The Lick Observatory Supernova Search

We report here the current status of the Lick Observatory Supernova Search (LOSS) with the Katman Automatic Imaging Telescope (KAIT). The progress on both the hardware and the software of the system is described, and we present a list of recent discoveries. LOSS is the world' most successful search engine for nearby supernovae.Comment: 4 pages, 1 figure, Submitted to the proceedings of the 10th Annual October Astrophysics Conference in Maryland on Cosmic Explosion

Coherent eta photoproduction on the deuteron in the S11S_{11} resonance region

Coherent eta photoproduction on the deuteron is studied in the $S_{11}$ resonance region neglecting eta rescattering and two-body processes. For the elementary reaction on the nucleon, we have considered the dominant $S_{11}(1535)$ resonance and as background the nucleon pole terms as well as $\rho$ and $\omega$ meson exchange. We have studied the influence of different choices for the neutron resonance amplitude, different prescriptions for fixing the invariant mass of the resonance amplitude and different methods for deriving the elementary production amplitude for an arbitrary reference frame.Comment: 33 pages revtex including 13 postscript figure

Near-threshold measurement of the 4He(g,n) reaction

A near-threshold 4He(g,n) cross-section measurement has been performed at MAX-lab. Tagged photons from 23 < Eg < 42 MeV were directed toward a liquid 4He target, and neutrons were detected by time-of-flight in two liquid-scintillator arrays. Seven-point angular distributions were measured for eight photon energies. The results are compared to experimental data measured at comparable energies and Recoil-Corrected Continuum Shell Model, Resonating Group Method, and recent Hyperspherical-Harmonic Expansion calculations. The angle-integrated cross-section data is peaked at a photon energy of about 28 MeV, in disagreement with the value recommended by Calarco, Berman, and Donnelly in 1983.Comment: 10 pages, 3 figures, some revisions, submitted to Physics Letters

Decay of Hypernuclei

We present a nonrelativistic transition potential for the weak strangeness-changing reaction $\Lambda N \to NN$. The potential is based on a one meson exchange model (OME), where, in addition to the long-ranged pion, the exchange of the pseudoscalar $K, \eta$, as well as the vector $\rho, \omega, K^*$ mesons is considered. Results obtained for different hypernuclear decay observables are compared to the available experimental data.Comment: 8 pages. Invited talk given at the KEK-Tanashi International Symposium on Physics of Hadrons and Nuclei. Tokyo, Japan, December 14-17, 1998. In honor of Prof. K. Yazaki. Submitted to Nucl. Phys. A. LateX file (uses espcrc1.sty

New method for extracting quasi-bound states from the continuum

A new parameter-free method is proposed for treatment of single-particle resonances in the real-energy continuum shell model. This method yields quasi-bound states embedded in the continuum which provide a natural generalization of weakly bound single-particle states.Comment: 22 pages, 10 figure

The ηNN\eta NN-system at low energy within a three-body approach

The role of the $\eta NN$-interaction is studied in the low energy regime in $\eta$-deuteron reactions as well as in coherent and incoherent $\eta$-photoproduction on the deuteron using a three-body model with separable two-body interactions. The three-body approach turns out to be quite essential in the most important lowest partial wave. Results are presented for differential and total cross sections as well as for the $\eta$-meson spectrum. They differ significantly from those predicted by a simple rescattering model in which only first-order $\eta N$- and $NN$-interactions in the final state are considered. The major features of the experimental data of $\eta$-photoproduction in the near-threshold region are well reproduced.Comment: 20 pages revtex including 10 figures, revised version accepted for publication in Nucl. Phys.