Top 10 Scientific and Technological

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Top 10 Scientific and Technological Highlights at
Jefferson Lab
Strategy Picked 8 scientific and 2 (3?)
technological highlights Version 2 Changed to
7 scientific, 2 12-GeV-related. Ordering/numbe
ring is my own, should we remove? For each,
gave 2-4 descriptions of findings, in easy
terms Added impact statement to
each Tony/Larry suggested to (later?) include
figure for each Should we use these, with
figures and some additional text from the
research highlights, for the Open House?
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Top 10 Scientific Highlights at JLab
1. Mapped the charge and the magnetization
distribution of nucleons to unprecedented
precision
The proton charge distribution was found to
differ surprisingly from its magnetization
distribution, emphasizing the strong role of
relativity in nucleon structure. The neutron
charge distribution, elusive for decades,
confirmed the expectation of a positively-charged
core and negatively-charged cloud, expected from
meson cloud models. The neutron magnetization
distribution was precisely mapped and found to be
less diffuse, and more like the proton, than
believed. The high-precision of the measurements
provoked new calculations on the role of
two-photon exchange contributions. Impact
Precise maps for all four nucleon form factors
exist now in the region relevant for nuclear
structure calculations.
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Top 10 Scientific Highlights at JLab
2. Accumulated high-quality nucleon structure
function data spanning the nucleon resonance and
low-W2 deep inelastic region that show a
surprisingly smooth transition at unexpected
large distance scales.
A striking similarity between structure functions
measured at high and low energies has been
observed, at much larger distance scales and in
far more limited energy regions, than
expected. Moments of unpolarized structure
functions show a remarkable lack of quark-quark
interactions to scales of 1/10th the nucleon
size. The size of constituent quarks has been
determined to be of order 0.3 fm, about 1/3rd the
nucleon size. Impact Measurements in the
valence-quark region at JLab are now world-wide
included in QCD-based parton distribution fits.
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Top 10 Scientific Highlights at JLab
3. Observed the transition between nucleon-meson
and quark-gluon descriptions of nuclei
Precision measurements of the internal structure
of deuterium proved that a nucleon-meson
description prevails down to distance scales half
the size of the nucleons themselves. Measurements
to vehemently break the deuterium nucleus apart
found that a quark-gluon description becomes more
applicable at distance scales corresponding to
1/10th the size of the nucleons. Impact
Calculations of nuclear structure at distance
scales larger than half the size of nucleons have
solid foundation in the nucleon-meson framework.
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Top 10 Scientific Highlights at JLab
4. Found the strange quarks to contribute to less
than 5 of the proton magnetic moment and charge
radius squared
A series of electron-proton parity-violating
experiments have uncovered that strange quarks
only make a small contribution to the protons
charge radius and magnetic moment. Motivated by
this, a recent JLab theory calculation predicts
the contribution of strange quarks to the
protons magnetic moment to be less than 0.5, a
shockingly small value. Impact The knowledge on
the weak nuclear force at low energies has been
enhanced by a factor of five, severely
constraining new physics beyond the Standard
Model to the TeV energy scale.
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Top 10 Scientific Highlights at JLab
5. Mapped the integral distribution of spin
inside the nucleons from small to large distance
scales
Measurements of the spin structure functions
indicate a smooth, yet dramatic transition how
the nucleon spin gets redistributed from large to
small distance scales, from a static magnetic
moment, through quark excitations, to single
quarks. The axial charge of the nucleon was
precisely calculated ab initio using lattice QCD.
The valence up and down quarks in the proton
were found to be spinning in opposite directions
at large quark momenta. Impact Precise data
have been accumulated to benchmark any
calculation describing the transition from weak
to strong QCD
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Top 10 Scientific Highlights at JLab
6. Determined the probabilities to find clusters
of two and three nucleons due to short-range
correlations in the Carbon nucleus to be 20 and
1, respectively.
Nucleons repel each other at short inner
distances. This provides the foundation for the
success of the independent-particle shell model,
but can also temporarily relocate nucleons to
large binding energies and momenta. The latter
strength has been quantitatively located. The
proton momenta have been precisely mapped well
beyond the naïve expectation in light nuclei, up
to 1 GeV. Pairs of two nucleons receiving large
momenta from the short-range repulsion have been
directly measured. Hypernuclei have been
created, where a L particle is embedded in the
nuclear medium. These impurities do not feel the
strong repulsion and can thus probe deep inside
the nucleus. Impact The validity and
limitations of the Mean-Field Approximation of
Nuclei have been quantified.
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Top 10 Scientific Highlights at JLab
7. Determined the transition form factors of the
lowest-lying nucleon excitations
The transition of the proton into its
lowest-lying excited stated, the D, has been
precisely mapped and was found to remain slightly
oblate down to the smallest distance scales,
consistent with a meson cloud model. The elusive
Roper resonance transition form factor has been,
for the first time, measured and shows a
meson-cloud behavior at large and a small-sized
quark-core behavior at shorter distance
scales. Candidates for new excited states of the
proton have been found. Impact The radial
distributions of the nucleons excited states
become known, challenging any baryon-meson model
calculation.
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Top 10 Scientific Highlights at JLab
8. Developed the experimental and theoretical
framework to probe the internal quark-gluon
structure of the nucleons
A formalism unifying the concepts of the quarks
transverse spatial distributions with their
longitudinal momenta has been developed, allowing
tomographic imaging of protons and neutrons. The
feasibility of this framework has been proven
with a series of DVCS experiments at DESY and
JLab. The further experimental pursuit at 12 GeV
will allow access to the spin-orbit force and
quark-quark correlations in nucleons. Impact
Future research now allows for 3-dimensional
imaging of nucleon structure, and to determine
the impact of the orbital motions of quarks and
gluons to the nucleon spin.
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Top 10 Scientific Highlights at JLab
9. Measured, for the first time, the charge
distribution in the pion away from the region
where it solely reflects the charge radius
Due to its simple valence-quark structure,
measurement of the pion charge distribution
provides a holy grail test bed of QCD. The pion
charge distribution was found to remain well
described by a Yukawa-type distribution up to the
smallest distance scales measured. Future
measurements at 12 GeV will approach the smallest
and perturbatively calculable distance
scales. Impact Determination of the charge
distribution in the simplest quark system from
the largest to smallest distance scales will
provide benchmark data for QCD calculations.
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Top 10 Scientific and Technological Highlights at
Jefferson Lab
I. Proved a novel approach of high-energy SRF
linear accelerator technology
The technique was later applied to provide the
highest-power (14.2 kilowatts) FEL laser in the
IR region. Energy-recovery linear accelerator
technology was proven at low beam energy (45 MeV)
and high beam currents, and at high beam energy
(1 GeV).
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Top 10 Scientific and Technological Highlights at
Jefferson Lab
II. Revolutionized the development of polarized
beams and targets
FOM for polarized beams. Helicity-dependent
precision for PV experiments. FOM for polarized
3He experiments.
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Top 10 Scientific and Technological Highlights at
Jefferson Lab
III. Invented Floating Pressure technique as a
more efficient and cost-saving cryogenic cooling
technique
Direct savings at JLab amount to 1K per
day. Portions of new technique applied at other
DOE facilities such as RHIC at BNL and SNS at
ORNL. Technique now being integrated in non-US
facilities.