The hadronization process for quarks combining into two mesons, qq¯→${\mathit{MM}}^{\prime }$ at temperature T is described within the SU(3) Nambu–Jona-Lasinio model with finite current quark masses. Invariant matrix elements, cross sections, and transition rates are calculated to leading order in a 1/${\mathit{N}}_{\mathit{c}}$ expansion. Four independent classes, ud¯, us¯, uū, and ss¯→hadrons are analyzed and the yield is found to be dominated by pion production. Threshold behavior is determined by the exothermic or endothermic nature of the processes constituting the hadronization class. A strong suppression of transition rates is found at the pionic Mott temperature ${\mathit{T}}_{\mathit{M}\mathrm{\pi }}$=212 MeV, at which the pion becomes a resonant state. The mean time for hadronization is calculated to be 2–4 fm/c near the Mott temperature. The calculation of strangeness changing processes indicates that hadronization accounts for a 1% increase in the absolute value of the kaon to pion ratio at T=150 MeV. © 1996 The American Physical Society.

We present the results of an energy-dependent and set of single-energy partial-wave analyses of single-pion photoproduction data. These analyses extend from threshold to 2 GeV in the laboratory photon energy, and update our previous analyses to 1.8 GeV. Photodecay amplitudes are extracted for the baryon resonances within this energy range. We consider two photoproduction sum rules and the contributions of two additional resonance candidates found in our most recent analysis of πN elastic scattering data. Comparisons are made with previous analyses. © 1996 The American Physical Society.

We investigate the weak kaon-nucleon (NNK) S-wave and P-wave interactions using heavy baryon chiral perturbation theory. The leading one-loop SU(3) breaking contributions to the ppK, pnK, and nnK couplings are computed. We find that they suppress all NNK amplitudes by 30% to 50%. The ratio of neutron-induced to proton-induced hypernuclear decay widths is sensitive to such reductions. It has been argued that the discrepancy between the predicted and observed P-wave amplitudes in Δs=1 hyperon decay results from an accidental cancellation between tree-level amplitudes, and is not a fundamental problem for chiral perturbation theory. Agreement between experimentally determined NNK P-wave amplitudes and our estimates would support this explanation. © 1996 The American Physical Society.

We argue that the nonperturbative Schwinger mechanism may play an important role in the hadronic production of charm. We present a flux tube model which assumes that the colliding hadrons become color charged because of gluon exchange, and that a single nonelementary flux tube is built up as they recede. The strong chromoelectric field inside this tube creates quark pairs (including charmed ones) and the ensuing color screening breaks the tube into excited hadronic clusters. In their turn these clusters, or ‘‘fireballs,’’ decay statistically into the final hadrons. The model is able to account for the soft production of charmed, strange, and lighter hadrons within a unified framework. © 1996 The American Physical Society.

The β-delayed neutron decay of ${}_{}{}^{17}{}_{}{}^{}\mathrm{B}$ was studied using a radioactive ion beam. The neutron energies, measured via time of flight, give information on states in ${}_{}{}^{17}{}_{}{}^{}\mathrm{C}$ above the ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$+neutron threshold. States in ${}_{}{}^{17}{}_{}{}^{}\mathrm{C}$ were found at excitation energies of 2.25(2), 2.64(2), and 3.82(5) MeV, and possibly at 1.18(1) MeV. These low-lying states are of possible interest for nuclear physics as well as for astrophysics. © 1996 The American Physical Society.

The neutron capture rate on ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ is of considerable interest in the interpretation of nucleosynthesis in inhomogeneous big bang scenarios and for stellar helium burning in massive red giant stars as well as AGB stars. We measured the reaction cross section of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$(n,γ${)}^{19}$O at the Forschungszentrum Karlsruhe with a fast cyclic neutron activation technique at laboratory neutron energies of 25, 129, 152, 250, and 370 keV. Direct capture and shell model calculations were performed to interpret the results as well as previous unpublished data. Contributions to the reaction cross section and to the new stellar reaction rate will be discussed. © 1996 The American Physical Society.

