Within the framework of an isospin and momentum-dependent hadronic transport model, the single and double ${\pi }^{-}/{\pi }^{+}$ ratios in mirror reaction systems of ${}^{22}\mathrm{O}+{}^{22}\mathrm{Na}$ and ${}^{22}\mathrm{Si}+{}^{22}\mathrm{Na}$ at the incident beam energy of 400 MeV/nucleon are studied. It is found there are opposite symmetry energy effects on the single ratios from the neutron-rich and the proton-rich reactions. Due to the opposite isospin degrees of freedom, the double ${\pi }^{-}/{\pi }^{+}$ ratio taken from neutron-rich and proton-rich reactions displays more sensitivity to the density dependence of the nuclear symmetry energy in broader pion kinetic energy region; thus the double charged pion ratio from the mirror systems may be a useful probe for the high-density behavior of the nuclear symmetry energy.

Background: Inelastic neutrino-nucleus scattering through the weak neutral-current plays an important role in a stellar environment where the transport of neutrinos determines the rate of cooling. Since there are no direct experimental data on neutral-current neutrino-nucleus cross sections available, only the modeling of these reactions provides the relevant input for supernova simulations.

Purpose: To establish a fully self-consistent framework for neutral-current neutrino-nucleus reactions based on a relativistic nuclear energy density functional.

Methods: Neutrino-nucleus cross sections are calculated using a weak Hamiltonian and nuclear properties of initial and excited states are obtained with a relativistic Hartree-Bogoliubov model and a relativistic quasiparticle random phase approximation that is extended to include pion contributions for unnatural parity transitions.

Results: Inelastic neutral-current neutrino-nucleus cross sections for ${}^{12}$C, ${}^{16}$O, ${}^{56}$Fe, ${}^{56}$Ni, and even isotopes ${}^{92-100}$Mo as well as respective cross sections averaged over distribution of supernova neutrinos.

Conclusions: The present study provides insight into neutrino-nucleus scattering cross sections in the neutral channel, their theoretical uncertainty in view of recently developed microscopic models, and paves the way for systematic self-consistent large-scale calculations involving open-shell target nuclei.

I have reanalyzed previous data from the ${}^9$Be($t,p$) reaction to extract energies and widths for the two states near 3.9 MeV. Results are energies of 3889.27 ± 1.03 and 3954.53 ± 1.16 and widths of 3.2(8) and 7.9(7), all in keV, for the 5/2${}^{-}$ and 3/2${}^{-}$ states, respectively.

Rotational bands in ${}^{158}$Er at ultrahigh spin have been studied in the framework of relativistic and nonrelativistic nuclear density-functional theories. Consistent results are obtained across the theoretical models used but some puzzles remain when confronted with experiment. Namely, the many-body configurations which provide good description of experimental transition quadrupole moments and dynamic moments of inertia require substantial increase of the spins of observed bands as compared with experimental estimates, which are still subject to large uncertainties. If, however, the theoretical spin assignments turned out to be correct, experimental band 1 in ${}^{158}$Er would be the highest spin structure ever observed.

Low-lying collective states of ${}^{154}$Sm are studied via the ${}^{12}$C(${}^{154}$Sm,${}^{154}$Sm${}^{*}$) Coulomb excitation reaction at 85$\%$ of the Coulomb barrier (570 MeV) using the Gammasphere Ge-detector array. Absolute transition strengths are obtained from the Coulomb excitation cross sections deduced from the relative $\gamma$-ray yields. The results include transition strengths for $E2$ decays of energy levels in the low-spin part of the first excited $K^{\pi }=0^{+}$ rotational band of ${}^{154}$Sm. The agreement of these results with the confined $\beta$-soft rotor model predictions establishes the assignment of this band as a $\beta$ band.

We present ab initio calculations of the binding energy and radii of the two-neutron halo nucleus ${}^6$He using two-body low-momentum interactions based on chiral effective field theory potentials. Calculations are performed via a hyperspherical-harmonics expansion where the convergence is sped up introducing an effective interaction for nonlocal potentials. The latter is essential to reach a satisfactory convergence of the extended matter radius and of the point-proton radius. The dependence of the results on the resolution scale is studied. A correlation is found between the radii and the two-neutron separation energy. The importance of three-nucleon forces is pointed out comparing our results and previous calculations to experiment.

