Probing the Quark Sea and Gluons: the Electron-Ion Collider Project
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Probing the Quark Sea and Gluons: the Electron-Ion Collider Project. Rolf Ent ( JLab ). 2007 Long-Range Plan EIC: “half” recommendation. 2010 JLab User Workshops. EIC white paper – to be published. INT10-3 program >500 page report. Fermilab : Joint Experimental-Theoretical Seminar

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Fermilab : Joint Experimental-Theoretical Seminar January 11, 2013

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Probing the Quark Sea and Gluons: the Electron-Ion Collider Project

Rolf Ent (JLab)

2007 Long-Range Plan

EIC: “half” recommendation

2010 JLab User Workshops

EIC white paper

– to be published

INT10-3 program

>500 page report

Fermilab: Joint Experimental-Theoretical Seminar

January 11, 2013

Probing the Quark Sea and Gluons: the Electron-Ion Collider Project

  • Electron-Ion Colliders Worldwide

  • Electron-Ion Collider Nuclear Science

  • Electron-Ion Collider Accelerator Design

  • Integrated Detector and Interaction Region

  • Electron-Ion Collider Status and Plans

EIC is the generic name for the Nuclear Science-driven Electron-Ion Collider, presently considered in the US

Electron Ion Colliders on the World Map








Electron Ion Colliders


Possible Future

High-Energy Physics

Nuclear Physics


EIC: L = 1033-1034cm-2s-1

Ecm = 20-70+ GeV

LHeC: L = 1.1x1033 cm-2s-1

Ecm = 1.4 TeV

  • Variable energy range

  • Polarized and heavy ion beams

  • High luminosity in energy region

  • of interest for nuclear science

  • Add 70-100 GeV electron ring to

  • interact with LHC ion beam

  • Use LHC-B interaction region

  • High luminosity mainly due to

  • large g’s (= E/m) of beams

  • Nuclear sciencegoals:

  • Map the spin and spatial structure of quarks and gluons in nucleons

  • Discover the collective effects of gluons in atomic nuclei

  • Understand the emergence of hadronic matter from color charge

  • High-Energy/Nuclear physics goals:

  • Parton dynamics at the TeVscale

  • - high-Q2 electron-quark scattering

  • (constrain the size of the quark)

  • - physics beyond the Standard Model

  • - physics of high partondensities (low x)

high-energy e-p collider to follow on DESY, plus plans for e-A collider

“world’s first polarized e-p collider and world’s first e-A collider”

A High-Luminosity US-Based Electron Ion Collider

Stage I


Stage I



√s = 25 – 100GeV

Ee = 3 – 10 GeV

Ep = 50 – 250 GeV

EPb = up to 100 GeV/A

√s = 15 – 66 GeV

Ee = 3 – 11 GeV

Ep = 20 – 100 GeV

EPb = up to 40 GeV/A

(Hall A & C)




eRHIC: take advantage of higher proton/ion energies



MEIC: take advantage of lower proton/ion energies for detector/IR design

“world’s first polarized e-p collider and world’s first e-A collider”

Stage 1 MEIC: dedicated ~1 km ring optimized for 30-100 GeV protons

Into the “sea”: the EIC

  • With 12 GeV we study mostly the valence quark component

  • An EIC aims to study the sea quarks and gluon-dominated matter.



12 GeV

The Structure of the Proton

Naïve Quark Model:proton = uud (valence quarks)

QCD:proton = uud + uu + dd + ss + …

The proton sea has a non-trivial structure: u ≠ d

& gluons are abundant

The proton is far morethan just its up + up + down (valence) quark structure

Nuclear physicists are trying to answer how basic properties like mass, shape, and spin come about from the flood of gluons, quark/anti-quark pairs, and a few ever-present quarks.

QCDand the Origin of Mass

  • 99% of the proton’s mass/energy is due to the self-generating gluon field

    • Higgs mechanism has no role here.

  • The similarity of mass between the proton and neutron arises from the fact that the gluon dynamics are the same

    • Quarks contribute almost nothing.

M(up) + M(up) + M(down) ~ 10 MeV << M(proton)

The Physics Program of an EIC

I) Map the spin and spatial structure of quarks and gluons in nucleons

Sea quark and gluon polarization

Transverse spatial distributions

Orbital motion of quarks/gluons

Parton correlations: beyond one-body densities

(show the nucleon structure picture of the day…)

II) Discover the collective effects of gluons in atomic nuclei

Color transparency: Small-size configurations

Nuclear gluons: EMC effect, shadowing

Strong color fields: Unitarity limit, saturation

Fluctuations: Diffraction

(without gluons there are no protons, no neutrons, no atomic nuclei)

III) Understand the emergence of hadronic matter from color charge

Materialization of color: Fragmentation, hadron breakup, color correlations

Parton propagation in matter: Radiation, energy loss

(how does M = E/c2 work to create pions and nucleons?)

