Background: At extremely low incident energies, unexpected decreases in fusion cross sections, compared to the standard coupled-channels (CC) calculations, have been observed in a wide range of fusion reactions. These significant reductions of the fusion cross sections are often referred to as the fusion hindrance. However, the physical origin of the fusion hindrance is still unclear.

Purpose: To describe the fusion hindrance based on an adiabatic approach, I propose a novel extension of the standard CC model by introducing a damping factor that describes a smooth transition from sudden to adiabatic processes, that is, the transition from the separated two-body to the united dinuclear system. I demonstrate the performance of this model by systematically investigating various deep sub-barrier fusion reactions.

Method: I extend the standard CC model by introducing a damping factor into the coupling matrix elements in the standard CC model. This avoids double counting of the CC effects, when two colliding nuclei overlap one another. I adopt the Yukawa-plus-exponential (YPE) model as a basic heavy ion-ion potential, which is advantageous for a unified description of the one- and two-body potentials. For the purpose of these systematic investigations, I approximate the one-body potential with a third-order polynomial function based on the YPE model.

Results: Calculated fusion cross sections for the medium-heavy mass systems of ${}^{64}\mathrm{Ni}+{}^{64}\mathrm{Ni}$, ${}^{58}\mathrm{Ni}+{}^{58}\mathrm{Ni}$, and ${}^{58}\mathrm{Ni}+{}^{54}\mathrm{Fe}$, the medium-light mass systems of ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$, ${}^{48}\mathrm{Ca}+{}^{48}\mathrm{Ca}$, and ${}^{24}\mathrm{Mg}+{}^{30}\mathrm{Si}$, and the mass-asymmetric systems of ${}^{48}\mathrm{Ca}+{}^{96}\mathrm{Zr}$ and ${}^{16}\mathrm{O}+{}^{208}\mathrm{Pb}$ are consistent with the experimental data. The astrophysical S factor and logarithmic derivative representations of these are also in good agreement with the experimental data. The values obtained for the individual radius and diffuseness parameters in the damping factor, which reproduce the fusion cross sections well, are nearly equal to the average value for all the systems.

Conclusions: Since the results calculated with the damping factor are in excellent agreement with the experimental data in all systems, I conclude that a coordinate-dependent coupling strength is responsible for the fusion hindrance. In all systems, the potential energies at the touching point $V_{\mathrm{Touch}}$ strongly correlate with the incident threshold energies for which the fusion hindrance starts to emerge, except for the medium-light mass systems.

The thermodynamical cluster model is known to present a first-order liquid-gas phase transition in the idealized case of an uncharged, infinitely extended medium. However, in most practical applications of this model, the system is finite and charged. In this paper we study how the phase diagram is modified by finite size and Coulomb effects. We show that the thermodynamic anomalies which are associated to the finite-system counterpart of first-order phase transitions are correctly reproduced by this effective model. However, approximations in the calculation of the grand-canonical partition sum prevent obtaining the exact mapping between statistical ensembles which should be associated to finite systems. The ensemble inequivalence associated to the transition persists in the presence of Coulomb effects, but the phase diagram is deeply modified with respect to the simple liquid-gas phase transition characteristic of the neutral system.

The dependence of electron screening in nuclear reactions on projectile or target atomic number has been studied by bombarding different hydrogen-containing targets with beams of ${}^7\mathrm{Li}$, ${}^{11}\mathrm{B}$, and ${}^{19}\mathrm{F}$. The largest electron screening potentials were obtained in a graphite target containing hydrogen as an impurity. Some measured potentials are almost two orders of magnitude above the theoretical predictions. To explain the measurements, a new concept of electron screening is introduced.

Background: Significant enhancement of sub-barrier fusion cross sections owing to neutron transfer with positive $Q$ values was observed in many combinations of colliding nuclei. This degree of freedom has not yet been included into the rigorous quantum coupled-channels (QCC) approach. However, the empirical coupled-channels model with neutron rearrangement [Zagrebaev, Phys. Rev. C 67, 061601 (2003)] has already been successfully used in several papers to reproduce and predict cross sections for sub-barrier fusion reactions of stable nuclei.

