Formation of superheavy nuclei is greatly hindered by the inner barrier and strong dissipation on the way from the contact point of two colliding nuclei to the compound nucleus configuration. One of the dissipation mechanisms is related to the exchange of particles across the window between two nuclei in relative motion, which is the “window” term in the “wall-plus-window” formula. By means of the dynamic analysis for the symmetric systems ${}^{132}\mathrm{Xe}$ + ${}^{132}\mathrm{Xe}$ and ${}^{136}\mathrm{Xe}$ + ${}^{136}\mathrm{Xe}$, we have shown that the window component of friction tensor retards the elongation of the fusing composite nucleus, decreases the height of the inner barrier, and hence increases the fusion probability. Therefore, the friction associated with “window” term enhances the formation cross sections of superheavy nuclei. Besides, we have shown the mass difference (in units of the temperature) of the fission and neutron emission saddle points as a function of mass number of the hassium isotopes, which may provide a useful reference for synthesis and study of the nuclei adjacent to the doubly magic nucleus ${}^{270}\mathrm{Hs}$.

The kinetic freeze-out for the hydrodynamical description of relativistic heavy-ion collisions is discussed using a background-fluctuation splitting of the hydrodynamical fields. For a single event, the particle spectrum, or its logarithm, can be written as the sum of the background part that is symmetric with respect to azimuthal rotations and longitudinal boosts and a part containing the contribution of fluctuations or deviations from the background. Using a complete orthonormal basis to characterize the initial state allows one to write the double differential harmonic-flow coefficients determined by the two-particle correlation method as matrix expressions involving the initial fluid correlations. We discuss the use of these expressions for a mode-by-mode analysis of fluctuating initial conditions in heavy-ion collisions.

With increasing beam energies the angular momentum of the fireball in peripheral heavy-ion collisions increases, and the proposed differential Hanbury Brown and Twiss analysis is able to estimate this angular momentum quantitatively. The method detects specific space-time correlation patterns, which are connected to rotation.

Posterior distributions for physical parameters describing relativistic heavy-ion collisions, such as the viscosity of the quark-gluon plasma, are extracted through a comparison of hydrodynamic-based transport models to experimental results from $100A\text{GeV}+100A\text{GeV}$ $\mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy Ion Collider. By simultaneously varying six parameters and by evaluating several classes of observables, we are able to explore the complex intertwined dependencies of observables on model parameters. The methods provide a full multidimensional posterior distribution for the model output, including a range of acceptable values for each parameter, and reveal correlations between them. The breadth of observables and the number of parameters considered here go beyond previous studies in this field. The statistical tools, which are based upon Gaussian process emulators, are tested in detail and should be extendable to larger data sets and a higher number of parameters.

The particle production and their ratios for $\pi$, $K$, $p$, and $\Lambda$ are studied in Pb + Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV based on a blast-wave model with thermal equilibrium mechanism. The transverse momentum spectra of the above-mentioned particles at the kinetic freeze-out stage are discussed. The modification of the inverse slope of pion transverse momentum spectrum due to resonance decay has also been investigated. In addition, we found that the antiparticles-to-particles ratio as well as the kaons-to-pions ratio agree with the data by the LHC-ALICE Collaboration reasonably well, while the $p/\pi$ ratio is overestimated by a factor of 1.5, similar to those from other thermal model calculations. It is found that the ratios of $p/\pi$ and $K/\pi$ are dominated by the radial flow but slightly affected by the baryon chemical potential. Our study thus constrains the parameters at the chemical and kinetic freeze-out stages within the framework of thermal model in Pb + Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV, and will help us better understand the properties of the dense and hot matter created in high-energy heavy-ion collisions at freeze-out stage.

Using the vishnu hybrid model that couples (2+1)-dimensional viscous hydrodynamics to a microscopic hadronic transport model, we calculate the multiplicity, $p_T$ spectra, and elliptic flow for pions, kaons, and protons in 2.76$A$ TeV Pb+Pb collisions, using mc-kln initializations with smoothed initial conditions, obtained by averaging over a large number of events. The results from our calculations are compared to data from the ALICE Collaboration, showing nice agreement over several centrality bins. Using the same inputs, we predict the $p_T$ spectra and elliptic flow for $\varphi$ mesons and explore their flow development in the strong and weak coupling limits through hydrodynamic calculations with different decoupling temperatures. In addition we study the influence of baryon and antibaryon annihilation processes on common observables and demonstrate that, by including annihilation processes below a switching temperature of 165 MeV, vishnu provides a good description of the multiplicity and $p_T$ spectra for pions, kaons, and protons measured by PHENIX and ALICE at both the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC).