Needs high luminosity and range of energies

+ some developing ideas for fundamental symmetry tests

Helicity PDFs at an EIC

Q2 = 10 GeV2

current data

5 x 250 starts here

w/ EIC data

5 x 100 starts here

Sea Quark Polarization

  • Spin-Flavor Decomposition of the Light Quark Sea


Needs intermediate √s ~ 30(and good luminosity)




Many models predict

Du > 0, Dd < 0




| p = + + + …










TMD PDFs f1u(x,kT), .. h1u(x,kT)‏

Unified View of Nucleon Structure

6D Dist.

Wpu(x,kT,r) Wigner distributions

d2kT drz


3D imaging

dx &

Fourier Transformation



Form Factors




f1u(x), .. h1u(x)‏


Towards Imaging - Two Approaches



2+1 D picture in momentum space

2+1 D picture in impact-parameter space









bx [fm]

(Lattice Calculation of the IP density of up quark, QCDSF/UKQCD Coll., 2006)

Quark Siversfunction fit to SIDIS (Anselminoet al. 2009)

  • intrinsic transverse motion

  • spin-orbit correlations = indicator of OAM

  • non-trivial factorization

  • accessible in SIDIS, DY

  • collinear but long. momentum transfer

  • indicator of OAM; access to Ji’s total Jq,g

  • existing factorization proofs

  • DVCS, deep exclusive meson production

Transverse Quark & Gluon Imaging

Deep exclusive measurements in ep/eA with an EIC:

diffractive:transverse gluon imagingJ/y, f, ro, g (DVCS)

non-diffractive:quark spin/flavor structurep, K, r+, …

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

Are gluons & various quark flavors similarly distributed?

(some hints to the contrary)

Describe correlation of longitudinal momentum and transverse position of quarks/gluons 

Transverse quark/gluon imaging of nucleon


Detailed differential images from nucleon’s partonic structure

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

Hints from HERA:

Area (q + q) > Area (g)

Dynamical models predict difference:

pion cloud, constituent quark picture



[Transverse distribution derived directly from t dependence]


EIC: singlet quark size from deeply virtual compton scattering

EIC: strange and non-strange (sea) quark size from p and K production

  • Q2 > 10 GeV2

  • for factorization

  • Statistics hungry

  • at high Q2!

Example: Transverse Spatial Distribution of Gluons from J/Y

DVCS transverse spatial projections in progress

Image the Transverse Momentum of the Quarks

Swing to the left, swing to the right:

A surprise of transverse-spin experiments

The difference between the p+, p–, and K+ asymmetries reveals that quarks and anti-quarks of different flavor are orbiting in different ways within the proton.

dsh ~ Seq2q(x) dsfDfh(z)

Sivers distribution

Image the Transverse Momentum of the Quarks

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

Gray band: present “knowledge”

Purple band: EIC (2s)



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

Gluons in Nuclei

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

Tomography: Hard Diffraction

Diffractive event

No activity in proton direction

A 7 TeV equivalent electron bombarding the proton … but nothing happens to the proton in 15% of cases

  • Predictions for eA for such hard diffractive events range up to: ~30-40%... given saturation models

Hadronization – parton propagation in matter






DpT2 = pT2(A) – pT2(2H)


“pT Broadening”

Can we learn more from correlating with the target fragmentation region?

  • Comprehensive studies possible:

  • wide range of energy v = 10-1000 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

Accardi, Dupre


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

To cover the physics we need…

x = Q2/ys


Range in y


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

  • Detecting the electron ymax / ymin ~ 10

  • Also detecting hadrons ymax / ymin ~ 100

    • Requires hermetic detector (no holes)

Range in s

C. Weiss

C. Weiss

C. Weiss

  • Accelerator considerations limit smin

    • Depends on smax (dynamic range)

pQCD radiation

Vacuum fluct.

Range of kinematics

  • At fixed s, changing the ratio Ee / Eion can for some reactions improve resolution, particle identification (PID), and acceptance

radiative gluons/sea

valence quarks/gluons

non-pert. sea quarks/gluons

Range of nuclei

A High-Luminosity US-Based Electron Ion Collider

NSAC 2007 Long-Range Plan:

“An Electron-Ion Collider (EIC)with polarized beams has been embraced by the U.S. nuclear science community as embodying the vision for reaching the next QCD frontier. EIC would provide unique capabilities for the study of QCD well beyond those available at existing facilities worldwide and complementary to those planned for the next generation of accelerators in Europe and Asia.”

