MEIC Overview:
Physics, Project & Timeline
Rolf Ent
MEIC Accelerator Design Review
September 15-16, 2010
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
The proton is far more than just its up + up + down (valence) quark structure
QCD and the Origin of Mass
 99% of the proton’s
mass/energy is due to the
self-generating gluon field
– Higgs mechanism has
almost 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.
Gluons and QCD
• QCD is the fundamental theory that describes structure
and interactions in nuclear matter.
• Without gluons there are no protons, no neutrons, and
no atomic nuclei
• Gluons dominate the structure
of the QCD vacuum
• Facts:
– The essential features of QCD (e.g. asymptotic freedom, chiral
symmetry breaking, and color confinement) are all driven by the
gluons!
– Unique aspect of QCD is the self interaction of the gluons
– 99% of mass of the visible universe arises from glue
– Half of the nucleon momentum is carried by gluons
Nuclear Physics – 12 GeV to EIC
Study the Force Carriers of QCD
The role of Gluons and Sea Quarks
EIC@JLab High-Level Science Overview
• Hadrons in QCD are relativistic many-body systems, with a fluctuating number of
elementary quark/gluon constituents and a very rich structure of the wave function.
• With 12 GeV we study mostly
the valence quark component,
which can be described with
methods of nuclear physics
(fixed number of particles).
12 GeV
• With an (M)EIC we enter the region where the
many-body nature of hadrons, coupling to
vacuum excitations, etc., become manifest and
the theoretical methods are those of quantum
field theory. An EIC aims to study the sea
quarks, gluons, and scale (Q2) dependence.
The Science of an (M)EIC
Nuclear Science Goal: How do we understand the visible
matter in our universe in terms of the fundamental quarks
and gluons of QCD?
Overarching EIC Goal: Explore and Understand QCD
Three Major Science Questions for an EIC (from NSAC LRP07):
1) What is the internal landscape of the nucleons?
2) What is the role of gluons and gluon self-interactions in nucleons and nuclei?
3) What governs the transition of quarks and gluons into pions and nucleons?
Or, Elevator-Talk EIC science goals:
Map the spin and 3D quark-gluon structure of protons
(show the nucleon structure picture of the day…)
Discover the role of gluons in atomic nuclei
(without gluons there are no protons, no neutrons, no atomic nuclei)
Understand the creation of the quark-gluon matter around us
(how does E = Mc2 work to create pions and nucleons?)
+ Hunting for the unseen forces of the universe
Slide 7
Why a New-Generation EIC?
• Obtain detailed differential transverse quark and gluon images
(derived directly from the t dependence with good t resolution!)
- Gluon size from J/Y and f electroproduction
- 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 these 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). longitudinal
• At high gluon density, the recombination
momentum
of gluons should compete with gluon
orbital
splitting, rendering gluon saturation.
motion
Can we reach such state of saturation?
quark to
• Map the physical mechanism of
hadron
fragmentation of correlated quarks
conversion
and gluons, and understand how
Dynamical structure!
we can calculate it quantitatively.
Gluon saturation?
transverse distribution
A High-Luminosity ELectron Ion Collider at JLab
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.”
• Requirements in our view:
• range in energies from s = few 100 to s = few 1000 & 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
• upgradable to higher energies
Current Ideas for a Collider
Design Goals for Colliders Under Consideration World-wide
Energies
s
Design
Luminosity
(M)EIC@JLab
Up to 11 x 60+
240-3000
Close to 1034
Future
ELIC@JLab
Up to 11 x 250
(20? x 250)
11000
(20000?)
Close to 1035
Staged
MeRHIC@BNL
Up to 5 x 250
600-5000
Close to 1034
eRHIC@BNL
Up to 20 x 325
(30 x 325)
26000
(39000)
Close to 1034
ENC@GSI
Up to 3 x 15
180
Few x 1032
LHeC@CERN
Up to 150 x 7000
4200000
Close to 1033
Present focus of interest (in the US) are the (M)EIC and Staged MeRHIC
versions, with s up to ~3000 and 5000, respectively
Slide 10
EIC Advisory Committee
Both laboratories (BNL & JLab) are working together to get advice on the
best steps towards a US Electron-Ion Collider.
