffractive vector Diffraction in eA

Two possibilities for the diffractive events in nuclei:

CoherentNo-breakup

IncoherentWith breakup into nucleons

The gap is still there

gapgap

A AA A’

pn

ee e

e

coherent in-coherent

16

-t (GeV2) -t (GeV2) -t (GeV2)0 0.05 0.1 0.15 0.2 0.25 0.3

2 )

-610

-510

-410

-310

-210

-110

1

10

210e+Al e+Cu e+Au

0 0.05 0.1 0.15 0.2 0.25 0.3

-510

-410

-310

-210

-110

1

10

210

310

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

-210

-110

1

10

210

310

410

510

610

sum

• eA→e{ρ,Φ,J/Ψ,γ}A

• Novel “strong” probe to investigate gluonic structure of nuclei: color dipole coherent and incoherent diffractive interaction: Sensitive to saturation (√s,b,A)

• Access to spatial distribution of gluons

x < x ~ x ~

Proton tomography via

exclusive reactions

polarized e + p at eRHIC:Spin and 3d imaging of nucleon

• DIS, photon-gluon fusion ⇒

Probing gluon spin ΔG at small-x (x > few × 10−4)

• SIDIS ⇒ Flavor decomposition of sea in broad x

range

• DIS at High Q2 ⇒ Electroweak probes of proton

spin structure

• Polarized DVCS, exclusive reactions + Lattice QCD ⇒ GPD’s ⇒ map low-x transverse position-dependent

PDF’s

Important Extension of Nucleon Structure Studies at HERA, RHIC, JLab,…

17

Summary The new proposed versatile and high-luminosity electron-Ion collider (eRHIC) is to study one of the outstanding fundamental questions in QCD:

• Establish and explore new degree of freedom of gluonic property of matter - saturation regime by systematically studying the unprecedentedly accessed kinematic regime.

• Deeply extend the current understanding of nucleon structure: spin and 3d landscape.

18

eRHIC: New Opportunities also for Hadron Spectroscopy

• High luminosity (~5 fb-1/year)

• Detector and machine designs to accommodate from exclusive photo-production to semi-inclusive DIS over a wide kinematic range with excellent particle reconstruction and PID

• Broad range of reactions and energies with polarization

• Spectroscopy programs being developed: searches for Exotics, heavy quark spectroscopy...

• Join us...19

E.C. Aschenauer Seminar at Indiana University, April 2011 20

NSRLLINAC

Booster

AGS

Tandems

STAR6:00 o’clock

PHENIX8:00 o’clock RF

4:00 o’clock

EBIS

ERL Test Facility

e

e

eRHIC!"#$%&!'(") *(+,%&!'(")

-%*(&%.#

/"#$%&.012"*%$.)(,($

34!2"*%$.)(,($

562/

/.7!18!$(9!%*#12($(&:%;

<652

8$"0:.&7

4T Solenoid

eRHIC-Detector12:00 o’clock

Thank you

Back-up slides

21

From Fall 2010 INT Workshop

eA Science Matrix

22

ep Spin Physics Matrix

23

ScienceDeliverable

BasicMeasurement

Uniqueness and

FeasibilityRequirements

spin structure at small x

contribution of Δg, ΔΣto spin sum rule

inclusive DIS ✔minimal

large x,Q2 coverageabout 10C-‐1

full flavor separationin large x,Q2 range

strangeness, s(x)-‐s(x)semi-‐inclusive DIS ✔

very similar to DISparticle ID

improved FFs (Belle,LHC)

electroweak probesof proton structureflavor separation

electroweak parameters

inclusive DIS at high Q2

✔some unp. results from HERA

20x250 to 30x325positron beam

polarized 3He beam

treatment ofheavy flavors

in pQCD

DIS (g1, F2, and FL)with tagged charm

✔some results from HERA

large x,Q2 coveragecharm tag

(un)polarized γ PDFs

relevant for γγ physicsat an ILC

photoproductionof inclusive

hadrons, charm, jets

✔unp. not completely unknown

tag low Q2 eventsabout 10 C-‐1

Saturation at RHIC

• Multiple scattering in the dense nucleus at forward in dAu lead to mono-jet (decorrelation at ΔΦ=π) in CGC frame work ( J. Albacete and C. Marquet, to appear in PRL 2010)

