Physics with ELIC at JLab
Introduction
ELIC Concept
Physics with ELIC
Rolf Ent
05/23/2003
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
ELIC@JLab - Science
Science addressed by ELIC:
• 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
ELIC
Rolf Ent
Thomas Jefferson National Accelerator Facility
12 GeV
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy

ELIC@JLab - Science
Clear scientific case by 12-GeV JLab Upgrade, addressing outstanding issues in
Hadron Physics:
•
•
•
Unprecedented measurements to region in x (> 0.1) where basic three-quark
structure of nucleons dominates.
Measurements of correlations between quarks, mainly through Deep-Virtual Compton
Scattering (DVCS) and constraints by nucleon form factors, in pursuit of the
Generalized Parton Distributions.
Finishing the job on the transition from hadronic to quark-gluon degrees of freedom.

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 luminosity

What energy and luminosity, fixed-target facility or collider (or both)?
• 25 GeV Fixed-Target Facility?
• Electron-Light Ion Collider, center-of-mass energy of 20-65 GeV?
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
Basis of the ELIC Proposal
(Lia Merminga, Slava Derbenev, et al.)
 A Linac-Ring Collider Design (with additional Circulator Ring)
 Linac
 CEBAF is used for the (one-pass) acceleration of
electrons
 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 requirements
Luminosity of up to 1035 cm-2 sec-1
But .... still needs integration of detector
with interaction region ....
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
ELIC Layout
One accelerating & one decelerating pass through CEBAF
Ion Source
Snake
IR Solenoid
IR
5 GeV electrons
Snake
50-100 GeV light ions
Injector
CEBAF with Energy Recovery
Beam Dump
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
The same electron accelerator can also provide 25 GeV
electrons for fixed target experiments for physics
 Implement 5-pass recirculator, at 5 GeV/pass, as in present CEBAF
(straightforward upgrade, no accelerator R&D needed)
 Exploring whether
collider and fixed
target modes can
run simultaneously
(can in alternating
mode)
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
Luminosity Potential with ELIC
Parameter
Units
Design
e-
Ions
Energy
GeV
5
50/100
Electron
Cooling
-
-
Yes
Circulator
Ring
-
Yes
-
Luminosity
cm-2
sec-1
Iave
A
fc
MHz
6x1034 / 1x1035
2.5
x10,000
2.5
1500
More info: Talk on ELIC Project by Lia Merminga
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
ELIC@JLab - 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 > 1 GeV2 implies
(Bjorken) x down to 5 times 10-4
• Significant results for 200
events/pb for inclusive scattering
If Q2 > 10 GeV2 required for Deep
Exclusive Processes, can reach x
down to 5 times 10-3
• Typical cross sections factor 1001,000 smaller than inclusive
scattering  still easily
accessible
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
The Structure of the Proton – F2
F2 Structure Function measured
over impressive range of x and Q2.
Q2 evolution also constrains glue!
Still large uncertainty in glue,
especially at Q2 < 20 GeV2
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
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 > 0.3
>
>
20
known
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
The Spin Structure of the Proton
• From
NLO-QCD analysis of DIS
measurements … (SMC analysis)
•
•
•
•
DS = 0.38 (in AB scheme)
DG = 1.0+1.9
,,
-0.6
quark polarization Dq(x)
first 5-flavor separation from
HERMES (see later)
transversity dq(x)
a new window on quark spin
azimuthal asymmetries from
HERMES and JLab-6
gluon polarization DG(x)
RHIC-spin and COMPASS will
provide some answers!
orbital angular momentum L
how to determine?  GPD’s
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
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
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),
~
E(x,x,t)
3-dimensional GPDs give
spatial distribution of partons
and spin
 Angular Momentum Jq = ½ DS + Lq !
“skewedness parameter” x
mismatch between quark momenta
sensitive to partonic correlations
New Roads:
 Deeply Virtual Meson
Production @ Q2 > 10 GeV2
 disentangles flavor and
spin!
 r and f Production give access
to gluon GPD’s at small x (<0.2)
Can we achieve same level of understanding as with F2?
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
Generalized Parton Distributions
What could be the role of a 25 GeV Fixed Target facility?
Enhances phase space to Q2>10 GeV2
Comfortable to do flavor separation of GPD’s
Also L/T separations to verify how hard process really is!
Deep Virtual Meson Production
sL dominant, and ~ Q-6?
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
New Spin Structure Function: Transversity
dq(x) ~
•
•
•
-
(in transverse
basis)
Nucleon’s transverse spin
content  “tensor charge”
No transversity of Gluons in
Nucleon  “all-valence object”
Chiral Odd  only measurable
in semi-inclusive DIS
Estimates for TESLA-N (Ecm = 22 GeV)
first glimpses exist in data
(HERMES, JLab-6)
COMPASS, RHIC-spin plans
Future: Flavor decomposition?
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
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)
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
Hadronization as a Tool
Quark Polarization from
Semi-Inclusive DIS


First 5-flavor
fit to Dq(x)
_
(Ds(x) = Ds(x) assumed)
- -
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 functions
Chiral-Quark Soliton Model
Light sea quarks polarized
but Data consistent with zero
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
Hadronization
(Or: The Long-Range Dynamics of Confinement)
What do we know?
What don’t we (exactly) know?
The Lund String Model
Phenomenological description in terms of
color-string breaking and parton clustering
•
Evolution of the fragmentation functions
•
•
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
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
Nuclear Binding
 Natural Energy Scale of


How can one understand
nuclear binding in terms
of quarks and gluons?
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 explanation?
Complete spin-flavor structure
of modifications to quarks and
gluons in nuclear system may be
best clue.
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
Quarks in a Nucleus
F2A/F2D
“EMC Effect”
10-4
10-3
10-2
10-1
x
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!)
1
Space-Time Structure of Photon
Nuclear attenuation negligible
for n > 50 GeV hadrons escape
nuclear medium undisturbed
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
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
F2
G
Flavor tagging can also (in principle)
disentangle sea-quark contributions
Compatible with EMC effect?
Precise measurements possible of
 Nuclear ratio of Sn/C (25 GeV)
 J/Psi production (ELIC)
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
ELIC@JLab – 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

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
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
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)
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
R&D Topics

Several important R&D topics have been identified:
 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
Rolf Ent
Thomas Jefferson National Accelerator Facility
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy
Luminosity Potential with ELIC
Parameter
Units
Final Design
e-
Ions
Energy
GeV
5
50/100
Electron
Cooling
-
-
Yes
Circulator
Ring
-
Yes
-
Luminosity
cm-2
6x1034
1x1035
sec-1
Iave
A
fc
MHz
/
2.5
x100
EIC
2.5
1500
Rolf Ent
Thomas Jefferson National Accelerator Facility
x10,000
CIPANP 05/23/2003
Operated by the Southeastern Universities Research Association for the U. S. Department of Energy