Impulse Approximation limitations to the (e,e’p) reaction on 208Pb and 12C

Jefferson Lab, Newport News, VAand the Hall A Collaboration

E06-007Spokespersons: K. Aniol, A. Saha, J. Udias, G. Urciuoli Students: Juan Carlos Cornejo, Joaquin Lopez Herraiz

Research Associate: Alexandre Camsonne

(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 identified as due to LRC.

c) Search for Q2 dependence of spectroscopic factors.

(II) Identify dynamical relativistic e ects in nuclear structure.ff

Measure cross section asymmetry ATL

around the three momentum transfer. Relativistic mean

field theory predicts an ATL

dependence on pmiss

< 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 AffTL

behavior.

Physics Objective: How well do we understand nuclear structure?

Activities in 2008

1) Continuing analysis of the 2007 data.

2) 5 day run in January 2008 to get more data for pmiss

> 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.

Raster/Optics optimization

- A great expenditure of effort has been made in: Establishing the Raster Correction Improving the coincidence time (resolution <5ns) Improving the optics database.

- This part of the analysis is almost finished and we obtain

reasonably good resolution.

RASTER

ON

RASTER

OFFGood

Coincidence

Time

Preliminary Results (208Pb, Pmiss=0)

Ex (MeV) Shell

0 3s1/2

0.351 2d3/2

1.348 1h11/2

1.683 2d5/2

3.470 1g7/2

Low lying states in 207Tl

EEmissmiss vs p vs pmissmiss

( ( ppmissmiss = 0, nominal = 0, nominal))

We can distinguish between Lead and Carbonand at low Pmiss we can separate some Lead Peaks.

*

*

- 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.

Ex (MeV) Shell

0 3s1/2

0.351 2d3/2

1.348 1h11/2

1.683 2d5/2

3.470 1g7/2

Low lying states in 207Tl

Preliminary Results (208Pb, Pmiss=0)

208Pb12C

1b) Cross sections

• Cross sections vs acceptance for solid angle and momentum bite cuts

• Cross sections vs raster pattern cut

12C(e, e′ p)11B, pmiss

= +100 setting, restricted solid angles. The fit to the

spectrum is shown.

sigma = 3.35 nb/Mev/Sr2

data/theory = 0.65

12C(e, e′ p)11 B, pmiss = +100 setting, full solid angles. The fit to the spectrum is shown.

sigma = 2.92 nb/MeV/Sr2

data/theory = 0.58

1b) Cross sections

• Cross sections vs acceptance for solid angle and momentum bite cuts

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.

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

cos(phi)

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.

12C(e,e'p)11B, 3 MeV wide region around ground state, pmiss

= 0 setting

pmiss

= + 100 MeV/c setting pmiss

= + 200 MeV/c setting

cos(phi) cos(phi)

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 = П, the comparison

between data and theory is reasonable only for large pmiss

.

Q2 lead carbon

GeV2 data theory† data theory†

0<E<6 MeV 0<E<6 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.

pmiss

= 0 , preliminary cross sections and Q2 dependence.

pm

iss

+10

0 M

eV

/c

pm

iss

+20

0 M

eV

/c

pm

iss

+30

0 M

eV

/cp

mis

s

-3

00 M

eV

/c

pm

iss

-2

00 M

eV

/c

pm

iss

-1

00 M

eV

/c

Q2

0.81GeV2

Q2

1.97GeV2Q2

1.40GeV2

pm

iss

0 M

eV/c p

mis

s

0 MeV

/cE

06-

00

7 E

XP

ER

IME

NT

1

2 C(e

,e’p

)

d5/

d

ed

pd

Ef

[n

b/S

r2M

eV

] PR

EL

IMIN

AR

Y R

ES

UL

TS

Kin pmiss data/MF MF(LRC+SRC)/MF

6 300 1.0±0.2 2.3

7 -300 0.45±0.09 2.2

8 400 1.33±0.27 2.6

9 -400 1.27±0.25 2.6

Preliminary Long range correlation results

There does not seem to be the need to invoke long range correllations for the

large pmiss

cross sections.

208Pb(e,e'p)207Tl, integrated cross sections from 0 to 6 MeV excitation.

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.

List of runs and charge collected in January 2008 5 day run.

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

Future Plans

• detailed check on optics/raster optimization for pmiss

< 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