Impulse Approximation limitations to the (e,e'p) reaction on 208Pb: search for long range correlations at high missing

momenta  Juan Carlos Cornejo Joaquin Lopez Herraiz

(Cal. State Univ., Los Angeles) (U. Comp. de Madrid)

  Alexandre Camsonne  

(Jefferson Lab)

for the Hall A collaboration

•Shell model (mean field) calculations: the shape of the cross-section is well described, but the measured spectroscopic factors are below the mean field prediction. How large/small must be the spectrocopic factors?

About 30% depletion is observed for states near the Fermi level. This cannot be explained only with short-range correlations

Shape at moderate pm and parallel kinematics is well understood

Long range correlations are predicted to be visible at large pm

Physics motivation

E06-007 experiment 208Pb(ee’)p

• Use of 2 Hall A High Resolution Spectrometer to detect the scattered electron and proton in coincidence

• Scattered electron beam energy = 2216 MeV• Need stable good resolution beam: keep beam vertical

distribution < 100 um and beam energy spread less than 3.10-5

• Diamond/lead/diamond sandwich cryogenic target for high beam currents:

0.2mm thick lead + 0.3mm diamond

E06-007 experiment 208Pb(ee’)pKinematic

sq

[GeV/c]Eo

[GeV]ω

[GeV]Ee

[GeV]θe

[degrees]Pp

[GeV]θp

[degrees]pm

[GeV/c]

Kin01 1.000 2.649 0.433 2.216 21.44 0.989 54.101 0.000

Kin02 1.000 2.649 0.433 2.216 21.44 0.989 59.830 0.100

Kin03 1.000 2.649 0.433 2.216 21.44 0.989 48.371 0.100

Kin04 1.000 2.649 0.433 2.216 21.44 0.989 65.625 0.200

Kin05 1.000 2.649 0.433 2.216 21.44 0.989 42.576 0.200

Kin06 1.000 2.649 0.433 2.216 21.44 0.989 71.440 0.300

Kin07 1.000 2.649 0.433 2.216 21.44 0.989 36.762 0.300

Kin08 1.000 2.649 0.433 2.216 21.44 0.989 77.299 0.400

Kin09 1.000 2.649 0.433 2.216 21.44 0.989 30.902 0.400

Kin10 1.000 2.649 0.433 2.216 21.44 0.988 83.222 0.500

Kin11 1.000 2.649 0.433 2.216 21.44 0.988 24.980 0.500

Kin12 1.400 2.649 0.745 1.904 30.60 1.388 43.816 0.000

Kin13 1.750 2.649 1.045 1.604 39.81 1.738 35.936 0.000

E06-007 experiment 208Pb(ee’)p

• Extract the 208Pb(ee’)p crossection as a fonction of pmiss

208Pb(e,e’p)207Tl(all 5 shells)

With correlations

Without correlations

High pmiss predictions are robust at

xB = 1

• Carbon results for calibration and crosschecks

12C(ee’)p data

12C(e,e’p) (p-shell) REDUCED CROSS-SECTION

Q2 DEPENDENCE of the SPECTROSCOPIC FACTOR

Recross-section for the p12 shell in duced

12C(e,e’p) are independent of Q2

SIMULATION

DATA

Pmiss

vs Emiss

for the kin01 ( pmiss

= 0, nominal) setting.

208Pb(e,e’p) data

• Cross section as function of pmiss

•Extraction of individual excitation states for some kinematics

Lead data EMISS RESOLUTION

Lead data EMISS RESOLUTION (Pmiss=[-100,100] MeV/c)

EMISS RESOLUTION (Pmiss=[280,380] MeV/c)

208Pb(e,e’p) (Valence shells) CROSS-SECTION

• Preliminary results on C are in good agreement with data and calculations this gives a good cross check Pb (ee’)p

• Finalizing the data analysis and corrections to have final systematics

• Within our current error bars standard long range correlation seems to be ruled out

Conclusions