Background: Since 1919, when Rutherford measured the first nuclear reaction, and 1954, when Feshbach et al. [Phys. Rev. 96, 448 (1954)] proposed the optical model (OM), as the simplest mathematical approach for describing nuclear reactions, a general description for stable, tightly and weakly bound, and exotic nuclei reactions is still missing. The Feshbach OM presents two advantages: (i) it converts a complicated problem of many bodies (nucleons) into a problem of two bodies (nuclei) through an average potential of interaction, and (ii) it proposes a complex (real and imaginary) mathematical description for the so-called optical potential (OP).

Purpose: We propose to study the OP (real and imaginary) strengths and their energy dependence, in reactions involving stable, tightly and weakly bound, and exotic nuclei projectiles on a ${}^{64}\mathrm{Zn}$ target, at energies around the respective Coulomb barriers. We also propose to compare the current results to previous ones obtained for the same projectiles reacting on the heavier ${}^{120}\mathrm{Sn}$ target.

Method: We analyze experimental elastic scattering angular distributions of ${}^{4,6}\mathrm{He}, {}^{6,7}\mathrm{Li}, {}^{9,10,11}\mathrm{Be}$, and ${}^8\mathrm{B}$ impinging on the same (${}^{64}\mathrm{Zn}$) target, at bombarding energies around the respective Coulomb barriers. Within the data set, we report on OM calculations and the determined OP, with the respective uncertainties quantification, based on the double-folding (DF) São Paulo potential (SPP).

Results: Within the SPP approach, we compare the sensitivity of the OM theoretical predictions to different models assumed for the nuclear matter densities and to variations in the OP form factor and strengths. The best-fit parameters from OP study correlate with projectile breakup process, at scattering energies around the Coulomb barrier. Thus, we propose optimum energies for which the projectile breakup yield could be favored, as a function of the projectile breakup $Q$ value and the Coulomb barrier of the system. The results are shown to be systematical, when analyzing different weakly bound nuclei projectiles impinging on targets with different masses (and atomic numbers). As a test of consistency, we apply the method to another specific case: ${}^7\mathrm{Li}+{}^{80}\mathrm{Se}$.

Conclusion: The results represent important advances toward a fundamental mathematical description mainly for weakly bound nuclei reactions. The capability of predicting optimum projectile breakup yields, as a function of energy, represents an important tool for planning new experiments on weakly bound nuclei reactions. The determined OP must be of value for application to further calculations on such nuclei reactions, at energies around the Coulomb barrier, besides studying the OP dependence with energy.

In this paper, we critically examine hierarchies between the energy scales that determine quarkonium dynamics in the quark gluon plasma. A particularly important role is played by the ratio of the binding energy of species ($E_b$) and the medium scales; temperature ($T$) and Debye mass ($m_D$). It is well known that if these ratios are much larger than 1 then the dominant process governing quarkonium evolution is dissociation by thermal gluons (gluodissociation). On the other hand, if the ratio $E_b/T$ is much smaller than one then quarkonium dynamics is dominated by screening and Landau damping of the exchanged gluons. Here we show that over most of the evolution, the scale hierarchies do not fall in either limit and one needs to use the full structure of the gluonic spectral function to follow the dynamics of the $Q\overline{Q}$ pair. This has a significant bearing when we follow the quantum dynamics of quarkonia in the medium. The inverse medium relaxation time is also $\approx T$ and if $E_b$ is comparable (or larger) in magnitude to $T$, the quantum evolution of $Q\overline{Q}$ is nonlocal in time within the Brownian approximation.

We analyze the isospin equilibration properties of neutrinoless nuclear ($npe$) matter in the temperature and density range that is relevant to neutron star mergers. Our analysis incorporates neutrino-transparency corrections to the isospin (“beta”) equilibrium condition which become noticeable at $T\gtrsim 1\text{MeV}$. We find that the isospin relaxation rate rises rapidly as temperature rises, and at $T\approx 5\text{MeV}$ it is comparable to the timescale of the density oscillations that occur immediately after the merger. This produces a resonant peak in the bulk viscosity at $T\approx 5\text{MeV}$, which causes density oscillations to be damped on the timescale of the merger. Our calculations suggest that isospin relaxation dynamics may also be relevant when neutrinos are treated more accurately via neutrino transport schemes.

