The H-1(e, e'K+)Lambda reaction was studied as a function of the squared four-momentum transfer, Q(2), and the virtual photon polarization, epsilon. For each of four Q(2) settings, 0.52, 0.75, 1.00, and 2.00 (GeV/c)(2), the longitudinal and transverse virtual photon cross sections were extracted in measurements at three virtual photon polarizations. The Q(2) dependence of the sigma(L)/sigma(T) ratio differs significantly from current theoretical predictions. This, combined with the precision of the measurement, implies a need for revision of existing calculations.

Exclusive measurements of the analyzing power and two spin-transfer observables for nucleon knockout from an 16 O target are presented, at kinematic conditions chosen to emphasize interactions in the nuclear interior. The analyzing power data are substantially reduced in comparison with values calculated in the distorted wave impulse approximation ~DWIA! using the free nucleon-nucleon interaction, particularly for knockout of the deeply bound 1s 1/2 nucleons. Inclusion of density dependence for the interaction in the calculations improves the agreement with the data, but does not provide a satisfactory description for nucleon knockout from 16 O. Spin-orbit distortions are shown to strongly affect the DWIA predictions of the 1 s 1/2 analyzing powers over most of the experimental kinematic range, but notably not near the points of negligible recoil momentum. Hence these data offer constraints on the optical potentials and independently on the two-body effective interaction. @S0556-2813~98!02104-9# PACS number~s!: 25.40.Ep, 24.70.1s, 24.10.Eq, 13.75.2n

The ${}^{1}\mathrm{H}({e,e}^{\ensuremath{'}}{K}^{+})\ensuremath{\Lambda}$ reaction was studied as a function of the squared four-momentum transfer, ${Q}^{2}$, and the virtual photon polarization, $\ensuremath{\varepsilon}$. For each of four ${Q}^{2}$ settings, 0.52, 0.75, 1.00, and 2.00 $(\mathrm{GeV}/c{)}^{2}$, the longitudinal and transverse virtual photon cross sections were extracted in measurements at three virtual photon polarizations. The ${Q}^{2}$ dependence of the ${\ensuremath{\sigma}}_{L}/{\ensuremath{\sigma}}_{T}$ ratio differs significantly from current theoretical predictions. This, combined with the precision of the measurement, implies a need for revision of existing calculations.

The Saskatchewan-Alberta Large Acceptance Detector (SALAD) is a 4π detector designed and built for studies of photonuclear reactions with a tagged photon beam. The design and performance of the detector are described. Its characteristics have been studied by examining p-p elastic scattering with a proton beam at TRIUMF.

We have measured the polarization transfer asymmetries of the reaction pp → dπ+ from the longitudinally polarized proton to the sideways polarized deuteron for deuteron center-of-mass angles from 25° to 140°. Our longitudinal to sideways polarization transfer data are best represented by the partial-wave amplitude fits of Bugg et al. while several model calculations are only in qualitative agreement.

Singles $^{16}\mathrm{O}$(${\mathrm{\ensuremath{\pi}}}^{+}$,p) and coincidence $^{16}\mathrm{O}$(${\mathrm{\ensuremath{\pi}}}^{+}$,2p${)}^{14}$N measurements have been made at ${\mathit{T}}_{\mathrm{\ensuremath{\pi}}}$=115 MeV over an extended range of the phase space of the two final-state protons. The coincidence measurements have a missing-mass resolution of 4 MeV. The direct two-nucleon absorption cross section extracted from the data is 58\ifmmode\pm\else\textpm\fi{}8 mb. After corrections for final-state interactions, it was found that the two-nucleon ${\mathrm{\ensuremath{\pi}}}^{+}$+np\ensuremath{\rightarrow}pp process accounts for about 76% of the total absorption cross section, and thus is the dominant absorption mechanism. Evidence for absorption on s-p pairs is seen as a broad bump near 32 MeV of excitation. At backward angles the inclusive $^{16}\mathrm{O}$(${\mathrm{\ensuremath{\pi}}}^{+}$,p) spectra show a distinct absorption peak, an important feature not previously observed. Comparisons of distorted wave impulse approximation calculations to both the coincidence data and inclusive data are presented.

In this talk I survey recent data on the reaction mechanism of in-flight true pion absorption for A>4.

New data for the {sup 16}O({pi}{sup +},2{ital p}) reaction at {ital T}{sub {pi}}=165 MeV are presented. Significant differences with previously published data are discussed. It is found that below 20 MeV excitation approximately 14% of the total absorption cross section is due to a two-nucleon mechanism. Evidence for direct two-nucleon absorption at higher excitation energy is also presented. Including estimates for final state interactions, the present results suggest that about 50% of the abosrption cross section is due to two-nucleon processes.

We have measured np\ensuremath{\rightarrow}d${\ensuremath{\pi}}^{0}$ cross sections at eleven beam energies within 16 MeV of threshold. Total cross sections are only 0.67\ifmmode\pm\else\textpm\fi{}0.10 of the value which has been generally accepted for s-wave pion production strength near threshold. The differential cross sections are anisotropic at only 1 MeV (c.m.) above threshold. Our results are compared to ${\ensuremath{\pi}}^{+}$d\ensuremath{\rightarrow}pp data and to predictions of two models.

The analyzing power for quasi-free nucleon-nucleon scattering has been found to differ substantially from that for the free interaction. This medium modification was first noticed in inclusive scattering experiments. In the present work, it has been demonstrated that kinematically complete exclusive measurements are capable of demonstrating this effect more clearly. This advantage arises by virtue of the possibility of selecting nucleons bound in states localized in the nuclear interior.

New data for the $^{16}\mathrm{O}$(${\ensuremath{\pi}}^{+}$,2p) reaction at ${T}_{\ensuremath{\pi}}$=165 MeV are presented. Significant differences with previously published data are discussed. It is found that below 20 MeV excitation approximately 14% of the total absorption cross section is due to a two-nucleon mechanism. Evidence for direct two-nucleon absorption at higher excitation energy is also presented. Including estimates for final state interactions, the present results suggest that about 50% of the abosrption cross section is due to two-nucleon processes.

The (p,p\ensuremath{\alpha}) cluster knockout reaction on $^{9}\mathrm{Be}$ was investigated using polarized incident protons. Coincident data for eight quasifree angle pairs were obtained at a bombarding energy of 150 MeV. Both differential cross sections and analyzing powers were measured for the energy-sharing distribution. Distorted wave impulse approximation calculations indicate that the reaction is dominated by a quasifree knockout process, and that a D-state component of the cluster-core wave function is important for larger momentum transfer. Extracted absolute spectroscopic factors for both S- and D-state knockout are in good agreement with theoretical predictions. The analyzing power follows the trend of free p${\mathrm{\ensuremath{-}}}^{4}$He scattering and agrees with the distorted wave impulse approximation calculation reasonably well. Near zero recoil momentum, the spin-orbit interaction in the distorted waves plays little role.