Quarks and Gluons in the Nuclear Medium – Opportunities at JLab@12 GeV and an EIC
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Transcript of Quarks and Gluons in the Nuclear Medium – Opportunities at JLab@12 GeV and an EIC
Quarks and Gluons in the Nuclear Medium – Opportunities at JLab@12
GeV and an EICRolf 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
The Quark Structure of Nuclei
The QCD Lagrangian and
Nuclear “Medium
Modifications”
Leinweber, Signal et al.
The QCD vacuum
Long-distance gluonic fluctuations
Lattice calculation demonstrates reduction of chiral condensate of QCD vacuum in presence of hadronic matter
Does the quark structure of a nucleon get modified by the suppressed QCD vacuum fluctuations in a nucleus?
Quarks in a Nucleus
Effect well measured,over large range of x and A, but remains poorly understood
1) ln(A) or dependent?
Observation that structure functions are altered in nuclei stunned much of the HEP community ~25 years
ago
2) valence quark effect only?
A=3 EMC Effect at 12 GeV
E772
Is the EMC effect a valence quark phenomenon or are sea quarks involved?
Anti-Quarks in a Nucleus
Solution: Detect a final state hadron in addition to scattered electron
Deep inelastic electron scattering probes only the sum of quarks and anti-quarks requires assumptions on the role of sea quarks
0.5
1.0
gluonssea
valence
0.1 1.0
S. Kumano, “Nuclear Modification of Structure Functions in Lepton Scattering,” hep-ph/0307105
x
RCa
Can ‘tag’ the flavor of the struck quark by measuring the hadrons produced: ‘flavor tagging’
Tremendous opportunity for experimental improvements!
p
A
gg
1
1
2
2
A
D
F
F
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
Valence only
Valence + Sea
Miller, SmithValence 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 x>0.3 due to sea quarks
Sea is not much modified
Chiral Quark-Soliton model(quarks in nucleons (soliton) exchange infinite
pairs of pions, vector mesons with nuclear medium)
• 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
p
A
gLig
1
71 (polarized EMC effect)
Curve follows calculation by W. Bentz, I. Cloet, A. W. Thomas.
g1(A) – “Polarized EMC Effect”
Extend measurements on nucleito x > 1: Superfast quarks
Correlated nucleon pair
Six-quark bag (4.5% of wave function)
Fe(e,e’)5 PAC days
Mean field
Does the quark structure of a nucleon get modified by the suppressed QCD vacuum fluctuations in a nucleus?
1) Measure the EMC effect on the mirror nuclei 3H and 3He
2) Is the EMC effect a valence quark only effect?3) Is the spin-dependent EMC effect larger?4) 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?
Reminder: EMC effect is effect that quark momenta in nuclei are altered
Now: use the nuclear arena to look for QCD
Use the Nuclear Arena to Study QCD
Total Hadron-Nucleus Cross Sections
Hadron– Nucleustotal cross section
Fit to
K
pp_
Hadron momentum60, 200, 250 GeV/c
< 1 interpreted as due to the strongly interacting nature of the probe A. S. Carroll et al. Phys. Lett 80B 319
(1979)
= 0.72 – 0.78, for p, , k
Traditional nuclear physics expectation: transparency nearly energy independent.
T
1.0
Energy (GeV)
Ingredients
• h-N cross-section
• Glauber multiple scattering approximation(or better transport calculation!)
• Correlations & Final-State Interaction effects
hN
Physics of Nuclei: Color Transparency
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
Quantum ChromoDynamics:
A(e,e’h), h = hadron
Search for Color Transparency in Quasi-free
A(e,e’p) Scattering
Constant value line fits give good description:2/df = 1
Conventional Nuclear Physics Calculation by Pandharipande et al. (dashed) also gives good description
Fit to = Aa
= constant = 0.75
Close to proton-nucleus total cross section data No sign of CT yet
Physics of Nuclei: Color Transparency
AGSA(p,2p)
Glauber calculation
Pp (GeV/c)5.1 7.3 9.62.9
Results inconsistent with CT only. But can be explained by including additional mechanisms such as nuclear filtering or charm resonance states.
