The new Hamiltonians USDA and USDB for the $\mathit{sd}$ shell are used to calculate $M1$ and $E2$ moments and transition matrix elements, Gamow-Teller $\beta$-decay matrix elements, and spectroscopic factors for $\mathit{sd}$-shell nuclei from $A=17$ to $A=39$. The results are compared with those obtained with the older USD Hamiltonian and with experiment to explore the interaction sensitivity of these observables.

We calculate medium photons due to Compton and annihilation processes in an anisotropic media. The effects of time-dependent momentum-space anisotropy of quark-gluon plasma (QGP) on the medium photon production are discussed. Such an anisotropy can result from the initial rapid longitudinal expansion of the matter, created in relativistic heavy ion collisions. A phenomenological model for the time-dependence of the parton hard momentum scale, $p_{\mathrm{hard}}(\tau )$, and anisotropy parameter, $\xi (\tau )$, has been used to describe the plasma space-time evolution. We find significant dependency of photon yield on the isotropization time (${\tau }_{\mathrm{iso}}$). It is shown that the introduction of early time momentum-space anisotropy can enhance the photon production by a factor of $10(1.5)$ (in the central rapidity region) for the free streaming (collisionally-broadened) interpolating model if we assume fixed initial condition. On the other hand, enforcing the fixed final multiplicity significantly reduces the enhancement of medium photon production.

We investigate photoproduction of $\eta$ mesons off protons and neutrons within a coupled-channels effective-Lagrangian method that is based on the $\mathsf{K}$-matrix approach. The two-body final channels included are $\pi N$, $\eta N$, $\varphi N$, $\rho N$, $\gamma N$, $K\Lambda$, and $K\Sigma$. Nonresonant meson-baryon interactions are included in the model via nucleon intermediate states in the $s$ and $u$ channels and meson exchanges in the $t$-channel amplitude and the $u$-channel resonances. The nucleon resonances $S_{11}(1535)$, $S_{11}(1650)$, $S_{31}(1620)$, $P_{11}(1440)$, $P_{11}(1710)$, $P_{13}(1720)$, $P_{33}(1232)$, $P_{33}(1600)$, $D_{13}(1520)$, $D_{13}(1700)$, and $D_{33}(1700)$ are included explicitly in calculations. Our model describes simultaneously the available data as well on total and differential cross sections as on beam and target asymmetries. This holds for the $\gamma p\to \eta p$ reaction for photon energies ranging from very close to threshold to up to 3 GeV. The polarization observables show strong sensitivity to resonances that otherwise contribute only weakly to the total cross section. It is found that the pronounced bumplike structure seen in the excitation function of the $\gamma n\to \eta n$ cross section at $\gamma$ energies around 1 GeV can be explained by the interference effects of $S_{11}$, $P_{11}$, and $P_{13}$ resonance contributions.

Within an effective nonlinear chiral model, we evaluate nuclear matter parameters exploiting the uncertainties in the nuclear saturation properties. The model is sternly constrained with minimal free parameters, which display the interlink among nuclear incompressibility ($K$), the nucleon effective mass ($m^{\star }$), the pion decay constant ($f_{\pi }$), and the σ-meson mass ($m_{\sigma }$). The best fit among the various parameter set is then extracted and employed to study the resulting equation of state (EOS). Further, we also discuss the consequences of imposing constraints on the nuclear EOS from heavy-ion collision and other phenomenological model predictions.

High-spin structures in the neutron-rich ${}^{108}\mathrm{Tc}$ nucleus have been reinvestigated by measuring the prompt $\gamma$-rays from spontaneous fission of ${}^{252}\mathrm{Cf}$. A previously known collective band has been extended up to higher spin states and a new side band has been identified. These doublet bands are proposed as pseudospin partner bands with configurations $\pi 1/2^{+}[431]\otimes \nu [\widetilde{312}\hspace{0.5em}5/2^{+},3/2^{+}]$, which is a first identification in $A~100$ region. The particle-rotor model (PRM) was applied to calculate levels and $B(M1)/B(E2)$ ratios of the bands in ${}^{108}\mathrm{Tc}$. The calculated results are in good agreement with the experimental values.

