[en] Relative populations of states in ¹¹B following the ¹²C(γ,p)¹¹B reaction have been measured with high resolution using a 70% HpGe γ detector to observe decay γ rays from the residual nucleus. The triplet of states near 7 MeV in ¹¹B are resolved and the measured populations compared to previous data. The analysis includes a consideration of γ-proton angular correlations, which was not made in the previous measurement. The new and previous results corrected for angular correlation effects agree reasonably well with calculations that include one- and two-body nuclear currents, pion exchange, and Δ currents, under the assumption that the photons are mainly absorbed on exchanged pions

[en] This measurement forms part of a series of experiments designed to resolve the nature of the reaction mechanism involved between high-energy photons and the nucleus. Of the several theoretical models currently available, microscopic calculations, such as those of Gari and Hebach, and more recently Ryckebusch seem to better describe the experimental observations. These models include multi-particle effects by specific reference to short range correlations between the nucleons, meson-exchange effects and ground state correlations. Measurement of the population of excited residual states following photonuclear reactions, severely constrains the model parameters. This is particularly true for residual states with configurations involving terms with multiple holes. A study of the population of residual states in ¹¹B following the ¹²C(γ,p) reaction, has provided compelling data that has helped to refine the model parameters. This measurement exploited a technique where γ-rays from residual excited states are used to provide better resolution of the relative population of these states. This de-excitation γ-ray technique is used in the present experiment, so as to provide a measure of the population strength to the +ve-parity doublet of states in ¹⁵O near 5.2 MeV. These states have a predominant 2p-lh structure, and hence provide an important test of the theoretical models. Without access to the de-excitation γ-ray spectrum it would not be possible to resolve population of these states from the -ve parity state at 6.2 MeV. (authors)

[en] The reactions ¹³C(γ,d) and ¹³C(γ,t) were studied using tagged photons in the intermediate energy range E_γ =50-70 MeV. An unexpectedly large number of deuterons and tritons were emitted from ¹³C compared with the same reactions on ¹²C. These results may be understood in terms of the break-up of the cluster nucleus ¹²C by the addition of an extra neutron to form ¹³C. The valence neutron in ¹³C produces strong final state interactions with the ejected proton, enhancing the deuteron emission. (authors)

[en] The 2H(e,ep)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility near the top of the quasielastic peak (xBj = 0.964) at a four-momentum transfer squared, Q2 = 0.665 (GeV/c)2 (0.368GeV, W = 2.057GeV), and for recoil momenta up to 550MeV/c. The measured cross section deviates by 1-2 from a state-of-the-art calculation at low recoil momenta. At high recoil momenta the cross section is well described by the same calculation; however, in this region, final-state interactions and interaction currents are predicted to be large, and alternative choices of nucleon-nucleon potential and nucleon current operator may result in significant spread in the calculations

[en] We report the results of a new Rosenbluth measurement of the proton form factors at Q² values of 2.64, 3.20 and 4.10 GeV². Cross sections were determined by detecting the recoiling proton in contrast to previous measurements in which the scattered electron was detected. At each Q², relative cross sections were determined to better than 1%. The measurement focused on the extraction of G_E/G_M which was determined to 4-8% and found to approximate form factor scaling, i.e. μ_pG_E ∼ G_M. These results are consistent with and much more precise than previous Rosenbluth extractions. However, they are inconsistent with recent polarization transfer measurements of comparable precision, implying a systematic difference between the two techniques

[en] The first complete measurements of the angular distributions of the two-body deuteron photodisintegration differential cross section at photon energies above 1.6 GeV were performed at the Thomas Jefferson National Accelerator Facility. The results show a persistent forward-backward asymmetry up to Egamma = 2.4 GeV, the highest-energy measured in this experiment. The Hard Rescattering and the Quark-Gluon string models are in fair agreement with the results

[en] Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s = 5-11 and -t = 2-7 GeV2 with statistical accuracy of a few percent. The scaling power for the s-dependence of the cross section at fixed center of mass angle was found to be 8.0 +/- 0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark

[en] Kaon electroproduction on hydrogen, deuterium and helium targets has been measured at a beam energy of 3.245 GeV and four-momentum transfer, Q², ranging from 0.34 to 0.5 GeV². Associated hyperon production off a nucleon in the deuteron exhibits a quasifree production mechanism. Excess yield close to the respective thresholds for Λ and Σ production is observed. This can be accounted for by final-state interaction between the electroproduced hyperon and the spectator nucleon. The effects predicted from three different hyperon-nucleon potentials are compared to the data. The measurement on the helium targets is the first ever performed. Very preliminary results are presented

[en] The A(e,eK+)X reaction has been investigated at Jefferson Laboratory. Data were taken for Q² approx. 0.35 GeV² at a beam energy of 3.245 GeV for 1H,3He and 4He targets. Evidence for Lambda-hypernuclear bound states is seen for 3,4He targets. This is the first time that the electroproduction of these hypernuclei has been observed

[en] The A(e,eiK+)YX reaction on H, D, ³He, and ⁴He was investigated in Hall C at CEBAF. Data were obtained for Q² ∼ 0.35 and 0.5 GeV² 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 Sigma⁰/Sigma^- ∼ 2, and excess yield close to the thresholds for Lambda and Sigma production can be attributed to final-state interactions; models 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