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 国家自然科学基金子 * Supported by the National Natural Science Foundation of China( ) 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 high Energy theory (QCD) ?

Response Functions Coulomb Sum 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 at the sufficiently large q Deviation of the Coulomb Sum at small q Pauli blocking Nucleon-nucleon long-range Correlation at large q (>>2K F )‏ Short-range correlation ~10% Modification of the free nucleon electromagnetic properties 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) q  550MeV/c At SLAC(Stanford) q=1140MeV/c CSR experiment ( E05-110) at JLab Covers a region 550MeV/c  q  1000MeV/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 S L (q)‏

２.CSR Experiment (E05-110) at JLab Commissioned in early 1990s first experiment in 1994 High luminorsity electron beam:10 39 cm -2 s -1 High density target Maximum current 200 μA The gain of each linac is adjustable 400MeV-500MeV, Maximum Energy 5.7GeV

JLab Hall A

Hall A Beamline and Spectrometers ARC: beam momentum BCM: Beam Charge eP: Beam energy Compoton Polarimetry& Moller Polarimetry: beam polarization Raster & BPM: beam position NaI

Parameters of HRS +/- 5 cm 1 mm Transverse Length Acceptance Transverse Position Resolution (FWHM) 0.5 mr 1.0 mr Angular Resolution: (FWHM) Horizontal Vertical 6 msrSolid Angle: +/- 30 mr +/- 60 mr Angular Acceptance: Angular Acceptance: Horizontal Vertical 1 x Momentum Resolution (FWHM) 12.4 mDispersion (D) +/- 4.5%Momentum Acceptance 23.4 mOptical Length 45 o Bend Angle QQDQConfiguration 0.3 – 5.7 GeV/cMomentum 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 4 He, 12 C, 56 Fe, 208 Pb Study A or density dependent effect Study of Coulomb corrections (small for 4 He or 12 C, but large for 208 Pb) 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 R L and R T forward angle (f)‏ backward angle (b)‏

Estimation of Accuracy of R L and R T Ratio of longitudinal and transverse virtual photo-absorption cross section At JLab Previous Experiment

Kinematic Coverage in ε versus 

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.Summary Experiment in smooth progress Completed by Jan 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