Neutron matter at densities somewhat above nuclear densities is believed to be superfluid due to the condensation of neutron pairs in the ${}^3{P}_2$ channel. This condensate breaks rotational symmetry spontaneously and leads to the existence of Goldstone bosons (angulons). We show that the coupling to magnetic fields mediated by the magnetic moment of the neutron makes angulons massive and capable of decaying into a neutrino-antineutrino pair. We compute the rate for this process and argue they become competitive with other cooling processes for temperatures around ${10}^7$ K as long as the interior magnetic field of the star is in the $B\approx {10}^{15}$ G range or above.

The equation of state of neutron matter is affected by the presence of a magnetic field due to the intrinsic magnetic moment of the neutron. Here we study the equilibrium configuration of this system for a wide range of densities, temperatures, and magnetic fields. Special attention is paid to the behavior of the isothermal compressibility and the magnetic susceptibility. Our calculation is performed using both microscopic and phenomenological approaches of the neutron matter equation of state, namely the Brueckner-Hartree-Fock (BHF) approach using the Argonne V18 nucleon-nucleon potential supplemented with the Urbana IX three-nucleon force, the effective Skyrme model in a Hartree-Fock description, and the quantum hadrodynamic formulation with a mean-field approximation. All these approaches predict a change from completely spin polarized to partially polarized matter that leads to a continuous equation of state. The compressibility and the magnetic susceptibility show characteristic behaviors which reflect that fact. Thermal effects tend to smear out the sharpness found for these quantities at $T=0$. In most cases a thermal increase of $\Delta T=10$ MeV is enough to hide the signals of the change of polarization. The set of densities and magnetic field intensities for which the system changes it spin polarization is different for each model. However, we found that under the conditions examined in this work there is an overall agreement between the three theoretical descriptions.

This paper shows the importance of the incompressibility of nuclear matter on analyzing the fusion excitation functions, average angular momenta, and astrophysical $S$ factor at energies far below the Coulomb barrier for the asymmetric systems ${}^{28}\mathrm{Si}$ + ${}^{94}\mathrm{Mo}$ and ${}^{28}\mathrm{Si}$ + ${}^{100}\mathrm{Mo}$. Moreover, our predictions for threshold energy of fall-off phenomena, $E_S$, are in good agreement with semi-empirical formulas of $E_S$ for ${}^{28}\mathrm{Si}$ + ${}^{94,100}\mathrm{Mo}$ systems.

Background: The increase of collectivity in the nuclear spectra, with increasing numbers of valence proton and neutron pairs, is a well-known phenomenon, yielding a decreasing $E\left(2_1{}^{+}\right)$ and increasing $B$($E$2)↑, which is the basis of Grodzins $E\left(2_1{}^{+}\right)\times B\left(E2\right)\uparrow$ product constancy rule.

Purpose: In the $N$ = 88 isotones, this product varies sharply with $Z$. This breakdown of the product rule in the Ba to Dy region is illustrated and its origin is analyzed.

Method: Empirical data on energy level structure in various forms along with the $E$2 transition rates, vis-à-vis the level structure and the nature of the $Z$ = 64 subshell effect, are presented.

Results: The complex nuclear structure of $N$ = 88 isotones is highlighted and the genesis of the underlying physics is made more transparent.

Conclusion: Besides the static shape of the nucleus, it involves the dynamics of the nucleus, as reproduced in the dynamic pairing plus quadrupole model.

We apply the complex scaling method to the calculation of scattering phase shifts and extract the contributions of resonances in a phase shift and a cross section. The decomposition of the phase shift is shown to be useful in understanding the roles of resonant and nonresonant continuum states. As examples, we apply this method to several two-body systems: (i) a schematic model with the Gyarmati potential, which produces many resonances, (ii) the $\alpha \text{−}\alpha$ system, which has a Coulomb barrier potential in addition to an attractive nuclear interaction, and (iii) the $\alpha \text{−}n$ system, which has no barrier potential. Using different kinds of potentials, we discuss the reliability of this method to investigate the resonance structure in the phase shifts and cross sections.

We describe the fusion-fission processes within the two-stage reaction model. On the first stage (the entrance channel) the time evolution of the system up to the touching point is calculated. All possible orientations of the colliding nuclei are taken into account. The distributions at the touching point obtained on the first step are used for the transition from separated ions to the compact system and as the initial conditions for the description of evolution of compact system (second stage). Both the approach of ions and the evolution of the compact system are described with the help of Langevin equations for the collective coordinates (deformation parameters) which specify the configuration of the system. In both stages the shell structures of the colliding ions and the compound nucleus are taken into account. Within this model we obtain the information on the touching probability and the observable measured in the fusion-fission reactions (mass and energy distributions of the fission fragments, the compound nucleus, and the evaporation residue formation cross sections). In the present work we have carried out the calculations for the reactions ${}^{64}\mathrm{Ni}+{}^{238}\mathrm{U}\to {}^{302-x}120+xn$, ${}^{58}\mathrm{Fe}+{}^{244}\mathrm{Pu}\to$ ${}^{302-x}120+xn$, ${}^{54}\mathrm{Cr}+{}^{248}\mathrm{Cm}\to {}^{302-x}120+xn$, leading to the synthesis of an element with $Z=120$. The calculated results are compared with the available experimental data and other theoretical predictions.

