The 12 GeV Upgrade of Jefferson Lab

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The 12 GeV Upgrade of Jefferson Lab

• Volker Burkert
• Jefferson Lab

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Highlights of the 12 GeV Science Program

• New and revolutionary access to the structure of
  the proton and neutron (GPDs, TMDs)
• Unlocking the secrets of QCD confinement and
  space-time dynamics
• Exploring the quark structure of nuclei
• Precision tests of the Standard Model

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JLab Upgrade to 12 GeV
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New Capabilities in Halls A, B, C, and a New
Hall D
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New and revolutionary access to the structure of
the proton and neutron
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CLAS12

• Lum gt 1035cm-2s-1
• GPDs TMDs
• Nucleon Spin Structure
• N Form Factors
• Baryon Spectroscopy
• Hadron Formation

Forward Detector
Central Detector
2m
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Generalized Parton Distributions and 3D Quark
Imaging
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Basic Process Handbag Mechanism
Deeply Virtual Compton Scattering (DVCS)
x
x longitudinal quark momentum fraction
2x longitudinal momentum transfer
GPDs depend on 3 variables, e.g. H(x, x, t). They
probe the quark structure at the amplitude level.
xB
x

2-xB
What is the physical content of GPDs?
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Physical content of GPDs
Nucleon matrix element of the Energy-Momentum
Tensor contains three form factors
M2(t) Mass distribution inside the nucleon
J (t) Angular momentum distribution d1(t)
Forces and pressure distribution
GPDs are related to these form factors through
moments
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Kinematics of deeply virtual exclusive processes
H1, ZEUS
27 GeV
200 GeV
JLab Upgrade
JLab _at_ 12 GeV
COMPASS
W 2 GeV
Study of high xB domain requires high luminosity
HERMES
0.7
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The path towards the extraction of GPDs
e p epg
DsLUsinfF1H..df
Kinematically suppressed
Selected Kinematics
Extract H(?,t)
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Projected precision in extraction of GPD H at x
?
Spatial Image
Projected results
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Exclusive r0 production on transverse target
Should be known from DVCS
A 2Hu Hd
r0
B 2Eu Ed
Separate with ?
Eu, Ed measure the contributions of the quark
orbital angular momentum to the nucleon spin.
r0
B
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Tomographic Images of the Proton
M. Burkardt
The guts of the proton?
CAT scan slice of human abdomen
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Valence structure function flavor dependence
Hall B 11 GeV with CLAS12
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Valence structure function spin dependence
Proton
Deuteron He-3
W gt 2 Q2 gt 1
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Improvements in ?u, ?d, ?G, ?s
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Important complement to RHIC Spin data
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Proton electric form factor
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Neutron Magnetic Form Factor
At 12 GeV extend knowledge of magnetic structure
of neutron to much shorter distances. Needed for
constraints of GPDs at large t related to
moments of GPDs F1(t) ?H(t,x,?)dx, F2(t)
?H(t,x,?)dx
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Projections for N Transition Amplitudes _at_ 12 GeV
Probe the transition from effective degrees of
freedom, e.g. constituent quarks, to elementary
quarks, with characteristic Q2 dependence.
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Hybrid mesons

• Flux Tube Model
• Provides a framework to understand gluonic
  excitations.
• Conventional mesons have the color flux tube in
  the ground state. When the flux tube is excited
  hybrid mesons emerge. For static quarks the
  excitation level above the ground state is 1
  GeV.
• The excitation of the flux tube, when combined
  with the quarks, can lead to spin-parity quantum
  numbers that cannot be obtained in the quark
  model
• (JPC - exotics).
• The decay of hybrid mesons leads to complex final
  states.

JPC 0-, 1-, 2-
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LQCD supports the idea of flux tubes.
Flux distribution between static quarks.
Flux tubes lead to a linear confining potential.

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Exotic Hybrid Mesons Masses
With 3 light quarks the conventional and hybrid
mesons form flavor nonets for each JPC.
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Photons may be more suited to excite exotics

• In the flux tube model, using photon beams, the
  production rate of hybrid mesons is not
  suppressed compared to conventional mesons.
• N. Isgur, PRD (1999) A. Afanasev A.
  Szczepaniak, PRD (2000) F. Close J. Dudek
  (2004)

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GlueX Exotic meson program at 12GeV
To meet these goals GlueX will
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Quark Propagation and Hadron FormationQCD
Confinement in Forming Systems
CLAS12

• How long can a light quark remain deconfined?
• The production time tp measures this
• Deconfined quarks emit gluons
• Measure tp via medium-stimulated gluon emission
• How long does it take to form the color field of
  a hadron?
• The formation time tfh measures this
• Hadrons interact strongly with nuclear medium
• Measure tfh via hadron attenuation in nuclei

