Electron Ion ColliderA. Accardi, R. Ent, V. Guzey, Tanja Horn, C. Hyde,

A. Prokudin, P. Nadel-Turonski, C. Weiss, …

+ CASA/accelerator team

LRP 2007 JLab User Workshops 2010

INT10-3 program EIC White PaperEIC half recommendation

>500 pages Under construction

EIC: Probing the Sea Quarks and EIC: Probing the Sea Quarks and GluonsGluons

Tanja Horn, Electron Ion Collider, JLab Strategic Planning 2011 2

Why care about sea quarks and gluons

• Structure of proton7̶ Naïve quark model: proton==uud (valence quarks)

7̶ QCD: proton == uud + + + + …

7̶ Proton sea has a non-trivial structure and

Proton is far more than just its up + up+down (valence) quark structure

• QCD and Origin of Mass7̶ 99% of the proton mass/energy is due to the self-

generating gluon field

o Higgs mechanism has almost no role there

7̶ Similarity of mass between proton/neutron arises from fact that gluon dynamics are the same

o Quarks contribute almost nothing

uuu

d

dd ss

valence quarks/gluons

sea quarks/gluonsradiative gluons/sea

• Hadrons in QCD are relativistic many-body systems

– Fluctuating number of elementary quark and gluon constituents

– Rich structure of the wave function

Internal Landscape of the NucleonInternal Landscape of the Nucleon

• Key physical interests– Transverse spatial distribution – Correlations: transverse, longitudinal,

and nuclear modifications– Tests of reaction mechanism

• Components probed in ep scattering:– JLab 12 GeV: valence region– EIC: probes sea quark and gluon

components

3

Q2 ~ xys

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

Why an Electron-Ion Collider?Why an Electron-Ion Collider?

Tanja Horn, Electron Ion Collider, JLab Strategic Planning 2011 4

• Easier to reach high Center of Mass energies ( )– for colliders (e.g., 4 x 10 x 100=4000 GeV2)

– for fixed target experiments (e.g., 2 x 11 x 0.938=20 GeV2)

sECM 2

peEEs 4

peMEs 2

• Spin physics with high Figure Of Merit (FOM)– Unpolarized FOM = Rate = Luminosity x Cross Section x Acceptance

– Polarized FOM = Rate x (Target Polarization)2 x (Target Dilution)2

– No dilution and high ion polarization (also transverse)

– No current (luminosity) limitations, no holding fields (acceptance)

– No backgrounds from target (Moller electrons)

• Easier detection of reaction products– Can optimize kinematics by adjusting beam energies

– More symmetric kinematics improve acceptance, resolution, particle ID, etc.

– Access to neutron structure with deuteron beams ( )

Target fdilution,

fixed_target

Pfixed_target f2P2fixed_target f2P2

EIC

p 0.2 0.8 0.03 0.5

d 0.4 0.5 0.04 0.5

0pp

Science of an EIC: Explore and Understand Science of an EIC: Explore and Understand QCDQCD

5

• Map the spin and spatial quark-gluon structure of nucleons7̶ Image the 3D spatial distributions of gluons and sea quarks through exclusive J/Ψ, γ (DVCS) and

meson production

7̶ Measure ΔG, and the polarization of the sea quarks through SIDIS, g1, and open charm production

7̶ Establish the orbital motion of quarks and gluons through transverse momentum dependent observables in SIDIS and jet production

• Discover collective effects of gluons in nuclei7̶ Explore the nuclear gluon density and coherence in shadowing through

e + A → e‘ + X and e + A → e‘ + cc + X

7̶ Discover novel signatures of dynamics of strong color fields in nuclei at high energies in e + A → e’ + X(A) and e + A → e’ + hadrons + X

7̶ Measure gluon/quark radii of nuclei through coherent scattering γ* + A → J/Ψ + A

• Understand the emergence of hadronic matter from quarks and gluons− Explore the interaction of color charges with matter (energy loss, flavor dependence, color

transparency) through hadronization in nuclei in e + A → e' + hadrons + X

− Understand the conversion of quarks and gluons to hadrons through fragmentation of correlated quarks and gluons and breakup in e + p → e' + hadron + hadron + X

[INT10-3 2010]

Needs high luminosity and range of energies

3D partonic picture of the nucleon

Information about 3D partonic picture is encoded in Generalized Parton Distributions and Transverse Momentum Dependent Distributions

