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Quarks and Gluons in the Nuclear Medium Opportunities at JLab12 GeV and an EIC

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Title: Quarks and Gluons in the Nuclear Medium Opportunities at JLab12 GeV and an EIC


1
Quarks and Gluons in the Nuclear Medium
Opportunities at JLab_at_12 GeV and an EIC
Rolf Ent, ECT-Trento, June 06, 2008
Nuclear Medium Effects on the Quark and Gluon
Structure of Hadrons Main Workshop
Topics Nuclear effects in polarized and
unpolarized deep inelastic scattering Nuclear
generalized parton distributions Hard exclusive
and semi-inclusive processes Nuclear
hadronization Color transparency Future
facilities and experiments
2
The Quark Structure of Nuclei
3
The QCD Lagrangian and Nuclear Medium
Modifications
The QCD vacuum
Long-distance gluonic fluctuations
Does the quark structure of a nucleon get
modified by the suppressed QCD vacuum
fluctuations in a nucleus?

Leinweber, Signal et al.
4
Quarks in a Nucleus
Observation that structure functions are altered
in nuclei stunned much of the HEP community 25
years ago
A3 EMC Effect at 12 GeV
Effect well measured,over large range of x and A,
but remains poorly understood 1) ln(A) or r
dependent?
2) valence quark effect only?
5
Anti-Quarks in a Nucleus
Is the EMC effect a valence quark phenomenon or
are sea quarks involved?
Tremendous opportunity for experimental
improvements!
E772
Deep inelastic electron scattering probes only
the sum of quarks and anti-quarks ? requires
assumptions on the role of sea quarks
Solution Detect a final state hadron in addition
to scattered electron
? Can tag the flavor of the struck quark by
measuring the hadrons produced flavor tagging
6
g1(A) Polarized EMC Effect
  • New calculations indicate larger effect for
    polarized structure function than for
    unpolarized scalar field modifies lower
    components of Dirac wave function
  • Spin-dependent parton distribution functions for
    nuclei nearly unknown
  • Can take advantage of modern technology for
    polarized solid targets to perform systematic
    studies Dynamic Nuclear Polarization

7
Chiral Quark-Soliton model
(quarks in nucleons (soliton) exchange infinite
pairs of pions, vector mesons with nuclear medium)
Miller, Smith
  • Valence only calculations consistent with Cloet,
    Bentz, Thomas calculations
  • Same model shows small effects due to sea quarks
    for the unpolarized case (consistent with data)

Large enhancement for xgt0.3 due to sea quarks
Sea is not much modified
8
g1(A) Polarized EMC Effect
  • New calculations indicate larger effect for
    polarized structure function than for
    unpolarized scalar field modifies lower
    components of Dirac wave function
  • Spin-dependent parton distribution functions for
    nuclei nearly unknown
  • Can take advantage of modern technology for
    polarized solid targets to perform systematic
    studies Dynamic Nuclear Polarization

Curve follows calculation by W. Bentz,
I. Cloet, A. W. Thomas.
9
Extend measurements on nuclei to x gt 1 Superfast
quarks
Fe(e,e) 5 PAC days
Six-quark bag (4.5 of wave function)
Mean field
Correlated nucleon pair
10
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
  • 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?
  • Is there any signature for 6-quark clusters?
  • Can we map the effect vs. transverse
    momentum/size?

Now use the nuclear arena to look for QCD
11
Use the Nuclear Arena to Study QCD
12
Total Hadron-Nucleus Cross Sections
Hadron Nucleus total cross section
K
p
_
p
a
p
Fit to
Hadron momentum 60, 200, 250 GeV/c
a 0.72 0.78, for p, p, k
a lt 1 interpreted as due to the strongly
interacting nature of the probe
A. S. Carroll et al. Phys. Lett 80B 319 (1979)
13
Physics of Nuclei Color Transparency
Traditional nuclear physics expectation
transparency nearly energy independent.
Quantum ChromoDynamics