In neutron capture for magic-shell nuclei the direct reaction mechanism can be important and may even dominate. As an example we investigated the reaction ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$(n,γ${)}^{49}$Ca for projectile energies below 250 keV in a direct capture model using the folding procedure for optical and bound state potentials. The obtained theoretical cross sections are in agreement with the experimental data showing the dominance of the direct reaction mechanism in this case. The above method was also used to calculate the cross section for ${}_{}{}^{50}{}_{}{}^{}\mathrm{Ca}$(n,γ${)}^{51}$Ca. © 1996 The American Physical Society.

Existing experimental proton stripping reaction data on ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$ leading to threshold states in ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$ are reinvestigated and reanalyzed in a consistent and improved manner. We use unbound state form factors in the DWBA analysis of the measured deuteron angular distributions to deduce absolute rather than relative proton partial widths. For higher-lying resonances these values are compared to widths obtained from (p,γ) work. It is also shown that several of the unique ${\mathit{J}}^{\mathrm{\pi }}$ values assigned previously to ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$ states are erroneous. This paper reports on a reanalysis of spins, parities, and isospins for ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$ states located at ${\mathit{E}}_{\mathit{x}}$<8.00 MeV. We deduce new stellar rates for the reaction ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$(p,γ${)}^{26}$Al and compare our results with previous values. Furthermore, shell-model calculations for the mass A=26 system are performed. Theoretical excitation energies, ${\mathit{J}}^{\mathrm{\pi }}$ values, γ-ray transition strengths, spectroscopic factors, and proton partial widths are compared to experimental data and new shell-model assignments of experimental states in ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$ are derived. We estimate Coulomb displacement energies of excited ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ and ${}_{}{}^{26}{}_{}{}^{}\mathrm{Si}$ mirror states and present new analog assignments for T=1 triplet states in A=26 nuclei. Based on shell-model results and analog state information we present updated stellar rates for the ${}_{}{}^{25}{}_{}{}^{}\mathrm{Al}$(p,γ${)}^{26}$Si reaction. © 1996 The American Physical Society.

The electronic rearrangement resulting from the β decay of ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ has been calculated in the framework of the sudden approximation using a numerical B-spline basis set approach. We have calculated the excitation probabilities to the final discrete states of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}_{}^{+}{}_{}{}^{}$ (including to the doubly excited autoionizing states) as well as the total probabilities for single and double ionization. The correct treatment of electronic correlation in the framework of the sudden approximation is shown to modify the ${\mathit{P}}_{\mathit{K}}$ value (the probability that an atomic K vacancy is created) by more than 2%. © 1996 The American Physical Society.

A pion exchange quark-quark force which is assumed to be general enough to include the charge dependent parts, based on the classification suggested by Henley and Miller, is invoked. With this interaction as input the nucleon-nucleon potential is derived using the properly symmetrized six-quark states for the two nucleon system. Most of the terms obtained here have the same structure as has generally been used, in the study of the charge symmetry breaking effects in n-p scattering. However, there are some new terms which essentially arise as a result of the detailed quark substructure of the nucleons considered here. In particular, we have contributions where only the isospin of the n-p system changes but the spin remains conserved. In addition, the quark exchange effect in the N-N system gives rise to terms which can be identified with the usual ρ, ω exchanges at the nucleon level. These new terms may have some experimentally observable effects on the difference of n-p analyzing power, ΔA. It may, therefore, be worthwhile to undertake a detailed quantitative study with a comparative estimate of the individual contributions on such experimental observables. © 1996 The American Physical Society.

The inelastic particle production process in ultrarelativistic heavy ion collision is modeled in terms of an effective scalar field produced by the colliding objects. The logarithmic increase of the inelastic cross section with the incident energy is obtained. It is also shown that this increase is intimately related to the size and surface diffuseness of the colliding objects: the larger the size and surface diffuseness are, the earlier the increase of the cross section starts. © 1996 The American Physical Society.