  • Base EIC Requirements per Executive Summary of Institute for Nuclear Theory Report:

    • range in energies from √s ~ 20 to √s ~ 70 & variable

    • fully-polarized (>70%), longitudinal and transverse

    • ion species from deuteriumto A = 200 or so

    • high luminosity: about 1034e-nucleons cm-2 s-1

    • multiple interaction regions

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

“world’s first polarized e-p collider and world’s first e-A collider”

How MEIC meets the Design Specs

  • Base EIC Requirements per Executive Summary INT Report:

    • 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

  • 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

  • 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 full acceptance detector space

    • bore of ion beam final focus quads sufficient to let particles pass through

    • up to t ~ 2 GeV2 (t ~ Ep2Q2)

  • upgradeable to center of mass energy of about √150 GeV

  • MEIC (= stage-I EIC @ JLab) Design

    • Collider is based on a figure eight concept

      • Avoids crossing polarization resonances

        • Improves polarization for all species

        • Makes polarized deuterons possible

      • Advantage of having a new ion ring

    • Highest luminosity comes with final focus quadrupoles close together

      • Interferes with detection of (spectator) particles at small angles

      • MEIC is designed around a full-acceptance

        detector with ±7 meters free space around

        the interaction point and a high-luminosity

        detector with ±4.5 meters free space

    • The present MEIC design takes a conservative technical approach by limiting

      several key design parameters within state-of-the-art. It relies on regular

      electron coolingto obtain the ion beam properties.

    • The present JLab EIC design focuses on a CM energy range from 12 up to 65 GeV

    Emphasis on integrated detector/interaction region

    EIC@JLab (MEIC) Technical Design Strategy

    Limit as many design parameters as we can to within or close tothe present state-of-art in order to minimize technical uncertainty and R&D tasks

    • Stored electron current should not be larger than 3 A

    • Stored proton/ion current should be less than 1 A (better below 0.5 A)

    • Maximum synchrotron radiation power density is 20 kW/m

    • Maximum peak field of warm electron magnet is 1.7 T

    • Maximum peak field of ion superconducting dipole magnet is 6 T

    • Maximum betatron value at FF quad is 2.5 km

  • New beta-star, appropriate to the detector requirements

    2.5 km βmax + 7 m  βy*= 2 cmFullacceptance

    2.5 km βmax + 4.5 m  βy*=0.8 cmLarge acceptance

  • This design will form a base for future optimization guided by

    • Evolution of the science program

    • Technology innovation and R&D advances

  • Medium Energy EIC@JLab

    Warm ion collider ring (up to 25 GeV)

    Cold ion

    collider ring

    (up to 100 GeV)

    Electron collider ring

    (3 to 11 GeV)

    • JLab Concept

    • Initial configuration (LEIC & MEIC):

      • 3-11 GeV on 10-25 & 20-100 GeVep/eAcollider

      • fully-polarized, longitudinal and transverse

      • luminosity: up to ~2 x 1034 e-nucleons cm-2s-1

        • Upgradable to higher energies (EIC)

      • 3-11 GeV on up to 250 GeVep/eA collider

      • luminosity: up to few x 1034 e-nucleons cm-2 s-1

    “Like Mike”


    MEIC Design Report

    • Posted: arXiv:1209.0757

    • Stable concept for 3 years

    “… was impressed by the outstanding quality of the present MEIC design”

    “The report is an excellent integrated discussion of all aspects of the MEIC concept.” (JSA Science Council 08//29/12)

    Design Feature: High & Flexible Polarization

    Fully integrated detector/interaction region

    • EPJA article by JLab theory on EIC science case

    • EIC white paper near-final (w. BNL & JLab users)

    Design Features: High Polarization

    All ion rings (two boosters, collider) have a figure-8 shape

    • Spin precessions in the left &right parts of the ring are exactly cancelled

    • Net spin precession (spin tune) is zero, thus energy independent

    • Ensures spin preservation and ease of spin manipulation

    • Avoids energy-dependent spin sensitivity for ion all species

    • The only practical way to accommodate medium energy polarized deuterons

      This design feature promises a high polarization for all light ion beams

      (The electron ring has a similar shape since it shares a tunnel with the ion ring, section 4.7)

      Use Siberian Snakes/solenoids to arrange polarization at IPs

    longitudinal axis


    Vertical axis

    Proton or Helium-3 beams

    Deuteron beam


    Longitudinal polarization at both IPs

    Transverse polarization at both IPs

    Longitudinal polarization at one IP

    Transverse polarization at one IP

    Slide 30

    Design Features: High Luminosity

    • Based on high bunch repetition rate CW colliding beams

      • Very high bunch repetition rate Very small bunch charge

      • Very short bunch length (sz ~ b*) Very small β*

      • Crab crossing Small transverse emittance

    • A proven concept: KEK-B @2x1034/cm2/s

    • JLab aims to replicate this in colliders w/ hadron beams

      • The electron beam from CEBAF possesses a high bunch repetition rate

      • Ion beams from a new ion complex to match the electron beam

    A New Ion Complex at JLab



    to high energy collider ring

    ion sources

    SRF Linac


    (accumulator ring)

    large booster

    medium energy collider ring

    Pre-booster (by NIU)

