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The CEBAF IIELIC Upgrade at JLab


... 'Absolutely Central' to Advancing Nuclear Science 'Scientific/Engineering Challenges to Resolve' ... 'Strong consensus among nuclear scientists to pursue R&D ... – PowerPoint PPT presentation

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Title: The CEBAF IIELIC Upgrade at JLab

The CEBAF II/ELIC Upgrade at JLab
  • Highly likely to be Absolutely Central to
    Advancing Nuclear Science
  • Scientific/Engineering Challenges to Resolve
  • Rolf Ent
  • 02/15/2003

CEBAF Beyond 12 GeV
  • Clear scientific case by 12-GeV JLab Upgrade,
    addressing outstanding issues in Hadron Physics
  • Unprecedented measurements to region in x (gt 0.1)
    where basic three-quark structure of nucleons
  • Measurements of correlations between quarks,
    mainly through Deep-Virtual Compton Scattering
    (DVCS) and constraints by nucleon form factors,
    in pursuit of the Generalized Parton
  • Finishing the job on the transition from hadronic
    to quark-gluon degrees of freedom.
  • Over the next 5-10 years, data from facilities
    worldwide concurrent with vigorous accelerator
    RD and design will clarify the key physics and
    machine issues, revealing the relative advantages
    and technical feasibility of these accelerator
    designs and permitting an informed choice of
    design approaches.
  • 25 GeV Fixed-Target Facility?
  • Electron-Light Ion Collider, center-of-mass
    energy of 20-65 GeV?

CEBAF II/ELIC Upgrade - Science
  • Science addressed by this Upgrade
  • How do quarks and gluons provide the binding and
    spin of the nucleons?
  • How do quarks and gluons evolve into hadrons?
  • How does nuclear binding originate from quarks
    and gluons?

(x 0.01)
Glue 100
12 GeV
CEBAF II/ELIC Upgrade - Science
  • At present, uncertain what range of Q2 really
    required to determine complete structure of the
    nucleon. Most likely Q2 10 GeV2?
  • Upcoming years wealth of data from RHIC-Spin,
    COMPASS, HERMES, JHF, JLab, etc.
  • DVCS (JLab-12!) and single-spin asymmetries
    possible at lower Q2
  • Range of Q2 directly linked to required
  • What energy and luminosity, fixed-target facility
    or collider
  • (or both)?
  • JLab Science Policy Advisory Group The goal
    must be to find the best match to the science
    needs on the time scale of the next NSAC long
    range plan.
  • Upgrade is highly likely to be Absolutely
    Central to Field

CEBAF II/ELIC Upgrade - Readiness
  • Electron-Light Ion Collider (ELIC)
  • RD needed on
  • High Charge per Bunch and High Average Current
    Polarized Electron Source
  • High Energy Electron Cooling of Protons/Ions
  • High Current and High Energy demonstration of
    Energy Recovery
  • Integration of Interaction Region design with
    Detector Geometry
  • NSAC Report Strong consensus among nuclear
    scientists to pursue RD over the next three
    years to address a number of design issues
  • 25-GeV Fixed-Target Facility
  • Use existing CEBAF footprint
  • Upgrade Cryo modules to 12-GeV design (7-cell
    design, 18 MV/m)
  • Change ARC magnets, Switchyard, Hall Equipment
  • Significant Scientific/Engineering Challenges
    to Resolve

CEBAF II/ELIC Upgrade - Kinematics
ELIC kinematics at Ecm 45 GeV, and beyond the
resonance region.
  • Luminosity of up to 1035 cm-2 sec-1
  • One day ? 5,000 events/pb
  • Supports precision experiments
  • DIS Limit for Q2 gt 1 GeV2 implies (Bjorken) x
    down to 5 times 10-4
  • Significant results for 200 events/pb for
    inclusive scattering
  • If Q2 gt 10 GeV2 required for Deep Exclusive
    Processes, can reach x down to 5 times 10-3
  • Typical cross sections factor 100-1,000 smaller
    than inclusive scattering ? still easily

