Presentation on theme: "Impulse Approximation limitations to the (e,ep) reaction on 208 Pb and 12 C Jefferson Lab, Newport News, VA and the Hall A Collaboration E06-007 Spokespersons:K."— Presentation transcript:
Impulse Approximation limitations to the (e,ep) reaction on 208 Pb and 12 C Jefferson Lab, Newport News, VA and the Hall A Collaboration E Spokespersons: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 identied as due to LRC. c) Search for Q 2 dependence of spectroscopic factors. (II) Identify dynamical relativistic e ects in nuclear structure. Measure cross section asymmetry A TL around the three momentum transfer. Relativistic mean eld theory predicts an A TL dependence on p miss < 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 A TL behavior. Physics Objective: How well do we understand nuclear structure?
Activities in ) Continuing analysis of the 2007 data. 2) 5 day run in January 2008 to get more data for p miss > 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 p miss 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 OFF Good Coincidence Time
Preliminary Results ( 208 Pb, P miss =0) Ex (MeV)Shell 03s 1/ d 3/ h 11/ d 5/ g 7/2 Low lying states in 207 Tl E miss vs p miss ( p miss = 0, nominal ) ( p miss = 0, nominal ) We can distinguish between Lead and Carbon and at low Pmiss we can separate some Lead Peaks. * *
- Due to our finite resolution, only two peaks can be separated in 208 Pb E miss spectrum. Both of them are composed of two peaks. -The strength of the 1g 7/2 shell can be neglected at this low p miss. Ex (MeV)Shell 03s 1/ d 3/ h 11/ d 5/ g 7/2 Low lying states in 207 Tl Preliminary Results ( 208 Pb, P miss =0) 208 Pb 12 C
1b) Cross sections Cross sections vs acceptance for solid angle and momentum bite cuts Cross sections vs raster pattern cut 12 C(e, e p) 11 B, p miss = +100 setting, restricted solid angles. The t to the spectrum is shown. sigma = 3.35 nb/Mev/Sr 2 data/theory = 0.65
12 C(e, e p) 11 B, pmiss = +100 setting, full solid angles. The t to the spectrum is shown. sigma = 2.92 nb/MeV/Sr 2 data/theory = b) 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/Sr 2
cos(phi) phi is the angle between the electron scattering plane and the qxp plane. The response functions R TT and R TL must be included in the simulation of the theory in the experimental conditions. 12 C(e,e'p) 11 B, 3 MeV wide region around ground state, p miss = 0 setting
p miss = MeV/c settingp miss = MeV/c setting cos(phi) 12 C(e,e'p) 11 B, 3 MeV wide region around ground state, The low p miss 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 p miss.
Q 2 lead carbon GeV 2 data theory data theory 0
pmiss +100 MeV/c pmiss +200 MeV/c pmiss +300 MeV/c pmiss -300 MeV/c pmiss -200 MeV/c pmiss -100 MeV/c Q GeV 2 Q GeV 2 Q GeV 2 pmiss 0 MeV/c E EXPERIMENT 12 C(e,ep) d 5 /d e d p dE f [nb/Sr 2 MeV] PRELIMINARY RESULTS
Kin pmiss data/MFMF(LRC+SRC)/MF ± ± ± ± Preliminary Long range correlation results There does not seem to be the need to invoke long range correllations for the large p miss cross sections. 208 Pb(e,e'p) 207 Tl, integrated cross sections from 0 to 6 MeV excitation. Left – Right Asymmetry, A TL A TL 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 A TL which is more consistent with the data.
List of runs and charge collected in January day run.
Beam entranceBeam 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 p miss < 300 MeV/c with improved resolution attempt to extract cross sections for 207 Tl 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