    Beam from LINAC

    Extraction to large booster

    ARC 1

    Electron Cooling


    Injection Insertion


    ARC 3







    Ion Sources

    RF Cavities



    ARC 2


    Normal conducting


    Ion Linac (by ANL)

    MEIC Layout

    • Interaction point locations:

    • Downstream ends of the electron straight sections to reduce synchrotron radiation background

    • Upstream ends of the ion straight sections to reduce residual gas scattering background

    • Vertical stacking for identical ring circumferences

    • Horizontal crab crossing at IPs due to flat colliding beams

    • Ion beams execute vertical excursion to the plane of the electron orbit for enabling a horizontal crossing

    Ion path

    Interaction Regions

    Electron path

    Warm large booster

    (up to 25 GeV/c)




    Ion transfer beam line

    Large Ion Booster

    Electron Collider

    Ion Collider

    SRF linac

    Cold 97 GeV/c proton collider ring

    Three Figure-8

    rings stacked vertically

    Electron ring

    Medium energy IP with

    horizontal crab crossing


    • Ring circumference: 1340 m

    • Maximum ring separation: 4 m

    • Figure-8 crossing angle: 60 deg.

    12 GeV CEBAF

    Crab Crossing

    High bunch repetition rate requires crab crossing of colliding beams to avoid parasitic beam-beam collisions

    Present baseline: 50 mrad crab crossing angle

    Crab cavity State-of-the-art:

    KEKB Squashed cell@TM110 Mode

    Vkick=1.4 MV, Esp= 21 MV/m

    750 MHz SRF crab cavity design ongoing

    Crab Crossing

    • Restore effective head-on bunch collisions with 50 mrad crossing angle  Preserve luminosity

    • Dispersive crabbing (regular accelerating / bunching cavities in dispersive region) vs.Deflection crabbing (novel TEM-type SRF cavity at ODU/JLab, very promising!)


    At IP


    Electron Cooling

    • Essential to achieve high luminosity for MEIC

    • Traditional electron cooling, not Coherent Electron Cooling

    • MEIC cooling scheme

      Pre-booster: Cooling for assisting accumulation of positive ion beams

      (Using a low energy DC electron beam, existing technology)

      Collider ring: Initial cooling after injection

      Final coolingafter boost & re-bunching, for reaching design values

      Continuous coolingduring collision for suppressing IBS

      (Using new technologies)

    • Challenges in cooling at MEIC collider ring

      • High ion energy

        (State-of-the-art: Fermilab recycler, 8 GeV anti-proton, DC e-beam)

      • High current, high bunch repetition rate CW cooling electron beam

    Staged Electron Cooling In Collider Ring

    • Initial cooling: after injection for reduction of longitudinal emittance < acceleration

    • Final cooling: after boost & rebunching, for reaching design values of beam parameters

    • Continuous cooling: during collision for suppressing IBS & preserving luminosity lifetime

    ERL Circulator Electron Cooler


    • Design Choices

    • Energy Recovery Linac (ERL)

    • Compact circulator ring

    • to meet design challenges

    • Large RF power (up to 81 MW)

    • Long gun lifetime (average current 1.5 A)

    • Required technologies

    • High bunch charge magnetized gun

    • High current ERL (55 MeV, 15 to150 mA)

    • Ultra fast kicker

    30 m

    Solenoid (20 m)

    ion bunch


    electron bunch

    energy recovery


    Cooling section

    Fast kicker

    e-bunches circulates 10 -100 times reduction of current from an ERL by a same factor

    Fast kicker

    circulator ring


    • Optimization

    • eliminating a long return path

    • could double the cooling rate

    Proposal: A technology demonstration

    using JLab FEL facility



    SRF Linac

    Slide 38

    MEIC Collider Ring Footprint


    Spin Rotator

    (8.8°/4.4°, 50 m)

    1/4 Electron Arc (106.8°, 140 m)

    IR(125 m)

    IR(125 m)


    Spin Rotator (8.8°/4.4°, 50 m)

    Experimental Hall (radius 15 m)

    RF (25 m)

    Figure-8 Crossing Angle: 2x30°


    Spin Rotator (8.8°/4.4°, 50 m)

    Compton Polarimeter (28 m)

    1/4 Electron Arc (106.8°, 140 m)

    3rd IR (125 m)


    Spin Rotator (8.8°/4.4°, 50 m)

    Injection from CEBAF

    • Ring design is a balance between

      • Synchrotron radiation  prefers a large ring (arc) length

      • Ion space charge  prefers a small ring circumference

    • Multiple IPs require long straight sections

    • Straights also hold required service components (cooling, injection and ejection, etc.)