Sam Aronson and Christoph Leemann/Hugh Montgomery have named an
international EIC Advisory Committee:
Joachim Bartels
Allen Caldwell
Albert De Roeck
Walter Henning (chair)
David Hertzog
Xiangdong Ji
Robert Klanner
Alfred Mueller
Katsunobu Oide
Naohito Saito
Uli Wienands
*likely add few more accelerator experts
• 1st meeting Feb. 16, 2009 at SURA headquarters, D.C.
• 2nd meeting Nov. 2&3, 2009 at Jefferson Lab
• 3rd meeting anticipated Fall 2010 (at BNL?)
Concrete design for EIC@Jlab requested by this meeting
Internal reviewed cost estimate requested by this meeting
EIC Project - Roadmap
Year
CEBAF Upgrade
Electron-Ion Collider
1994
1st CEBAF at Higher Energies
Workshop
1996 (LRP)
CEBAF Upgrade an Initiative
~2000
Energy choice settled,
“Golden Experiments”
1st workshops on US Electron-Ion
Collider
2002 (LRP)
JLab 12-GeV Upgrade
4th recommendation
Electron-Ion Collider an Initiative
2007 (LRP)
JLab 12-GeV Upgrade
highest recommendation
Electron-Ion Collider
“half-recommendation”
EIC “Golden Experiments”???
~2010
2013? (LRP)
JLab 12-GeV construction &
operation, FRIB construction
highest recommendation(s)?
EIC a formal (numbered)
recommendation?
2015
JLab 12-GeV Upgrade
construction complete
EIC Mission Need,
formal R&D ongoing?
2025?
EIC construction complete?
Slide 12
EIC – JLab User Meetings Roadmap
• March 12 + 13
• March 14 + 15
• April 07, 08, 09
• May 17 +18
• June 04 + 05
• June 07,08,09
@Rutgers: Electron-Nucleon Exclusive Reactions
@Duke: Partonic Transverse Momentum in Hadrons:
Quark Spin-Orbit Correlations and Quark-Gluon Interactions
@ANL: Nuclear Chromo-Dynamic Studies
@W&M: Electroweak Studies
@JLab: MEIC Detector Workshop
2010 JLab Users Group Meeting
(with session dedicated to a summary of users workshops,
held in Spring 2010, that explored physics motivations of
an Electron-Ion Collider, entitled
“Beyond the 12 GeV Upgrade: an EIC at JLab?”)
• In parallel: MEIC/ELIC design worked out following highest EICAC
(Nov. 2009 meeting) recommendation related to accelerator
Energy-Luminosity profile of EIC design will likely be optimized over time
to adjust to novel accelerator science ideas & the nuclear science case
 For now we assume a base luminosity, ~1034 e-nucleons/cm2/s
 Study what luminosity is required at what energies to optimize the
science output, and fold in implications for the detector/acceptance
Slide 13
EIC Collaboration – Roadmap
• EIC (eRHIC/ELIC) webpage: http://web.mit.edu/eicc/
• Weekly meetings at both BNL and JLab
• Wiki pages at http://eic.jlab.org/ & https://wiki.bnl.gov/eic
• EIC Collaboration has biannual meetings since 2006
• Last EIC meeting: July 29-31, 2010 @ Catholic University, DC
• Long INT10-03 program @ Institute for Nuclear Theory, centered around
spin, QCD matter, imaging, electroweak Sept. 10 – Nov. 19, 2010
• Periodic EIC Advisory Committee meetings (convened by BNL & JLab)
After INT10-03 program (2011 – next Nuclear Science Long Range Plan)
• need to produce single, community-wide White Paper
laying out full EIC science program in broad, compelling strokes
• and need to adjust EIC designs to be conform accepted energy-luminosity
profile of highest nuclear science impact
• followed by an apples-to-apples bottom-up cost estimate comparison
for competing designs, folding in risk factors
• and folding in input from ongoing Accelerator R&D, EICAC and community
Slide 14
Summary
The 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 …
Generalized Parton Distributions, Transverse Momentum Dependent
Parton Distributions, Lattice QCD
This has led to new frontiers of nuclear science:
- the possibility to truly explore the nucleon
- a new QCD regime of strong color fields in nuclei
- mapping the mechanism of nucleon and pion creation
The EIC presents a unique opportunity to maintain US
leadership in high energy nuclear physics and precision QCD
physics
Slide 15
Backup
Slide 16
EIC@JLab assumptions
(x,Q2) phase space directly correlated with s (=4EeEp) :
@ Q2 = 1 lowest x scales like s-1
2/ys
x
=
Q
@ Q2 = 10 lowest x scales as 10s-1
General science assumptions:
(“Medium-Energy”) EIC@JLab option 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
Slide 17
Why a Novel High-Luminosity EIC?
