Transcript The Frontiers of Nuclear Science: from 12 GeV to EIC Rolf Ent INT10-03 Program, Institute for Nuclear Theory, Seattle, WA Workshop on “The Science.

The Frontiers of Nuclear Science:
from 12 GeV to EIC
Rolf Ent
INT10-03 Program, Institute for Nuclear Theory, Seattle, WA
Workshop on “The Science Case for an EIC”, November 16-19, 2010
A personal perspective on the 12-GeV and EIC science
•The 12-GeV Upgrade
-The 12 GeV science (relevant to an EIC)
Highlights & Shortcomings
-The 12 GeV Roadmap
•The Electron-Ion Collider
- The EIC science
- The EIC Roadmap
• Conclusions
NSAC 2007 Long Range Plan
Recommendation I
“We recommend completion of the
12 GeV Upgrade at Jefferson
Lab. The Upgrade will enable new
insights into the structure of the
nucleon, the transition between
the hadronic and quark/gluon
descriptions of nuclei, and the
nature of confinement.”
A fundamental challenge for
modern nuclear physics is to
understand the structure and
interactions of nucleons and nuclei
in terms of QCD. Doubling the
energy of the JLAB accelerator will
enable three-dimensional imaging of
the nucleon, revealing hidden
aspects of the internal dynamics.
Highlights of the 12 GeV
Science Program
• Unlocking the secrets of QCD:
quark confinement
• New and revolutionary access to the
structure of the proton and neutron
• Discovering the quark structure of nuclei
• High precision tests of the Standard
Model
Items in blue related to
Measuring High-x Structure Functions
d/u
REQUIRES:
• High beam polarization
• High electron current
• High target polarization
• Large solid angle spectrometers
12 GeV will access the regime (x > 0.3),
where valence quarks dominate
Also with 3H/3He and EW
Beyond form factors and quark distributions –
Generalized Parton Distributions (GPDs)
X. Ji, D. Mueller, A. Radyushkin (1994-1997)
Proton form
factors, transverse
charge & current
densities
2000’s
Correlated quark momentum
and helicity distributions in
transverse space - GPDs
Structure functions,
quark longitudinal
momentum & helicity
distributions
Extend longitudinal quark momentum & helicity distributions
to transverse momentum distributions - TMDs
The path towards the extraction of GPDs
Use polarization!
Ds
s+ - sA = +
s + s- = 2s
ep
epg
DsLU ~ sinfIm{F1H + ...}df
Kinematically
suppressed
H(x,t)
x = xB/(2-xB)
Subset of projected results
Projected precision in extraction of
GPD H at x = x
Projected
results
Spatial Image
Rich program in DVCS in valence quark region
B (GeV-2)
Deep Exclusive Meson Production @ 12 GeV
Fit with ds/dt = e-Bt
Measurements at DESY of
diffractive channels (J/y, f,
r, g) confirm the applicability
of QCD factorization:
• t-slopes universal at high Q2
• flavor relations f:r
Pseudoscalar (and vector) meson production at 12 GeV:
typically up to Q2 = 10 GeV2  Experimental QCD
factorization tests of (e,e’p+) and (e,e’K+) essential
Valence Quark Structure and Parton Distributions
Access to valence quark region through DIS
at large x will be augmented with a SIDIS
program
Boer-Mulders asymmetry for pions as
function of Q2 and pT
Onset of the Parton Model in SIDIS @ JLab
1H,2H(e,e’p+/-)X
GRV & CTEQ,
@ LO or NLO
Good description for
p and d targets for
0.4 < z < 0.65
(Note: z = 0.65 ~
Mx2 = 2.5 GeV2)
Seq2q(x) Dqp(z)
Closed (open) symbols reflect data after (before)
events from coherent r production are subtracted
factorization
6 GeV: z > 0.4
12-GeV: study x-z Factorization for kaons
P.J. Mulders, hep-ph/0010199 (EPIC Workshop, MIT, 2000)
At large z-values easier to separate current and target fragmentation region
 for fast hadrons factorization (Berger Criterion) “works” at lower energies
If same arguments as
validated for p apply to K:
At W = 2.5 GeV: z > 0.6
(but, z < 0.65 limit may not apply for kaons!)