A(e,eh), h hadron
1.0
T
Energy (GeV)
Ingredients
From fundamental considerations (quantum
mechanics, relativity, nature of the strong
interaction) it is predicted (Brodsky, Mueller)
that fast protons scattered from the nucleus will
have decreased final state interactions
  • s h-N cross-section
  • Glauber multiple
  • scattering approximation
  • (or better transport calculation!)
  • Correlations Final-State
  • Interaction effects

hN
14
Search for Color Transparency in Quasi-free
A(e,ep) Scattering
Fit to s soAa
a
Constant value line fits give good
description c2/df 1 Conventional Nuclear
Physics Calculation by Pandharipande et al.
(dashed) also gives good description
a constant 0.75
Close to proton-nucleus total cross section data
? No sign of CT yet
15
Physics of Nuclei Color Transparency
Results inconsistent with CT only. But can be
explained by including additional mechanisms such
as nuclear filtering or charm resonance states.
AGS A(p,2p)
Glauber calculation
The A(e,ep) measurements will extend up to 10
GeV/c proton momentum, beyond the peak of the
rise in transparency found in the BNL A(p,2p)
experiments.
16
Physics of Nuclei Color Transparency
A(e,ep)
Total pion-nucleus cross section slowly
disappears, or … pion escape probability
increases ? Color Transparency ? Unique
possibility to map out at 12 GeV (up to Q2 10)
Total pion-nucleus cross section slowly
disappears, or … pion escape probability
increases ? Color Transparency?
17
Physics of Nuclei Color Transparency
A(e,er) at 12 GeV (at fixed coherence length)
12 GeV
18
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
Hadron attenuation
Quark is deconfined
CLAS
Time required to produce fully-developed hadron,
signaled by CT and/or usual hadronic interactions
Time required to produce colorless pre-hadron,
signaled by medium-stimulated energy loss via
gluon emission
19
Using the nuclear arena
How long can an energetic quark remain
deconfined? How long does it take a confined
quark to form a hadron? Or How do energetic
quarks transform into hadrons? How quickly
does it happen? What are the mechanisms?
dE/dx ltpT2gtL DE L (QED) L2 (QCD)?
20
Using the nuclear arena
How long can an energetic quark remain
deconfined? How long does it take a confined
quark to form a hadron? Or How do energetic
quarks transform into hadrons? How quickly
does it happen? What are the mechanisms?
Relevance to RHIC and LHC
Deep Inelastic Scattering
Relativistic Heavy-Ion Collisions
Initial quark energy is known Properties of
medium are known
21
DpT2 vs. n for Carbon, Iron, and Lead
CLAS
Hall B
Preliminary
Pb
dE/dx
100 MeV/fm (perturbative formula)
Fe
C
DpT2 (GeV2)
n (GeV)
22
Production length from JLab/CLAS 5 GeV data
(Kopeliovich, Nemchik, Schmidt, hep-ph/0608044)
  • What we have learned
  • Quark energy loss can be
  • estimated
  • Data appear to support the novel DE L2 LPM
    behavior
  • 100 MeV/fm for Pb at few GeV, perturbative
    formula
  • Deconfined quark lifetime
  • can be estimated, 5 fm
  • _at_ few GeV
  • Outstanding questions
  • Higher energy data to
  • confirm plateau for
  • heavy (large-A) nuclei
  • Much more theoretical
  • work needed to provide a
  • quantitative basis for jet
  • quenching at RHIC/LHC?

23
Using the nuclear arena
DpT2 reaches a plateau for sufficiently large
quark energy, for each nucleus (L is fixed).
DpT2
Projected Data
n
24
DOE Project Critical Decisions
  • CD-0 Approve Mission Need
  • CD-1 Approve Alternative Selection and Cost Range
  • Permission to develop a Conceptual Design Report
  • Defines a range of cost, scope, and schedule
    options
  • CD-2 Approve Performance Baseline
  • Fixes baseline for scope, cost, and schedule
  • Now develop design to 100
  • Begin monthly Earned Value progress reporting to
    DOE
  • Permission for DOE-NP to request construction
    funds
  • CD-3 Approve Start of Construction
  • DOE CD3 (IPR/Lehman) review scheduled for July
    22-24
  • DOE Office of Science CD-3 Approval meeting in
    late Sept 2008
  • CD-4 Approve Start of Operations or Project
    Close-out