By using an antisymmetrized molecular dynamics model (AMD), the data of kinematically complete events are compared with the experimental INDRA data through nuclear stopping in $\text{Xe}+\text{Sn}$ collisions at 10 to $100A$ MeV. The sensitivity of the nuclear stopping is studied through interactions with different equations of state (EOSs) (soft and stiff) and in-medium $NN$ cross sections in different energy domains. Above $25A$ MeV, both EOSs and different $NN$ cross sections can affect the nuclear stopping, but none of these parameters used in the AMD model can reproduce the experimental data at 20 to $30A$ MeV. On the other hand, below $25A$ MeV, nuclear stopping is not sensitive to both of the EOSs and the $NN$ cross sections because of complete nuclear stopping. This indicates that some important mechanisms may be missing in AMD or that the selection of central collision events may be significantly different between the experiments and the simulations at this energy range.

Background: The structure of weakly bound/unbound nuclei close to particle drip lines is different from that around the valley of beta stability. A comprehensive description of these systems goes beyond the standard shell model (SM) and demands an open quantum system description of the nuclear many-body system.

Purpose: For that purpose, we are using the Gamow shell model (GSM), which provides a fully microscopic description of bound and unbound nuclear states, nuclear decays, and reactions. We formulate the GSM in coupled-channel (GSM-CC) representation to describe low-energy elastic and inelastic scattering of protons on ${}^{18}\mathrm{Ne}$.

Method: The GSM-CC formalism is applied to a translationally invariant Hamiltonian with an effective finite-range two-body interaction. We discuss in detail the GSM-CC formalism in coordinate space and give the description of the novel equivalent potential method for solving the GSM-CC system of integrodifferential equations. This method is then applied for the description of $(p,p^{\prime })$ reaction cross-sections. The reactions channels are built by GSM wave functions for the ground state $0^{+}$ and the first excited $2^{+}$ of ${}^{18}\mathrm{Ne}$ and a proton wave function expanded in different partial waves. The completeness of this basis is verified by comparing GSM and GSM-CC energies of low-energy resonant states in ${}^{19}\mathrm{Na}$. The differences between the two calculations provide a measure of the missing configurations in the GSM-CC calculation of low-energy states of ${}^{19}\mathrm{Na}$ due to the restriction on the number of excited states of ${}^{18}\mathrm{Ne}$.

Results: We present the first application of the GSM-CC formalism for the calculation of excited states of ${}^{18}\mathrm{Ne}$ and ${}^{19}\mathrm{Na}$, the excitation function, and the elastic/inelastic differential cross-sections in the ${}^{18}\mathrm{Ne}$$(p,p^{\prime })$ reaction at different energies. This is the first unified description of the spectra and reaction cross-sections in the GSM formalism. The method is shown to be both feasible and accurate. The approximate equivalence of GSM and GSM-CC in describing spectra of ${}^{19}\mathrm{Na}$ has been demonstrated numerically.

Conclusions: The GSM in the coupled-channel representation opens a possibility for the unified description of low-energy nuclear structure and reactions using the same Hamiltonian. While both GSM and GSM-CC can describe energies, widths, and wave functions of the many-body states, the GSM-CC can in addition yield reaction cross-sections. The combined application of GSM and GSM-CC to describe energies of resonant states allows to test the exactitude of calculated cross-sections for a given many-body Hamiltonian.

Existing quantum mechanics methods to study fusion reactions with weakly bound nuclei cannot evaluate separately the complete fusion and the incomplete fusion cross sections. We develop a semiclassical procedure that can calculate these cross sections, apply it to ${}^{6,7}\mathrm{Li}+{}^{209}\mathrm{Bi}$ collisions at energies just above the barrier, and show that its predictions for the different fusion cross sections are in good agreement with the data. We find that the contribution from the sequential fusion of the Li fragments to the complete fusion cross section is substantial in the case of ${}^6\mathrm{Li}$, reaching almost 40% of that from the direct process, which illustrates the importance of calculating correctly the different components of the fusion cross section.