Access to sea/strange quarks not clear with 12 GeV
R = sL/sT in (e,e’p) SIDIS
Knowledge on R = sL/sT in SIDIS is essentially non-existing!
• If integrated over z (and pT, f, hadrons), RSIDIS = RDIS
• RSIDIS may vary with z
• At large z, there are known contributions from exclusive
and diffractive channels: e.g., pions from D and r  p+p• RSIDIS may vary with transverse momentum pT
+
• Is RSIDISp = RSIDISp ? Is RSIDISH = RSIDISD ?
• Is RSIDIS
K+
p+
= RSIDIS ? Is RSIDIS
K+
K-
= RSIDIS ?
We measure kaons too! (with about 10% of pion statistics)
• RSIDIS = RDIS test of dominance of quark fragmentation
Seq2q(x) Dqp(z)
p
quark
R = sL/sT in SIDIS (ep  e’pX)
Cornell data of 70’s
RDIS
RDIS (Q2 = 2 GeV2)
Cornell data
conclusion:
“data both
consistent
with R = 0
and R = RDIS”
Some hint of
large R at
large z in
Cornell data?
JLab@12:
scans vs.
Q2/x, z (Q2
= 2& 4) & PT
Transverse Momentum Dependence of
Semi-Inclusive Pion Production
• Not much is known about the orbital motion of partons
• Significant net orbital angular momentum of valence
quarks implies significant transverse momentum of quarks
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 + z kt
+ O(kt2/Q2)
z = Ep/n
pT ~ L < 0.5 GeV optimal for studies as theoretical framework for
Semi-Inclusive Deep Inelastic Scattering has been well developed
at small transverse momentum [A. Bacchetta et al., JHEP 0702 (2007) 093].
Unpolarized SIDIS – JLab @ 6 GeV
Constrain kT dependence of up and down quarks separately
1) Probe p+ and p- final states
2) Use both proton and neutron (d) targets
3) Combination allows, in principle,
separation of quark width from
fragmentation widths
(if sea quark contributions small)
Simple model, host of assumptions
(factorization valid, fragmentation
functions do not depend on quark
flavor, transverse momentum widths
of quark and fragmentation functions
are gaussian and can be added in
quadrature, sea quarks are negligible,
assume Cahn effect, etc.) 
12 GeV: start testing assumptions!
<pt2> (favored)
1st example: Hall C, PL B665 (2008) 20
x = 0.32
z = 0.55
<kt2> (up)
Does the quark structure
of a nucleon get modified
by the suppressed QCD
vacuum fluctuations in a
nucleus?
Reminder: EMC effect is effect that quark momenta in nuclei are altered
1)
2)
3)
4)
Measure the EMC effect on the mirror nuclei 3H and 3He
Is the EMC effect a valence quark only effect?
Is the spin-dependent EMC effect larger?
Can we reconstruct the EMC effect on 3He and 4He from
all measured reaction channels?
5) Is there any signature for 6-quark clusters?
6) Can we map the effect vs. transverse momentum/size?
12 GeV is probably our best chance to understand the
origin of the EMC effect in the valence quark region
Using the nuclear arena
How long can an energetic quark remain deconfined?
How long does it take a confined quark to form a hadron?
Formation time tfh
Hadron is formed
Production time tp
Quark is deconfined
Hadron attenuation
CLAS
Time required to produce colorless “prehadron”, signaled by medium-stimulated
energy loss via gluon emission
Time required to produce fullydeveloped hadron, signaled by CT
and/or usual hadronic interactions
Transverse Momentum Broadening
DpT2 reaches a “plateau” for sufficiently large quark energy,
for each nucleus (L is fixed), related to production length
(start seeing this effect in 6-GeV data).
DpT2
Projected Data
n
Sensitivity: C1 and C2 Plots after 12 GeV
(Vector quark and axialvector quark couplings)
6 GeV
World’s data
Precision Data
(w. Qweak,
6 GeV/PVDIS,
12 GeV/PVDIS)
Gain factor of
80 or so in C2
combination
with 12 GeV!
