Session DA: Nucleon Baryon Interactions

Measurements of the Spin Structure of the Deuteron

As a spin-1 object composed of two nucleons, the deuteron exhibits a spin structure that can be probed by elastic and quasielastic electron scattering through single and double polarization observables. Such measurements of spin-dependent electron scattering from deuterium have been carried out recently at the MIT-Bates Linear Accelerator Center with the Bates Large Acceptance Spectrometer Toroid (BLAST). The experiment uses a longitudinally polarized ($>$65\%) electron beam in com- bination with an isotopically pure, highly-polarized ($>$70\%) internal target of vector- and tensor- polarized deuterium. BLAST consists of a toroidal magnetic spectrometer with the two in-plane sectors symmetrically equipped with detectors, which allows for simultaneous measurement of the inclusive and exclusive reaction channels in elastic and quasielastic kinematics. Due to its D-wave content, the deuteron has an elastic quadrupole form factor. Unpolarized elastic scattering only provides a combination of the charge and quadrupole form factor, their separation requires a spin observable such as the tensor analyzing power T20, which is determined with BLAST from the single-spin asymmetry in elastic electron scattering from tensor-polarized deuterium. While the small D-wave component modifies the nucleon momentum distribution only little, the corresponding tensor single-spin and vector double-spin asymmetries AT d and AV ed in exclusive deuteron electrodisintegration are much more sensitive to nucleons in the D-state. In the quasifree limit, AT d vanishes and AV ed is determined by the form factors of the free nucleon. The above sets of polarization observables have been measured with small statistical and system- atic errors and are compared with recent theoretical calculations. PACS numbers: Electronic address: kohlm@mit.edu   

Electromagnetic Meson Production Reaction in the Resonance Region

Properties of $N^*$ and meson-baryon dynamics in the resonance energy region are of fundamental importance to understand how non-perturbative dynamics of quark and gluon are realized in nucleon resonances. The $N^*$ properties can be extracted by investigating the recent precise and systematic data of meson production reactions with GeV photon and electron. However, it is a non-trivial problem to connect data and QCD predictions and reaction theory of meson production will play an important role. In this talk, recent development of the theoretical study on meson production reaction and the $N^*$ properties will be discussed.   

Probing Nucleon-Nucleon Correlations via the (e,e$'$p) and (e,e$'$pN) Reactions

Probing nucleon-nucleon correlations has proven to be difficult due to competing mechanisms, such as final state rescattering and two-body currents, which can produce the same final state as one would expect from correlations. Recent A(e,e$'$p) and A(e,e$'$pN) measurements have sought to minimize the effects of competing mechanisms by going to special kinematics. For example going to kinematics where the particle with most of the kinetic energy is parallel to the momentum transfer vector, going to high momentum transfers, and/or going to large Bjorken x. The results of these measurements will be presented along with state-of-the-art theoretical calculations.   

Spectroscopy of $\Lambda$ hypernuclei

Spectroscopy of $\Lambda$ hypernuclei has recently become one of the most valuable tools for the experimental investigation of strangeness nuclear physics. Following the pioneering pikr~spectroscopy experiments at the BNL AGS in the 1970's, excitation spectra have been measured using this reaction for a wide variety of $\Lambda$ hypernuclei with the superconducting kaon spectrometer(SKS) at the KEK 12~GeV PS. More recently, $\Lambda$ hypernuclear spectroscopy was carried out for the first time using the eek reaction and the continuous electron beam at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). This reaction will be further explored using a new high-resolution kaon spectrometer (HKS) installed at Jefferson Lab. At the same time, precision $\gamma$-ray spectroscopy with a germanium detector array (Hyperball) has been successfully performed for $p$-shell $\Lambda$ hypernuclei at the KEK 12~GeV PS and at the BNL AGS. Quantitative information on $\Lambda$ hypernuclear structure as well as strengths of the spin-dependent hyperon- nucleon interaction in the $p$-shell region were derived. In this talk, the progress of $\Lambda$ hypernuclear spectroscopy, reaction spectroscopy and $\gamma$-ray spectroscopy, and their future prospects are presented.