• Estimated xA ~ 10-3 24

20

Low gluon density (pp):pQCD predicts 2!2 process ! back-to-back di-jet

beam view

q q-jet

g-jet

g

side view

High gluon density (pA):2!1 (2!many) process ! mono-jet

pT balanced by many gluons

Mono-jet beam view

Hints from RHIC: Saturation at x=10-3?Disappearance of angular correlations in Run 8 dAu data at forward rapidities (log x ~ 2.5 - 3)

STAR Preliminary

Unc

orre

cted

Coi

ncid

ence

Pro

babi

lity

(rad-

1 )

p+p → π0 π0 + X, √s = 200 GeV d+Au → π0 π0 + X, √s = 200 GeV d+Au → π0 π0 + X, √s = 200 GeV

STAR Preliminary STAR Preliminaryd+Au peripheral d+Au centralp+p

pT,L > 2 GeV/c, 1 GeV/c < pT,S < pT,L〈ηL〉=3.2, 〈ηS〉=3.2



Δφ Δφ Δφ

CGC+offset

σ0.41 ± 0.010.68 ± 0.01

PeaksΔφ0π

σ0.46 ± 0.020.99 ± 0.06

PeaksΔφ0π

σ0.44 ± 0.021.63 ± 0.29

PeaksΔφ0π

-1 0 1 2 3 4 5 -1 0 1 2 3 4 5-1 0 1 2 3 4

0.02

0.15

0.01

0.05

0

0.03

0.025

0.02

0.015

0.01

0.005

0

0.016

0.014

0.012

0.01

0.008

0.006

0.004

0.002

0

Monday, September 27, 2010

François Gelis

Gluon saturationWhy small-x gluons matterGluon evolutionMultiple scatterings

Hydro initial conditionsStages of AA collisionsTmunu at LOLeading Log resummationRole of causality

CGC and correlationsInitial color fieldsMultiplicity distributionThe ridgeCorrelations in dAu

Quantum fluctuationsand hydro behaviorPlain CGC calculationUnstable fluctuationsToy model of fluctuations

Summary

Extra

39

Forward azimuthal correlations in dAu

Azimuthal correlations in dAu collisions at NLO

p

q

x

y

• Multiple scatterings in the nucleus (dense at forward η)lead to a decorrelation at ∆φ = π

The strength of the rescatterings depends on Qs: it islarger at forward η and for central collisions

• Since the collinear parton fragmentation happens outside,it is unaffected by the dense nucleus! the peak at ∆φ = 0 is not modified

François Gelis





Summary

Extra

38

Forward azimuthal correlations in dAu

Azimuthal correlations in pp collisions at NLO

p

q

x

y

• Collinear factorization ! the transverse momenta takento the projectiles are soft

!p⊥ + !q⊥ = !0

• At NLO, one of the final state partons can fragment! appearance of a correlation at ∆φ = 0 and slightbroadening of the correlation at ∆φ = π

Implication on understanding initial dynamics at RHIC

• Shattering CGC sheets provides the initial conditions for QGP evolution: “Glasma”

• Considerable success describing

• Rapid thermalization

• Long range rapidity correlation (ridge at RHIC and CMS)

25

François Gelis





Summary

Extra

15

Stages of a nucleus-nucleus collision

z

t

strong fields classical dynamics

gluons & quarks out of eq. viscous hydro

gluons & quarks in eq. ideal hydro

hadrons kinetic theory

freeze out

• The Color Glass Condensate provides a framework todescribe nucleus-nucleus collisions up to a time τ ∼ Q−1

s

Glasma

11

Definition:

Non-equilibrium state between Color Glass Condensate and Quark Gluon Plasma which is created in high-energy heavy-ion collisions.

Expanding Flux Tubes

1/Qs

E or B, or E&B

Boost invariant Glasma (without rapidity dependence) cannot thermalize Need to violate the boost invariance !!!

! origin: fluctuation

Considerable success

describing:

1) rapid thermalization

2) Long-range rapidity

correlations (ridge)

3) Baryon stoppingsee talk by F. Gelis

The Electron-Ion Collider at BNL

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