We investigate two-proton correlation functions for reactions in which fast dynamical and slow evaporative proton emission are both present. In such cases, the width of the correlation peak provides the most reliable information about the source size of the fast dynamical component. The maximum of the correlation function is sensitive to the relative yields from the slow and fast emission components. Numerically inverting the correlation function allows one to accurately disentangle fast dynamical from slow evaporative emission and extract details of the shape of the two-proton source.

Further improvements and refinements are brought to the microcanonical multifragmentation model [Al. H. Raduta and Ad. R. Raduta, Phys. Rev. C 55, 1344 (1997); 61, 034611 (2000)]. This version of the model is tested on the recently published experimental data concerning the Xe+Sn at 32 MeV/nucleon and Gd+U at 36 MeV/nucleon reactions. A remarkable good simultaneous reproduction of fragment size observables and kinematic observables is to be noted. It is shown that the equilibrated source can be unambiguously identified.

Using the Warsaw cyclotron beam we have determined barrier distributions from the quasielastic scattering of ${}^{16}\mathrm{O}$ on ${}^{116,119}\mathrm{Sn}$ targets. They turned out to be similar in both systems. To improve the signal/noise ratio, digital filters were applied in the data analysis procedure and are discussed in detail. Experimental results were compared with coupled-channels calculations performed using the FRESCO code. Reasonable agreement between experiment and theory was obtained but some disagreements remain.

A theoretical model of one-body nuclear friction, which was developed earlier, namely, the chaos-weighted wall formula, is applied to a dynamical description of compound nuclear decay in the framework of the Langevin equation coupled with statistical evaporation of light particles and photons. We have used both the usual wall formula friction and its chaos-weighted version in the Langevin equation to calculate the fission probability and prescission neutron multiplicity for the compound nuclei ${}^{178}\mathrm{W},$ ${}^{188}\mathrm{Pt},$ ${}^{200}\mathrm{Pb},$ ${}^{213}\mathrm{Fr},$ ${}^{224}\mathrm{Th},$ and ${}^{251}\mathrm{Es}.$ We have also obtained the contributions of the presaddle and postsaddle neutrons to the total prescission multiplicity. A detailed analysis of our results leads us to conclude that the chaos-weighted wall formula friction can adequately describe the fission dynamics in the presaddle region. This friction, however, turns out to be too weak to describe the postsaddle dynamics properly. This points to the need for a suitable explanation for the enhanced neutron emission in the postsaddle stage of nuclear fission.

Using a multiphase transport model, we study $J/\psi$ production from interactions between charm and anticharm quarks in the initial parton phase and between D and $\overline{D}$ mesons in the final hadron phase of relativistic heavy ion collisions at the relativistic heavy ion collider. Including also the inverse reactions of $J/\psi$ absorption by gluons and light mesons, we find that the net number of $J/\psi$ from the parton and hadron phases is smaller than that expected from the superposition of initial nucleon-nucleon collisions, contrary to the $J/\psi$ enhancement predicted by the kinetic formation model. The production of $J/\psi$ is further suppressed if one includes the color screening effect in the parton phase. We have also studied the dependence of $J/\psi$ production on the charm quark mass and the effective charm meson mass.

The orthogonal transformation from the spin representation to the pseudospin representation for the nucleon-nucleon scattering matrix is derived. The phase shifts and mixing angles are calculated in the pseudospin representation using the measured phase shifts and mixing angles in the spin representation. The scattering matrix in both representations is investigated and the extent of spin and pseudospin symmetry violation is determined. Finally, a speculation is made that the pseudospin symmetry generators relevant for relativistic mean field models and optical models may need to be generalized for the two-nucleon interaction.