The A(e,e’p) 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.
6 7 8 9 10
Physics of Nuclei: Color Transparency
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?
A(e,e’+)
Physics of Nuclei: Color Transparency
A(e,e’+) at 12 GeV(at fixed coherence length)
12 GeV
Using the nuclear arenaHow long can an energetic quark remain
deconfined?How long does it take a confined quark to form a hadron?
Formation time tfh
Production time tp
Quark is deconfined
Hadron is formed
Hadron attenuation
CLAS
Time required to produce colorless “pre-hadron”, signaled by medium-stimulated energy loss via gluon emission
Time required to produce fully-developed hadron, signaled by CT and/or usual hadronic interactions
Using the nuclear arena
Le
e’
*
+
pT
pT2 = pT
2(A) – pT2(2H)
“pT Broadening”
dE/dx ~ <pT2>L
E ~ L (QED) ~ L2 (QCD)?
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?
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?
Deep Inelastic ScatteringRelativistic Heavy-Ion Collisions
Initial quark energy is knownProperties of medium are known
e e’
Using the nuclear arena
Relevance to RHIC and LHC
ppTT22 vs. vs. for Carbon, Iron, and Lead for Carbon, Iron, and Lead
C
Pb
Fe
pp
TT22 (
GeV
(G
eV
22))
(GeV)(GeV)
~ 100 MeV/fm (perturbative formula)
~d
E/d
x
Preliminary CLASHall B
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 E ~L2 ‘LPM’ behavior• ~100 MeV/fm for Pb at few GeV, perturbative formula
• Deconfined quark lifetime can be estimated, ~ 5 fm @ 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?
Using the nuclear arenapT
2 reaches a “plateau” for sufficiently large quark energy, for each nucleus (L is fixed). pT
2
Projected Data
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
DOE CRITICAL DECISION SCHEDULE
CD-0 Mission Need MAR-2004 (A)
CD-1 Preliminary Baseline Range FEB-2006 (A)
CD-2 Performance Baseline NOV-2007 (A)
CD-3 Start of Construction SEP-2008
CD-4A Accelerator Project Completion and Start of Operations
DEC-2014
CD-4B Experimental Equipment Project Completion and Start of Operations
JUN-2015
(A) = Actual Approval Date
Note → 6 to 18 months schedule float included
Note → 6 to 18 months schedule float included
Now split in two to ease transition into operations phase
2004-2005 Conceptual Design (CDR) - finished
2004-2008 Research and Development (R&D) - 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
12 GeV Upgrade: Phases and Schedule
(based on funding guidance provided by DOE-NP in June-2007)
The Gluon Structure of Nuclei
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!
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The Low Energy View of Nuclear Matter• nucleus = protons + neutrons• nucleon quark model • quark model QCD
The High Energy View of Nuclear MatterThe visible Universe is generated by quarks, but dominated by the dark glue!
Removefactor 20
Exposing the high-energy (dark) side of the nuclei
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 world’s first high energy polarized proton
collider• ~2003 RHIC sees tantalizing hints of saturation• ~2006 electron cooling for high-energy beams
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.”
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?
How do we understand the visible matter in our universe in terms of the fundamental quarks and gluons of QCD?
Explore the structure of the nucleon • Parton distribution
functions• Longitudinal and transverse spin distribution functions• Generalized parton distributions•Transverse momentum distributions
RHIC-Spin region
Precisely image the sea quarksSpin-Flavor Decomposition of the Light Quark Sea
| p = + + + …>u
u
d
u
u
u
u
d
u
u
dd
dMany
models predict
u > 0, d < 0No competition foreseen!