Qweak
12 GeV
PVDIS
12 GeV
PVDIS
Cs
Solid
19
Møller Parity-Violating Experiment: New Physics Reach
(example of large installation experiment with 11 GeV beam energy)
JLab Møller
LHC
Lee ~ 25 TeV
New Contact Interactions
Not “just another measurement” of sin2(Qw)
N
AFB(b) measures product of e- and b-Z couplings
ALR(had) measures purely the e-Z couplings
Proposed APV(b) measures purely the
e-Z couplings at a different energy scale
12 GeV Upgrade: Phases and Schedule
2004-2005 Conceptual Design (CDR) - finished
2004-2008 Research and Development (R&D) - finished
2006
Advanced Conceptual Design (ACD) - finished
2006-2009 Project Engineering & Design (PED) - finished
2009-2014
Construction –
in second year of construction
Parasitic machine shutdown May 2011 through Oct. 2011
Accelerator shutdown start mid-May 2012
Accelerator commissioning start mid-May 2013
2013-2015
Pre-Ops (beam commissioning)
Hall A commissioning start October 2013
Hall D commissioning start April 2014
Halls B and C commissioning start October 2014
Timescale (for 310M$ project): over 10 years – after numbered recommendation
Highlights (& Shortcomings) of
the 12 GeV Science Program
• New and revolutionary access to the
structure of the proton and neutron
- Form factors to high Q2 (about 10 GeV2)
- Large x PDFs, DVCS & TMD measurements for x > 0.1
- No strange/sea quarks, probing r/p/K production
• Discovering the quark structure of nuclei
- Disentangle the origin of the (valence) EMC effect
- Establish Color Transparency for meson production
- No target fragmentation, limited hadronization studies
• High precision tests of the Standard
Model - Probably as good as anyone can do in EW at E < Mz
Nuclear Physics – 12 GeV to EIC
Study the Force Carriers of QCD
The role of Gluons and Sea Quarks
A High-Luminosity 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:
• 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
Why an Electron-Ion Collider?
• Longitudinal and Transverse Spin Physics!
- 70+% polarization of beam and target without dilution
- transverse polarization also 70%!
• Detection of fragments far easier in collider environment!
- fixed-target experiments boosted to forward hemisphere
- no fixed-target material to stop target fragments
- access to neutron structure w. deuteron beams (@ pm = 0!)
• Easier road to do physics at high CM energies!
- Ecm2 = s = 4E1E2 for colliders, vs. s = 2ME for fixed-target
 4 GeV electrons on 12 GeV protons ~ 100 GeV fixed-target
- Easier to produce many J/Y’s, high-pT pairs, etc.
- Easier to establish good beam quality in collider mode
Longitudinal polarization FOM
Target
p
d
fdilution,
Pfixed_target
f2P2fixed_target
f2P2EIC
0.2
0.8
0.03
0.5
0.4
0.5
0.04
0.5
fixed_target
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 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 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 longitudinal
momentum
of gluons should compete with gluon
splitting, rendering gluon saturation.
orbital
motion
Can we reach such state of saturation?
• Explore the interaction of color charges
quark to
hadron
with matter and understand the
conversion
conversion of quarks and gluons to
hadrons through fragmentation and
Dynamical
structure!
transverse
breakup.
Gluon saturation?
distribution
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 spatial structure of quarks and gluons in nucleons
(show the nucleon structure picture of the day…)
Discover the collective effects of gluons in atomic nuclei
(without gluons there are no protons, no neutrons, no atomic nuclei)
Understand the emergence of hadronic matter from quarks and gluons
(how does E = Mc2 work to create pions and nucleons?)
+ Hunting for the unseen forces of the universe?
The Science of an (M)EIC
Or, Elevator-Talk EIC science goals:
Map the spin and spatial structure of quarks and gluons in nucleons
(show the nucleon structure picture of the day…)
Discover the collective effects of gluons in atomic nuclei
(without gluons there are no protons, no neutrons, no atomic nuclei)
Understand the emergence of hadronic matter from quarks and gluons
(how does E = Mc2 work to create pions and nucleons?)
+ Hunting for the unseen forces of the universe?
