Impulse Approximation limitations to

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Impulse Approximation limitations to the (e,ep)
reaction on 208Pb and 12C
Jefferson Lab, Newport News, VA and the Hall A
Collaboration E06-007 Spokespersons K. Aniol,
A. Saha, J. Udias, G. Urciuoli Students Juan
Carlos Cornejo, Joaquin Lopez Herraiz Research
Associate Alexandre Camsonne
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Physics Objective How well do we understand
nuclear structure?
(I) Long Range Correlations search and
spectroscopic factors a) Measure spectroscopic
factors for states near the Fermi level.
Spectroscopic factors depend on short range
correlations (SRC) and long range correlations
(LRC). b) Measure cross sections for these low
lying states to 500 MeV/c in pmiss . Excess
strength here is theoretically identi?ed as due
to LRC. c) Search for Q2 dependence of
spectroscopic factors.
(II) Identify dynamical relativistic e?ects in
nuclear structure. Measure cross section
asymmetry ATL around the three momentum transfer.
Relativistic mean ?eld theory predicts an ATL
dependence on pmiss lt 300 MeV/c due to dynamical
enhancement of the lower component of the nucleon
wave function. Calculations which do not include
the enhancement of the lower component predict a
substantially di?erent ATL behavior.
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Activities in 2008
1) Continuing analysis of the 2007 data. 2) 5
day run in January 2008 to get more data for
pmiss gt 300MeV/c.
1a) Raster and Optics Studies Extensive
optics/raster studies on a run by run basis.
Raster on resolution matches geant simulation, 1
MeV FWHM Expect a lengthy analysis to achieve
same resolution for low pmiss runs.
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• Raster/Optics optimization
• - A great expenditure of effort has been made
  in
• Establishing the Raster Correction
• Improving the coincidence time (resolution
  lt5ns)?
• Improving the optics database.
• - This part of the analysis is almost finished
  and we obtain reasonably good resolution.

RASTER ON
RASTER OFF
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Preliminary Results (208Pb, Pmiss0)?
Low lying states in 207Tl


Emiss vs pmiss ( pmiss 0, nominal)?
We can distinguish between Lead and Carbonand at
low Pmiss we can separate some Lead Peaks.
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Preliminary Results (208Pb, Pmiss0)?

• Due to our finite resolution, only two peaks can
  be separated in 208Pb Emiss spectrum. Both of
  them are composed of two peaks.
• The strength of the 1g7/2 shell can be neglected
  at this low pmiss.

Low lying states in 207Tl
12C
208Pb
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1b) Cross sections
Cross sections vs acceptance for solid angle
and momentum bite cuts Cross sections vs raster
pattern cut
sigma 3.35 nb/Mev/Sr2
data/theory 0.65
12C(e, e' p)11B, pmiss 100 setting, restricted
solid angles. The ?t to the spectrum is shown.
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1b) Cross sections
Cross sections vs acceptance for solid angle
and momentum bite cuts
sigma 2.92 nb/MeV/Sr2
data/theory 0.58
We expect the ratio of data/theory to depend on
the solid angle cut because of instrumental and
physical effects.
(small solid angle)/(full solid angle) 1.12 This
factor should be the acceptance efficiency cut.
12C(e, e' p)11 B, pmiss 100 setting, full
solid angles. The ?t to the spectrum is shown.
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1b) Preliminary cross sections
Cross sections vs raster pattern cut Large
raster pattern sometimes caused the beam to hit
the frame
Hall A raster pattern is very uniform. Checked
uniformity by examining count rate vs raster
pattern cut Present estimate of systematic
error is 20 cross sections in nb/MeV/Sr2
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cos(phi)
12C(e,e'p)11B, 3 MeV wide region around ground
state, pmiss 0 setting
phi is the angle between the electron scattering
plane and the qxp plane. The response functions
RTT and RTL must be included in the simulation of
the theory in the experimental conditions.
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cos(phi)
cos(phi)
pmiss 100 MeV/c setting
pmiss 200 MeV/c setting
12C(e,e'p)11B, 3 MeV wide region around ground
state,
The low pmiss settings are particularly sensitive
to the phi variation. With the present theory
simulation of the data assuming phi 0 or phi
?, the comparison between data and theory is
reasonable only for large pmiss.
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pmiss 0 , preliminary cross sections and Q2
dependence.
Q2 lead
carbon GeV2 data theory
data theory 0ltElt6 MeV
0ltElt6 MeV gnd state gnd state 0.81
4.07 3.6 2.8
2.07 1.40 0.745 0.90
0.54 0.24 1.97
0.246 0.18
0.20 0.06
These are pmiss 0 setting cross sections and
must include the cos(phi) dependence in the
theory simulation to allow for a reliable
comparison of data and theory.
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Q21.97GeV2
Q20.81GeV2
Q2 1.40GeV2
pmiss 0 MeV/c
pmiss 0 MeV/c
pmiss -100 MeV/c
pmiss 100 MeV/c
pmiss -200 MeV/c
pmiss 200 MeV/c
E06-007 EXPERIMENT 12C(e,ep) d5?/d?ed?pdEf
nb/Sr2MeV
PRELIMINARY RESULTS
pmiss -300 MeV/c
pmiss 300 MeV/c
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Preliminary Long range correlation results
208Pb(e,e'p)207Tl, integrated cross sections from
0 to 6 MeV excitation.
Kin pmiss data/MF MF(LRCSRC)/MF 6
300 1.00.2 2.3 7 -300 0.450.09 2.2 8 4
00 1.330.27 2.6 9 -400 1.270.25 2.6

There does not seem to be the need to invoke long
range correllations for the large pmiss cross
sections.
Left Right Asymmetry, ATL
ATL measured to 400 MeV/c given current
systematic uncertainty there is no striking
difference between the relativistic and non
relativistic treatment nevertheless the
relativistic theory gives a more negative ATL
which is more consistent with the data.
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List of runs and charge collected in January 2008
5 day run.
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Beam entrance
Beam exit
New target for 2008 with PREX collaboration,
January 2008 most of data collected at 60 uA
8 hour data run at 80 uA 3 hour run by PREX at
100 uA on 0.5mm natural lead target
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Future Plans
detailed check on optics/raster optimization
for pmiss lt 300 MeV/c with improved resolution
attempt to extract cross sections for 207Tl
states incorporate full theory into simulation
including the cos(phi) terms continue analysis
of the 2008 data, at present we have 4ns
coincidence time resolution