J. Arrington

Measurements of Deuteron Photodisintegration up to 4.0 GeV

The first measurements of the differential cross section for the d(γ,p)n reaction up to 4.0 GeV were performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson Laboratory. We report the cross sections at the proton center-of-mass angles of 36°, 52°, 69°, and 89°. These results are in reasonable agreement with previous measurements at lower energy. The 89° and 69° data show constituent-counting-rule behavior up to 4.0 GeV photon energy. The 52° and 36° data disagree with the counting-rule behavior. The quantum chromodynamics (QCD) model of nuclear reactions involving reduced amplitudes disagrees with the present data.

A-dependence of nuclear transparency in quasielastic A(e, ef'p) at high Q2

The A-dependence of the quasielastic A(e,ep) reaction has been studied at SLAC with ^2H, C, Fe, and Au nuclei at momentum transfers Q^2 = 1, 3, 5, and 6.8 (GeV/c)2. We extract the nuclear transparency T(A,Q^2), a measure of the average probability that the struck proton escapes from the nucleus A without interaction. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as Color Transparency. Within the measurement uncertainty, no increase is seen for any of the nuclei studied.

Electroproduction of kaons on light nuclei

The A(e,e{prime}K{sup +})YX reaction on H, D, {sup 3}He, and {sup 4}He was investigated in Hall C at CEBAF. Data were obtained for Q{sup 2} {approx} 0.35 and 0.5 GeV{sup 2} at 3.245 GeV. The missing mass spectra for both H and D are fitted with Monte-Carlo simulations incorporating peaks corresponding to {Lambda} production on the proton and {Sigma} production on both the proton and neutron. For D, the cross section ratio {Sigma}{sup 0}/{Sigma}{sup {minus}} {approx} 2, and excess yield close to the thresholds for {Lambda} and {Sigma} production can be attributed to final-state interactions that are compared to the data. The analysis of the data for the He targets is in a more preliminary state with broader quasi-free peaks resulting from the higher Fermi momenta. Evidence for bound {Lambda}-hypernuclear states is seen and other structure may be present.

Electroproduction of kaons and light hypernuclei

A detailed investigation of the basic hyperon-nucleon interactions in nuclei is one of the aims of Experiment 91-016, approved with high priority at CEBAF, to study the electroproduction of kaons on targets of deuterium, {sup 3}He, and {sup 4}He. Inasmuch as both the electron and K{sup +} are particles that interact relatively weakly with nucleons, electroproduction of light hypernuclei provides a low-distortion method for investigating the fundamental interactions between nucleons, {Alpha}`s, and {Epsilon}`s in few-body systems. In particular, the (e,e`K{sup +}) reactions on cryogenic targets of D, {sup 3}He, and {sup 4}He will be studied at incident electron energies near 3 GeV with coincident detection of the emergent e and K{sup +} in the HMS and SOS magnetic spectrometers in Hall C. Construction of the He target, operating at {approximately}10 atm, {approximately}50 K and capable of dissipating {approximately}30 W, is expected to be complete prior to commencement of production runs in Hall C. The first data runs for E91-016, expected to begin late in FY 1995, will also be the basis for a doctoral thesis at Hampton University. In addition to providing new information on the phases of hyperon-nucleon interactions, measurements of cross sections for hypernuclear formation, and interference phenomena,morexa0» the data may provide evidence for the presence of bound {Epsilon}`s and strange di-baryonic states that are the subject of considerable theoretical discussion.«xa0less

Inclusive Electron Scattering from Nuclei at x ≃ 1

The inclusive A(e, e{prime}) cross section for x {approx_equal} 1 was measured on {sup 2}H, C, Fe, and Au for momentum transfers Q{sup 2} from 1-7 (GeV/c){sup 2}. The scaling behavior of the data was examined in the region of transition from y-scaling to x-scaling. Throughout this transitional region, the data exhibit {zeta}-scaling, reminiscent of the Bloom-Gilman duality seen in free nucleon scattering.

The SAMPLE experiment: Parity‐violating electron scattering from the proton and deuteron

Recent experimental evidence on nucleon structure has provided indications that some strange quark matrix elements can be comparable to those involving up and down quarks. The SAMPLE experiment will determine the strange magnetic form factor GsM at Q2=0.1 (GeV/c)2 from a measurement of the asymmetry in the scattering of polarized electrons from the proton. The error on the extraction of GsM is ultimately limited by a theoretical uncertainty—the uncertain electroweak hadronic radiative correction to the axial form factor, RT=1A. To address this issue, the collaboration is also approved to measure the asymmetry in parity‐violating quasielastic electron scattering from the deuteron. The combination of the proton and deuteron measurements will yield a value of GsM that is almost completely free of the uncertainty in RT=1A.

Measurement of the neutron magnetic form factor from inclusive quasielastic scattering of polarized electrons from polarized 3He

We report a measurement of the asymmetry in spin-dependent quasielastic scattering of longitudinally polarized electrons from a polarized 3 ~ e target. The neutron magnetic form factor G;, has been extracted from the measured asymmetry based on recent PWIA calculations using spin-dependent spectral functions. Our determination of G& at ~ ~ = 0 . 1 9 (G~VIC) agrees with the dipole parametrization. This experiment represents the first measurement of the neutron magnetic form factor using spin-dependent electron scattering.