PR89-046

Conditionally approved

Should demonstrate that the experiment can extract information from states separated by 0.35 MeV

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

- Identifying correlations and relativistic effects in the nuclear

medium

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K. Aniol , B. Reitz, A. Saha, J. M. Udias

Spokespersons

Hall A Collaboration MeetingJune 23, 2005

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

1. What is being proposed

Measure 208Pb(e,e’p)207Tl cross sections in quasielastic kinematics

Study low lying states in 207Tl : g.s. 3s1/2

0.351 2d3/2

1.348 1h11/2

1.683 2d5/2

3.470 1g7/2

1. Quasielastic kinematics: xB = 1, q = 1 GeV/c , ω = 0.433 GeV/c 2. Determine momentum distributions: 0 < pmiss < 500 MeV/c3. Determine ATL by measuring cross sections on either side of q.

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

2. Physics Motivation

How well do we understand nuclear structure ?

The shell model Basis upon which most model calculations of nuclear structure rely. The underlying physical picture Dense system of fermions whose motions to first order can be treated as independent particles moving in a mean field. Electromagnetic interactions Best probes for investigating the validity of the independent particle picture because they are sensitive to a much larger fraction of the nuclear volume

V.R. Pandharipande, I. Sick and P.K.A. deWitt Huberts, Independentparticle motion and correlations in fermions systems, Reviews of Modern Physics 69 (981) 1997

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

2. Physics Motivation

Deviations from independent particle motion for orbits near the Fermi surface are attributed to various correlations which reveal their effects in two ways:

(i) Changes in the occupation probabilities of mean-field orbits.

(ii) Changes in the momentum distribution of particles, especially above the Fermi momentum

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

(i) Changes in the occupation probabilities of mean-field orbits

12C(e,e’p) data over wide range of Q2.There appears to be a Q2 dependence to the spectroscopic factors from this reaction[2]. This interpretation has been disputed and the Q2 dependence attributed to analysis methods of SRC[3].

208Pb(e,e'p) has been studied in the past at low momentum transfers and reliable spectroscopic factors in the range of 0.6 to 0.7 have been extracted from parallel kinematics [4,5,6]

A measurement at high Q2 may help address the question of a momentum transfer dependence of the spectroscopic factors.

data [4], theory [5].

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

(ii) Momentum distributions > 300 MeV/c

This was explained via long-range correlations in a nonrelativistic formalism [Bobeldijk,6], but also by relativistic effects in the mean field model [Udias,7].

I. Bobeldijk et al., PRL 73 (2684)1994

xB ≠ 1

E. Quint, thesis, 1988, NIKHEF

J. M. Udias et al. PRC 48(2731) 1994

J.M. Udias et al. PRC 51(3246) 1996

Excess strength at high pmiss

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

2. Physics Motivation

Both spectroscopic factors and the strength at high pmiss can be explained by two approaches:

(1) Quasiparticle orbits plus nonrelativistic DWIA.

(2) RDWIA using independent particle orbit solutions to the Dirac equation.

Are there other observables which can help distinguish between these two explanations ?

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

Cross Section Asymmetry ATL

The cross section asymmetry is defined about q

[6] I. Bobeldijk et al., PRL 73 (2684)1994

The data taken at NIKHEF [6] were backward of q where both theoretical procedures agree. But forward of q the theories can disagree by two orders of magnitude

Looking for unmistakable signatures of correlations at high pmiss from (e,e’p) cross sections alone is a hard task

ATL in 3He, 4He and 16O

If relativistic dynamical effects are the main cause responsible for the extra strength, a strong effect on ATL would be seen.

There is a notable difference in ATL between 3He and 4He due to the density difference and in 16O. 16O: ATL

p1/2

p3/2

M. Rvachev et al. PRL 94:12320,2005

E04-107,2004J. Gao et al. PRL84:3265, 2000

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

ATL in 208Pb

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

ATL in 208Pb

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

Target Issues and Peak Extraction

Two tested targets configurations capable of high current running

(i) Stacked lead foils in a 15 cm beer can LH2 targetTest run showed that the upstream foil can withstand at least 60 μA with only the horizontal sweep of the raster working at the time.

(ii) Cold Lead in diamond sandwichE03-011 has demonstrated that a 0.5 mm lead foil sandwiched between two 0.15 mm diamond foils at cryogenic temperatures can withstand currents up to 80 uA and calculations indicate that they can operate at 100 μ A.

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

Resolution for Various Target Configurations

The realistic spectrometer settings use the published Hall A spectrometer characteristic. The ideal spectrometer settings contribute no width. NIKHEF-target refers to using the NIKHEF two foil or one foil targets in our spectrometers and kinematics. NIKHEF-paper refers to the results from [6]. In that experiment the scattered electron energy was almost 7 times lower than in the proposed kinematics. A comparison of the widths for the same target between the realistic and ideal spectrometers gives us a measure of the spectrometers' contribution to the experimental FWHM. Assuming the target effects and spectrometer effects add in quadrature we conclude that the spectrometers contribute about 0.5 Mev to the FWHM for our kinematics

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

GEANT Simulation and Peak Extraction

A 0.2 mm thick lead target is a good compromise between resolution and count rate.

Excitation Energy (MeV), pm=100MeV/c

Bismuth run to provide an experimental line shape.

209Bi(e,e’p)208Pb, pm = 200 MeV/c

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

Beam Time Request

Cross Section Measurements 180 hrs

Spectrometer position changes, Optics and Bismuth run

32 hrs

Arc and EP Energy Measurements 4 hrs

Total 216 hrs(9 days)

The time estimates for the data runs have been adjusted up by 30% to account for radiative losses.

Optics data taken with the carbon target will help establish the missing mass calibration, which is needed for the peak fitting. The bismuth run will provide a line shape and also give a missing mass calibration.

THOMAS JEFFERSON NATIONAL ACCELERATOR LABORATORY

K.Aniol, Hall A Collaboration Mtg., June 23, 2005

Summary

(1) The first measurements ever made in quasielastic kinematics on the paradigmatic shell model nucleus, 208Pb at high Q2 are proposed.

(2) Strength for pmiss > 300 MeV/c will give insight into nuclear structure issues and confront theoretical models.

(3) A new observable ATL for the five low lying states of 207Tl will be measured.

Heavy Metal

Collaboration