TransverseMomentum Dependentdistributions

GeneralizedParton Distributions

Wigner distribution

SIDIS DES

J/Ψ, φ

Transverse Spatial Imaging through Transverse Spatial Imaging through

GPDsGPDs

Tanja Horn, Electron Ion Collider, JLab Strategic Planning 2011

Mesons select definite charge, spin, flavor component of GPD

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

pointlike? π, ρ, K, K*

Λ, Σ

γ

BMN *

√s~140 GeV

d+d

dd=ALU

√s~30 GeV

ep → e'π+n

~100 days, ε=1.0, L=1034 s-1cm-2

ep → e'K+Λ

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

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

EIC: singlet quark size from deeply virtual compton scattering

EIC: Imaging of strange sea quarks!

EIC: Gluon size from J/ and electroproduction (Q2 > 10 GeV2)

40<W2<60 GeV2

[Weiss INT10-3 report]

80<W2<100 GeV2

-t (GeV2)

Cro

ss s

ectio

n

3<Q2<6 GeV2

1.6E-3 < xB < 2.5E-3

√s~140 GeV

~30 days, L=1034 s-1cm-2

√s~30 GeV

~100 days, ε=1.0, L=1034 s-1cm-2

-t (GeV2)

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

terra incognitaGray band: present “knowledge” of TMDs with current experimental data

Dark gray band: EIC (1)

Exact kT distribution presently poorly known!Mapping of kT distribution is crucial to our understanding of interplay of collinear and 3D partonic pictures

[Prokudin, Qian, Huang]

An EIC with good luminosity & high transverse polarization is the optimal tool to study this!

Image the Transverse Momentum of the Quarks

[Prokudin, Qian, Huang]

3D partonic picture is encoded in TMDs

Nucleon Structure: Orbital

MotionGoal: explore quark/gluon orbital motion and its polarization dependence through both deep exclusive and semi-inclusive multi-dimensional processes

Can we learn about orbital motion from a comprehensive approach based on TMDs, GPDs, etc., even if model-dependent?

Potential new insight from jets or p’T of target fragmentation?

EIC: wide kinematic range low to high pT

Gluons in Nuclei

NOTHING!!!

What do we know about gluons in a nucleus?

Ratio of gluons in lead to deuterium

• EIC: access gluons through FL (needs variable energy) and dF2/dln(Q2)

• Knowledge of gluon PDF essential for quantitative studies of onset of saturation

Hadronization: Parton propagation in matter

EIC: Explore the interaction of fast color charges with matter

pT2 vs. Q2

-Time scales for color neutralization tCN and hadron formation tF

- eA/A complementary to jets in AA: cold vs. hot matter

EIC: Understand the conversion of color charge to hadrons through fragmentation and breakup

[Accardi, Dupre INT10-03 Report]

Le

e’*

+

pT

pT2 = pT

2(A) – pT2(2H)

Comprehensive studies possible:• wide range of energy v = 10-100 GeV move hadronization inside/outside nucleus, distinguish energy loss and attenuation• wide range of Q2: QCD evolution of fragmentation functions and medium effects• Hadronization of charm, bottom Clean probes with definite QCD predictions• High luminosity Multi-dimensional binning and correlations• √s > 30: jets and their substructure in eA

C. Weiss

s

• For large or small y, uncertainties in the kinematic variables become large

Range in yQ2 ~ xys

Range in s

Range of kinematics

• Detecting only the electron ymax

/ ymin

~ 10

• Also detecting all hadrons ymax

/ ymin

~ 100

– Requires hermetic detector (no holes)

• Accelerator considerations limit smin

– Depends on smax

(dynamic range)

• At fixed s, changing the ratio Ee / E

ion can for

some reactions improve resolution, particle identification (PID), and acceptance

C. WeissC. Weiss

valence quarks/gluons

non-pert. sea quarks/gluons

radiative gluons/sea

[Weiss 09]

s

To cover the physics we need…To cover the physics we need…

12

Vacuum fluct.

pQCD radiation

EIC: Critical EIC: Critical CapabilitiesCapabilities

But we get there in different ways:Input passed on to INT10-03 program:

• Base EIC Requirements per Executive Summary INT Report:• range in energies from √s ~ 20 to √s ~ 70 & variable• fully-polarized (>70%), longitudinal and transverse• ion species up to A = 200 or so• high luminosity: about 1034 e-nucleons cm-2 s-1

