precision measurement of r l and r t of quasi-elastic electron scattering
DESCRIPTION
Precision Measurement of R L and R T of Quasi-Elastic Electron Scattering In the Momentum Transfer Range 0.55GeV/c ≤|q|≤1.0GeV/c *. Yan Xinhu. Department of Modern Physics of USTC. 2008/04/28. * Supported by the National Natural Science Foundation of China(10605022) - PowerPoint PPT PresentationTRANSCRIPT
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
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