Purpose: The objective of this study is to combine the QCC approach and the empirical model to account for additional channels of neutron rearrangement.

Method: Coupling of relative motion to collective degrees of freedom (rotation of nuclei and/or their surface vibrations) are taken into account within the QCC approach. The probability of transfer of $x$ neutrons with a given $Q$ value is estimated semiclassically.

Results: The proposed new model was successfully tested on a few combinations of fusing nuclei ${}^{40}\text{Ca}+{}^{90,94,96}\text{Zr}, {}^{32}\text{S}+{}^{90,94,96}\text{Zr}$, and ${}^{60,64}\text{Ni}+{}^{100}\text{Mo}$. The calculated fusion cross sections and barrier distribution functions agree well with experimental data.

Conclusions: The model developed in this work confirms all the conclusions previously made within the empirical coupled-channels model with neutron rearrangement [see Rachkov et al., Phys. Rev. C 90, 014614 (2014)]. Moreover, it has an advantage of a more reliable microscopic account for the coupling between relative motion and the collective degrees of freedom. The proposed model can also be used to reproduce the structure of the barrier distribution function. This is a step forward to a complete solution of the long-term problem of accounting for neutron transfer channels in the QCC model.

By analyzing preliminary experimental measurements of charge-balance functions from the STAR Collaboration at the Relativistic Heavy Ion Collider (RHIC), it is found that scenarios in which balancing charges are produced in a single surge, and therefore separated by a single length scale, are inconsistent with data. In contrast, a model that assumes two surges, one associated with the formation of a thermalized quark-gluon plasma and a second associated with hadronization, provides a far superior reproduction of the data. A statistical analysis of the model comparison finds that the two-surge model best reproduces the data if the charge production from the first surge is similar to expectations for equilibrated matter taken from lattice gauge theory. The charges created in the first surge appear to separate by approximately one unit of spatial rapidity before emission, while charges from the second wave appear to have separated by approximately a half unit or less.

Systematic calculations on the $\alpha$-decay energies $\left(Q_{\alpha }\right)$ and $\alpha$-decay half-lives of the superheavy nuclei (SHN) with $Z\ge 100$ are performed by using 20 models and 18 empirical formulas, respectively. According to the comparisons between the calculated results and experimental data, it is shown that the WS4 mass model is the most accurate one to reproduce the experimental $Q_{\alpha }$ values of the SHN. Meanwhile it is found that the SemFIS2 formula is the best one to predict the $\alpha$-decay half-lives of the SHN because the parameters in this formula are from the experimental $\alpha$ emitter data of transuranium nuclei including SHN $\left(Z=92\text{–}118\right)$. In addition, the UNIV2 formula with fewest parameters and the VSS, SP and NRDX formulas with fewer parameters work well in prediction on the SHN $\alpha$-decay half-lives. Finally, the $\alpha$-decay half-lives of $Z=110\text{–}120$ isotopes are predicted within the above mentioned five formulas by inputting the $\mathrm{WS}4 Q_{\alpha }$ values. By analyzing the $Q_{\alpha }$ values and the $\alpha$-decay half-lives of this region, it is found that for $Z=110\text{–}114$ isotopes $N=162$ and $N=184$ are the submagic number and magic number, respectively. However, for the isotopes of $Z=116\text{–}120$ the submagic number is $N=178$.

Four quantities deducible from nuclear structure experiments have been claimed to correlate with the slope parameter $L$ of the symmetry energy: neutron skin thickness, cross section of low-energy dipole (LED) mode, dipole polarizability ${\alpha }_D$, and ${\alpha }_D{S}_0$ (i.e., product of ${\alpha }_D$ and symmetry energy $S_0$). By means of calculations in the Hartree-Fock plus random-phase approximation with various effective interactions, we compare the correlations between $L$ and these four quantities. The correlation derived from different interactions and the correlation from a class of interactions that are identical in symmetric matter as well as in $S_0$ are simultaneously examined. These two types of correlation may behave differently, as exemplified in the correlation of ${\alpha }_D$ to $L$. It is found that the neutron skin thickness and ${\alpha }_D{S}_0$ correlate well to $L$, and therefore are suitable for narrowing down the value of $L$ via experiments. The LED emergence and upgrowth makes the ${\alpha }_D{S}_0\text{−}L$ correlation strong, although these correlations are disarranged when a neutron halo appears in the ground state.

