The peripheral and semiperipheral reactions in ${}^{35}\mathrm{Cl}{+}^{197}\mathrm{Au}$ have been studied at 30 and 43 MeV/nucleon. The nonequilibrium $\alpha$ and IMF components have been observed in the experiment. The fraction of nonequilibrium emission decreases with an increase in the atomic number of the projectilelike fragments but, for a given projectilelike fragment, it increases with the charge of the emitted particles. The characteristics of quasiprojectiles reconstructed from their decay products reveal several features reminiscent of damped reactions at lower bombarding energies. The atomic number and deflection angle of projectilelike fragments depend strongly on their kinetic energy or dissipated energy. At 30 MeV/nucleon, the experimental data can be explained by a deep inelastic transfer model. One-body dissipation is still the main mechanism for the energy and angular momentum dissipation. However, at 43 MeV/nucleon, deep inelastic transfer models can predict only the experimental tendency. Two-body dissipation plays a more important role at higher incident energies. The similarity observed in the decay product distributions, as a function of excitation energy, suggests that the excited quasiprojectiles formed in binary collisions might approach thermal equilibrium for both incident energies. The decay products have been analyzed with sequential-binary and simultaneous-disassembly statistical decay models. Both statistical models are able to provide good agreement with the experimental observables except for the mean kinetic energy of the products.

We study fragmentation of small atomistic clusters via molecular dynamics. We calculate the time scales related to fragment formation and emission. We also show that some degree of thermalization is achieved during the expansion process, which allows the determination of local temperature. In this way we can calculate the breakup temperature as a function of excitation energy, i.e., the fragmentation caloric curve. Fragmentation appears as a rather constant temperature region of the caloric curve. Furthermore, we show that different definitions of temperature, related to different degrees of freedom, yield very similar values.

Experiments with ${\Xi }^{-}$ atoms are proposed in order to study the nuclear interaction of $\Xi$ hyperons. The production of ${\Xi }^{-}$ in the ${(K}^{-}{,K}^{+})$ reaction, the ${\Xi }^{-}$ stopping in matter, and its atomic cascade are incorporated within a realistic evaluation of the results expected for ${\Xi }^{-}$ x-ray spectra across the periodic table, using an assumed $\Xi$-nucleus optical potential $V_{\mathrm{opt}}.$ Several optimal targets for measuring the strong-interaction shift and width of the x-ray transition to the “last” atomic level observed are singled out: F, Cl, I, and Pb. The sensitivity of these observables to the parameters of $V_{\mathrm{opt}}$ is considered. The relevance of such experiments is discussed in the context of strangeness $-2$ nuclear physics and multistrange nuclear matter. Finally, with particular reference to searches for the H dibaryon, the properties of ${\Xi }^{-}d$ atoms are also discussed. The role of Stark mixing and its effect on S and P state capture of ${\Xi }^{-}$ by the deuteron together with estimates of the resulting probability for producing the H dibaryon are considered in detail.

Recently observed rare heavy ion fusion processes, where the entire available energy is carried away by a single pion, is an example of extreme collectivity in nuclear reactions. We calculate the cross section in the approximation of sudden overlap, modeling the initial and final nuclei by moving harmonic oscillator potentials. This allows for a fully quantum-mechanical treatment, exact conservation of linear and angular momenta and fulfillment of the Pauli principle. The results are in satisfactory agreement with data. Mass number dependence and general trends of the process are discussed.

Elastic and inelastic scattering of 800 MeV protons from the axially deformed nucleus ${}^{24}\mathrm{Mg}$ is investigated using microscopic relativistic impulse approximation optical potentials in Dirac-coupled channel formalism. A rotational collective model is used to obtain the transition optical potentials for the low-lying excited states of the ground state rotational band. The effect of multistep processes is investigated by including the channel coupling between two excited states in addition to the coupling between the ground state and excited states. The theoretical results agree with the experimental data for the elastic and the $2^{+}$ and $4^{+}$ excited states reasonably well.