F2p & F2d @ high x still needed from EIC
• Similar improvement in F2p at large x
• F2n tagging measurements relatively
F2
straightforward in EIC designs
• EIC will have excellent kinematics to
further measure/constrain n/p at large x!
Similar reduction
with neural networks
(Rojo + Accardi)
Q2 (GeV2)
• s = 1000
• One year of running
(26 weeks) at 50%
efficiency, or 35 fb-1
Sensible reduction in PDF error, likely
larger reduction if also energy scan
Projected g1p Landscape of the EIC
Access to Dg/g is possible from the
g1p measurements through the QCD
evolution, or from open charm (D0)
production (see below), or from dijet measurements.
RHIC-Spin
Similar for g2p (and g2n)!
Sea Quark Polarization
• Spin-Flavor Decomposition of the Light Quark Sea
100 days, L =1033, s = 1000
}
Access requires s ~ 1000 (and good luminosity)
| p
>
u
=
u
d
u
+
u
d
u
u
u
+
u
d
d
d
+ …
Many models
predict
Du > 0, Dd < 0
Transverse Quark & Gluon Imaging
Deep exclusive measurements in ep/eA with an EIC:
diffractive:
transverse gluon imaging
non-diffractive:
quark spin/flavor structure
J/y, f, ro, g (DVCS)
p, 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
(“tomography”)
Detailed differential images from nucleon’s partonic structure
EIC: Gluon size
from J/Y and f
electroproduction
(Q2 > 10 GeV2)
t
[Transverse distribution derived directly from t dependence]
Hints from HERA:
Area (q + q) > Area (g)
Dynamical models predict difference:
pion cloud, constituent quark picture
-
EIC: singlet quark
size from deeply
virtual compton
scattering
• Q2 > 10 GeV2
for factorization
• Statistics hungry
at high Q2!
EIC: strange and
non-strange (sea)
quark size from p
and K production
t
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.
An EIC with high transverse
polarization is the optimal
tool to to study this!
Only a small subset of the (x,Q2) landscape
has been mapped here: terra incognita
Correlation between Transverse Spin and
Momentum of Quarks in Unpolarized Target
(Harut Avakian, Antje Bruell)
All Projected Data
Perturbatively
Calculable at
Large pT
Assumed
100 days
of 1035
luminosity
Vanish like
1/pT (Yuan)
The Science of an (M)EIC
Or, Elevator-Talk EIC science goals:
Map the spin and spatial structure of quarks and gluons in nucleons
(show the nucleon structure picture of the day…)
Discover the collective effects of gluons in atomic nuclei
(without gluons there are no protons, no neutrons, no atomic nuclei)
Understand the emergence of hadronic matter from quarks and gluons
(how does E = Mc2 work to create pions and nucleons?)
+ Hunting for the unseen forces of the universe?
Gluons in Nuclei
Ratio of gluons in lead to deuterium
• What do we know about
gluons in a nucleus?
NOTHING!!!
• Large uncertainty in gluon distributions
• need range of Q2 in shadowing region,
 x ~ 10-2-10-3  sEIC = 1000+
+ Transverse distribution of gluons on nuclei
from coherent Deep-Virtual Compton
Scattering and coherent J/Y production
[Measurements at DESY of diffractive channels (J/y, f,
confirmed the applicability of QCD factorization:
t-slopes universal at high Q2 & flavor relations f:r hold]
r, g)
Gluon radius
of a nucleus?
Sea-Quarks in Nuclei
Drell-Yan: Is the EMC
effect a valence quark
phenomenon or are sea
quarks involved?
Tremendous opportunity for
experimental improvements!
RCa
E772
1.0
gluons
sea
0.5
valence
S. Kumano, “Nuclear Modification of Structure
Functions in Lepton Scattering,” hep-ph/0307105
0.1
x
 Use combination of FLA & F2A
measurements, EW measurements,
‘flavor tagging’, etc.
1.0
Unresolved Questions in Nuclei
F2A/F2D
• F2 structure functions, or quark distributions, are altered in nuclei
• ~1000 papers on the topic; the best models explain the curve by
change of nucleon structure - BUT we are still learning (e.g. local
density effect) – and 12 GeV optimal to attack the valence region.
