The ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$+${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ reaction has been studied at 15 MeV/nucleon bombarding energy. Correlations between two to seven final fragments with $Z>~8$ have been measured using CR-39 nuclear track detectors. An event-by-event kinematic analysis was carried out for three-body exit channel reactions which exhaust about half of the final fragment production cross section. Most of these ternary processes can be associated with intermediate and peripheral impact parameters. The dominant reaction mechanism is shown to be that of a first binary quasielastic or dissipative collision followed by the sequential binary fission of the excited quasi-$U$ (or to a lesser extent of the excited target remnant). We observe also a net drift of nucleons from the target to the projectile prior to its decay.

The fission fragment angular distributions were measured at energies above the fusion barrier, for the systems ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$. An analysis of the present data along with those already available for the systems ${}_{}{}^{6,7}{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ was made in terms of the saddle-point statistical model. While the anisotropies were ‘‘normal’’ for ${}_{}{}^{6,7}{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{238}$U systems, the ones for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$${+}^{238}$U systems were found to be ‘‘anomalous.’’ The entrance channel mass asymmetry dependence of the anisotropies as observed here is consistent with the expectations of preequilibrium fission dynamics. This result emphasizes the importance of preequilibrium fission in heavy-ion induced fusion-fission reactions.

The isoscalar giant monopole resonance in the nucleus ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ was investigated by inelastic ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ scattering at $E_{\mathrm{Li}}=156\mathrm{}$ MeV. At extreme forward angles fragmented $E0\mathrm{}$ strength was observed up to $E_x=23\mathrm{}$ MeV. The extracted strength centered at 18.3±0.5 MeV excitation energy with a width of $\Gamma =4.8\mathrm{}\pm 0.5$ MeV corresponds to 97.3%±15% of the $E0\mathrm{}$ energy weighted sum rule.

Differential cross sections and ${\mathit{T}}_{20}$ and ${}_{20}{}^{\mathit{TT}}{}_{}{}^{}$ analyzing powers have been measured for 70 MeV ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ breakup into the α particle plus triton channel, on a ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$ target. Measurements were made for both continuum breakup and sequential breakup via the 4.63 MeV state in ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$. The ${\mathit{T}}_{20}$ data for the continuum breakup do not agree with a semiclassical Coulomb model, indicating that the breakup at small angles does not proceed solely via a Coulomb force. The data generally show a somewhat better agreement with continuum discretized coupled channels calculations, indicating the importance of the nuclear force and channel coupling in the reaction mechanism.

Expressions are presented for the modification due to the nuclear potential apart from the Coulomb potential both for the eikonal and the noneikonal trajectories. Calculations for heavy ion total reaction cross sections are performed using these expressions. Results are given for several systems. It is found that the expression used by Cha leads to unrealistic values for the distance of closest approach at small impact parameters at low energies and therefore lead to inaccurate values of the total reaction cross section. The exactly calculated distance of closest approach leads to improved results both for the eikonal and the noneikonal trajectories.

Heavy ion collisions can be used to study the thermodynamics of hot and dense nuclear matter only if the initial mass and energy fluctuations that lead to fragmentation are of thermal origin and survive the disassembly process. If this is the case, the observed fragment multiplicity should be directly related to those initial fluctuations and to the conditions of temperature and density causing them. The feasibility of this scenario is demonstrated with a molecular dynamics study of the evolution of mass and energy fluctuations, and fluctuations of the phase-space density. First, it is verified that the fluctuations leading to fragmentation are indeed early ones. Second, it is determined that different initial conditions of density and temperature can indeed produce varying final fragment multiplicities. The ρ-T plane is mapped to the fragment multiplicity with good precision. This mapping should be easily reproducible with existing experimental data.