We have studied pure neutron matter using a derivative scalar coupling (DSC) model and different nonlinear models. It is found that small bound energy of pure neutron matter at equilibrium density is due to the high value of effective nucleon mass ${\mathit{m}}_{\mathit{n}}^{\mathrm{*}}$ in this model. Other nonlinear models having large ${\mathit{m}}_{\mathit{n}}^{\mathrm{*}}$(${\mathrm{\rho }}_0$) also yield bound neutron matter. It is also shown that the role of symmetry energy is very significant in the study of neutron matter and the beta stability of neutron matter. © 1996 The American Physical Society.

The distorted wave–peripheral three-body coupling model has been applied for knockout of particles bound in l = 1 state. As an example the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(α,2α${)}^3$H reaction at 77, 99, and 119 MeV has been analyzed. The distorted wave impulse approximation peripheral three-body coupling model calculations are compared with the conventional kinematic coupling approximation and with the data. © 1996 The American Physical Society.

The reduced nuclear density in the surface layer of a nucleus gives rise to an increase in the level density parameter and also makes the fission barrier of the nucleus temperature dependent. The manner in which these effects can be consistently incorporated in the transition state formalism for statistical model calculations is discussed. The naive replacement of zero temperature with temperature-dependent fission barriers in the standard formula to obtain the level density at the saddle-point configuration is incorrect. © 1996 The American Physical Society.

The Bloch-Brink microscopic α-cluster model is used to investigate the structure of the positive and negative parity yrast bands of ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$. Unlike the resonating group method or the local potential model, we approximate the wave function of ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ti}$ by an intrinsic configuration which is obtained from a variational principle. States with good angular momenta are constructed using angular momentum projection techniques. The wave function is completely antisymmetrized and the center of mass motion is treated properly. The calculated E2 transition strengths reproduce experiment very well, but the energy spectra are in a poor agreement with the data. © 1996 The American Physical Society.

An n-p scattering observable Δ${\mathrm{\sigma }}_{\mathrm{tensor}}$ is presented which uniquely determines the tensor spin-spin part of the nucleon-nucleon forward scattering amplitude. © 1996 The American Physical Society.

The density dependence of hadron masses has been calculated from different versions of the Zimanyi-Moskowski (ZM) model and the results have been compared with the Walecka model. The ZM model has been extended to include pions. The meson masses have been calculated in the random phase approximation self-consistently. The σ, ω, and π masses are found to increase with density, as also in the Walecka model; interestingly, it has been found that the abnormal increase of pion mass with density, which is found in the Walecka model, can be avoided in the ZM models. © 1996 The American Physical Society.

In a recent paper by Horowitz [Phys. Rev. C 48, 2920 (1993)] a heavy meson exchange is incorporated into threshold NN→dπ to enhance the underestimated cross section. However, that calculation uses an unjustified assumption on the initial and final momenta, which causes an overestimate of this effect by a factor of 3–4. Further, I point out that the inclusion of the Δ(1232) isobar increases the cross section significantly even at threshold. © 1996 The American Physical Society.

We present new qualitative arguments regarding some effects and correlations in few-body systems. In particular we show, by using the three-body zero-range model analytically continued to the second energy sheet, that the three-body S-matrix poles scale with the two-body binding energy (${\mathit{B}}_2$). We apply this to the three-neutron ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ interaction model, where the dineutron is artificially bound, and explain the curious pole at ${\mathit{B}}_2$=${\mathit{B}}_3$=0, where ${\mathit{B}}_3$ is the three-body binding energy for nonzero total angular momentum. © 1996 The American Physical Society.

Spin observables for the reaction γp→${\mathit{K}}^{+}$Λ are examined using three recent dynamical models and are compared to the general features of such observables deduced earlier by Fasano, Tabakin, and Saghai. These general features, such as the energy dependence of spin observables and the location of nodes in their angle dependence, are realized. Several instructive surprises, which occur in this comparison to the conjectures of Fasano et al., are then discussed. The sensitivity of spin observables to isobar and t-channel dynamics is analyzed and suggestions for selecting experiments which provide important dynamical information are presented. © 1996 The American Physical Society.