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Expected data Hadronic multiplicity ratio
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Color transparency in ? electroproduction

• Color Transparency is a spectacular prediction of
  QCD under the right conditions, nuclear matter
  will allow the transmission of hadrons with
  reduced attenuation
• Totally unexpected in an hadronic picture of
  strongly interacting matter, but straightforward
  in quark gluon basis
• Why ?? Should be evident first in mesons

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• The signature of CT is the rising of the nuclear
  transparency TA with increasing hardness of the
  reaction (Q)

• Measurement at fixed coherence length needed for
  unambiguous interpretation

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Color transparency in ? electroproduction
56Fe

• Predicted results high-precision, will permit
  systematic studies

CLAS12 projected
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Precision Tests of the Standard Model
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Electron-Quark Phenomenology
V
A
A
V
C1u and C1d will be determined to high precision
by APV and Qweak
C2u and C2d are small and poorly known can be
accessed in PV DIS
 
 
New physics such as compositeness, new gauge
bosons
Deviations in C2u and C2d might be fractionally
large
Proposed JLab upgrade experiment will improve
knowledge of 2C2u-C2d by more than a factor of 20
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Parity Violating Electron DIS
e-
e-
?
Z
X
N
For an isoscalar target like 2H, one can write in
good approximation
provided Q2 and W2 are high enough and x 0.3
Must measure APV to fractional accuracy better
than 1

• 11 GeV at high luminosity makes very high
  precision feasible
• JLab is uniquely capable of providing beam of
  extraordinary stability
• Control of systematics being developed at 6 GeV

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2H Experiment at 11 GeV
APV 290 ppm
E 6.8 GeV 10
?lab 12.5o
800 hours
60 cm LD2 target
Ibeam 90 µA
xBj 0.45 Q2 3.5 GeV2 W2 5.23 GeV2
1 MHz DIS rate, p/e 1 HMSSHMS
?(APV)1.0 ppm
?(2C2u-C2d)0.01
PDG -0.08 0.24
Theory 0.0986
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Conclusions

• The JLab Upgrade has well defined physics goals
  of fundamental importance for the future of
  hadron physics, addressing in new and
  revolutionary ways the quark and gluon structure
  of mesons, nucleons, and nuclei by
• accessing generalized parton distributions
• exploring the valence quark structure of nucleons
  
• understanding quark confinement and hadronization
  processes
• extending nucleon elastic and transition form
  factors to short distances
• mapping the spectrum of gluonic excitations of
  mesons
• searching for physics beyond the standard model
• Design of accelerator and equipment upgrades are
  underway
• Construction scheduled to begin in 2009
• Accelerator shutdown scheduled for 2012

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2007 NSAC Long Range Plan (4 recommendations)
Recommendation 1

• We recommend the completion of the 12 GeV Upgrade
  at Jefferson Lab.
• - It will enable three-dimensional imaging of
  the nucleon, revealing hidden aspects of its
  internal dynamics.
• It will complete our understanding of the
  transition between the hadronic and quark/gluon
  descriptions of nuclei.
• It will test definitively the existence of exotic
  hadrons, long-predicted by QCD as arising from
  quark confinement.
• It will provide low-energy probes of physics
  beyond the Standard Model complementing
  anticipated measurements at the highest
  accessible energy scales.

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DOE Generic Project Timeline
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A first search for exotic meson with photons
Experiment planned to run in 2008.

• Clarify evidence for exotic meson states, e.g.
  at 1600 MeV with high statistics.
• Prepare for full study with GlueX.

Events from previous CLAS experiment.
a2
45 35 25 15 5
p2
a1
102 Events/ 20 MeV
Gluonic Meson? p1(1600)
0.8 1.2
1.6 2.0
Expect 1-2 million 3-pion events, 3 orders more
than any previously published meson
photoproduction results, allowing a partial wave
analysis.
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Physical content of GPDs
In the Chiral Quark Soliton Model
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CLAS12 - DVCS/BH Target Asymmetry
e p epg
E 11 GeV
Longitudinally polarized target

DssinfImF1Hx(F1F2)H...df

• L 2x1035 cm-2s-1
• T 1000 hrs
• DQ2 1GeV2
• Dx 0.05

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Separating GPDs in Flavor Spin
DVMP
DVCS
hard vertices

• DVCS depends on all 4 GPDs
• Photons cannot separate u/d quark
• contributions.

Isolate longitudinal photons by decay angular
distribution.
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CAT scan slice of human abdomen
Can we do similar imaging in the microscopic
world?
Tools are being developed to add this new
dimension to nuclear research.
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GPDs PDFs
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Tomographic Images of the Proton II
z
X. Ji and F. Yuan, 2003
Charge density distributions for u-quarks
3D image obtained by rotation around the z-axis