Medium modified effective two nucleon interactions are defined for protons incident upon ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ with energies in the range 200 to 800 MeV. Those effective interactions have been folded with the ground-state density to specify nonlocal optical potentials that were then used to analyze the elastic scattering differential cross sections and analyzing powers. A select set of isoscalar and isovector, positive and negative parity, inelastic proton scattering transitions have also been analyzed using the same (microscopic) optical models to define the distorted wave functions needed in distorted wave approximation (DWA) calculations of the associated differential cross sections and analyzing powers. All results are compared with ones found using the Love-Franey effective interactions. The nuclear structure relating to these transitions was chosen from (0+2)ħω and (1+3)ħω shell model calculations of the positive and negative parity spectra of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, respectively. In comparison to previous DWA analyses, very good fits to most data over a range of energies are achieved with no variation being made to any of the input details, save for the choice of the effective interaction. Evidence of limitations of the spectroscopy and of specifics in the defined effective interactions at higher energies is found.

Δ degrees of freedom are introduced into antisymmetrized molecular dynamics (AMD). This is done by increasing the number of basic states in the AMD wave function, introducing a Skyrme-type delta-nucleon potential, and including NN⇆NΔ reactions in the collision description. As a test of the delta dynamics, the extended AMD is applied to (p,${\mathit{p}}^{\prime }$) reactions at ${\mathit{E}}_{\mathrm{lab}}$=800 MeV for a ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ target. It is found that the ratio and the absolute values for delta peak and quasielastic peak (QEP) in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p,${\mathit{p}}^{\prime }$) reaction are reproduced for angles ${\mathrm{\Theta }}_{\mathrm{lab}}$≳40°. For forward angles the QEP is overestimated, but generally the agreement between AMD calculations and experimental data is reasonable. The results of the AMD calculations are compared to one-step Monte Carlo (OSMC) calculations and a detailed analysis of multi-step and delta potential effects is given. Along this analysis a decomposition of the cross section into various reaction channels is presented and the reaction dynamics is discussed in detail. As important side results we present a way to apply a Galilei invariant theory for (N,${\mathit{N}}^{\prime }$) reactions up to ${\mathit{E}}_{\mathrm{lab}}$≊800 MeV which ensures approximate Lorentz invariance and we discuss how to fix the width parameter ν of the single particle momentum distribution for outgoing nucleons in the AMD calculation.

The sub-barrier fusion cross section for the weakly bound neutron system ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$+${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ is discussed in the framework of the coupled-reaction-channel (CRC) approach for the valence neutron in ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ and in connection with the molecular orbital formation. In the calculation we observe a big enhancement of the fusion process as well as the formation of a covalent molecule (${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}+n+{}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$) due to very strong multistep processes in the inelastic and transfer transitions of the active neutron. As a consequence of the strong CRC effects sharp resonances are observed as fine structure of the fusion cross section, in the case that the absorption effects of the internuclear potential are weak.

Important E2 contributions to the (e,${\mathit{e}}^{\prime }$) cross sections of low-lying orbital M1 excitations are found in heavy deformed nuclei, arising from the small energy separation between the two excitations with ${\mathit{I}}^{\mathrm{\pi }}$K=$2^{+}$1 and $1^{+}$1, respectively. They are studied microscopically in QRPA using DWBA. The accompanying E2 response is negligible at small momentum transfer q but contributes substantially to the cross sections measured at θ=165° for 0.6<${\mathit{q}}_{\mathrm{eff}}$<0.9 ${\mathrm{fm}}^{\mathrm{-}1}$ (40≤${\mathit{E}}_{\mathit{i}}$≤70 MeV) and leads to a very good agreement with experiment. The electric response is of longitudinal C2 type for θ≤175° but becomes almost purely transverse E2 for larger backward angles. The transverse E2 response remains comparable with the M1 response for ${\mathit{q}}_{\mathrm{eff}}$≳1.2 ${\mathrm{fm}}^{\mathrm{-}1}$ (${\mathit{E}}_{\mathit{i}}$≳100 MeV) and even dominant for ${\mathit{E}}_{\mathit{i}}$≳200 MeV. This happens even at large backward angles θ≳175°, where the M1 dominance is limited to the lower q region.