• multiple interaction regions• upgradable to higher energies (√s ~ 150 GeV)

Proton Energy (GeV)

Lu

min

osi

ty (

x10

32)

eRHIC-1, Ee=5 GeV

Ee=5 GeV

Ee=10 GeV

14

Exclusive Meson Production

√s=31.6 GeV √s=44.7 GeV √s=100GeV

Mom

entu

m (

GeV

/c)

Mom

entu

m (

GeV

/c)

Mom

entu

m (

GeV

/c)

Lab Scattering angle (rad) Lab Scattering angle (rad) Lab Scattering angle (rad)

Q2 > 10 GeV2 → events of interest for imaging studies

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

Ep = 250 GeVEp = 30 GeV

Δθ=1-2˚ Δθ<0.3˚

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

Nuclear Science: Map t between tmin and 1 (2) GeV2

Must cover between 1-5 deg Should cover between 0.5-5 deg Like to cover between 0.2-7 deg

t ~ Ep22 Angle recoil baryons = t½/Ep

[Horn 08+, INT10-3 report]

e- Beamp/A Beam

solenoid

electron FFQs50 mrad

0 mrad

ion dipole w/ detectors

ions

electrons

IP

ion FFQs

2+3 m 2 m 2 m

• Detect particles with angles below 0.5o.

detectors

Central detector

EM

Ca

lorim

ete

r

Ha

dro

n C

alo

rime

ter

Mu

on

De

tect

or

EM

Ca

lorim

ete

r

Solenoid yoke + Muon DetectorTOF

HT

CC

RIC

H

RICH or DIRC/LTCC

Tracking

2m 3m 2m

4-5m

Solenoid yoke + Hadronic Calorimeter • Very-forward detector, Large dipole bend @ 20 meter from IP allows for very-small angle detection (<0.3o)

MEIC: FullFull Acceptance Detector

7 meters

• Detect particles with angles down to 0.5o. Need 1-2 Tm dipole.

GEANT4 model

EIC: Design ParametersEIC: Design Parameters Base EIC Requirements per Executive Summary INT Report:

• highly polarized (>70%) electron and nucleon beams- longitudinally polarized electron and nucleon beams- transversely polarized nucleon beams

• ion species from deuterium to A = 200 or so• center of mass energies from √s ~ 20 to √s ~ 70 GeV & variable

- electron energies above 3 GeV to allow efficient electron trigger- proton energy adjustable to optimize particle identification

• upgradeable to center of mass energy of about √150 GeV• high luminosity ~1034 e-nucleons cm-2 s-1

- optimal luminosity in √s ~ 30-50 region- luminosity ≥1033 e-nucleons cm-2 s-1 in √s ~ 20-70 region

• multiple interaction regions• integrated detector/interaction region

- non-zero crossing angle of colliding beams- crossing in ion beam to prevent synchrotron background- ion beam final focus quads at ~7 m to allow for detector space- bore of ion beam final focus quads sufficient to let particles pass through up to

t ~ 2 GeV2 (t ~ Ep2Q2)

• positron beam desirable16

MEIC : Medium Energy

EICUse CEBAF “as-is” after the 12-GeV Upgrade

polarimetry

low-energy IP

medium-energy IPs

Three compact rings:• 3 to 11 GeV electron• Up to 12 GeV/c proton (warm)• Up to 100 GeV/c proton (cold)

Proton Energy (GeV)

Lu

min

osi

ty (

x10

32)

eRHIC-1, Ee=5 GeV

Ee=5 GeV

Ee=10 GeV

EIC Realization Imagined

Activity Name 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025

12 Gev Upgrade

FRIB

EIC Physics Case

NSAC LRP

EIC CD0

EIC Machine Design/R&D

EIC CD1/Downsel

EIC CD2/CD3

EIC Construction

Note: 12 GeV LRP recommendation in 2002 – CD3 in 2008

(Mont@INT)

19

SummarySummary

• Collider environment provides tremendous advantages – polarization

– Target fragmentation

• EIC is needed to completely understand nucleon structure and the role of gluons in nuclei

• EIC is a mature project– Designs ongoing at JLab and BNL

– White paper for next LRP under construction

– Accelerator R&D funds have been allocated

– Joint detector R&D projects have started

• EIC is the ultimate tool to study sea quarks and gluons– Sea quarks and gluons play a prominent role in nucleon structure