Background: The understanding of the impact of initial deformation and collision orientation on quasifission and fusion-fission reactions remains incomplete.

Purpose: This paper aims to explore how the orientation of deformed nuclei influences quasifission and fusion-fission reactions around $1.2V_B$, employing a microdynamical method in systems with diverse shapes, namely ${}^{24}\mathrm{Mg}+{}^{178}\mathrm{Hf}, {}^{34}\mathrm{S}+{}^{168}\mathrm{Er}$, and ${}^{48}\mathrm{Ti}+{}^{154}\mathrm{Sm}$.

Method: Utilizing the Boltzmann-Uehling-Uhlenbeck model, this paper investigates quasifission and fusion-fission reactions. The model elucidates microdynamic processes and microscopic observables through the definition of the window and event-by-event simulations.

Results: The findings reveal that the orientation of deformed nuclei significantly influences the nucleus-nucleus interaction potential, thereby impacting the competition between quasifission and fusion-fission reactions. Particularly, the orientation of the deformed target nucleus emerges as the primary factor affecting this competition. Notably, a higher proportion of fusion-fission events is observed when the target nucleus is in the belly orientation compared to the tip orientation. The paper also observes that the configuration of the dinuclear system contributes to fluctuations and dissipation. Collisions with different orientations result in distinct dinuclear system configurations, with belly-oriented collisions leading to larger fluctuations between events, while tip-oriented collisions exhibit smaller fluctuations.

Conclusions: Considering diverse orientations of nuclei with distinct initial deformations, this paper concludes that the orientation of the target nucleus is the key factor influencing quasifission and fusion-fission reactions around $1.2V_B$.

Measurements of the ${}^6\mathrm{Li}+{}^9\mathrm{Be}$ collision above the Coulomb barrier ($E_{\mathrm{lab}}=11.2$ MeV; $V_{\mathrm{Cou}}^{\mathrm{lab}}=3.2$ MeV) were performed using the ${}^6\mathrm{Li}$ secondary beam selected by the RIBRAS (Radioactive Ion Beams in Brasil) first solenoid. The total reaction cross section was obtained from the ${}^6\mathrm{Li}+{}^9\mathrm{Be}$ elastic scattering angular distribution, measured in the same experiment and analyzed by optical model calculations [U. Umbelino et al., Phys. Rev. C 106, 054602 (2022)]. Proton, deuteron, triton, and $\alpha$ yields were measured at angles around ${45}^{\circ }$ in the laboratory and total fusion cross sections were deduced from the comparison between compound nucleus calculations and the measured light particle yields. The difference between the total reaction cross section and the obtained total fusion cross section provided an estimation of the contribution from other direct reaction mechanisms such as elastic and nonelastic breakup.

The dynamics of a many-particle system are often modeled by mapping the Hamiltonian into a Schrödinger equation. An alternative approach is to solve the Hamiltonian equations directly in a model space of many-body configurations. In a previous paper the numerical convergence of the two approaches was compared with a simplified treatment of the Hamiltonian representation. Here, we extend the comparison to the nonorthogonal model spaces that would be obtained by the generator-coordinate method. With a suitable choice of the collective-variable grid, a configuration-interaction Hamiltonian can reproduce the Schrödinger dynamics very well. However, the method as implemented here requires that the barrier height is not much larger than the zero-point energy in the collective coordinates of the configurations.

