precision measurement of r l and r t of quasi-elastic electron scattering in the momentum transfer...

Precision Measurement of RL and RT of Quasi-Elastic Electron ScatteringIn the Momentum Transfer Range 0.55GeV/c≤|q|≤1.0GeV/c*

Yan Xinhu

Department of Modern Physics of USTC

2008/04/28

国家自然科学基金子

* Supported by the National Natural Science Foundation of China(10605022) and Natural Science Foundation of Anhui Educational Committee(KJ2007B028)

Outline

1.Introduction

２ .CSR Experiment (E05-110) at JLab

３ .Summary

1.Introduction

Motivation:

How nucleon properties are affected by the nuclear medium?

How can we connect the low energy theories and highEnergy theory (QCD) ?

Response Functions

Coulomb Sum

22 1

2

2(| |, , ) [1 tan ]

2

qq

Q

20

( , )1( )E

LL G

R qS q dZ

2 22 2 2 2 2

2 2

1 4( ) ([ ( )] ( / )[ ( )] )

1 2p n

E E E

Q MG Q G Q N Z G Q

Q M

One photon exchange assumption , inclusive electron scattering

2

T. de Forest, Jr., Nucl. Phys. A414 (1984) 347.

Saturation/Deviation of Coulomb Sum Rule

Saturation of the Coulomb Sum

( ) 1LS q at the sufficiently large q

Deviation of the Coulomb Sumat small q

Pauli blocking

Nucleon-nucleon long-range Correlationat large q (>>2KF)

Short-range correlation ~10%

Modification of the free nucleon electromagneticproperties inside the nuclear medium

One of the long lasting question in nuclear physics

Overview

Comprehensive measurements of the Coulomb sum at various labs for over 20 years

Limited range in q and At Bates(MIT) and Saclay(France) q550MeV/c

At SLAC(Stanford) q=1140MeV/c

CSR experiment ( E05-110) at JLab Covers a region 550MeV/cq1000MeV/c

Previous Measurements

For the past twenty years, a large experimental program at Bates, Saclay and SLAC

Limited kinematic coverage in q and due to machine limitations

Controversy on CSR

Early data shows significant quenching of the CSR

With the addition of forward angle data, Bates claims no significant quenching

Saclay new analysis claims that quenching persists

SL

(q)

２ .CSR Experiment (E05-110) at JLab

Commissioned in early 1990sfirst experiment in 1994

High luminorsity electron beam:1039cm-2s-1

High density targetMaximum current 200 μA

The gain of each linac is adjustable400MeV-500MeV,Maximum Energy 5.7GeV

JLab Hall A

Hall A Beamline and Spectrometers

ARC: beam momentumBCM: Beam ChargeeP: Beam energy

Compoton Polarimetry&Moller Polarimetry: beam polarizationRaster & BPM: beam position

NaI

Parameters of HRS

+/- 5 cm1 mm

Transverse Length AcceptanceTransverse Position Resolution (FWHM)

0.5 mr1.0 mr

Angular Resolution: (FWHM)HorizontalVertical

6 msrSolid Angle:

+/- 30 mr+/- 60 mr

Angular Acceptance: HorizontalVertical

1 x 10-4 Momentum Resolution (FWHM)

12.4 mDispersion (D)

+/- 4.5% Momentum Acceptance

23.4 m Optical Length

45o Bend Angle

QQDQ Configuration

0.3 – 5.7 GeV/c Momentum Range

Installation of NaI detector

Performance

~3% at 1GeV Or ~9% at 0.1GeV

CSR Experiment at JLab (Hall A)

Scattering Angles 15°,60°,90°,120°compromise between counting rates and lowest Momentum setting

two more angles at 60°90°, equally spaced ε ─ improved systematic uncertainties

Beam Energy 0.4 to 4.0GeV

Range of q ~ 550MeV/c to 1000MeV/c

Targets 4He, 12C, 56Fe , 208PbStudy A or density dependent effect

Study of Coulomb corrections (small for 4He or 12C, but large for 208Pb)

Scattered Energy covers complete range of QE peak and beyond

Coverage at 15°

Coverage at 60°

Coverage at 90°

Coverage at 120°

Kinematic Coverage

Separation of RL and RT

4

4

| | 1( )

( )L f f b bM f b

qR

Q

2

2

2| |( )

( )f b

T b fM f b

qR

Q

f

b

forward angle (f)

backward angle (b)

f

b

Estimation of Accuracy of RL and RT

2 21 1 1L

f bL

R

R R R

2 22 21 1Tf b b f

T

R R

R R R

L

T

R

Ratio of longitudinal and transverse virtual photo-absorption cross section

0.85f b At JLab

0.5 Previous Experiment

Kinematic Coverage in ε versus

Preliminary

Results

Preliminary

Results

Expected

Coulomb Correction

Need to take into account the effect of the nucleus Coulomb field to the incoming/outgoing electrons

Approximate corrections via EMA

Full treatment of Coulomb corrections via DWBA

Up to now, some disagreement between EMA & DWBA

What to do ,then?

Whatever is the best way for corrections

Comparison of Various Methods

3.SummaryExperiment in smooth progress

Completed by Jan. 2008

Hope to answer the question on the CSR

High enough momentum transfer, previously unexplored.

A few new features

Independent energy measurement for background reduction

Thanks