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?

 

- How do the gluons contribute to the structure of the nucleon?

50% of momentum carried by gluons … but still unknowns in our knowledge g

S

S

xS > xg ???

A low Q2 puzzle …

Parameterize as = -lnF2/lnx

Hadron-hadron scattering energy dependenceObserve transition from partons to

hadrons (gluon clumps?) in data at a distance scale 0.3 fm ??

50% of momentum carried by gluons … but still unknowns in our knowledge

50% of momentum carried by gluons … but still unknowns in our knowledge

Longitudinal Structure Function FL

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

+ 12-GeV data+ EIC alone

(includes systematic uncertainties)

The Spin Structure of the Nucleon

We know from lepton scattering experiments over the last three decades that:

• quark contribution ΔΣ ≈ 0.3 • gluon contribution ΔG ≈ 1 ± 1 • u > 0, d < 0, s ~ 0• measured anti-quark polarizations are

consistent with zero

½ = ½ + G + Lq + Lg

Proton helicity sum rule:

G: a “quotable” property of the proton (like mass, momentum contrib., …)

The Quest for GFirst approach: use scaling violations of world g1 spin structure function measurements

Not enough range in x and Q2

g1 = q eq2 fq(x,Q2)

PHENIX, STAR

The Quest for G

HERMES, COMPASS

World Data on F2p World Data on g1

p

50% of momentum carried by gluons

20% of proton spin carried by quark spin

The dream is to

produce a similar plot

for xg(x) vs x

World Data on F2p World Data on g1

p

The dream is to produce

a similar EIC plot for

g1 (x,Q

2) over similar x

and Q2 range

An EIC makes it possible!Region of existing g1p data

The Gluon Contribution to the Proton Spin

at small x

Superb sensitivity to g

at small x!

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

K- + +

Access to g/g is also possible from the g1p

measurements through the QCD evolution, and from di-jet measurements.

RHIC-Spin

The Gluon Contribution to the Proton Spin

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

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

g/g

RHIC-Spin region

Precisely image the sea quarksSpin-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 < 0No competition foreseen!

GPDs and Transverse Gluon ImagingDeep exclusive measurements in ep/eA with an EIC:

diffractive: transverse gluon imaging J/, o, (DVCS) non-diffractive: quark spin/flavor structure , K, +, …

[ or J/, , 0

, K, +, … ]

Describe correlation of longitudinal momentum and transverse position of

quarks/gluons

Transverse quark/gluon imaging of nucleon

(“tomography”)

Are gluons uniformly distributed in nuclear matter or are there small clumps of glue?

GPDs and Transverse Gluon Imaging

gives transverse size of quark (parton) with longitud. momentum fraction x

EIC:1) x < 0.1: gluons!

x < 0.1 x ~ 0.3 x ~ 0.8

Fourier transform in momentum transfer

x ~ 0.001

2) ~ 0 the “take out” and “put back” gluons act coherently.

2) ~ 0 x - x +

d

GPDs and Transverse Gluon ImagingTwo-gluon exchange dominant for J/, , production at large energies sensitive to gluon distribution squared!LO factorization ~ color dipole picture access to gluon spatial distribution in nuclei: see eA!

Measurements at DESY of diffractive channels (J/, , , ) confirmed the applicability of QCD factorization:• t-slopes universal at high Q2

• flavor relations :Unique access to transverse gluon imaging at EIC!

Fit with d/dt = e-Bt

GPDs and Transverse Gluon Imaging

k

k'

*q q'

p p'

e

A Major new direction in Nuclear Science aimed at the 3-D mapping of the quark structure of the nucleon.

Simplest process:Deep-Virtual Compton Scattering

Simultaneous measurements over large range in x, Q2, t at EIC!

At small x (large W): ~ G(x,Q2)2

GPDs and Transverse Gluon ImagingGoal: Transverse gluon imaging of nucleon over wide range of x: 0.001 < x < 0.1Requires: - Q2 ~ 10-20 GeV2 to facilitate interpretation

- Wide Q2, W2 (x) range - Sufficient luminosity to do differential measurements in Q2, W2, t

Q2 = 10 GeV2 projected data

Simultaneous data at other Q2-values

EIC enables gluon imaging!

Scaled from 2 to 16 wks.

EIC(16 weeks)

The Future of Fragmentation

p

h

xTMD

D

Current Fragmentation h

qCan we understand the physical mechanism of fragmentation and how do we calculate it quantitatively?

Target Fragmentation

pM

h

dh ~ q fq(x) Dfh(z) dh ~ q

Mh/pq(x,z)

QCD Evolution

Correlate at EIC

Proposed EIC recommendation

for the Galveston meeting A high luminosity Electron-Ion Collider (EIC) is the highest

priority of the QCD community for new construction after the JLab 12 GeV and RHIC II luminosity upgrades. EIC will

address compelling physics questions essential for understanding the fundamental structure of matter:

- 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.