We investigate the emergence and evolution of shape coexistence in the neutron-deficient lead isotopes within the interacting boson model (IBM) plus configuration mixing with microscopic input based on the Gogny energy density functional (EDF). The microscopic potential-energy surface obtained from the constrained self-consistent Hartree-Fock-Bogoliubov method employing the Gogny-D1M EDF is mapped onto the coherent-state expectation value of the configuration mixing IBM Hamiltonian. In this way, the parameters of the IBM Hamiltonian are fixed for each of the three relevant configurations (spherical, prolate, and oblate) associated to the mean-field minima. Subsequent diagonalization of the Hamiltonian provides the excitation energy of the low-lying states and transition strengths among them. The model predictions for the $0^{+}$ level energies and evolving shape coexistence in the considered lead chain are consistent both with experiment and with the indications of the Gogny-EDF energy surfaces.

An improved variational ansatz is proposed and implemented for variational many-body wave functions for light nuclei with nucleons interacting through Argonne (AV${}_{18}$) and Urbana IX (UIX) three-nucleon interactions. The new ansatz is based upon variationally distinguishing between the various components of the two-body Jastrow and operatorial correlations, which are operated upon by three-body and spin-orbit correlations. We obtain noticeable improvement in the quality of the wave function and lowering of the energies compared to earlier results. The new energies are −8.38(1), −28.07(1), and −29.90(1) MeV for ${}^3$H, ${}^4$He, and ${}^6$Li, respectively. Though, the present improved ansatz still fails to stabilize the ${}^6$Li nucleus against a breakup into an α particle and a deuteron by 390 KeV; nonetheless, it is an improvement over previous studies.

Background: Gamow-Teller (GT) transition strength distributions in stable and unstable $pf$-shell isotopes are key inputs for estimating electron-capture rates important for stellar evolution. Charge-exchange experiments at intermediate beam energies have long been used to test theoretical predictions for GT strengths, but previous experiments were largely restricted to stable nuclei. Since a large fraction of the nuclei relevant for astrophysical applications (including key nuclei such as ${}^{56}$Ni) are unstable, new methods are needed to perform charge-exchange experiments in inverse kinematics with unstable isotopes.

Purpose: The ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were measured in inverse kinematics in order to extract GT strengths for transitions to ${}^{56}$Cu and ${}^{55}$Ni, respectively. The extracted strength distributions were compared with shell-model predictions in the $pf$ shell using the KB3G and GXPF1J interactions. By invoking isospin symmetry, these strength distributions are relevant for electron captures on the ground states of ${}^{56}$Ni and ${}^{55}$Ni to final states in ${}^{56}$Co and ${}^{55}$Co, respectively.

Method: Differential cross sections and excitation energy spectra for the ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were determined by measuring neutrons recoiling from a liquid hydrogen target into the Low Energy Neutron Detector Array. GT contributions to the spectra were extracted by using a multipole decomposition analysis and were converted to strengths by employing the proportionality between GT strength and differential cross section at zero linear momentum transfer.

Results: GT strengths from ${}^{56}$Ni and ${}^{55}$Co were extracted up to excitation energies of 8 and 15 MeV, respectively. Shell-model calculations performed in the $pf$ shell with the GXPF1J interaction reproduced the experimental GT strength distributions better than calculations with the KB3G interaction.

Conclusions: A new technique for measuring ($p,n$) charge-exchange reactions on unstable nuclei was successfully developed. It can be used to study the isovector response of unstable nuclei in any mass region and for excitation energies beyond the particle decay threshold. In the first experiment, ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were studied and GT transition strengths were extracted for the purpose of testing shell-model calculations used to estimate electron-capture rates in simulations of late stellar evolution. The calculation using the GXPF1J interaction was found to best reproduce the experimental strength distribution.

We perform no-core full configuration calculations for the lithium isotopes ${}^6$Li, ${}^7$Li, and ${}^8$Li with the realistic nucleon-nucleon interaction JISP16. We obtain a set of observables, including spectra, radii, multipole moments, and transition probabilities, and compare with experiment where available. We also present one-body density distributions for selected states. Convergence properties of these density distributions shed light on the convergence properties of one-body observables. We obtain underbinding by 0.5, 0.7, and 1.0 MeV for ${}^6$Li, ${}^7$Li, and ${}^8$Li, respectively. Magnetic moments are well converged and agree with experiment to within 20$\%$.