The equations for the pseudospin pair levels become of the same form as those of the spin pair levels at the limit where the derivatives of potentials are zero. However, the centrifugal terms of four amplitudes among eight components in the pseudospin pair levels have pseudo-$l_z,$ while those in the spin pair-levels have natural $l_z.$ When both of the pseudospin and spin symmetries are well satisfied, there appears a triple degeneracy. The relativistic mean-field calculation over ${}^{154}\mathrm{Sm}$ gives [400]1/2, [402]3/2, and [402]5/2 levels as such a candidate. The relation between the deformed wave function and the spherical wave function are discussed at the spherical limit by using the transformation from the cylindrical coordinate into the polar coordinate.

In order to study the effects of heavy projectile neutron number on complete fusion with a well-deformed target, we have measured the excitation functions of the evaporation residue cross sections for $xn,$ $pxn,$ and $\alpha \mathrm{xn}$ channels $(x=2\mathrm{}–6)$ by using the JAERI recoil mass separator in the reactions of ${}^{60}\mathrm{Ni}{+}^{154}\mathrm{Sm}$ and ${}^{64}\mathrm{Ni}{+}^{154}\mathrm{Sm}$ at energies around the Coulomb barrier. In the ${}^{64}\mathrm{Ni}$-induced reaction, the evaporation residue cross section was larger by about two orders of magnitude than that in the ${}^{60}\mathrm{Ni}$-induced reaction. This is mainly due to the exit channel effect of the small neutron separation energy in the more neutron-rich compound nucleus. The fusion probability has been obtained from the calculated survival probability, which had agreed with the evaporation residue cross sections measured in the same compound nucleus system of ${}^{32}\mathrm{S}{+}^{182}\mathrm{W}.$ No obvious difference in the extracted fusion probability between the ${}^{64}\mathrm{Ni}$- and ${}^{60}\mathrm{Ni}$-induced fusion reactions was observed in the excitation functions. In both reaction systems, the fusion probabilities at the lowest energies, where collisions only at the tip of the deformed ${}^{154}\mathrm{Sm}$ nucleus are possible, were significantly smaller than the coupled channel calculation by three orders of magnitude. On the other hand, fusion hindrance was negligible at higher energies where side collisions with the deformed ${}^{154}\mathrm{Sm}$ become possible. This is consistent with our previous conclusion that tip collisions need some extra kinetic energy over the fusion barrier in order to fuse, while side collisions lead to complete fusion without such extra energy.

We study the ratio of differential cross sections $d\sigma {/dE}_T$ of $J/\psi$ to minimum bias event samples in Pb-Pb collisions at SPS energy. The NA50 data exhibit a sharp turnover at $E_T\sim 100\hspace{0.5em}\mathrm{GeV}$ (close to the knee of the $E_T$ distribution) followed by a steady, steep decrease at larger $E_T.$ We show that this behavior can be explained by the combined effects of a small decrease of the hadronic $E_T$ in the $J/\psi$ event sample (due to the $E_T$ taken by the $J/\psi$ trigger), together with a sharp decrease of the $E_T$ distributions in this $E_T$ region (tail). This phenomenon does not affect the (true) ratio of $J/\psi$ to DY differential cross sections (obtained by the NA50 standard analysis), but it does affect the one obtained by the so-called minimum-bias analysis. A good agreement is obtained with the data coming from both analysis—as well as with those on the ratios of $J/\psi$ and DY to minimum-bias differential cross sections – in the whole $E_T$ region.

We describe the $\pi \overrightarrow{N}\omega N$ cross section from threshold to a center-of-mass energy of 2 GeV in a unitary coupled-channel model and analyze it in terms of rescattering and resonance excitations. The amplitude is mainly composed of $D_{13},$ $P_{13},$ and $P_{11}$ contributions, where the $D_{13}$ dominates over the complete considered energy range. We also outline the generalization of the standard partial-wave formalism necessary for the decomposition of the $\omega N$ final state.