The surrogate ratio method was used to convert experimentally determined relative $\gamma$-decay probabilities for excited ${}^{171}\mathrm{Yb}$ and ${}^{161}\mathrm{Dy}$ nuclei, populated using (${}^3\mathrm{He}$, ${}^3{\mathrm{He}}^{\text{'}}$) and (${}^3\mathrm{He}$, $\alpha$) reactions, into neutron-induced $\gamma$-decay cross sections in an equivalent neutron energy range of 165–465 keV. The relative $\gamma$-decay probabilities were measured using the CACTUS array at the Oslo Cyclotron Laboratory and were found to agree with the ratio of neutron-induced $\gamma$-decay cross sections for the same compound nuclei over the range of excitation energies measured. No significant entrance-channel effects on the extracted ($n,\gamma$) cross sections were observed. The cross sections obtained using the surrogate ratio method were compared to directly measured neutron-capture cross sections and found to agree within the total estimated uncertainty over the range of equivalent neutron energies measured.

It is increasingly important to understand, in detail, two-pion correlations measured in $p+p$ and $d+A$ collisions. In particular, one wishes to understand the femtoscopic correlations to compare to similar measurements in heavy-ion collisions. However, in the low-multiplicity final states of these systems, global conservation laws generate significant $N$-body correlations that project onto the two-pion space in nontrivial ways and complicate the femtoscopic analysis. We discuss a formalism to calculate and account for these correlations in collisions dominated by a single particle species (e.g., pions). We also discuss effects on two-particle correlations between nonidentical particles, the understanding of which may be important in the study of femtoscopic space-time asymmetries.

Model calculations that include the effects of irreversible, environmental couplings on top of a coupled-channels dynamical description of the collision of two complex nuclei are presented. The Liouville-von Neumann equation for the time evolution of the density matrix of a dissipative system is solved numerically providing a consistent transition from coherent to decoherent (and dissipative) dynamics during the collision. Quantum decoherence and dissipation are clearly manifested in the model calculations. Energy dissipation, due to the irreversible decay of giant-dipole vibrational states of the colliding nuclei, is shown to result in a hindrance of quantum tunneling and fusion.

Evidence for the dependence of excitation energy sharing between two heavy remnants on the difference in the lost mass in two-body peripheral heavy ion reactions at Fermi energy is presented, based on experimental results for the reactions ${}^{93}\mathrm{Nb}$$+$${}^{116}\mathrm{Sn}$, ${}^{116}\mathrm{Sn}$$+$${}^{93}\mathrm{Nb}$, and ${}^{93}\mathrm{Nb}$$+$${}^{93}\mathrm{Nb}$ at $38A$ MeV. An observable based on the experimental velocities of the heavy residues is used to select reactions with equal preevaporative masses of projectile-like fragments and target-like fragments. The excitation energy, evaluated by means of a complete average calorimetry, is found to be larger for the nucleus that finally retains a larger part of the hot interaction region.

We present results of a two-pion correlation analysis performed with the $\mathrm{Pb}+\mathrm{Au}$ collision data collected by the upgraded CERES experiment in the fall of 2000. The analysis was done in bins of the reaction centrality and the pion azimuthal emission angle with respect to the reaction plane. The pion source, deduced from the data, is slightly elongated in the direction perpendicular to the reaction plane, similarly as was observed at the Brookhaven National Laboratory Alternating Gradient Synchrotron and Relativistic Heavy Ion Collider.

Transverse-mass spectra of protons, pions, and kaons produced in collisions of heavy nuclei are analyzed within the model of three-fluid dynamics. It was demonstrated that this model consistently reproduces these spectra in wide ranges of incident energies, $4A$ GeV $\lesssim E_{\mathrm{lab}}\lesssim 160A$ GeV, rapidity bins, and centralities of the collisions. In particular, the model describes the “step-like” dependence of kaon inverse slopes on the incident energy. The key point of this explanation is interplay of hydrodynamic expansion of the system with its dynamical freeze-out.

Gamma-ray branching ratios of the 7.12-MeV state in ${}^{16}\mathrm{O}$ have been measured using the $\gamma \text{−}\gamma$ coincidence technique. The extrapolations of several components of the important ${}^{12}\mathrm{C}$($\alpha ,\gamma$)${}^{16}\mathrm{O}$ cross section to helium-burning energies are dependent upon the $7.12\to 6.92$ MeV branching ratio. An experimental upper limit has been placed on this transition; the $7.12\to 6.13$ MeV branching ratio has also been measured. Relative cross sections and $\gamma$-ray angular distributions have been measured for the ${}^{19}\mathrm{F}$($p,\alpha \gamma$) reaction at several energies near $E_p=2$ MeV, leading to the 6.13-, 6.92-, and 7.12-MeV states of ${}^{16}\mathrm{O}$. Monte Carlo simulations of the various detectors have been developed and the simulated detector efficiencies have been compared and adjusted to experimental measurements. The available experimental data relating to the ${}^{12}\mathrm{C}$($\alpha ,\gamma$)${}^{16}\mathrm{O}$ cross section have been fitted with the $R$-matrix formalism. The new upper limit on the $7.12\to 6.92$ MeV branching ratio impacts the extrapolation of both the $E2$ ground-state cross section and the cascade cross section through the 6.92-MeV state.