The phenomenon of spontaneous fission, which includes both binary and ternary decay modes, is observed within heavy and superheavy nuclei. Extensive efforts have been made to investigate the binary and ternary decay patterns exhibited by various nuclei belonging to the heavy-mass region. In this context, our study systematically examines the ground-state binary and ternary decay mechanisms of the ${}^{252}\mathrm{Cf}$ nucleus. To accomplish this, we have used the quantum mechanical fragmentation theory approach. It is known that the orientation angles of the decaying fragments play an important role in mass distribution. Therefore, in the present work probable orientation (both optimum and fixed) effects with deformations (up to quadrupole ${\beta }_2$) of nuclei participating in the fragmentation process are taken into account. Further, the fission fragments for binary ($A_1+A_2$) and for ternary ($A_1+A_2+A_3$) decay processes are identified by selecting channels of local minima in the fragmentation potential, with the third fragment $A_3$ being ${}^4\mathrm{He}$ for the ternary fission. The inclusion of hot-compact/(${90}^{\circ }-{90}^{\circ }$)/($0^{\circ }-{90}^{\circ }$)/(${90}^{\circ }-0^{\circ }$) orientations leads to the emergence of symmetric fission fragments, where shell effects are found to play the key role, whereas the cold-elongated/($0^{\circ }-0^{\circ }$) leads to the participation of highly deformed nuclei with large mass asymmetry. In addition to this, two types of tripartition of the radioactive nucleus are considered: equatorial cluster tripartition and collinear cluster tripartition. Both configurations are studied by considering $A_3$ = ${}^{30}\mathrm{Mg}$ and ${}^{48}\mathrm{Ca}$ as fixed fragments. The most probable fragments in the exit channel $\left[{}^{72}\mathrm{Ni}\right(Z=\mathbf{28}, N=44$) $+ {}^{132}\mathrm{Sn}(Z=$ 50, $N=$ 82)$+{}^{48}\mathrm{Ca}(Z=\mathbf{20}, N=\mathbf{28}$)] indicate that the deformations and the proton/neutron shell closure play a vital role in the spontaneous fission analysis of binary and ternary channels. The calculated results are aligned with available experimental data. In addition to this, relative yield for different ternary combinations is calculated for the ${}^{252}\mathrm{Cf}$ nucleus.

We propose a novel approach to probe primordial inhomogeneity in hot and dense matter which could be realized in noncentral heavy-ion collisions. Although the Hanbury Brown and Twiss (HBT) interferometry is commonly used to infer the system size, the cluster size should be detected if substructures emerge in space. We demonstrate that a signal peak in the HBT two-particle correlation stands at the relative momentum corresponding to the spatial scale of pseudo one-dimensional modulation. We assess detectability using the data prepared by an event generator (AMPT model) with clustering implemented in the particle distribution.

Probing the $\alpha$ cluster of ${}^{16}\mathrm{O}$ with the relativistic ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ collisions has raised great interest in the heavy ion community. However, the effects of the $\alpha$ cluster on the soft hadron observables vary largely among different studies. In this paper, we explain the differences by the compactness of the $\alpha$ cluster in oxygen, using iEBE-VISHNU hydrodynamic simulations with different initial state $\alpha$ cluster configurations. We also find several observables, such as the intensive skewness of the $\left[p_{\mathrm{T}}\right]$ correlator ${\mathrm{\Gamma }}_{p_{\mathrm{T}}}$, the harmonic flows $v_2\left\{2\right\}, v_2\left\{4\right\}, v_3\left\{2\right\}$, and the $v_n^2-\delta \left[p_{\mathrm{T}}\right]$ correlations $\rho (v_2^2,\left[p_{\mathrm{T}}\right]), \rho (v_3^2,\left[p_{\mathrm{T}}\right])$ in ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ collisions are sensitive to the compactness of the $\alpha$ cluster in the colliding nuclei, which can be used to constrain the configurations of ${}^{16}\mathrm{O}$ in the future. Our study serves as an important step toward the quantitative exploration of the $\alpha$ cluster configuration in the light nuclei with relativistic heavy ion collisions.

This work presents the first experimentally determined nuclear level density and $\gamma$-ray strength function of the short-lived fission product ${}^{93}\mathrm{Sr}$, accomplished using the $\beta$-Oslo method. Direct measurement of the ${}^{92}\mathrm{Sr}(n,\gamma ){}^{93}\mathrm{Sr}$ cross section is not currently possible, as the half-life of 2.66 hours is too short; instead, ${}^{93}\mathrm{Sr}$ was formed through $\beta$ decay of ${}^{93}\mathrm{Rb}$ to excitation energies around the neutron separation energy. The $\gamma$-ray spectra were measured using a total absorption spectrometer at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). The statistical properties of the ${}^{93}\mathrm{Sr}$ nucleus were experimentally determined, including the $\gamma$-ray strength function and nuclear level density. At low energies, the $\gamma$-ray strength function exhibits a constant $\gamma$-decay strength, rather than a slightly increasing strength with decreasing $\gamma$-ray energy as had been previously observed for several nuclei in this mid-mass region. These statistical properties were then implemented in the reaction code talys1.95 to calculate the ${}^{92}\mathrm{Sr}(n,\gamma ){}^{93}\mathrm{Sr}$ cross section.