We calculate the imaginary part of the retarded two-loop self-energy of a static vector boson in a plasma of quarks and gluons at a temperature T, using the imaginary time formalism. We recombine the various cuts of the self-energy to generate physical processes. We demonstrate how cuts containing loops may be reinterpreted in terms of interference between the $O\left(\alpha \right)$ tree diagrams and the Born term along with spectators from the medium. We apply our results to the rate of dilepton production in the limit of dilepton invariant mass $E\gg T.\mathrm{}$ We find that all infrared and collinear singularities cancel in the final result obtained in this limit.

We present an example of a partial dynamical symmetry (PDS) in an interacting fermion system and demonstrate the close relationship of the associated Hamiltonians with a realistic quadrupole-quadrupole interaction, thus shedding light on this important interaction. Specifically, in the framework of the symplectic shell model of nuclei, we prove the existence of a family of fermionic Hamiltonians with partial SU(3) symmetry. We outline the construction process for the PDS eigenstates with good symmetry and give analytic expressions for the energies of these states and $E2\mathrm{}$ transition strengths between them. Characteristics of both pure and mixed-symmetry PDS eigenstates are discussed and the resulting spectra and transition strengths are compared to those of real nuclei. The PDS concept is shown to be relevant to the description of prolate, oblate, as well as triaxially deformed nuclei. Similarities and differences between the fermion case and the previously established partial SU(3) symmetry in the interacting boson model are considered.

The isotope ${}^{178}\mathrm{Tl}$ was produced in a bombardment of ${}^{102}\mathrm{Pd}$ by ${}^{78}\mathrm{Kr}$ ions at 340 MeV. Reaction products were separated from the beam by the Berkeley Gas-Filled Separator, and implanted into a silicon strip detector where the subsequent $\alpha$ decays were measured. Four distinct $\alpha$ transitions from ${}^{178}\mathrm{Tl}$ were observed correlated to 6.54 MeV $\alpha$ decays from the previously known ${}^{174}\mathrm{Au}$ daughter. In some cases, the ${}^{174}\mathrm{Au}$ decay was followed by a 5.815-MeV $\alpha$ decay. This new transition is tentatively assigned to the decay of the ${}^{170}\mathrm{Ir}$ ground state. The half-life of ${}^{178}\mathrm{Tl}$ was measured to be ${254}_{-9}^{+11\mathrm{}}\hspace{0.5em}\mathrm{ms}.$ The $\alpha$ decay branch of ${}^{174}\mathrm{Au}$ was determined to be 90(6)%.

The nucleus ${}^{66}\mathrm{Zn}$ is investigated using $\gamma \gamma$-coincidence studies following the $\beta$ decay of the $0^{+}$ ground state of ${}^{66}\mathrm{Ga}.$ The data survey short-lived $J^{\pi }{=1\mathrm{}}^{+}{,2\mathrm{}}^{+}$ states, $E2/M1\mathrm{}$ mixing ratios, and, together with the previously known lifetimes, also absolute transition strengths $B\left(\sigma L\right).\mathrm{}$ The proton-neutron mixed-symmetry states $2_{\mathrm{ms}}^{+}$ (isovector quadrupole excitation) and $1_{\mathrm{ms}}^{+}$ (“scissors mode”) were identified from their decay patterns and absolute transition strengths. A $\gamma$ transition between these mixed-symmetry states was observed and its rate is discussed. We additionally present a candidate for the two-phonon $2_{2,ms}^{+}$ state, whose structure is closely related to the $1_{\mathrm{ms}}^{+}$ excitation. Fifteen $M1\mathrm{}$ and $E2\mathrm{}$ strengths involving mixed-symmetry states show a reasonable agreement with the prediction of the pure O(6) limit of the proton-neutron extension of the interacting boson model (IBM-2) using the effective quadrupole boson charges $e_{\pi }{+e}_{\nu }$ and the g-factor difference $g_{\pi }-g_{\nu }$ as the only free parameters.