25
DOE CRITICAL DECISION SCHEDULE
(A) Actual Approval Date
26
12 GeV Upgrade Phases and Schedule
(based on funding guidance provided by DOE-NP in
June-2007)
  • 2004-2005 Conceptual Design (CDR) - finished
  • 2004-2008 Research and Development (RD) -
    ongoing
  • 2006 Advanced Conceptual Design (ACD) - finished
  • 2006-2009 Project Engineering Design (PED) -
    ongoing
  • 2009-2014 Construction starts in 1/2 year!
  • 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

27
The Gluon Structure of Nuclei
28
Gluons dominate 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
  • 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
  • 98 of mass of the visible universe arises from
    glue
  • Half of the nucleon momentum is carried by gluons
  • However, gluons are dark they do not interact
    directly with light
  • ? high-energy collider!

29
Exposing the high-energy (dark) side of the
nuclei
  • The Low Energy View of Nuclear Matter
  • nucleus protons neutrons
  • nucleon ? quark model
  • quark model ? QCD

The High Energy View of Nuclear Matter The
visible Universe is generated by quarks, but
dominated by the dark glue!
Remove factor 20
30
EIC science has evolved from new insights and
technical accomplishments over the last decade
  • 1996 development of GPDs
  • 1999 high-power energy recovery linac technology
  • 2000 universal properties of strongly
    interacting glue
  • 2000 emergence of transverse-spin phenomenon
  • 2001 worlds first high energy polarized proton
    collider
  • 2003 RHIC sees tantalizing hints of saturation
  • 2006 electron cooling for high-energy beams

31
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. In support of this new
    direction
  • We recommend the allocation of resources to
    develop accelerator and detector technology
    necessary to lay the foundation for a polarized
    Electron Ion Collider. The EIC would explore the
    new QCD frontier of strong color fields in nuclei
    and precisely image the gluons in the proton.

32
How do we understand the visible matter in our
universe in terms of the fundamental quarks and
gluons of QCD?
Explore the new QCD frontier strong color
fields in nuclei   - How do the gluons
contribute to the structure of the nucleus? -
What are the properties of high density gluon
matter? - How do fast quarks or gluons
interact as they traverse nuclear
matter?
Precisely image the sea-quarks and gluons
in the nucleon - How do the gluons and
sea-quarks contribute
to the spin structure of the nucleon? - What
is the spatial distribution of
the gluons and sea quarks in the
nucleon? - How do hadronic final-states form in
QCD?
33
Explore the structure of the nucleon
  • Parton distribution functions
  • Longitudinal and transverse spin distribution
    functions
  • Generalized parton distributions
  • Transverse momentum distributions

34
Precisely image the sea quarks
Spin-Flavor Decomposition of the Light Quark Sea
u
u
u
gt
u
d
Many models predict Du gt 0, Dd lt 0
p …
u
u
u
u
d
d
d
d
RHIC-Spin region
No competition foreseen!
35
GPDs and Transverse Gluon Imaging
Deep exclusive measurements in ep/eA with an
EIC diffractive transverse gluon imaging J/y,
ro, g (DVCS) non-diffractive quark
spin/flavor structure p, K, r, …
Are gluons uniformly distributed in nuclear
matter or are there small clumps of glue?
36
GPDs and Transverse Gluon Imaging
Fourier transform in momentum transfer
gives transverse size of quark (parton) with
longitud. momentum fraction x
EIC 1) x lt 0.1 gluons!
2) x 0 ? the take out and put back gluons
act coherently.
2) x 0
37
GPDs and Transverse Gluon Imaging
Goal Transverse gluon imaging of nucleon over
wide range of x 0.001 lt x lt 0.1 Requires - Q2
10-20 GeV2 to facilitate interpretation - Wide
Q2, W2 (x) range - Sufficient luminosity to do
differential measurements in Q2, W2, t
EIC enables gluon imaging!
Q2 10 GeV2 projected data
EIC (16 weeks)
Scaled from 2 to 16 wks.
Simultaneous data at other Q2-values
38
eA Landscape and a New Electron Ion Collider
  • Well mapped in ep
  • Not so for lA (nA)
  • Electron Ion Collider (EIC)
  • L(EIC) gt 100 ? L(HERA)
  • eRHIC (eAu)
  • Ee 10 (20) GeV
  • EA 100 GeV
  • ?seN 63 (90) GeV
  • LeAu (peak)/n 2.91033 cm-2 s-1
  • ELIC (eAu)
  • Ee 9 GeV
  • EA 90 GeV
  • ?seN 57 GeV
  • LeAu (peak)/n 1.61035 cm-2 s-1