Several pluses of (M)EIC/ELIC conceptual design
- Four Interaction Regions available (only two can run simultaneously)
- novel design ideas promise high luminosity (& full acceptance)
- more symmetric beam energies (“central” angles facilitates detection)
- figure-8 design optimized for spin (allows for polarized deuteron beams)
High luminosity in our view a must
- Semi-inclusive and deep exclusive processes depend on many
kinematic variables beyond x, Q2, and y:
• e.g. t and f for DES
•
z, pT and f for SIDIS
- More exclusive cross sections drop rapidly with Q2, t and/or pT
- True progress only possible by multi-dimensional experiments
- Multiple running conditions required:
• Longitudinal and transversely polarized beam,
• Various ion species: 1H, 2H, 3He, heavy A
• Low Ecm and high Ecm runs
Full science program needs “n times 100 days of good luminosity”
Science versus Luminosity Matrix
JLAB6&12
HERMES
ENC@GSI
COMPASS
EW
 Luminosity [cm-2 s-1]
1035
MEIC
1034
ELIC
DES
1033
SIDIS
JETS
10
Legend:
DIS
SIDIS
DES
DIFF
JETS
EW
deep inelastic scattering
semi-inclusive DIS
deep exclusive
(pseudoscalar and
vector mesons)
diffractive scattering
jet production
electroweak processes
Illustration only
DIS
1032
No scientific judgment
applied: luminosity is
taken from what EIC
simulations assumed
DIFF
100
1000
10000
100000
 s [GeV2]
Slide 19
Rough Ideas of Energies (don’t take these too strict)
Energy combination
(Ee & Ep)
Physics discussed in workshops
3 on 12 to 3 on 20
(s ~ 150 - 300)
Longitudinal/Transverse separations for meson electroproduction, form factor measurements
5 on 20
(s ~ 400)
Low-Q2 part of semi-inclusive deep-inelastic scattering
physics
5 on 30 to 5 on 60
(s ~ 600 – 1200)
Deep exclusive scattering experiments aimed at
nucleon/nucleus imaging
5 on 60 to 10 on 60
(s ~ 1200 - 2400)
Shadowing region of electron-nucleus scattering
High-Q2 part of semi-inclusive deep-inelastic scattering
physics. Start of jet physics.
10 on 80-100
(s ~ 3200-4000)
Push to smaller x (~10-3, with reasonable lever-arm in
Q2) for e-D and e-3He cases
(Luminosity x s) high
e.g., L ~ 1034, s ~ 3000
Electroweak searches
Highest energies (but
low luminosities)
Push for small x, saturation
Slide 20
MEIC Design Efforts - Status
• Near-term design concentrates on parameters that are
within state-of-the-art (exception: small bunch length & small
vertical b* for proton/ion beams)
• Detector/IR design has concentrated on maximizing
acceptance for deep exclusive processes and processes
associated with very-forward going particles
 detect remnants of both struck & spectator quarks
• Optimal energy/luminosity profile still a work in progress
• Many parameters related to the MEIC detector/IR design
seem well matched now (lattices, ion crossing angle, magnet
apertures, gradients & peak fields, range of proton energies,
detector requirements), such that we do not end up with large
“blind spots”.
Slide 21
Reaching Saturation: EIC Options
boost in
“virtual” x reach
gluon density boost over HERA
over HERA at Q2 = const
Energies
(GeV x GeV)
s
(GeV2)
sEIC/sHERA
11 x 38
1700
1/60
1.73
6
5 x 100
2000
1/50
1.83
8
20 x 100
8000
1/12
2.81
31
30 x 130
15600
1/6
3.46
63
Energies for
heavy-ion
beams
G ~ A1/3 x s0.3
(A = 208)
At high gluon density, gluon
recombination should
compete with gluon splitting
 density saturation.
Color glass
condensate
Slide 22