We estimate the event-by-event (e-by-e) distribution of the ratio $\left(\sigma \right)$ of the magnetic and electric field energy density to the fluid energy density in the transverse plane of Au-Au collisions at $\sqrt{s_{NN}}=200$ GeV. A Monte Carlo (MC) Glauber model is used to calculate $\sigma$ in the transverse plane for impact parameter $b=0$, 12 fm at time ${\tau }_i\sim 0.5$ fm. The fluid energy density is obtained by using Gaussian smoothing with two different smoothing parameter ${\sigma }_g=0.25$, 0.5 fm. For $b=0\mathrm{fm}$ collisions $\sigma$ is found to be $\ll 1$ in the central region of the fireball and $\sigma \gtrsim 1$ at the periphery. For $b=12$ fm collisions $\sigma \gtrsim 1$ is observed for some events. The e-by-e correlation between $\sigma$ and the fluid energy density $\left(\varepsilon \right)$ is studied. We did not find strong correlation between $\sigma$ and $\varepsilon$ at the center of the fireball, whereas they are mostly anticorrelated at the periphery of the fireball.

We present calculations for the incoherent photoproduction of $J/\psi$ vector mesons in ultraperipheral heavy ion collisions (UPCs) in terms of hadronic interactions. This study was carried out using the recently developed Monte Carlo model CRISP extended to include UPCs at energies available at the CERN Large Hadron Collider. A careful study of rescattering and destruction of the $J/\psi$ particles is presented for Pb + Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. We have also compared our method to Au + Au collisions at $\sqrt{s_{NN}}=200$ GeV measured at the BNL Relativistic Heavy Ion Collider.

In this study we model early-time dynamics of relativistic heavy ion collisions by an initial color-electric field which then decays to a plasma by the Schwinger mechanism, coupling the dynamical evolution of the initial color field to the dynamics of the many particles system produced by the decay. The latter is described by relativistic kinetic theory in which we fix the ratio $\eta /s$ rather than insisting on specific microscopic processes, and the backreaction on the color field is taken into account by solving self-consistently the kinetic and the field equations. We study isotropization and thermalization of the system produced by the field decay for a static box and for a $1+1\mathrm{D}$ expanding geometry. We find that regardless of the viscosity of the produced plasma, the initial color-electric field decays within 1 fm/$c$; however, in the case where $\eta /s$ is large, oscillations of the field are effective along all the entire time evolution of the system, which affect the late-time evolution of the ratio between longitudinal and transverse pressure. In the case of small $\eta /s$ ($\eta /s\lesssim 0.3$) we find ${\tau }_{\text{isotropization}}\approx 0.8$ fm/$c$ and ${\tau }_{\text{thermalization}}\approx 1$ fm/$c$, in agreement with the common lore of hydrodynamics. Moreover, we have investigated the effect of turning from the relaxation time approximation to the Chapman-Enskog one: We find that this improvement affects mainly the early-time evolution of the physical quantities, the effect being milder in the late-time evolution.

The production of non-$\varphi K^{+}{K}^{-}$ pairs by protons at 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated by using the COSY-ANKE magnetic spectrometer. The $K^{-}$ momentum dependence of the differential cross section has been measured for laboratory polar angles ${\theta }_{K^{\pm }}\le {12}^{\circ }$ over the 0.2–0.9 GeV/$c$ range. The comparison of the data with detailed model calculations indicates an attractive $K^{-}$-nucleus potential of about $-60$ MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/$c$. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low-$K^{-}$ momenta.