An extended version of the interacting boson model (IBM), encompassing two-particle–two-hole (2p-2h) excitations originating from below a valence shell and one-particle–one-hole (1p-1h) excitations extending to the upper next-nearest major shell, is developed to investigate cross-shell excitation effects in the transitional nucleus ${}^{98}\mathrm{Mo}$. This extended IBM framework is utilized to reproduce experimentally observed properties such as low-lying positive-parity level energies, $B\left(E2\right)$ values, and the electric quadrupole moment of the $2_1^{+}$ state, ${\rho }^2(E0,0_2^{+}\to 0_{\mathrm{g}}^{+})$, as well as the strength functions of the isoscalar giant monopole resonance (ISGMR) and the isoscalar giant quadrupole resonance (ISGQR) in ${}^{98}\mathrm{Mo}$. It is shown that the extended consistent-$Q$ IBM, incorporating configuration mixing of both 2p-2h excitations from below the valence shell and 1p-1h excitations to the upper next-nearest major shell, describes the low-lying structural properties and the ISGMR and ISGQR strength distributions of ${}^{98}\mathrm{Mo}$ quite well, with the ISGMR and the ISGQR strength distributions comparable to the results of the self-consistent quasiparticle random-phase approximation with Skyrme interactions.

The ${}^{232}\mathrm{Th}$(${}^{48}\mathrm{Ca},5n$)${}^{275}\mathrm{Ds}$ and ${}^{238}\mathrm{U}$(${}^{40}\mathrm{Ar},5n$)${}^{273}\mathrm{Ds}$ reactions have been studied at the gas-filled separator DGFRS-2 at the Superheavy Element Factory at Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. For the first time, a new isotope ${}^{275}\mathrm{Ds}$ with a half-life of $0.{43}_{-0.12}^{+0.29}$ ms and α-particle energy of $11.20\pm 0.02$ MeV was synthesized in the ${}^{48}\mathrm{Ca}$-induced reaction with the actinide nucleus and identified by measuring correlated α decays ending in known nuclei. The decay properties of nuclei originating from ${}^{273}\mathrm{Ds}$ and ${}^{275}\mathrm{Ds}$ are compared with theoretical calculations and decay schemes are proposed. The cross sections of the ${}^{232}\mathrm{Th}$(${}^{48}\mathrm{Ca},5n$)${}^{275}\mathrm{Ds}$ reaction of $0.{11}_{-0.09}^{+0.46}$ and $0.{34}_{-0.16}^{+0.59}$ pb were measured at excitation energies of the ${}^{280}\mathrm{Ds}$ compound nucleus $E^{*}=51$ and 56 MeV, respectively. The cross section of the $5n$-evaporation channel of the ${}^{238}\mathrm{U}+{}^{40}\mathrm{Ar}$ reaction at $E^{*}=49$ MeV of $0.{18}_{-0.12}^{+0.44}$ pb turned out to be comparable to that for ${}^{275}\mathrm{Ds}$ at close excitation energy.

Background: The no-core shell model (NCSM) is an ab initio method that solves the nuclear many-body problem by expanding the many-particle wave function into a (typically) harmonic oscillator basis and minimizing the energy to obtain the expansion coefficients. Extensions of the NCSM, such as its coupling with microscopic-cluster basis states, further allow for an ab initio treatment of light-ion nuclear reactions of interest for both astrophysics and nuclear technology applications. A downside of the method is the exponential scaling of the basis size with increasing number of nucleons and excitation quanta, which limits its applicability to mass $A\lesssim 16$ nuclei, except for variants where the basis is further down-selected via some truncation scheme.

Purpose: We consider a basis selection method for the NCSM that was first introduced in the context of the large-scale shell model and captures the essential degrees of freedom of the nuclear wave function leading to a favorable complexity scaling for calculations and enabling ab initio reaction calculations in $sd$-shell nuclei.