EIC:
• Is shadowing a leading- or
higher-twist phenomenon?
• What is the dynamical
origin of anti-shadowing?
x
12 GeV
The Science of an (M)EIC
Or, Elevator-Talk EIC science goals:
Map the spin and spatial structure of quarks and gluons in nucleons
(show the nucleon structure picture of the day…)
Discover the collective of gluons in atomic nuclei
(without gluons there are no protons, no neutrons, no atomic nuclei)
Understand the emergence of hadronic matter from quarks and gluons
(how does E = Mc2 work to create pions and nucleons?)
+ Hunting for the unseen forces of the universe?
Hadronization
EIC: Understand the
conversion of quarks and
gluons to hadrons through
fragmentation and breakup
un-integrated parton distributions
current
fragmentation
Fragmentation
from
QCD vacuum
target
fragmentation
EIC: Explore the interaction
of color charges with matter
+h ~ 4
E
I
C
-h ~ -4
Transverse Momentum Broadening
DpT2 reaches a “plateau” for sufficiently large quark energy,
for each nucleus (L is fixed). In the pQCD region, the effect
is predicted to disappear (arbitrarily put at n =1000)
DpT2
n
Hadronization
EIC: Explore the interaction of color charges with matter
(1 month only)
EIC: Understand the conversion of quarks and gluons
to hadrons through fragmentation and breakup
EIC Realization
From Hugh Montgomery’s presentation at the INT10-03 Program in Seattle
Assumes endorsement for an EIC at the next ~2012/13 NSAC Long Range Plan
Summary
The last decade+ has seen tremendous progress in our understanding
of the partonic sub-structure of nucleons and nuclei, due to:
• Findings at the US nuclear physics flagship facilities: RHIC and CEBAF
• The surprises found at HERA (H1, ZEUS, HERMES), and now COMPASS/CERN.
• The development of a theory framework allowing for a revolution in our
understanding of the inside of hadrons … GPDs, TMDs, Lattice QCD
• … hand in hand with the stellar technological advances in polarized beam and
parity-quality electron beam delivery.
This has led to new frontiers of nuclear science:
- the possibility to truly explore and image the nucleon
- the possibility to understand and build upon QCD
and study the role of gluons in structure and dynamics
- the unique possibility to study the interaction of color-charged
objects in vacuum and matter, and their conversion to hadrons
- utilizing precision electroweak studies to complement direct
searches for physics beyond the Standard Model
We have unique opportunities to make a (future textbook)
breakthrough in nucleon structure and QCD dynamics.
EIC is intended to create
and study gluons, which
bind subatomic particles
Einstein’s famous equation,
E = mc2, predicts that small
amounts of mass can be
transformed into large
amounts of energy. Although
we have demonstrated this
prediction and its practical
applications, the truth is that
we do not yet understand
how the process works – the
underlying mechanisms by
which mass is transformed into
energy and vice versa. EIC will
allow scientists to tackle this
very fundamental question in
physics.
Appendix
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.
Towards a “3D” spinflavor landscape
Wu(x,k,r)
(Wigner Function)
m
p
TMDu(x,kT)
f1,g1,f1T ,g1T
h1, h1T , h1L , h1
f1(x)
g1, h1
GPDu(x,x,t)
Hu,
Eu,
~ ~
Hu, Eu
dx
d2kT
Want PT >
L but not
too large!
p
x
TMD
TransverseLink to
Momentum
Orbital
Dependent
Momentum
Parton
Distributions
m
u(x)
Du, du
Parton
Distributions
F1u(t)
F2u,GAu,GPu
Form Factors
GPD
B
Link to
Generalized
Orbital
Parton
Distributions
Momentum
E00-108: Onset of the Parton Model
Seq2q(x) Dqp(z)
factorization
p
quark
D4 -R

D+ 4 * R - 1
Collinear
Fragmentation
R
Nπ +
Nπ -
(Deuterium
data)
(Resonances cancel (in SU(6)) in D-/D+ ratio extracted from deuterium data)
So what about R = sL/sT for pion electroproduction?