The distorted spin-dependent spectral function of a nucleon inside an $A=3$ nucleus is introduced as a novel tool for investigating the polarized electron scattering off polarized ${}^3\mathrm{He}$ in the semi-inclusive DIS regime (SiDIS), going beyond the standard plane-wave impulse approximation. This distribution function is applied to the study of the spectator SiDIS, $\overrightarrow{{}^3\mathrm{He}}(\vec{e},e^{\prime }{}^2\mathrm{H})X$, to properly take into account the final-state interaction between the hadronizing quark and the detected deuteron, with the final goal of a more reliable extraction of the polarized parton distribution $g_1\left(x\right)$ inside a bound proton. Our analysis allows one to single out two well-defined kinematical regions where the experimental asymmetries could yield very interesting information: the region where the final-state effects can be minimized, and therefore the direct access to the parton distributions in the proton is feasible, and the one where the final-state interaction dominates, and the spectator SiDIS reactions can elucidate the mechanism of the quark hadronization itself. The perspectives of extending our approach (i) to the mirror nucleus, ${}^3\mathrm{H}$, for achieving a less model-dependent flavor decomposition and (ii) to the asymmetries measured in the standard SiDIS reactions, $\vec{e}+\overrightarrow{{}^3\mathrm{He}}\to e^{\prime }+h+X$, with $h$ a detected fast hadron, with the aim of extracting the neutron transversity, are discussed.

We present updated calculations for observables in the processes ${}^3\text{He}$($e,e^{\prime }p$)${}^2\text{H}$, ${}^4\text{He}$($e,e^{\prime }p$)${}^3\text{H}$, and ${}^4\text{He}$($\vec{e},e^{\prime }\vec{p}$)${}^3\text{H}$. This update entails the implementation of improved nucleon-nucleon ($NN$) amplitudes to describe final-state interactions (FSI) within a Glauber approximation and includes full spin-isospin dependence in the profile operator. In addition, an optical potential, which has also been updated since previous work, is utilized to treat FSI for the ${}^4\text{He}$($e,e^{\prime }p$)${}^3\text{H}$ and ${}^4\text{He}$($\vec{e},e^{\prime }\vec{p}$)${}^3\text{H}$ reactions. The calculations are compared with experimental data and show good agreement between theory and experiment. Comparisons are made between the various approximations in the Glauber treatment, including model dependence owing to the $NN$ scattering amplitudes, rescattering contributions, and spin dependence. We also analyze the validity of the Glauber approximation at the kinematics the data is available by comparing to the results obtained with the optical potential.

In view of the mass spectrum of heavy mesons in vacuum, the analytical properties of the solutions of the truncated Dyson-Schwinger equation for the quark propagator within the rainbow approximation are analyzed in some detail. In Euclidean space, the quark propagator is not an analytical function possessing, in general, an infinite number of singularities (poles) which hamper solving the Bethe-Salpeter equation. However, for light mesons (with masses $M_{q\overline{q}}\le 1$ GeV) all singularities are located outside the region within which the Bethe-Salpeter equation is defined. With an increase of the considered meson masses this region enlarges and already at masses $\ge$1 GeV, the poles of propagators of $u$, $d$, and $s$ quarks fall within the integration domain of the Bethe-Salpeter equation. Nevertheless, it is established that for meson masses up to $M_{q\overline{q}}\simeq 3$ GeV only the first, mutually complex conjugated poles contribute to the solution. We argue that, by knowing the position of the poles and their residues, a reliable parametrization of the quark propagators can be found and used in numerical procedures of solving the Bethe-Salpeter equation. Our analysis is directly related to the future physics program at FAIR with respect to open charm degrees of freedom.

A container picture is proposed for understanding cluster dynamics where the clusters make nonlocalized motion occupying the lowest orbit of the cluster mean-field potential characterized by the size parameter $``B$” in the Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function. The nonlocalized cluster aspects of the inversion-doublet bands in ${}^{20}\mathrm{Ne}$ which have been considered as a typical manifestation of localized clustering are discussed. An as-yet-unexplained puzzling feature of the THSR wave function, namely that after angular-momentum projection for two-cluster systems the prolate THSR wave function is almost 100$\%$ equivalent to an oblate THSR wave function, is clarified. It is shown that the true intrinsic two-cluster THSR configuration is nonetheless prolate. The proposal of the container picture is based on the fact that typical cluster systems, 2$\alpha$, 3$\alpha$, and ${}^{16}\text{O}+\alpha$, are all well described by a single THSR wave function. It is shown for the case of linear-chain states with 2- and 3$\alpha$ clusters, as well as for the ${}^{16}\text{O}+\alpha$ system, that localization is entirely of kinematical origin, that is, attributable to the intercluster Pauli repulsion. It is concluded that this feature is general for nuclear cluster states.