Primary decay caloric curves are calculated via a sharp microcanonical multifragmentation model for three representative sample nuclei. In all cases, a plateau corresponding to temperatures of around 5 MeV is manifested for the excitation energy range 2.5 to around 8.5 MeV/nucleon, a fact resembling the experimental evidence and sign of liquid-gas phase transition. Correlations of different parts of the temperature curves with the energy deposited in the availables degrees of freedom and with the relative probabilities of different fragmentation modes are discussed. He-Li isotopic temperatures calculated for the same sample nuclei manifest a similar behavior. Calculated microcanonical and He-Li temperatures are compared with experimental He-Li temperatures.

The NA44 Collaboration has measured charged kaon and pion distributions at midrapidity in sulphur and proton collisions with nuclear targets at 200 and $450\hspace{0.5em}\mathrm{GeV}/c$ per nucleon, respectively. The inverse slopes of kaons, are larger than those of pions. The difference in the inverse slopes of pions, kaons, and protons, all measured in our spectrometer, increases with system size and is consistent with the buildup of collective flow for larger systems. The target dependence of both the yields and inverse slopes is stronger for the sulphur beam, suggesting the increased importance of secondary rescattering for $\mathrm{S}A$ reactions. The rapidity density $dN/dy$ of both $K^{+}$ and $K^{-}$ increases more rapidly with system size than for ${\pi }^{+}$ in a similar rapidity region. This trend continues with increasing centrality, and according to RQMD, it is caused by secondary reactions between mesons and baryons. The $K^{-}{/K}^{+}$ ratio falls with increasing system size but more slowly than the $\overline{p}/p$ ratio. The ${\pi }^{-}/{\pi }^{+}$ ratio is close to unity for all systems. From $p\mathrm{Be}$ to $\mathrm{SPb}$ the $K^{+}/p$ ratio decreases while $K^{-}/\overline{p}$ increases and $\sqrt{{(K}^{+}\cdot K^{-})/(p\cdot \overline{p})}$ stays constant. These data suggest that as larger nuclei collide, the resulting system has a larger transverse expansion and baryon density and an increasing fraction of strange quarks.

Triple-differential cross sections for neutrons from high-multiplicity La-La collisions at 250 and 400 MeV per nucleon and Nb-Nb collisions at 400 MeV per nucleon were measured at several polar angles as a function of the azimuthal angle with respect to the reaction plane of the collision. The reaction plane was determined by a transverse-velocity method with the capability of identifying charged-particles with $Z=1,$ $Z=2,$ and $Z>\mathrm{}2.\mathrm{}$ The flow of neutrons was extracted from the slope at mid-rapidity of the curve of the average in-plane momentum vs the center-of-mass rapidity. The squeeze-out of the participant neutrons was observed in a direction normal to the reaction plane in the normalized momentum coordinates in the center-of-mass system. Experimental results of the neutron squeeze-out were compared with BUU calculations. The polar-angle dependence of the maximum azimuthal anisotropy ratio $r\left(\theta \right)$ was found to be insensitive to the mass of the colliding nuclei and the beam energy. Comparison of the observed polar-angle dependence of the maximum azimuthal anisotropy ratio $r\left(\theta \right)$ with BUU calculations for free neutrons revealed that $r\left(\theta \right)$ is insensitive also to the incompressibility modulus in the nuclear equation of state.

The predictions of event anisotropy parameters from transport model RQMD are compared with the recent experimental measurements for $158A\mathrm{GeV}$ $\mathrm{P}\mathrm{b}+\mathrm{P}\mathrm{b}$ collisions. Using the same model, we study the time evolution of event anisotropy at $2A\mathrm{GeV}$ and $158A\mathrm{GeV}$ for several colliding systems. For the first time, both momentum and configuration space information are studied using the Fourier analysis of the azimuthal angular distribution. We find that, in the model, the combination of the size of the colliding system and nuclear passing time plays a dominant role in determining the behavior of the anisotropy parameters.