The role of system size and momentum dependent effects are analyzed in multifragmenation by simulating symmetric reactions of $\mathrm{Ca}+\mathrm{Ca}$, $\mathrm{Ni}+\mathrm{Ni}$, $\mathrm{Nb}+\mathrm{Nb}$, $\mathrm{Xe}+\mathrm{Xe}$, $\mathrm{Er}+\mathrm{Er}$, $\mathrm{Au}+\mathrm{Au}$, and $\mathrm{U}+\mathrm{U}$ at incident energies between 50 MeV/nucleon and 1000 MeV/nucleon and over full impact parameter zones. Our detailed study reveals that there exists a system size dependence when the reaction is simulated with momentum dependent interactions. This dependence exhibits a mass power law behavior.

The light-quark nonstrange scalar mesons $a_0(980)$, $f_0(980)$, $f_0(1370)$, $a_0(1450)$, $f_0(1500)$, and $f_0(1710)$ are of great interest because there is no generally accepted view of their structure that can encompass $\mathit{qq}\overline{q}\overline{q}$, molecular, $q\overline{q}$, and glueball states in various combinations. It has been shown previously that the radiative decay of the scalar mesons to ρ and ω is a good probe of their structure and provides good discrimination among models. Scalar meson photoproduction is proposed as an alternative to measuring radiative decay, and it is shown to be a feasible proposition.

We study the validity of the substitution of interaction cross sections for total reaction cross sections for a nucleus incident on a target nucleus at relativistic energies. We show that, for incident stable nuclei, the predicted difference between interaction and total reaction cross sections is large enough to probe the nuclear structure, particularly in a mass region of less than around 40. For analyses of the difference, we construct “pseudo data” for the reaction cross sections because empirical data are very limited at high energies. The construction of the pseudo data is based on our assumption that empirically unknown total reaction cross sections are precisely predicted by the phenomenological black-sphere model of nuclei that we developed recently. The comparison with the empirical interaction cross sections suggests a significant difference between the reaction and interaction cross sections for stable projectiles on a carbon target, which is of the order of 0–100 mb.

The systematics of the giant dipole resonance (GDR) widths in hot and rotating nuclei are studied in terms of temperature $T$, angular momentum $J$, and mass $A$. The different experimental data in the temperature range of $1-2$ MeV have been compared with the thermal shape fluctuation model (TSFM) in the liquid drop formalism using a modified approach to estimate the average values of $T$, $J$, and $A$ in the decay of the compound nucleus. The values of the ground state GDR widths have been extracted from the TSFM parametrization in the liquid drop limit for the corrected $T$, $J$, and $A$ for a given system and compared with the corresponding available systematics of the experimentally measured ground state GDR widths for a range of nuclei from $A=45$ to 194. Amazingly, the nature of the theoretically extracted ground state GDR widths matches remarkably well, though 1.5 times smaller, with the experimentally measured ground state GDR widths consistently over a wide range of nuclei.

The polarization potential for the elastic scattering of ${}^{6,7}\mathrm{Li}$ $+$ ${}^{28}\mathrm{Si}$ at near barrier energies has been investigated in the context of an optical model framework. The effect on the elastic scattering was found to be strong, energy dependent, and compatible with the transfer channel.

Magnetic dipole transitions in ${}^{17}\mathrm{C}$ are investigated by shell model calculations. The important role of the tensor interaction for magnetic dipole transitions in this exotic neutron-rich nucleus is pointed out. The recently observed anomalous quenching of the magnetic dipole transition in $1/2_1^{+}$ $\to 3/2_{\mathrm{g}.\mathrm{s}.}^{+}$ is shown to be well explained by using a modified shell model Hamiltonian that takes full account of the tensor force and monopole corrections in the isospin $T=1$ channel. The predicted quadrupole moment of ${}^{17}\mathrm{C}$ is smaller than the value obtained by conventional shell model Hamiltonians.