Claude F. Williamson

A system of dipole magnets for 180° electron scattering

Abstract The design and performance of a four-magnet system for the measurement of 180° scattering of electrons with energies up to 450 MeV is described. Two of the magnets are moved perpendicular to the incident beam direction during an experiment. The post-target beam is directed along the same line as the incident beam, and a constant solid angle for backscattering is maintained regardless of the inelasticity of the collision suffered by the electron. The system is used in conjunction with a dispersion-matching transport system and a large spectrometer set at a fixed angle of 160°. Measured resolutions of less than 3 × 10 −4 have been obtained.

Elastic magnetic electron scattering from 29Si and 31P

Abstract Elastic magnetic electron-scattering form factors from 29Si and 31P have been measured in the range of momentum transfer from 1.0 to 2.8 fm−1. Analysis of the data using a particle-core-coupling model yields 2 s 1 2 occupation probabilities for the valence nucleon of 0.46 ± 0.01 for the neutron in 29Si and 0.48 ± 0.01 for the proton in 31P. The radius of the 2 s 1 2 proton orbit in 31P has been found to be (5.3+2.6−1.5)% larger than the corresponding neutron orbit in 29Si. Recent large-basis shell-model calculations of the form factors do not accurately reproduce the experimental results.

Electroexcitation of the first excited state in 39K

Abstract Electroexcitation of the first excited state in 39 K has been studied in the momentum transfer region of 0.8–2.5 fm −1 . Separation of the longitudinal and transverse form-factor components has been obtained. The longitudinal form factor has been analyzed model-independently. A B (M1) value for this l -forbidden transition was also obtained. Presently available theoretical predictions are unable to reproduce the B (M1) value or the transverse form-factor data.

Nuclear Transparency with the gamma + n -> pi- + p Process in 4He

We have measured the nuclear transparency of the fundamental process gamman-->pi(-)p in He-4. These measurements were performed at Jefferson Lab in the photon energy range of 1.6-4.5 GeV and at theta(cm)(pi)=70degrees and 90degrees. These measurements are the first of their kind in the study of nuclear transparency in photoreactions. They also provide a benchmark test of Glauber calculations based on traditional models of nuclear physics. The transparency results suggest deviations from the traditional nuclear physics picture. The momentum transfer dependence of the measured nuclear transparency is consistent with Glauber calculations that include the quantum chromodynamics phenomenon of color transparency.

Quasielastic electron scattering from [Formula Presented]Ca

Differential cross sections for quasielastic electron scattering on {sup 40}Ca have been measured at laboratory scattering angles of 45.5{degree}, 90{degree}, and 140{degree} with bombarding energies ranging from 130 to 840 MeV. Transverse and longitudinal response functions have been extracted for momentum transfers from 300 to 500 MeV/c. Contrary to some previously reported results, the total observed longitudinal strength agrees with the relativistic Fermi gas prediction to within {plus_minus}18{percent}. {copyright} {ital 1997} {ital The American Physical Society}

Trinucleon Threshold Electrodisintegration

Inclusive inelastic electron scattering cross sections for 3H and 3He were measured for excitation energies below 18 MeV. For six values of the three-momentum transfer q in the range 0.88 < q < 2.87 fm−1, longitudinal and transverse response functions were determined. The experimental data are in good agreement with two recent calculations. One uses variational ground-state wave functions and the orthogonal correlated states method to describe the two- and three-body breakup channels. The other uses bound and continuum Faddeev wave functions for a simple central potential. The inclusion of final-state interactions (FSI) in the Faddeev continuum is found to be very important; inclusion of FSI changes the response functions in the threshold kinematics by a large amount, yielding excellent agreement with the data.

Deuteron Threshold Electrodisintegration

Cross sections for the D(e,e′)pn reaction in the region of the breakup threshold have been measured at the MIT/Bates Linac by a multi-institutional collaboration for 10 < Q2 < 40 fm−2. These measurements extend the previous Saclay data and are in excellent agreement with them in the region of overlap. The present cross sections averaged over 3 MeV from threshold appear to be consistently smaller than recently reported data from SLAC averaged over 10 MeV. None of the measurements shows a minimum in the cross sections for Q2 < 40 fm−2. Some recent potential model calculations appear to be in fair agreement with the data, but the existing calculations based on hybrid quark models appear to be in poor agreement with the data.

Deep Inelastic Electron Scattering Near and Above Pion Threshold

Recent experiments by two collaborations, the LSU-MIT groupA and the Saclay-LSU-Sanita-Clermont-Frascati-Basel effortB, have greatly multiplied the amount of data available on deep-inelastic electron scattering. This paper reviews some of the more recent results from those experiments1,2.