Methods: The particle configurations within the NCSM basis are ordered based on their contribution to the first moment of the Hamiltonian matrix that results from the projection onto the many-body basis. The truncation scheme then consists in retaining only the lowest-first-moment configurations, which typically contain only few many-body basis states (Slater determinants). As the energy threshold above which configurations are disregarded is increased, the size of the basis becomes an almost-continuous variable, allowing for tunable fidelity in the obtained wave functions. The resulting wave functions can then be used directly in ab initio reaction calculations.

Results: We present calculations for ${}^7\mathrm{Li}$ and $n+{}^{12}\mathrm{C}$ scattering using nucleon-nucleon interactions derived from chiral effective field theory and softened using the similarity renormalization group method. The obtained energy levels invariably demonstrate exponential convergence with the size of the basis, and we find improved convergence in scattering calculations. To demonstrate the possibilities enabled by the approach, we also present a first calculation for the scattering of neutrons from ${}^{24}\mathrm{Mg}$.

Conclusions: The method presented in this work appears promising for future studies of nuclei with mass $A>16$, opening multiple future research directions impacting both nuclear astrophysics and nuclear technology applications.

The production of doubly strange hyperon ${\mathrm{\Xi }}^{-}$ and trebly strange hyperon ${\mathrm{\Omega }}^{-}$ in relativistic $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=4.2$ GeV is explored based on a relativistic transport model that is interweaved with hadronic mean-field potentials for heavy-ion collisions. Upon comparison, it appears that relative to the double-strangeness observable ${\mathrm{\Xi }}^{-}$, the yield and collective flows of the triple-strange ${\mathrm{\Omega }}^{-}$ exhibit a higher sensitivity to the equation of state of dense matter. This characteristic makes the ${\mathrm{\Omega }}^{-}$ an essential observable for studying the properties of densely formed matter in relativistic heavy-ion collisions.

I study the elliptic and triangular flow of charmonium states, or $J/\psi , \psi \left(2S\right)$, and ${\chi }_c\left(1P\right)$ mesons in heavy ion collisions. Starting from the evaluation of charmonia transverse momentum distributions and yields, I calculate elliptic and triangular flow of charmonium states based on the coalescence model. I show that the internal structure, or the wave function distribution of charmonium states plays a significant role, especially when charmonium states are produced by charm quark recombination, leading to the transverse momentum distribution of the $\psi \left(2S\right)$ meson as half large as that of the $J/\psi$ meson. I also consider the dependence of the elliptic and triangular flow of charmonium states on internal structures of charmonium states, and find that the wave function effects as well as feed-down contributions are averaged out for elliptic and triangular flow, resulting in similar elliptic and triangular flow for all charmonium states. I investigate further the elliptic and triangular flow of charmonium states at low transverse momentum region, and also discuss the quark number scaling of elliptic and triangular flow for charmonium states.

Background: Low-lying bandhead states in axially prolate deformed odd-odd nuclei have long been described essentially within the $\text{rotor}+\text{two}$-quasiparticle picture. This approach allows one to explain the appearance of so-called Gallagher-Moszkowski doublets of bandheads with $K={\mathrm{\Omega }}_n\pm {\mathrm{\Omega }}_p$, sum and difference of neutron and proton angular momentum projections on the symmetry axis. According to an empirical rule stated by Gallagher and Moszkowski the spin-aligned configuration lies lower in energy than the spin-antialigned configuration. A recent study by Robledo, Bernard, and Bertsch [Phys. Rev. C 89, 021303(R) (2014)] within the Gogny energy-density functional with self-consistent blocking of the unpaired nucleons showed that calculations fail to reproduce this rule in about half of the cases, and points to the density-dependent term of the functional as responsible of this failure.

Purpose: In this paper we aim at pushing further this analysis to exhibit the mechanism underlying the energy splitting in a Gallagher-Moszkowski doublet.

Method: We work in the framework of the Skyrme energy-density functional approach, including BCS pairing correlations with self-consistent blocking. We use the SIII parametrization with time-odd terms and seniority pairing matrix elements extending a previous study of $K$-isomeric states in even-even nuclei [Phys. Rev. C 105, 044329 (2022)].

Results: We find that the energy splitting results from a competition between the spin-spin, density-dependent, and current-current terms of the Skyrme energy-density functional.