The Structure of the Proton F2
F2 Structure Function measured over impressive
range of x and Q2. Q2 evolution also constrains
Still large uncertainty in glue, especially at Q2
lt 20 GeV2
The Structure of the Proton FL
Great Opportunity to (finally) determine FL with
good precision (JLab-6 example here in the
nucleon resonance region only)
Complementarity of 25-GeV fixed-target and ELIC
for this example! ? Glue at low Q2
De gt 0.3
The Spin Structure of the Proton
  • From NLO-QCD analysis of DIS measurements … (SMC
  • DS 0.38 (in AB scheme)
  • DG 1.01.9 ,,
  • quark polarization Dq(x)
  • ?first 5-flavor separation from HERMES (see
  • transversity dq(x)
  • ?a new window on quark spin
  • ?azimuthal asymmetries from HERMES and
  • gluon polarization DG(x)
  • ?RHIC-spin and COMPASS will provide some
  • orbital angular momentum L
  • ?how to determine? ? GPDs

½ ½ DS DG Lq Lg
CEBAF II/ELIC Upgrade can solve this puzzle due
to large range in x and Q2 and precision due to
high luminosity
Orbital Angular Momentum
Analysis of hard exclusive processes leads to a
new class of generalized parton distributions
Four new distributions
helicity conserving ? H(x,x,t),
E(x,x,t) helicity-flip
? H(x,x,t),
  • skewedness parameter x
  • mismatch between quark momenta
  • ?sensitive to partonic correlations

  • New Roads
  • Deeply Virtual Meson
  • Production _at_ Q2 gt 10 GeV2
  • ? disentangles flavor and
  • spin!
  • r and f Production give access
  • to gluon GPDs at small x (lt0.2)

3-dimensional GPDs give spatial distribution of
partons and spin
  • Angular Momentum Jq ½ DS Lq !

Can we achieve same level of understanding as
with F2?
Hadronization as a Tool
First 5-flavor fit to Dq(x) (Ds(x) Ds(x)
Quark Polarization from Semi-Inclusive DIS
  • Goal Flavor Separation
  • of quark and antiquark helicity distributions
  • Technique Flavor Tagging
  • The flavor content of the final state
    hadrons is related to the flavor of the struck
    quark through the agency of the fragmentation

Chiral-Quark Soliton Model ?Light sea quarks
polarized but Data consistent with zero
Nuclear Binding
  • Natural Energy Scale of QCD O(100 MeV)
  • Nuclear Binding Scale O(10 MeV)
  • Does it result from a complicated detail of near
    cancellation of strongly attractive and repulsive
    terms in N-N force, or is there another

How can one understand nuclear binding in
terms of quarks and gluons?
Complete spin-flavor structure of modifications
to quarks and gluons in nuclear system may
be best clue.
Quarks in a Nucleus
Can pick apart the spin-flavor structure of EMC
effect by technique of flavor tagging, in the
region where effects of the space-time structure
of hadrons do not interfere (large n!)
EMC Effect
10-4 10-3 10-2 10-1

Nuclear attenuation negligible for n gt 50 GeV
?hadrons escape nuclear medium undisturbed
Space-Time Structure of Photon
Basis of the ELIC Proposal
  • A Linac-Ring Collider Design (with additional
    Circulator Ring)
  • Linac
  • CEBAF is used for the (one-pass) acceleration of
  • Energy recovery is used for rf power savings and
    beam dump requirements
  • Ring
  • Figure-8 storage ring is used for the ions for
    flexible spin manipulations of all light-ion
    species of interest
  • Circulator ring for the electrons may be used to
    ease high current polarized photoinjector

Luminosity of up to 1035 cm-2 sec-1
ELIC Layout
One accelerating one decelerating pass through
ELIC Physics Specifications
  • Center-of-mass energy between 20 and 65 GeV
  • (with energy asymmetry of 10)
  • Ee 3 GeV on Ei 30 GeV up to Ee 5 GeV on Ei
    100 GeV worked out in detail (gives Ecm up to
    45 GeV)
  • Ee 7 GeV on Ei 150 GeV seems o.k., but
    details to be worked out (extends Ecm to 65 GeV)
  • CW Luminosity up to 1035 cm-2 sec-1
  • Ion species of interest protons, deuterons, 3He,
    light-medium ions
  • Proton and neutron
  • Light-medium ions not necessarily polarized
  • Longitudinal polarization of both beams in the
    interaction region (Transverse polarization of
    ions Spin-flip of both beams)