    MEIC assumptions

    x = Q2/ys



    (x,Q2) phase space directly correlated with s (=4EeEp) :

    @ Q2 = 1 lowest x scales like s-1

    @ Q2 = 10 lowest x scales as 10s-1

    • Detecting only the electron ymax / ymin ~ 10

    • Also detecting all hadrons ymax / ymin ~ 100

    C. Weiss

    C. Weiss

    (“Medium-Energy”) MEIC@JLaboption driven by:

    access to sea quarks (x > 0.01 (0.001?)or so)

    deep exclusive scattering at Q2 > 10 (?)

    any QCD machine needs range in Q2

     s = few 100 - 1000 seems right ballpark

     s = few 1000 allows access to gluons, shadowing

    Requirements for deep exclusive and high-Q2 semi-inclusive reactions also drives request for (lower &) more symmetric beam energies.

    Requirements for very-forward angle detection folded in IR design

    Where do particles go - general


    p or A

    Token example: 1H(e,e’π+)n

    • Several processes in e-p:

    • “DIS” (electron-quark scattering)e + p  e’ + X

    • “Semi-Inclusive DIS (SIDIS)”e + p  e’ + meson + X

    • “Deep Exclusive Scattering (DES)”e + p  e’ + photon/meson + baryon

    • Diffractive Scatteringe + p  e’ + p + X

    • Target fragmentatione + p  e’ + many mesons + baryons

    • Even more processes in e-A:

    • “DIS”e + A  e’ + X

    • “SIDIS”e + A  e’ + meson + X

    • “Coherent DES”e + A  e’ + photon/meson + nucleus

    • Diffractive Scatteringe + A  e’ + A + X

    • Target fragmentatione + A  e’ + many mesons + baryons

    • Evaporation processese + A  e’ + A’ + neutrons

    In general, e-p and even more e-A colliders have a large fraction of their science related to the detection of what happens to the ion beams. The struck quark remnants can be guided to go to the central detector region with Q2 cuts, but the spectator quark or struck nucleus remnants will go in the forward (ion) direction.

    Transverse spatial imaging – recoil baryons

    40 mrad @ t = -1 GeV2

    ep → e'π+n

    8 mrad @ t = -1

    5x30 GeV

    DVCS on the proton

    5x250 GeV

    ~ √t/Ep

    J.H. Lee

    T. Horn

    • Colliders allow straightforward detection of recoil baryons, making it possible to map the t-distribution down to very low values of –t

      • eRHIC (partially) solves this by squeezing the high-energy recoil baryons through a high-gradient interaction region focusing magnet and the use of Roman Pots

    • At very high proton energies, recoil baryons are all scattered at small angles

      • Moderate proton energies give the best resolution

      • High luminosity at intermediate proton energies and excellent small-angle detection make the MEIC a perfect tool for imaging of the proton

    Detector/IR in pocket formulas

    • Luminosity ~ 1/b*

    • bmax~ 2 km = l2/b*(l = distance IP to 1st quad)

    Example: l = 7 m, b* = 20 mm  bmax = 2.5 km

    • IP divergence angle ~ 1/sqrt(b*)

    Example: l = 7 m, b* = 20 mm  angle ~ 0.3 mr

    Example:12 s beam-stay-clear area

     12 x 0.3 mr = 3.6 mr ~ 0.2o

    • FFQ gradient ~ Ep,max/sqrt(b*)(for fixed bmax, magnet length)

    Example:6.8 kG/cm for Q3 @ 12 m @ 60 GeV

     7 T field for 10 cm (~0.5o) aperture

    Making b* too small complicates small-angle (~0.5o) detection before ion Final Focusing Quads, and would require too high a peak field for these quads given the large apertures (up to ~0.5o).b* = 1-2 cm and Ep = 20-100 GeV ballpark right!

    MEIC:Fullacceptance detector – strategy

    7 meters

    In general, e-p and even more e-A colliders have a large fraction of their science related to the detection of what happens to the ion beams… spectator quark or struck nucleus remnants will go in the forward (ion) directionthis drives the integrated detector/interaction region design: NO HOLES!

    central detector

    with endcaps

    small angle

    hadron detection

    ultra forward

    hadron detection



    electron detection

    large aperture

    electron quads

    60 mrad bend

    ion quads


    small diameter

    electron quads



    50 mrad beam

    (crab) crossing angle



    ion FFQs

    ion dipole w/ detectors



    0 mrad


    electron FFQs

    50 mrad

    Three-stage detection

    2+3 m

    2 m

    2 m

    Central detector

    (P. Nadel-Turonski, V. Morozov, T. Horn, C. Hyde)

    MEIC: FullAcceptance Detector

    7 meters

    (P. Nadel-Turonski, V. Morozov, T. Horn, C. Hyde)



    ion FFQs

    ion dipole w/ detectors



    0 mrad


    electron FFQs

    50 mrad

    2+3 m

    2 m

    2 m

    Three-stage detection

    Central detector


    Detect particles with angles down to 0.5obefore ion FFQs.