Hydrodynamics with cylindrical symmetry in transverse direction and longitudinal scaling flow is employed to calculate the transverse momentum spectra of various hadrons and clusters (e.g., π, K, N, Φ, Λ, d, He) in central heavy-ion collisions at CERN-SPS and BNL-RHIC energies up to $p_T=4\mathrm{}\hspace{0.5em}\mathrm{GeV}.$ We discuss the sensitivity of these spectra with respect to the initial transverse density profile as well as to the choice of “freeze-out” hypersurface. For $\sqrt{s}=18A\hspace{0.5em}\mathrm{GeV}$ (SPS energy) and $p_T<2\mathrm{}\hspace{0.5em}\mathrm{GeV},$ overall good agreement of the $p_T$ distributions with data is found when freeze-out occurs along the $T=130\mathrm{}\hspace{0.5em}\mathrm{MeV}$ isotherm. Even high-$p_T$ neutral pion data can be described for a particular choice of the initial transverse density profile. It is shown that the average transverse velocity $〈v_T〉$ of heavy hadrons and hadronic clusters is a good measure for the collective flow velocity. The latter is found to be rather similar for SPS and RHIC energies, due to the “stall” of the flow within the long-lived mixed phase at RHIC. In the case of thermalization and hydrodynamical expansion, the mean transverse momentum $〈p_T〉$ increases linearly with the hadron mass. In contrast, the string model FRITIOF 7.02, which does not account for rescattering of secondary hadrons, predicts a strong dependence of $〈p_T〉$ on the quark composition of the hadron. Because of the different sensitivity to hard processes, hadrons with charm (anti)quarks acquire significantly more transverse momentum than hadrons without c (or even without $s$) quarks.

A multifractal Bernoulli distribution, which appears by a natural way at some morphological phase transition, is introduced and it is shown that this distribution gives a good fit to the data obtained in laboratory experiments and in a numerical simulation of the particle multiproduction in the heavy ions collisions at high energies.

The energy dependence of the total kaon production cross sections in baryon-baryon $(N$ and $\Delta )$ collisions are studied in the resonance model, which is a relativistic tree-level treatment. This study is the first attempt to complete a systematic consistent investigation of the elementary kaon production reactions for both the pion-baryon and baryon-baryon reactions. Our model suggests that the magnitudes of the isospin-averaged total cross sections for the $N\overrightarrow{N}\mathrm{NYK}$ and $\Delta \overrightarrow{N}\mathrm{NYK}\hspace{0.5em}(Y=\Lambda$ or $\Sigma )$ reactions are almost equal at energies up to about 200 MeV above threshold. However, the magnitudes for the $\Delta N$ reactions become about 6 times larger than those for the $\mathrm{NN}$ reactions at energies about 1 GeV above threshold. Furthermore, the magnitudes of the isospin-averaged total cross sections for the $N\overrightarrow{N}\Delta \mathrm{YK}$ reactions turn out to be comparable to those for the $N\overrightarrow{N}\mathrm{NYK}$ reactions at $\mathrm{NN}$ invariant collision energies about 3.1 GeV, and about 5 to 10 times larger at $\mathrm{NN}$ invariant collision energies about 3.5 GeV. The microscopic cross sections are parametrized in all isospin channels necessary for the transport model studies of kaon production in heavy-ion collisions. These cross sections are then applied in the relativistic transport model to study the sensitivity to the underlying elementary kaon production cross sections.

In fluid dynamical models the freeze-out of particles across a three-dimensional space-time hypersurface is discussed. The calculation of final momentum distribution of emitted particles is described for freeze-out surfaces, with both spacelike and timelike normals, taking into account conservation laws across the freeze-out discontinuity.

In the framework of a model based on nuclear absorption plus comover interaction, we compute the $E_T$ distribution of the $J/\psi$ in PbPb collisions at SPS and compare it with available NA50 data. Our analysis suggests that the existence of new physics (deconfinement phase transition) in the region $E_T\lesssim 100$ GeV is unlikely and that signals of new physics should rather be searched in the region $E_T\gtrsim 100$ GeV. The $E_T$ dependence of the $J/\psi$ transverse momentum has been computed. At large $E_T$ it turns out to be much flatter in the comover approach than in a phase transition framework. Estimates of the $J/\psi$ suppression at RHIC and LHC energies are also given.