The properties of the pairing interaction in the shell model framework are considered with the aid of an exact numerical solution utilizing the quasispin symmetry. We emphasize the features which are out of reach for the usual approximate techniques based on the BCS approach supplemented by the random phase approximation treatment of pair vibrations, especially in the region of weak pairing where the BCS plus random-phase-approximation theory fails. Chaotic aspects of the mixing generated by the pairing interaction are studied. The level repulsion and large information entropy of the eigenstates coexist with the absence of thermalization of single-particle motion. The full spectrum of pair vibration on average displays a spin dependence similar to that for a rigid rotor.

A microscopic study of ${}^{12}\mathrm{C}{-}^{12}\mathrm{C}$ elastic scattering at 1.016, 1.449, and 2.4 GeV has been made within the framework of the Coulomb modified Glauber model. The elastic S-matrix element has been evaluated considering the first two terms of the nuclear phase expansion series and using the realistic densities for the colliding nuclei. The effect of the phase variation of the NN scattering amplitude on the calculated elastic scattering differential cross sections has been studied. We find that a very good description of the experimental data at 1.016 and 1.449 GeV is achieved by considering the second order term of the phase expansion series and the phase variation of the NN scattering amplitude. However, at 2.4 GeV, although the second order phase term provides some improvement over the optical limit calculation, still the theoretical situation remains unsatisfactory.

A practical method based on Mayer’s cluster expansion to calculate critical values for a quark-gluon plasma (QGP) phase transition to hadrons is represented. It can be applied to a high-temperature QGP for clustering of quarks to mesons and baryons. The potential used is the Cornell potential, i.e., a potential containing both confining and gluon exchange terms. Debye screening effects are included. An equation of state (EOS) for hadron production is found by analytical methods, which is valid near the critical point. The example of the formation of $J/\psi$ and Υ is recalculated. It is shown that in the range of temperatures available by today’s accelerators, the latter particles are suppressed. This is further confirmation for heavy quarkonia suppression and, hence, for a signature of a QGP. The EOS presented here also shows that in future colliders there will be no heavy quarkonia production by the mechanism of phase transition. Hence, if there will be heavy quarkonia production, it must be based on some other mechanisms, perhaps on the basis of some recently suggested possibilities.

At high energies a quark-gluon plasma is expected to be formed in heavy-ion collisions at the Relativistic Heavy-Ion Collider and the Large Hadron Collider. The theoretical description of these processes is directly associated to a complete knowledge of the details of medium effects in the nuclear gluon distribution. In this paper we analyze the possibility to constrain the behavior of this distribution considering peripheral heavy ion collisions. We reanalyze the photoproduction of heavy quarks for the deduction of the in-medium gluon distribution using three current parametrizations for this parton distribution. Moreover, we show that the elastic photoproduction of vector mesons is a potential process to probe the nuclear gluon distribution.

For cylindrical systems endowed with a longitudinal Bjorken scaling expansion, the semiclassical linear sigma model is employed to calculate the self-consistent dynamical evolution from the initially hot configuration towards the asymptotic state of freely moving pions. The correlation function for charge-conjugate soft pions with similar rapidities and transverse energies exhibits pronounced azimuthal anticorrelations that may be used to probe the nonequilibrium chiral relaxation dynamics.

The antikaon optical potential in hot and dense nuclear matter is studied within the framework of a coupled-channel self-consistent calculation taking, as bare meson-baryon interaction, the meson-exchange potential of the Jülich group. Typical conditions found in heavy-ion collisions at GSI are explored. As in the case of zero temperature, the angular momentum components larger than $L=0\mathrm{}$ contribute significantly to the finite temperature antikaon optical potential at finite momentum. It is found that the particular treatment of the medium effects has a strong influence on the behavior of the antikaon potential with temperature. Our self-consistent model, in which antikaons and pions are dressed in the medium, gives a moderately temperature dependent antikaon potential which remains attractive at GSI temperatures, contrary to what one finds if only nuclear Pauli blocking effects are included.