    Need 1-2 Tm dipole

    Detect particles with angles below 0.5obeyond ion FFQs and in arcs.

    Need 4 m machine element free region

    Solenoid yoke + Muon Detector




    EM Calorimeter



    Muon Detector

    Hadron Calorimeter

    EM Calorimeter

    Very-forward detector

    Large dipole bend @ 20 meter from IP (to correct 50 mr ion horizontal crossing angle) allows for very-small angle detection (<0.3o).

    Need 20 m machine element free region

    Solenoid yoke + Hadronic Calorimeter

    All incorporated in MEIC design




    MEIC Detector & Interaction Region

    GEANT4 model of extended IR exists

    • Neutron detection in a 25 mrad cone down to zero degrees

    • Excellent acceptance for all ion fragments

    • Recoil baryon acceptance:

      • up to 99.5% of beam energy for all angles

      • down to 2-3 mrad for all momenta

    • Momentum resolution < 3x10-4

      • limited by intrinsic beam momentum spread

    Full acceptance

    • 100 GeV maximum ion energy allows using large-aperture magnets with achievable field strengths





    20 Tm dipole


    2 Tm dipole



    Extended Detector & Interaction Region

    Truly fully integrated detector & interaction region, also for eA

    Design Feature: Full-Acceptance Detector

    Forward acceptance horizontal plane

    Forward acceptance vertical plane

    Full acceptance detector

    • Demonstrated excellent acceptance & resolution

    • Completed the detector-optimized IR optics

    • Fully integrated detector and interaction region

    • Working on hardware engineering design

      Addressing accelerator challenges

    • Demonstrated chromaticity compensation (section 7.5)

    6 T max

    9 T max

    12 T max

    Reviews and Activities

    • 2nd EIC International Advisory Committee Review (Nov. 2-3, 2009)

      (Accelerator members: R. Gerig, U. Wienands)

    • Physics-Machine Joint Meeting (for a design goal) (Feb. 11&12, 2010)

    • MEIC Machine Design Week (March 4-8, 2010)

      (Detector/IR consultant: M. Sullivan of SLAC )

    • MEIC Internal Machine Design Review (Sept. 15-16, 2010)

      (Reviewers: A. Chao and G. Hoffstaetter)

    • RF & Beam Synchronization Mini-Workshop (Oct. 29, 2010)

    • MEIC Ion Complex Design Workshop (Jan. 27-28, 2011)

    • 3rdElC International Advisory Committee Review (April 9, 2011)

      (Accelerator members: R. Gerig, S. Nagaitsev, V. Shiltsev)

    • MEIC Detector and IR Design Mini-Workshop (Oct. 31, 2011)

    • ERL Circulator Cooler Test Facility Retreat (Jan. 31, 2012)

    EIC Progress

    • Close and frequent collaboration between accelerator and nuclear physicists regarding the machine, interaction region and detector requirements has taken place.

      • “We are proud to announce that we have achieved a fully integrated detector and interaction region”

  • Several JLab user proposals for generic detector R&D call

  • Draft MEIC Intermediate Design Report completed Aug. 2012

  • Concept for regular electron cooling further worked out

    • Many aspects of cooling can be tested at JLab/FEL

    • Mainly use “brute force”  lenient at lower energies

  • Cost Estimate developed, estimate being iterated

  • (3 main cost drivers: Ion Linac, SC Magnets & SRF Cooling, Civil construction)

  • Steering committee with many JLab users working on EIC white paper accessible to general nuclear science community

  • Integrate LEIC (up to 25 GeV/c protons) into design

  • Integrate LEIC into MEIC planning

    MEIC = MEIC + LEIC has large advantages:

    Design flexibility

    Ease of commissioning

    Separate warm ion ring from cold ion ring

    Reduce risk



    warm e-ring

    warm p-ring

    cold p-ring

    warm e-ring

    cold p-ring


    250 GeV

    100 GeV

    25 GeV


    LEIC as An Intermediate Technology Step

    LEIC minimizes technology challenges, and provides a test bed for MEIC

    • Electron cooling

      • Requires lower electron energies (13.6 MeV vs. 4.3 MeVFermilab cooler) and a lower (~0.5 A) current electron cooling beam

    • Ion linac/pre-booster

      • An accumulation of a lower current ion beam in the pre-booster

    • Beam synchronization

      • Variation of number of bunches in the LEIC ion collider ring provides a large set of synchronization energies for experiments

      • Variation of the warm LEIC ion ring path-length for covering other energies is technically feasible, RF frequency variation can be avoided

    • Crab cavity

      • The integrated kicking voltage is reduced by a factor of 4, now about 3 times of KEK-B

    • Chromaticity

      • Start with only one IR, the chromaticity is reduced by half.