“Semi-inclusive DIS”
quark
p
Seq2q(x) Dqp(z)
“Deep exclusive scattering”
is the z  1 limit of this
“semi-inclusive DIS” process
Here, R = sL/sT ~ Q2
(at fixed x)
RSIDIS  RDIS disappears with Q2!
Not
including a
comparable
systematic
uncertainty:
~1.6%
Have no idea
at all how R
will behave
at large pT
Planned scans in z at
Q2 = 2.0 (x = 0.2) and
4.0 GeV2 (x = 0.4) 
should settle the
behavior of sL/sT for
large
z. data cover
Planned
range Q2 = 1.5 – 5.0
GeV2, with data for
both H and D at Q2 = 2
GeV2
Planned data cover
range in PT up to ~ 1
GeV. The coverage in f
is excellent (o.k.) up to
PT = 0.2 (0.4) GeV.
Model PT dependence of SIDIS
Gaussian distributions for PT dependence, no sea quarks, and leading order in (kT/q)
Inverse of total width for each combination of
quark flavor and fragmentation function given by:
And take Cahn effect into account,
with e.g. (similar for c2, c3, and c4):
Parity-Violating Asymmetries
Weak Neutral Current (WNC) Interactions at Q2 << MZ2
Longitudinally Polarized Electron
Scattering off Unpolarized Fixed
Targets
(gAegVT + gVegAT)
V
A
The couplings
g depend on both electroweak physics and the weak
vector and axial-vector hadronic current, and are functions of sin2Qw
Mid 70s V
goal was to show A
sin2Qw was the same as in n scattering
1990-2010 e target
couplings
C2i probe
2gVe gAinovel aspects of hadron structure
C1i  2gA gVi
Ongoing
precision measurements with carefully chosen kinematics
to probe new physics at multi-TeV high energy scales
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
Where does the spin of the proton originate?
(let alone other hadrons…)
The Standard Model tells us that spin arises from the spins
and orbital angular momentum of the quarks and gluons:
½ = ½ DS + DG + L
• Experiment: DS ≈ 0.3
• Gluons contribute to much of
the mass and ≈ half of the
momentum of the proton, but…
• … recent results (RHIC-Spin,
COMPASS@CERN) indicate
that their contribution to the
proton spin is small: DG < 0.1?
(but only in small range of x…)
• Lu, Ld, Lg?
The Gluon Contribution to the Proton Spin
at small x
Superb sensitivity
to Dg at small x!
What’s the use of GPDs?
1. Allows for a unified description of form factors
and parton distributions
2. Describe correlations of quarks/gluons
3. Allows for Transverse Imaging
Fourier transform in momentum transfer
x < 0.1
x ~ 0.3
x ~ 0.8
gives transverse spatial distribution of quark (parton) with momentum fraction x
4. Allows access to quark angular momentum (in
model-dependent way)
GPDs and Transverse Gluon Imaging
Goal: Transverse gluon imaging of nucleon over wide range of x: 0.001 < x < 0.1
Requires: - Q2 ~ 10-20 GeV2 to facilitate interpretation
- Wide Q2, W2 (x) range
- luminosity of 1033 (or more) to do differential measurements in Q2, W2, t
Q2 = 10 GeV2 projected data
(Andrzej Sandacz)
EIC enables gluon imaging!
Simultaneous data at
other Q2-values
Single-Spin Asymmetry Projections with Proton
• 11 + 60 GeV
(Also π-)
36 days
L = 3x1034 /cm2/s
2x10-3 , Q2<10 GeV2
4x10-3 , Q2>10 GeV2
• 3 + 20 GeV
36 days
L = 1x1034/cm2/s
3x10-3 , Q2<10 GeV2
7x10-3 , Q2>10 GeV2
Polarization 80%
Overall efficiency 70%
z: 12 bins 0.2 - 0.8
PT: 5 bins 0-1 GeV
φh angular coverage incuded
Average of Collins/Sivers/Pretzelosity projections
Still with θh <40 cut, needs to be updated
Electron-Ion Collider – 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
• INT10-03 program @ Institute for Nuclear Theory ongoing
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 LRP)
• 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 energyluminosity 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