Luminosity Potential with ELIC
The same electron accelerator can also provide 25
GeV electrons for fixed target experiments for
  • Implement 5-pass recirculator, at 5 GeV/pass, as
    in present CEBAF

(straightforward upgrade, no accelerator RD
  • Exploring whether collider and fixed target
    modes can run simultaneously (can in alternating

RD Strategy
  • Several important RD topics have been identified
  • Our RD strategy is multi-pronged
  • Conceptual development
  • Circulator Ring concept promises to ease high
    current polarized photoinjector and ERL
    requirements significantly
  • Additional concepts for luminosity improvements
    are being explored
  • Analysis/Simulations
  • Electron cooling and short bunches
  • Beam-beam physics
  • ERL physics
  • Experiments
  • CEBAF-ER The Energy Recovery experiment at CEBAF
    to address ERL issues in large scale systems
    (March 2003)
  • JLab FEL (10mA), Cornell/JLab ERL Prototype
    (100mA), BNL Cooling Prototype (100mA) to address
    high current ERL issues

CEBAF II/ELIC Upgrade Conclusions
  • An excellent scientific case is developing for a
    high luminosity, polarized electron-light ion
    collider will address fundamental issues in
    Hadron Physics
  • The (spin-flavor) quark-gluon structure of the
    proton and neutron
  • How do quarks and gluons form hadrons?
  • The quark-gluon origin of nuclear binding
  • Highly Likely to be Absolutely Central to
  • JLab design studies have led to an approach that
    promises luminosities as high as 1035 cm-2 sec-1,
    for electron-light ion collisions at a
    center-of-mass energy between 20 and 65 GeV
  • This design, using energy recovery on the JLab
    site, can be cost-effectively integrated with a
    25 GeV fixed target program for physics
  • ELIC and a fixed-target program have a
    complementary physics reach.
  • Planned RD will address open readiness issues
  • Significant Scientific/Engineering
    Challenges to Resolve

New Spin Structure Function Transversity
(in transverse basis)
  • Nucleons transverse spin content ? tensor
  • No transversity of Gluons in Nucleon ?
    all-valence object
  • Chiral Odd ? only measurable in semi-inclusive
  • first glimpses exist in data (HERMES, JLab-6)
  • COMPASS, RHIC-spin plans
  • Future Flavor decomposition?

Estimates for TESLA-N (Ecm 22 GeV)
Generalized Parton Distributions
  • What could be the role of a 25 GeV Fixed Target
  • Enhances phase space to Q2gt10 GeV2
  • Comfortable to do flavor separation of GPDs
  • Also L/T separations to verify how hard process
    really is!

Deep Virtual Meson Production
sL dominant, and Q-6?
How Do Quarks and Gluons form Hadrons?
In semi-inclusive DIS a hadron h is detected in
coincidence with the scattered lepton
  • Study quark-gluon substructure of
  • nucleon target
  • ? parton distribution functions q(x,Q2)
  • hadron formation (or hadronization)
  • ? fragmentation functions D(z,Q2)

Process both of interest in its own right and as
a tool (see also next slides)
(Or The Long-Range Dynamics of Confinement)
What do we know?
What dont we (exactly) know?
The Lund String Model Phenomenological
description in terms of color-string breaking and
parton clustering Evolution of the fragmentation
  • Spin Transfer
  • Is the spin of the struck quark communicated to
    the hadronic final state?
  • Single-Spin Asymmetries
  • How important is intrinsic transverse momentum?
  • Space-Time Structure
  • How long does it take to form a hadron?

Present and future studies (HERMES, JLab-6,
JLab-12) use the nuclear radius as a yardstick to
measure the time scale of hadron formation
Sea-Quarks and Gluons in a Nucleus
Drell-Yan ? No Nuclear Modifications to
Sea-Quarks found at x 0.1 Where is the
Nuclear Binding?
Constraints on possible nuclear modifications of
glue come from 1) Q2 evolution of nuclear ratio
of F2 in Sn/C (NMC) 2) Direct measurement of
J/Psi production in nuclear targets
  • Compatible with EMC effect?
  • Precise measurements possible of
  • Nuclear ratio of Sn/C (24 GeV)
  • J/Psi production (ELIC)

Flavor tagging can also (in principle) disentangle
sea-quark contributions