    • IR magnets

      • The maximum fields are reduced by a factor of 4.

    • Ion polarization

      • Magnetic field of some spin rotators are reduced by a factor of 4.

    MEIC 2013 Plans/Goals

    • By Spring 2013:

      • Finalize First Optimization:

        • - Copy main IR into 2nd IR and do dynamical aperture studies

        • Shorten electron spin rotator & reshuffle to allow LEIC to 25+ GeV

      • Fold in Detector solenoid in accelerator design

        • optics requirements and initial return field optimization

        • ion beam deflection & optics compensation

        • polarization impact

  • By Summer 2013:

    • Completing:

      • Electron cooling channels in both warm and cold ion collider rings

      • Vertical chicane for separating two cooling beams

      • Ion vertical chicanes to electron ring plane

    • Ramp up detector studies: resolution, fast MC

    • First concepts/checks of all magnets

    • Cartoon drawings of full MEIC

  • Workshop adjacent to APS/DNP meeting October 2013

  • By end of 2013:

    • Polarization tracking study with misalignments, etc.

    • Initial results of resolution & fast MC studies

    • Supplement to MEIC design report to outline the completed integration of machine design and science capabilities utilizing protons/ions from the warm magnet ring

  • MEIC Planned Accelerator R&D

    MEIC Electron cooler

    Solenoid (15 m)

    • Electron Cooling

      • Proof of staged beam cooling concept

      • Design of an ERL Circulator cooler

      • Cooler test facility proposal

    • Interaction Region Design

      • Detector/IR integration, small angle

        (down to 0°) particle detection

      • Nonlinear beam dynamics, chromatic compensation and dynamic aperture

      • Implementation of crab crossing

    • Polarization

      • Electron spin matching

      • Proof of figure-8 ring concept

      • Realization of fast spin flip

    • Beam-beam effect

    • Electron cloud effect in ion ring





    e-Cooler Test Facility


    Interaction Region w/ Forward tagging

    EIC Realization Imagined

    Assumes endorsement for an EIC at the next NSAC Long Range Plan (2013/14?)

    New MEIC/EIC Layout


    • EIC is the ultimate tool to study sea quarks and gluons

      • Sea quarks and gluons play a prominent role in nucleon structure

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

    • We have a unique opportunity to make a breakthrough in nucleon structure and QCD dynamics:

    • -explore and image the nucleon

    • - discover the role of gluons in structure and dynamics

    • - understand the emergence of hadrons from color charge

    • Collider environment provides tremendous advantages

      • Kinematic coverage (high center-of-mass energy)

      • Polarization measurements with excellent Figure-of-Merit

      • Detection of spectators, recoil baryons, and target fragmentation

    • EIC is a maturing project

      • MEIC design report on arXiv, and elegant plans to integrate LEIC-MEIC: Everybody wants to be “Like Mike”

      • Accelerator R&D funds allocated, and joint detector R&D projects have started

    Why a New-Generation EIC? Why not HERA?

    • Obtain detailed differential transverse quark and gluon images

    • (derived directly from the t dependence with good t resolution!)

      • Gluon size from J/Y and felectroproduction

      • Singlet quark size from deeply virtual compton scattering (DVCS)

      • Strange and non-strange (sea) quark size from p and K production

  • Determine the spin-flavor decomposition of the light-quark sea

  • Constrain the orbital motions of quarks & anti-quarks of different flavor

    • - The difference between p+, p–, and K+ asymmetries reveals the orbits

  • Map both the gluon momentum distributions of nuclei (F2 & FL measurements)

  • and the transverse spatial distributions of gluons on nuclei

  • (coherent DVCS & J/Y production).

  • At high gluon density, the recombination

  • of gluons should compete with gluon

  • splitting, rendering gluon saturation.

  • Can we reach such state of saturation?

  • Explore the interaction of color charges

  • with matterand understand the

  • conversion of quarks and gluons to

  • hadrons through fragmentation and

  • breakup.

  • longitudinal momentum

    orbital motion

    quark to hadron conversion

    Dynamical structure!

    Gluon saturation?

    transverse distribution

    JLab accelerator CEBAF


    • Continuous Electron Beam

    • Energy 0.4 ─ 6.0 GeV

    • 200 mA, polarization 85%

    • 3 x 499 MHz operation

    • Simultaneous delivery 3 halls

    • 416 PhDs completed

    • On average 22 US PhDs per year, close to 30% of US PhDs in nuclear physics

    • On average 50 undergrads per year involved in research at Jefferson Lab

    • 1385 users in FY12, anticipated to grow to ~1500+ users with 12-GeV operations

    • International: non-US nuclear physics users = 1/3 of total, from 33 countries




    12 GeV Upgrade Project: $310M, ~80% obligated

    New Hall

    Add 5 cryomodules

    20 cryomodules

    Add arc

    20 cryomodules

    Add 5 cryomodules

    Enhanced capabilities

    in existing Halls

    Upgrade is designed to build on existing facility: vast majority of accelerator and experimental equipment have continued use

    Upgrade arc magnets

    and supplies

    Maintain capability to deliver lower pass beam energies: 2.2, 4.4, 6.6….