Terra incognita small-x, Q ? Qs high-x,
large Q2
39
F2 Sea (Anti)Quarks Generated by Glue at Low x
F2 will be one of the first measurements at
EIC nDS, EKS, FGS pQCD based models with
different amounts of shadowing
Syst. studies of F2(A,x,Q2) ? G(x,Q2) with
precision ? distinguish between models
40
FL at EIC Measuring the Glue Directly
Longitudinal Structure Function FL
  • Experimentally can be determined
  • directly IF VARIABLE ENERGIES!
  • Highly sensitive to effects of gluon

41
Explore gluon-dominated matter
Longitudinal Structure Function FL
  • What is the role of gluons and gluon
    self-interactions in nucleons and nuclei?
    NSAC-2007 Long-Range Plan Report.
  • The nucleus as a gluon amplifier

At high gluon density, gluon recombination should
compete with gluon splitting ? density saturation.
Color glass condensate
Oomph factor stands up under scrutiny. Nuclei
greatly extend x reach xEIC xHERA/18 for
10100 GeV, Au
42
Diffractive Surprises
Standard DIS event
Diffractive event
Detector activity in proton direction
No activity in proton direction
7 TeV equivalent electron bombarding the proton …
but proton remains intact in 15 of cases …
  • Predictions for eA for such hard diffractive
    evens range up to 30-40... given saturation
    models
  • Look inside the Pomeron
  • Diffractive structure functions
  • Diffractive vector meson production G(x,Q2)2

43
Explore the transition from partons to hadrons
  • What governs the transition of quarks and gluons
    in pions and nucleons? NSAC-2007
  • Fragmentation and parton energy loss
  • The nucleus as a femto-meter stick

Nuclear SIDIS Suppression of high-pT hadrons
analogous but weaker than at RHIC Clean
measurement in cold nuclear matter
Energy transfer in lab rest frame EIC 10 lt n lt
2000 GeV (HERMES 2-25 GeV) EIC can measure
heavy flavor energy loss
44
Using the nuclear arena
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
45
Quarks and Gluons in the Nuclear Medium
Opportunities at JLab_at_12 GeV and an EIC
Rolf Ent, ECT-Trento, June 06, 2008
Personal View
JLab 12 GeV Upgrade The 12 GeV Upgrade, with
its 1038 luminosity, is expected to allow for a
complete spin and flavor dependence of the
valence quark region, both in nucleons and in
nuclei. Electron Ion Collider
(eRHIC/ELIC) Provide a complete spin and flavor
dependence of the nucleon and nuclear sea, study
the explicit role that gluons play in the nucleon
spin and in nuclei, open the new research
territory of gluon GPDs, and study the onset of
the physics of saturation.
46
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47
FL at EIC Measuring the Glue Directly
Longitudinal Structure Function FL
  • Experimentally can be determined
  • directly IF VARIABLE ENERGIES!
  • Highly sensitive to effects of gluon

EIC alone
12-GeV data
48
Gluons in the Nucleus
eRHIC
Note not all models carefully checked against
existing data some models include
saturation physics
49
GPDs and Transverse Gluon Imaging
A Major new direction in Nuclear Science aimed at
the 3-D mapping of the quark structure of the
nucleon. Simplest process Deep-Virtual Compton
Scattering
At small x (large W) s G(x,Q2)2
Simultaneous measurements over large range in x,
Q2, t at EIC!
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