This goal requires that R&D resources be allocated for expeditious development of collider and detector design.

eRHIC: (ERL-based) linac-ring design

• Electron energy range from 3 to 10 (20) GeV• Peak luminosity of 2.6 1033 cm-2s-1 in electron-hadron collisions;• high electron beam polarization (~80%);• full polarization transparency at all energies for the electron

beam;• multiple electron-hadron interaction points (IPs) and detectors;• 5 meter “element-free” straight section(s) for detector(s);• ability to take full advantage of electron cooling of the hadron

beams;• easy variation of the electron bunch frequency to match it with

the ion bunch frequency at different ion energies.

PHENIX

STAR

e-cooling (RHIC II)

Four e-beam passes

Main ERL (2 GeV per pass)

eRHIC ring-ring design

AGS

BOOSTER

TANDEMS

RHIC

2 – 10 GeV e-ring

e-cooling

2 -10GeV Injector

LINAC

• Based on existing technology (+ electron cooling)

• Collisions at 12 o’clock interaction region

• 10 GeV, 0.5 A e-ring with 1/3 of RHIC circumference

(similar to PEP II HER)

• Inject at full energy 5 – 10 GeV

• Polarized electrons and positrons

• Peak luminosity of 4.7 1032 cm-2s-1 in electron-hadron

collisions

ELIC ring-ring designElectron Cooling

Snake

Snake

3-9 GeV electrons3-9 GeV positrons

30-225 GeV protons30-100 GeV/n ions

IR

IR

Visionary green-field design:• “Figure-8” lepton and ion rings to ensure spin preservation and ease of spin manipulation.• Peak luminosity up to ~1035 cm-2s-1 through short ion bunches, low β*, and high rep rate (crab crossing)• Four interaction regions with 3m “element-free” straight sections.• SRF ion linac concept for all ions ~ FRIB• 12 GeV CEBAF accelerator, with present JLab DC polarized electron gun, serves as injector to the electron ring.

Detector design

Main detector: learn from ZEUS (+ H1)But: low-field region around central tracker

better particle identificationforward-angle detectorsauxiliary detectors for exclusive eventsauxiliary detectors for normalization

Detector design

Main detector: Top view

Hadronic calorimete

r

Alternate detector:

Emphasize low-x, low-Q2

diffractive physics

(“HERA-III design”,

MPI-Munchen)

Main detector:

Emphasize high-

luminosity full physics

program

Si tracking stations

EM calorimete

r

e

p/A

Cost & Realization

Generic R&D to advance the ongoing EIC conceptual design efforts in order to pursue

the best EIC design by next LRP: $6M per year for 5 years

(see next slide)

“This goal requires that R&D resources be allocated for expeditious development of collider and detector design.”

Realization of the three different EIC design options (eRHIC linac-ring, eRHIC ring-ring, ELIC ring-ring) were discussed earlier in the BNL and JLab Facility Reports.

The cost scale of an EIC (here taken as the TPC of the 10 GeV x 250 GeV eRHIC linac-ring

design) is estimated at ~700M$.

(pre-)R&DGeneral: all designs require Electron Cooling

$4M/year Accelerator R&D encompasses:• Design Studies to Optimize Existing EIC Approaches• High-Intensity Polarized Electron Source (eRHIC L-R)• Energy Recovery Technology for High Energy and High Current Beams (eRHIC L-R)• Development of Compact Recirculation Loop Magnets (eRHIC L-R)• Design and Prototype of Multi-Cell Crab Cavities (ELIC) [required for L~1035 cm-2s-1]• Simulations of Stacking Intense Ion Beams in Pre-Booster (ELIC) [required for L~1035 cm-2s-1] • Simulations of Electron Cooling w/circulator ring and GHz kicker prototype (ELIC)• Precision High-Energy Ion Polarimetry• Polarized 3He Production (EBIS) and Acceleration

$2M/year Detector R&D encompasses:• Low-Angle Electron Tagging System• Multi-Level Triggering System to Include Tracking and Reject Background• High-Speed Data Acquisition System to Handle Small Bunch Spacing ( ELIC)• Central Tracker Development

• cost-effective and compact high-rate tracking solution• cost-effective method for hadron identification• tagging systems for recoiling neutrons and heavier nuclei

SummaryThe last decade or so has seen tremendous progress in our understanding of the partonic sub-structure of nucleons and nuclei based upon:• The US nuclear physics flagship facilities: RHIC and CEBAF• The surprises found at HERA (H1, ZEUS, HERMES)• The development of a theory framework allowing for a revolution in our understanding of the inside of hadrons …

QCD Factorization, Lattice QCD, Saturation

This has led to new frontiers of nuclear science:- the possibility to map the role of gluons- a new QCD regime of strong color fields

The EIC presents a unique opportunity to maintain US and BNL&JLab leadership in high energy nuclear physics and precision QCD physics

Proposed EIC recommendation

for the Galveston meeting A high luminosity Electron-Ion Collider (EIC) is the highest

priority of the QCD community for new construction after the JLab 12 GeV and RHIC II luminosity upgrades. EIC will

address compelling physics questions essential for understanding the fundamental structure of matter:

- 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.

This goal requires that R&D resources be allocated for expeditious development of collider and detector design.