GPDs and Transverse Gluon ImagingDeep exclusive measurements in ep/eA with an EIC:
diffractive: transverse gluon imaging J/, o, (DVCS) non-diffractive: quark spin/flavor structure , K, +, …
[ or J/, , 0
, K, +, … ]
Describe correlation of longitudinal momentum and transverse position of
quarks/gluons
Transverse quark/gluon imaging of nucleon
(“tomography”)
Are gluons uniformly distributed in nuclear matter or are there small clumps of glue?
GPDs and Transverse Gluon Imaging
gives transverse size of quark (parton) with longitud. momentum fraction x
EIC:1) x < 0.1: gluons!
x < 0.1 x ~ 0.3 x ~ 0.8
Fourier transform in momentum transfer
x ~ 0.001
2) ~ 0 the “take out” and “put back” gluons act coherently.
2) ~ 0 x - x +
d
GPDs and Transverse Gluon ImagingGoal: Transverse gluon imaging of nucleon over wide range of x: 0.001 < x < 0.1Requires: - Q2 ~ 10-20 GeV2 to facilitate interpretation
- Wide Q2, W2 (x) range - Sufficient luminosity to do differential measurements in Q2, W2, t
Q2 = 10 GeV2 projected data
Simultaneous data at other Q2-values
EIC enables gluon imaging!
Scaled from 2 to 16 wks.
EIC(16 weeks)
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eA Landscape and a New Electron Ion Collider
Well mapped in e+pNot so for ℓ+A (A)
Electron Ion Collider (EIC):L(EIC) > 100 L(HERA)
eRHIC (e+Au):Ee = 10 (20) GeVEA = 100 GeVseN = 63 (90) GeVLeAu (peak)/n ~ 2.9·1033 cm-2 s-1
ELIC (e+Au):Ee = 9 GeVEA = 90 GeVseN = 57 GeVLeAu (peak)/n ~ 1.6·1035 cm-2 s-1
Terra incognita: small-x, Q Qs
high-x, large Q2
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
),(2
),(2
14 2
22
2
2
4
2
2
2
QxFy
QxFy
yxQdxdQ
dL
eXep
Longitudinal Structure Function FL
• Experimentally can be determined directly IF VARIABLE ENERGIES!• Highly sensitive to effects of gluon
FL at EIC: Measuring the Glue Directly
),(2
),(2
14 2
22
2
2
4
2
2
2
QxFy
QxFy
yxQdxdQ
dL
eXep
Explore gluon-dominated matter
At high gluon density, gluon recombination should compete with gluon splitting density saturation.
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”
Color glass condensate
Oomph factor stands up under scrutiny.Nuclei greatly extend x reach:xEIC = xHERA/18 for 10+100 GeV, Au
Longitudinal Structure Function FL
Diffractive Surprises‘Standard DIS event’
Detector activity in proton direction
7 TeV equivalent electron bombarding the proton … but proton remains intact in 15% of cases …
Diffractive event
No activity in proton direction
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
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 frameEIC: 10 < < 2000 GeV
(HERMES: 2-25 GeV)EIC: can measure heavy flavor energy loss
Using the nuclear arena
pT2 reaches a “plateau” for sufficiently large quark
energy, for each nucleus (L is fixed).
pT2
In the pQCD region, the effect is predicted to disappear (arbitrarily put at =1000)
Quarks and Gluons in the Nuclear Medium – Opportunities at JLab@12
GeV and an EICRolf Ent, ECT-Trento, June 06, 2008
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.
Personal View:
Longitudinal Structure Function FL
• Experimentally can be determined directly IF VARIABLE ENERGIES!• Highly sensitive to effects of gluon
+ 12-GeV data+ EIC alone
FL at EIC: Measuring the Glue Directly
),(2
),(2
14 2
22
2
2
4
2
2
2
QxFy
QxFy
yxQdxdQ
dL
eXep
eRHIC
Gluons in the Nucleus
Note: not all models carefully checked against existing data + some models include saturation physics
GPDs and Transverse Gluon Imaging
k
k'
*q q'
p p'
e
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
Simultaneous measurements over large range in x, Q2, t at EIC!
At small x (large W): ~ G(x,Q2)2