With the addition of krypton and silver projectiles we have extended our previous studies of the fragmentation of heavy relativistic nuclei in targets ranging in mass from hydrogen to lead. These projectiles were studied at a number of discrete energies between 450 and $1500A$ MeV. The total and partial charge-changing cross sections were determined for each energy, target, and projectile, and the values compared with previous predictions. A new parametrization of the dependence of the total charge-changing cross sections on the target and projectile is introduced, based on nuclear charge radii derived from electron scattering. We have also parametrized the energy dependence of the total cross sections over the range of energies studied. New parameters were found for a previous representation of the partial charge-changing cross sections in hydrogen and a new parametrization has been introduced for the nonhydrogen targets. The evidence that limiting fragmentation has been attained for these relatively light projectile nuclei at Bevalac energies is shown to be inconclusive, and further measurements at higher energies will be needed to address this question.

Collective interactions in the preequilibrium quark matter and hadronic resonance gas stage of ultrarelativistic nucleus-nucleus collisions are studied in the framework of the transport theoretical approach RQMD. The paper reviews string fusion into color ropes and hadronic rescattering which serve as models for these interactions. Hadron production in central Pb(160A GeV) on Pb collisions has been calculated. The changes of the final flavor composition are more pronounced than in previous RQMD studies of light ion induced reactions at 200A GeV. The ratio of created quark pairs ss¯/(uū+dd¯) is enhanced by a factor of 2.4 in comparison to pp results. Color rope formation increases the initially produced antibaryons to 3 times the value in the ‘‘NN mode,’’ but only one quarter of the produced antibaryons survives because of subsequent strong absorption. The differences in the final particle composition for Pb on Pb collisions compared to S-induced reactions are attributed to the hadronic resonance gas stage which is baryon-richer and lasts longer.

Strong mean meson fields, which are known to exist in normal nuclei, experience a violent deformation in the course of a heavy-ion collision at relativistic energies. This may give rise to a new collective mechanism of the particle production, not reducible to the superposition of elementary nucleon-nucleon collisions. We study the baryon-antibaryon (NN¯,ΛΛ¯,...) pair production under some simplifying assumptions about the space and time variation of meson fields in the nuclear collision process. The mutual deceleration of nuclei is described schematically by introducing the time-dependent relative velocity. For comparison the yield of NN¯ pairs is also calculated within a convolution model assuming the same deceleration scenario. Due to the specific Lorentz structure, the vector meson field turns out to be more efficient for producing pairs than the scalar field. Within the perturbative approach we study two processes: the bremsstrahlung of a virtual meson and the fusion of two virtual mesons, both leading to the baryon-antibaryon final states. The calculated multiplicities of NN¯ and ΛΛ¯ pairs grow fast with the bombarding energy, reaching a saturation above the RHIC energy (√s=200A GeV). At lower energies the coherent production mechanism gives higher pair yields than predicted by microscopic cascade-like models. The rapidity spectra of antibaryons exhibit a characteristic two-hump structure which may serve as an observable signature of the bremsstrahlung mechanism. A strong sensitivity of the predicted yield to the baryon effective mass and the parameters characterizing the stopping power of nuclear matter is demonstrated.

Generalized Cherenkov-like effects based on four fundamental interactions are investigated and classified. Two general Cherenkov-like coherence conditions are found as two natural limiting extremes of the same spontaneous particle emission process in nuclear media. Nuclear pionic and nuclear kaonic Cherenkov-like radiation (NPICR and NKCR) produced by high-energy nucleons passing through a nuclear medium are systematically studied using a quantum theoretical approach. The pion and kaon refractive indices, the pion and kaon phase velocities as well as the NPICR and NKCR thresholds are calculated via the Foldy-Lax multiple scattering formalism having as input the experimental data for the elementary pion-nucleon and kaon-nucleon forward scattering amplitudes. The differential cross sections, the angle-energy correlations, as well as some other essential signatures of coherent pion and kaon production via Cherenkov mechanism with high-energy proton beams are presented. Compressed nuclear media with densities up to five times normal nuclear matter density are taken into account.

QCD sum rules for vector mesons (ρ, ω, φ) in nuclear matter are reexamined with an emphasis on the reliability of various sum rules. Monitoring the continuum contribution and the convergence of the operator product expansion plays a crucial role in determining the validity of a sum rule. The uncertainties arising from less than precise knowledge of the condensate values and other input parameters are analyzed via a Monte Carlo error analysis. Our analysis leaves no doubt that vector-meson masses decrease with increasing density. This resolves the current debate over the behavior of the vector-meson masses and the sum rules to be used in extracting vector meson properties in nuclear matter. We find a ratio of ρ-meson masses of ${\mathit{m}}_{\mathrm{\rho }}^{\mathrm{*}}$/${\mathit{m}}_{\mathrm{\rho }}$=0.78±0.08 at nuclear matter saturation density.