Inspired by the discovery of the dibaryon $d^{*}$ and the experimental search of $N\mathrm{\Omega }$ dibaryon with the STAR data, we study the strange dibaryon $N\mathrm{\Omega }$ further in the framework of the quark delocalization color screening model and the chiral quark model. We have shown $N\mathrm{\Omega }$ is a narrow resonance in $\mathrm{\Lambda }\mathrm{\Xi }$ D-wave scattering before. However, the $\mathrm{\Lambda }-\mathrm{\Xi }$ scattering data analysis is quite complicated. Here we calculate the low-energy $N\mathrm{\Omega }$ scattering phase shifts, scattering length, effective range, and binding energy to provide another approach of STAR data analysis. Our results show there exists an $N\mathrm{\Omega }$ “bound” state, which can be observed by the $N-\mathrm{\Omega }$ correlation analysis with RHIC and LHC data, or by the new developed automatic scanning system at J-PARC. In addition, we also find that the hidden-color channel coupling is important for the $N\mathrm{\Omega }$ system to develop intermediate-range attraction.

Probabilities for heavy-ion two-neutron transfer reactions $P_{2\mathrm{n}}$ are often discussed in comparison with the square of the corresponding probabilities for the one-neutron transfer process ${\left(P_{1\mathrm{n}}\right)}^2$, implicitly assuming that ${\left(P_{1\mathrm{n}}\right)}^2$ provides the probability of two-neutron transfer reactions in the absence of the pairing correlation. We use a schematic coupled-channels model, in which the transfers are treated as effective inelastic channels, and demonstrate that this model leads to $P_{2\mathrm{n}}={\left(P_{1\mathrm{n}}\right)}^2/4$, rather than $P_{2\mathrm{n}}={\left(P_{1\mathrm{n}}\right)}^2$, in the pure sequential limit. We argue that a simple model with spin-up and spin-down neutrons in a single-particle orbital also leads to the same conclusion.

We calculate the $\mathrm{\Lambda }$ polarization in an exact analytical, rotating model based on parameters extracted from a high resolution (3+1)D particle-in-cell relativistic hydrodynamics calculation. The polarization is attributed to effects from thermal vorticity and for the first time the effects of the radial and axial acceleration are also studied separately.

Background: Temperature is an important parameter in studying many important questions in heavy-ion collisions. A thermometer based on the isobaric yield ratio (IYR) has been proposed [Ma et al., Phys. Rev. C 86, 054611 (2012); Phys. Rev. C 88, 014609 (2013)].

Purpose: An improved thermometer $\left(T_{IB}\right)$ is proposed based on the difference between IYRs. $T_{IB}$ obtained from isobars in different reactions will be compared.

Methods: The yields of three isobars are employed in $T_{IB}$. The residual free energy of the three isobars are replaced by that of the binding energy. No secondary decay modification for odd $A$ fragment is used in $T_{IB}$.

Results: The measured fragment yields in the $140A\text{MeV}{}^{40,48}\text{Ca}+{}^9\text{Be}\left({}^{181}\text{Ta}\right)$ and ${}^{58,64}\text{Ni}+{}^9\text{Be}\left({}^{181}\text{Ta}\right)$, the $1A\text{GeV}{}^{124,136}\text{Xe}+\text{Pb}$, and the ${}^{112,124}\text{Sn}+{}^{112,124}\text{Sn}$ reactions have been analyzed to obtain $T_{IB}$ from IMFs. $T_{IB}$ from most of the fragments in the ${}^{40,48}\text{Ca}$ and ${}^{58,64}\text{Ni}$ reactions is in the range of $0.6\text{MeV}<T_{IB}<3.5\text{MeV}$. $T_{IB}$ from most of the fragments in the ${}^{124}\text{Xe}$ and ${}^{112,124}\text{Sn}$ reactions is in the range of $0.5\text{MeV}<T_{IB}<2.5\text{MeV}$, while the range is $0.5\text{MeV}<T_{IB}<4\text{MeV}$ from most of the fragments in the ${}^{136}\text{Xe}$ reaction. In general, for most of the fragments $T_{IB}$ in the ${}^{40,48}\text{Ca}$ and ${}^{58,64}\text{Ni}$ reactions are very similar (except in the very neutron-rich fragments), and $T_{IB}$ from IMFs in the ${}^{124,136}\text{Xe}$ and ${}^{112,124}\text{Sn}$ reactions is also similar. A slight dependence of $T_{IB}$ on $A$ is found.