The ${}^4\mathrm{He}\hspace{0.5em}\overrightarrow{p}{\hspace{0.5em}}^3\mathrm{H}\hspace{0.5em}\mathrm{pn}{\pi }^{+}$ reaction channel has been investigated at an incident ${}^4\mathrm{He}$ momentum of $8.6\hspace{0.5em}\mathrm{GeV}/c$ in an exclusive approach. It has been shown that the reaction mainly proceeds via $p\overrightarrow{p}\mathrm{pn}{\pi }^{+}$ interaction with $\left(p{\pi }^{+}\right)$ from ${\Delta }^{++},$ while triton is a spectator. The anisotropic angular distribution of the nucleons causes the splitting of ${(}^3\mathrm{H}n)$ invariant mass and leads to a natural separation of the interactions occuring either in proton or ${}^4\mathrm{He}$ vertices. Effects such as the shift of peak position in the $\left(p{\pi }^{+}\right)$ invariant mass distribution have not been observed.

A method to investigate possible loosely bound dibaryon states is suggested. The momentum dependence of a two-pion correlation function is shown to depend on the (non)existence of a bound state.

Nuclei can be described satisfactorily in a nonlinear chiral SU(3) framework, even with standard potentials of the linear σ model. The condensate value of the strange scalar meson is found to be important for the properties of nuclei even without adding hyperons. By neglecting terms which couple the strange to the nonstrange condensate one can reduce the model to a Walecka model structure embedded in SU(3). We discuss inherent problems with chiral SU(3) models regarding hyperon optical potentials.

We study the low-energy spectra of light mesons in the framework of constituent quark models. Several interactions including chiral symmetry breaking and designed for the description of the nucleon-nucleon system and/or the baryon spectra are used. We find that chiral quark models only based on Goldstone boson exchanges are not able to provide a reasonable description of the light meson spectra. However, if they are supplemented with a color-spin term, like the one present in the one-gluon-exchange or instanton-induced potentials, they reproduce in a satisfactory manner the light meson spectra at the same time that they are able to explain the main features of the baryon spectra and the baryon-baryon interaction.

We study the two point correlation function of two nucleon currents sandwiched between the vacuum and the rho meson state. The light cone QCD sum rules are derived for the $\rho \mathrm{NN}$ vector and tensor couplings simultaneously. The contribution from the excited states and the continuum is subtracted cleanly through the double Borel transform with respect to the two external momenta, $p_1^2,$ $p_2^2=(p-{q)}^2.$ Our results are $g_{\rho }=2.5\mathrm{}\pm 0.2,$ ${\kappa }_{\rho }=(8.0\mathrm{}\pm 2.0),$ in good agreement with the values used in the nuclear forces.

We study the two point correlation function of two nucleon currents sandwiched between the vacuum and the pion state. The light cone QCD sum rules are derived for the $\pi \mathrm{NN}$ coupling $g_{\pi \mathrm{NN}}$ and the $\pi \mathrm{NN}\left(1535\right)\mathrm{}$ coupling $g_{\pi {\mathrm{NN}}^{*}}.$ The contribution from the excited states and the continuum is subtracted cleanly through the double Borel transform with respect to the two external momenta $p_1^2,\hspace{0.5em}{p}_2^2=(p-{q)}^2.$ We first improve the original sum rule for $g_{\pi \mathrm{NN}}$ and determine the value of the pion wave function ${\phi }_{\pi }{(u}_0=\frac{1}{2})=1.5\mathrm{}\pm 0.2,$ which is a fundamental nonperturbative quantity similar to the quark condensate. Our calculation shows that the $\pi \mathrm{NN}\left(1535\right)\mathrm{}$ coupling is strongly suppressed.