In this paper we discuss the role of chiral symmetry in the description of the nucleon-nucleon interaction. We make use of a generalized Nambu—Jona-Lasinio model which exhibits chiral symmetry at the quark level and demonstrate how the various components of the boson-exchange model of the nucleon-nucleon interaction arise in this model. In this paper we make use of our recent analysis of correlated two-pion exchange. We have found that when correlated two-pion exchange is represented by an effective low-mass sigma meson, that meson may be seen to be the chiral partner of the pion. (That result pertains if the meson momentum $q$ is spacelike such that $t=q^2<0\mathrm{}$.) We give particular attention to the vertex functions appearing in the boson-exchange model. For monopole forms of the vertex functions the cutoff parameter ${\Lambda }^{\mathrm{OBE}}$ varies from about 1.3 GeV to 2.0 GeV. In our model the nucleon form factors are characterized by a parameter $\lambda$. We show how large cutoff parameters, such as ${\Lambda }^{\mathrm{OBE}}$, can arise in our analysis even if the meson-nucleon vertex is soft, with a characteristic cutoff of about 800 MeV. We present the values of $\lambda$ that puts the NJL analysis in good agreement with the boson-exchange model of the nucleon-nucleon force.

Mass shift of vector mesons in the nuclear medium is studied in two different approaches: the in-medium QCD sum-rule approach and the scattering-length approach. The latter is shown to be inapplicable to extract the hadron masses in the medium. Further elaboration of the in-medium QCD sum rules is also discussed.

We reexamine the predictions of a two-phase model of shadowing in nuclear deep-inelastic scattering in light of new NMC data on the x, A, and ${\mathit{Q}}^2$ dependence of the ratios of structure functions. The model, which combines vector meson dominance at low ${\mathit{Q}}^2$ with diffractive Pomeron exchange for large ${\mathit{Q}}^2$, agrees with the observed small, but nonzero, slopes in log${\mathit{Q}}^2$, which indicate the importance of higher twist shadowing effects in the transition region, 0.1≲${\mathit{Q}}^2$≲1 ${\mathrm{GeV}}^2$. We note also that the latest E665 data on the deuteron to proton ratio suggests the presence of a small amount of shadowing in the deuteron.

We discuss a mapping procedure from a space of colorless three-quark clusters into a space of elementary baryons and illustrate it in the context of a three-color extension of the Lipkin model recently developed. Special attention is addressed to the problem of the formation of unphysical states in the mapped space. A correspondence is established between quark and baryon spaces and the baryon image of a generic quark operator is defined both in its Hermitian and non-Hermitian forms. Its spectrum (identical in the two cases) is found to consist of a physical part containing the same eigenvalues of the quark operator in the cluster space and an unphysical part consisting only of zero eigenvalues. A physical subspace of the baryon space is also defined where the latter eigenvalues are suppressed. The procedure discussed is quite general and applications of it can be thought also in the correspondence between systems of 2n fermions and n bosons.

QCD sum rules are used to calculate the ${\mathit{q}}^2$ dependence of the πNN coupling ${\mathit{g}}_{\mathrm{\pi }\mathit{NN}}$(${\mathit{q}}^2$) in the spacelike region 0.5 ${\mathrm{GeV}}^2$≲${\mathit{q}}^2$≲1.5 ${\mathrm{GeV}}^2$. We study the Borel sum rule for the three point function of one pseudo- scalar and two nucleon currents up to order 4 in the operator product expansion. The Borel transform is performed with respect to the nucleon momenta, whereas the momentum ${\mathit{q}}^2$ of the pseudoscalar vertex is kept fixed at spacelike values. The results can be well fitted using a monopole form with a cutoff mass of about ${\mathrm{\Lambda }}_{\mathrm{\pi }}$≊800 MeV.