Conclusions: Using the binding energy of the nucleus, $T_{IB}$ can be obtained without knowledge of the free energies of fragments. In the investigated reactions, $T_{IB}$ from most of the IMFs is low.

Excited states in ${}^{135}\mathrm{Pr}$ have been investigated using the reaction ${}^{123}\mathrm{Sb}({}^{16}\mathrm{O},4n){}^{135}\mathrm{Pr}$ at an incident beam energy of 82 MeV. The partial level scheme has been established for negative-parity states with addition of new $\gamma$-ray transitions. The directional correlation and polarization measurements have been performed to assign spin parity for most of the reported $\gamma$-ray transitions. At high spin, a negative-parity dipole band $\left(\mathrm{\Delta }I=1\right)$ has been reported along with the observation of new crossover $E2$ transitions. Tilted Axis Cranking (TAC) calculations have been performed by considering a three-quasiparticle (3qp) configuration $\pi {\left(h_{11/2}\right)}^1\otimes \nu {\left(h_{11/2}\right)}^{-2}$ and a five-quasiparticle (5qp) configuration $\pi {\left(h_{11/2}\right)}^1{\left(g_{7/2}\right)}^2\otimes \nu {\left(h_{11/2}\right)}^{-2}$ for the lower and upper parts of the band, respectively. The observed results are compared with the results of the theoretical (TAC) calculations.

The $\beta$ decay of the $N=Z$ nucleus ${}^{72}\text{Kr}$ has been studied with the total absorption spectroscopy technique at ISOLDE (CERN). A total $B\left(\text{GT}\right)=0.79\left(4\right)g_A^2/4\pi$ has been found up to an excitation energy of 2.7 MeV. The $B\left(\text{GT}\right)$ distribution obtained is compared with predictions from state-of-the-art theoretical calculations to learn about the ground state deformation of ${}^{72}\text{Kr}$. Although a dominant oblate deformation is suggested by direct comparison with quasiparticle random phase approximation (QRPA) calculations, beyond-mean-field and shell-model calculations favor a large oblate-prolate mixing in the ground state.

Spin-polarized neutron matter is studied using chiral two- and three-body forces. We focus, in particular, on predictions of the energy per particle in ferromagnetic neutron matter at different orders of chiral effective field theory and for different choices of the resolution scale. We discuss the convergence pattern of the predictions and their cutoff dependence. We explore to what extent fully polarized neutron matter behaves (nearly) like a free Fermi gas. We also consider the more general case of partial polarization in neutron matter as well as the presence of a small proton fraction. In other words, in our calculations, we vary both spin and isospin asymmetries. Confirming the findings of other microscopic calculations performed with different approaches, we report no evidence for a transition to a polarized phase of neutron matter.

Based on the isospin-dependent Boltzmann–Uehling–Uhlenbeck (IBUU) transport model, effects of the $\mathrm{\Delta }$ resonance potential on the free $n/p$ and ${\pi }^{-}/{\pi }^{+}$ ratios in the central collision of ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ at beam energies of 200 and 400 MeV/nucleon are studied. It is found that the effect of the $\mathrm{\Delta }$ potential on the ratio of pre-equilibrium free $n/p$ is invisible. The effect of $\mathrm{\Delta }$ isovector potential on the kinetic-energy-integrating ratio of ${\pi }^{-}/{\pi }^{+}$ may be observable only at lower incident beam energies and with stiffer symmetry energy. The strength of the $\mathrm{\Delta }$ isoscalar potential affects the height of the ${\pi }^{-}/{\pi }^{+}$ ratio around the Coulomb peak but does not affect the kinetic-energy-integrating ratio ${\pi }^{-}/{\pi }^{+}$. In heavy-ion collisions at intermediate energies, relating to the question of nonconservation of energy on $\mathrm{\Delta }$ or $\pi$ productions, one can replace the $\mathrm{\Delta }$ potential by the nucleon isoscalar potential especially when a soft symmetry energy is employed.

We present a simple method to derive breakup probabilities of weakly bound nuclei by measuring only elastic (or quasi-elastic) scattering for the system under investigation and a similar tightly bound system. When transfer followed by breakup is an important process, one can derive only the sum of breakup and transfer probabilities.