Conclusions: In doublets where the larger $K$ value is lower in energy the Gallagher-Moszkowski rule is always satisfied by the SIII Skyrme energy-density functional. In doublets, in contrast, where the smaller $K$ value lies lower, the energy splittings are calculated to be rather small, and often a disagreement with the Gallagher-Moszkowski rule occurs.

The S-matrix which satisfies the unitarity, giving the poles as random-phase approximation (RPA) excited states, is derived using the extended Jost function within the framework of the RPA theory. An analysis on the correspondence between the component decomposition of the RPA strength function by the eigenphase shift obtained by diagonalization of the S-matrix and the S- and K-matrix poles was performed in the calculation of the ${}^{16}\mathrm{O}$ quadrupole excitations. The results show the possibility that the states defined by the eigenphase shift can be expressed as RPA-excited eigenstates corresponding to the S-matrix poles in the continuum region.

Background: The unexplained disagreement in the dependence of spectroscopic factors $\left(C^2{S}_{\exp }\right)$ on the binding energy obtained by nucleon knockout using different targets is still a puzzle that needs to be addressed.

Purpose: To find an explanation of this riddle through exclusive measurements using different targets.

Method: The exclusive measurements were performed by using a ${}^{17}\mathrm{Ne}$ beam with an energy of 500 MeV/u incident on $\mathrm{C}$ and ${\mathrm{CH}}_2$ targets. Through the standard theoretical approach, $C^2{S}_{\exp }$ were derived from the analysis of the experimental data on proton ejection from the proton halo in ${}^{17}\mathrm{Ne}$ as well as from its core ${}^{15}\mathrm{O}$.

Result: For the $\mathrm{C}$ target, proton ejection from the proton halo gave $C^2{S}_{\exp }$ about 37% smaller than for the $\mathrm{H}$ target. But when protons are ejected from the core of ${}^{17}\mathrm{Ne}$, $C^2{S}_{\exp }$ are identical within statistical uncertainties.

Conclusion: An explanation for the difference in $C^2{S}_{\exp }$ could be the removal of both halo protons, a more important reaction pathway for the $\mathrm{C}$ target. The $C^2{S}_{\exp }$ values obtained by analyzing the proton ejection from the core indicate that it is not affected by the interaction with the halo protons.

The Lanzhou Cooling Storage Ring (CSR) facility is set to conduct experiments involving uranium-uranium collisions at center-of-mass energies ranging from 2.12 to 2.4 GeV. Our investigation is focused on various bulk observables, which include charged particle multiplicity $\left(N_{\text{ch}}\right)$, average transverse momentum $(\langle p_{\text{T}}\rangle )$, initial eccentricity $\left({\epsilon }_n\right)$, and flow harmonics $\left(v_n\right)$, for different orientations of $\mathrm{U}+\mathrm{U}$ collisions within the range of $0^{\circ }<\theta <{120}^{\circ }$ at $\sqrt{s_{NN}}=2.12$ GeV $(p_{\mathrm{lab}}=500 \mathrm{MeV})$. Among the various collision configurations at this energy, the tip-tip scenario emerged with the highest average charged particle multiplicity, denoted as $\langle N_{\text{ch}}\rangle$. Notably, both the second- and third-order eccentricities, ${\epsilon }_{2,3}$, revealed intricate patterns as they varied with impact parameter across distinct configurations. The tip-tip configuration displayed the most pronounced magnitude of rapidity-odd directed flow $\left(v_1\right)$, whereas the body-body configuration exhibited the least pronounced magnitude. Concerning elliptic flow $\left(v_2\right)$ near mid-rapidity $\left(\right|\eta |<1.0)$, a negative sign is observed for all configurations except for the side-side which exhibited a distinctly positive sign. Within the spectrum of configurations, the body-body scenario displayed the highest magnitude of $v_2$. For reaction plane correlated triangular flow $\left(v_3\right)$, the body-body configuration emerged with the largest magnitude while the side-side exhibited the smallest magnitude. Our study seeks to establish a fundamental understanding of various $\mathrm{U}+\mathrm{U}$ collision configurations in preparation for the forthcoming CSR External-target Experiment (CEE).