C. F. Williamson

Measurement of tensor polarization in elastic electron–deuteron scattering at large momentum transfer

Tensor polarization observables ( t(20), t(21), and t(22)) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c)(2). The experiment was performed at the Jefferson Laboratory in Hall C using the electron High Momentum Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q2 the deuteron charge form factors G(C) and G(Q). They are in good agreement with relativistic calculations and disagree with perturbative QCD predictions.

Longitudinal response functions for 40Ca from quasi-elastic electron scattering

Abstract Longitudinal response functions were extracted from quasi-elastic electron scattering data on 40 Ca at angles of 45.5°, 90°, and 140° with bombarding energies ranging from 130 to 840 MeV and for constant three-momentum transfers of 300, 330, 370, 410 and 450 MeV/ c . Contrary to previously reported results, the present longitudinal response functions show no more than 20% missing strength when compared to the relativistic Fermi gas model. Calculations employing wavefunctions generated from a relativistic Hartree potential and using an effective momentum approximation yield results that are in much closer agreement with the experimental data and indicate essentially no longitudinal suppression.

High resolution spectrometers for electron scattering

Abstract In this article we discuss high-precision, high-resolution magnetic spectrometry as applied to electron scattering at intermediate energies (⩽1 GeV). Beginning with a brief summary of some aspects of the electron-scattering process, we develop the specifications for systems capable of achieving precision of about 1% in cross-section and 10 −4 in momentum resolution. Following a brief outline of the general formalism of magnetic optics, we describe in considerable detail the MIT DD electron energy-loss spectrometer including: (1) general optical specifications, (2) mechanical construction methods and special features, (3) focal plane instrumentation, and (4) examples of performance to date. In a concluding section we make some comparisons with more recent systems and indicate where further improvements in the MIT system may possibly be achieved.

Cross section measurements of charged pion photoproduction in hydrogen and deuterium from 1.1 to 5.5 GeV

The differential cross sections for the gamma n ->pi(-)p and the gamma p ->pi(+)n processes were measured at Jefferson Lab. The photon energies ranged from 1.1 to 5.5 GeV, corresponding to center-of-mass energies from 1.7 to 3.4 GeV. The pion center-of-mass angles varied from 50(degrees) to 110(degrees). The pi(-) and pi(+) photoproduction data both exhibit a global scaling behavior at high energies and high transverse momenta, consistent with the constituent counting rule prediction and the existing pi(+) data. The data suggest possible substructure of the scaling behavior, which might be oscillations around the scaling value. The data show an enhancement in the scaled cross section at center-of-mass energy near 2.2 GeV. The differential cross section ratios [d sigma/dt(gamma n ->pi(-)p)/d sigma/dt(gamma p ->pi(+)n)] at high energies and high transverse momenta can be described by calculations based on one-hard-gluon-exchange diagrams. (Less)

Meson-exchange currents and quasielastic predictions for charged-current neutrino-C 12 scattering in the superscaling approach

We evaluate and discuss the impact of meson-exchange currents (MECs) on charged-current quasielastic neutrino cross sections. We consider the nuclear transverse response arising from two-particle two-hole states excited by the action of electromagnetic, purely isovector meson-exchange currents in a fully relativistic framework based on the work by the Torino Collaboration [A. D. Pace, M. Nardi, W. M. Alberico, T. W. Donnelly, and A. Molinari, Nucl. Phys. A726, 303 (2003)]. An accurate parametrization of this MEC response as a function of the momentum and energy transfers involved is presented. Results of neutrino-nucleus cross sections using this MEC parametrization together with a recent scaling approach for the one-particle one-hole contributions (named SuSAv2) are compared with experimental data.

Superscaling of non-quasielastic electron-nucleus scattering

The present study focuses on the superscaling behavior of electron-nucleus cross sections in the region lying above the quasielastic peak, especially the region dominated by electroexcitation of the � . Non-quasielastic cross sections are obtained from all available high-quality data for 12 C by subtracting effective quasielastic cross sections based on the superscaling hypothesis. These residuals are then compared with results obtained within a scaling-based extension of the relativistic Fermi gas model, including an investigation of violations of scaling of the first kind in the region above the quasielastic peak. A way to potentially isolate effects related to meson-exchange currents by subtracting both impulsive quasielastic and impulsive inelastic contributions from the experimental cross sections is also presented.

Evidence for fragmentation of stretched 6− strength in Si (e, e′)

Abstract From natSi (e, e′) spectra taken at 90° and 160°, we present evidence for fragmented 6− T=1 strength in 28Si. A narrow peak at 17.35±0.10 MeV excitation is shown to be consistent with 6− T=1 strength.

A cryogenic tritium target system for nuclear physics experiments

Abstract A cryogenic tritium ( 3 H 2 ) gas target system was constructed and used for a program of electron scattering studies. The 3 H 2 was supplied and safely stored as solid U 3 H 3 . For the experiments, it was transferred to a thin walled cylindrical cell, where it was exposed to 25 μA electron beams with energies up to 800 MeV. During operation, the target cell contained 115000 Ci of tritium at 225 psia and 45 K. Multiple safety enclosures surrounded both target and gas transfer systems. A microprocessor-based control and monitoring system presented target parameters to the operators, identifying those out of range. The target system operated safely and effectively for about 2000 h, enabling completion of comprehensive elastic and elastic electron scattering study of the three nucleon system.

Tensor polarization in elastic electron-deuteron scattering to the highest possible momentum transfers

In elastic electron-deuteron scattering, the tensor polarization moments t 20 , t 21 and t 22 , together with the unpolarized cross-sections, have been measured up to a momentum transfer of 1.8 (GeV/c) 2 , or 6.8 fm −1 . The experiment was performed at Jefferson Laboratory using the recoil deuteron polarimeter POLDER. Preliminary results are presented and discussed, especially in view of their significance concerning the applicability of perturbative QCD to this exclusive process.

Quasielastic electron scattering from {sup 40}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}