On the migdal-watson approach to FSI effects in meson production in NN collisions
The influence of the nucleon-nucleon final-state interaction (FSI) on properties of the meson-production amplitude near threshold is discussed. For nucleon-nucleon interaction, a simple Yamaguchi potential and realistic potential models are considered. It is shown that FSI effects cannot be factorized from the production amplitude. The absolute magnitude of FSI effects depends on the momentum transfer (or on the mass of the produced meson) and hence is not universal. Only in the case of the production of rather heavy mesons like η′ or φ FSI do effects become universal. The Jost function approach to FSI effects is critically examined.
Many-body systems interacting via a two-body random ensemble. II. Average energy of each angular momentum
In this paper, we discuss the regularities of average energies with a fixed angular momentum I (denoted as ${E}_{I}'\mathrm{s})$ in many-body systems interacting via a two-body random ensemble. It is found that ${E}_{I}'\mathrm{s}$ with $I\ensuremath{\sim}{I}_{\mathrm{min}}$ (minimum of $I)$ or $I\ensuremath{\sim}{I}_{\mathrm{max}}$ (maximum of $I)$ have large probabilities [denoted as $\mathcal{P}(I)]$ to be the smallest in energy, and $\mathcal{P}(I)$ is close to zero elsewhere. A simple argument assuming the randomness of the two-particle coefficients of fractional parentage is given to explain these observations. A compact trajectory of the energy ${E}_{I}$ vs $I(I+1)$ is found to be robust. Other regularities, such that there are two or three sizable $\mathcal{P}(I)'\mathrm{s}$ with $I\ensuremath{\sim}{I}_{\mathrm{min}}$ but $\mathcal{P}(I)\ensuremath{\ll}\mathcal{P}{(I}_{\mathrm{max}})'\mathrm{s}$ with $I\ensuremath{\sim}{I}_{\mathrm{max}},$ and that the coefficients C defined by $〈{E}_{I}{〉}_{\mathrm{min}}=CI(I+1)$ are sensitive to the orbits and not sensitive to particle number, etc., are discovered and studied for the first time.
Measurement of the quasifree p + n --> d + eta reaction near threshold
The quasifree p + n --> d + eta reaction cross section has been measured in the near-threshold region using deuterium from an internal cluster-jet target and 1350 MeV protons in the CELSIUS storage ring of the The Svedberg Laboratory, Uppsala. The energy