    CHL upgrade

    The completion of the 12 GeV Upgrade of CEBAF was ranked the highest priority in the 2007 NSAC Long Range Plan.

    • Scope of the project includes:

    • Doubling the accelerator beam energy

    • New experimental Hall and beamline

    • Upgrades to existing Experimental Halls

    21st Century Science Questions

    • What is the role of gluonic excitations in the spectroscopy of light mesons?

    • Where is the missing spin in the nucleon?

      What is the role of orbital angular momentum?

    • Can we reveal a novel landscape of nucleon substructure through measurements of new multidimensional distribution functions?

    • What is the relation of short-range nuclear structure and parton dynamics?

    • Can we discover evidence for physics

      beyond the standard model

      of particle physics?

    Excited Glue





    The road to orbital motion

    SIDIS – kT Dependence


    f1,g1,f1T ,g1T

    h1, h1T ,h1L ,h1

    Final transverse momentum of the detected pion Pt arises from convolution of the struck quark transverse momentum kt with the transverse momentum generated during the fragmentation pt.

    Pt= pt +zkt+ O(kt2/Q2)

    Linked to framework of Transverse Momentum Dependent Parton Distributions

    Towards a “3D” spin-flavor landscape






    (Wigner Function)



    EIC: Transverse momentum distribution derived directly from semi-inclusive measurements, plus large gain in our knowledge of transverse momentum effects as function of x.


    • EIC: Transverse spatial distribution derived directly from t dependence:

      • Gluon size from J/Y and f

      • Singlet quark size from g

      • Strange and non-strange (sea)

      • quark size from p and K production

    Exact kT distribution presently unknown – EIC can do this well


    Hints from HERA: Area (q + q) > Area (g)

    Parameters for Full AcceptanceInteraction Point

    Parameters for High LuminosityInteraction Point

    Chromaticity and Dynamic Aperture

    Compensation of chromaticity with 2 sextupole families only using symmetry

    Non-linear dynamic aperture optimization under way



    5 p/p

    5 p/p

    p/p = 0.710-3 at 5 GeV/c

    p/p = 0.310-3 at 60 GeV/c

    Normalized Dynamic Aperture

    with Octupole

    w/o Octupole

    Use Crab Crossing for Very-Forward Detection too!

    (Reminder: MEIC/ELIC scheme uses 50 mr crab crossing)

    Present thinking: ion beam has 50 mr horizontal crossing angle

    Renders good advantages for very-forward particle detection

    ~60 mr bend would need 12 Tm dipole @ ~20 m from IP

    Detector/IR – Magnetic Fields

    Pion momentum = 5 GeV/c, 4T ideal solenoid field, 1.25 m tracking region

    • Goal: resolution dp/p (for pions) better than 1% for p < 10 GeV/c

    • obtain effective 0.5 Tm field by having 50 mr crossing angle (for 5 m long central solenoid)

    • probably suffices to add 1-2 Tm dipole field for small-angles (<10o?) only to get dp/p < 1% for pions of up to 10 GeV/c.

    Here we added dipole for angles smaller than 25o

    Add <2 Tm transverse field component in forward-ion direction to get dp/p roughly constant vs. angle

    Backgrounds and detector placement

    Synchrotron radiation

    • From arc where electrons exit and magnets on straight section

    Random hadronic background

    • Dominated by interaction of beam ions with residual gas in beam pipe between arc and IP

    • Comparison of MEIC (at s = 4,000) and HERA (at s = 100,000)

    • Distance from ion exit arc to detector: 50 m / 120 m = 0.4

    • Average hadron multiplicity: (4000 / 100000)1/4 = 0.4

    • p-p cross section (fixed target): σ(90 GeV) / σ(920 GeV) = 0.7

    • At the same ion current and vacuum, MEIC background should be about 10% of HERA

      • Can run higher ion currents (0.1 A at HERA)

      • Good vacuum is easier to maintain in a shorter section of the ring

    • Backgrounds do not seem to be a major problem for the MEIC

    • Placing high-luminosity detectors closer to ion exit arc helps with both background types

    • Beyond arcs proton/ion beams get manipulated (crab crossing angle), electron beam stays straight to go through detector  minimizes synchroton radiation

    • Signal-to-background will be considerably better at the MEIC than HERA

      • MEIC luminosity is more than 100 times higher (depending on kinematics)

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