In a recent paper [Phys. Rev. C 85, 011601(R) (2012)] we proposed that excitation energy at scission ($E_{\mathrm{sc}}^{*}$) measured at high initial excitation energy ($E^{*}$), which can be provided via proton induced spallation reaction approach, is a novel probe of nuclear dissipation ($\beta$). The present work is devoted to studying within the framework of the stochastic Langevin model the robustness of the conclusion with respect to the apparent changes in the spin of compound nuclei (CNs), in the magnitudes of the neutron-to-proton ratio of a CN and its fissility and size. In addition, the role of deformation effects as well as the influence resulting from different coefficients applied to deformation-dependent level-density parameters are investigated. All these factors have been found to have important effects on particle multiplicity, evaporation residue cross section, etc., which have widely been used as probes of nuclear dissipation. However, we find that the significant sensitivity of $E_{\mathrm{sc}}^{*}$ to $\beta$ at high $E^{*}$ is little affected by these factors. The result demonstrates that a measurement of $E_{\mathrm{sc}}^{*}$ in proton-nucleus reactions can place a robust constraint on the friction strength in the fission process of highly excited nuclei.

Mass-angle correlations and mass ratio distributions of fission fragments have been measured in ${}^{12}\mathrm{C}+{}^{238}\mathrm{U}$ and ${}^{18}\mathrm{O}+{}^{232}\mathrm{Th}$ reactions, both leading to the same compound nucleus ${}^{250}$Cf (fissility = 0.86), with matching excitation energies at near and sub-barrier energies. In both systems, there is no mass-angle correlation in the entire energy region studied. However, it is found that the variance of the mass ratio distribution in the ${}^{18}\mathrm{O}+{}^{232}\mathrm{Th}$ system is consistently higher than in the ${}^{12}\mathrm{C}+{}^{238}\mathrm{U}$ system at all excitation energies. This points to the fact that mass equilibration has not been fully achieved in the ${}^{18}\mathrm{O}+{}^{232}\mathrm{Th}$ reaction in comparison to the ${}^{12}\mathrm{C}+{}^{238}\mathrm{U}$ reaction, indicating the presence of quasifission in the ${}^{18}\mathrm{O}+{}^{232}\mathrm{Th}$ system.

The mass shift effect at finite temperature on $J/\psi$ production in relativistic heavy ion collisions is calculated in a detailed transport approach, including both mean field and collision terms. While the momentum-integrated nuclear modification factor $R_{AA}$ is not sensitive to the mass shift, the reduced threshold for $J/\psi$ regeneration in the quark-gluon plasma leads to a remarkable enhancement for the differential $R_{AA}$ at low transverse momentum.

In high-energy heavy ion collisions, the onset of the quark-gluon plasma is the color glass condensate, dominated by gluons. The final state is hadronic and dominated by pions and kaons. Here we investigate an effective approach of QCD with these bosonic fields that can help to describe the transition of gluons into light mesons. Formally, our approach consists in integrating out the quark fields from the QCD path integral. Because analytical or numerical approaches to compute the resulting fermion determinant are not yet available, we utilize symmetry principles to arrive at an effective gluon-meson action. In this way the fermionic fields are replaced by light mesons, such as the pions and the $\sigma$ field. We apply our effective action to compute the number of pions and kaons per gluon emitted by a Boltzmann gluon gas and determine their respective multiplicities as a function of a spontaneously generated gluon mass. We conclude that an effective gluon mass remains finite at $T=T_c$.

We study the sensitivity of the $r$-process abundance pattern to neutron capture rates along the rare earth region ($A\sim 150$ to $A\sim 180$). We introduce the concepts of large nuclear flow and flow saturation, which determine the neutron capture rates that are influential in setting the rare earth abundances. We illustrate the value of the two concepts by considering high entropy conditions favorable for rare earth peak production and identifying important neutron capture rates among the rare earth isotopes. We also show how these rates influence nuclear flow and specific sections of the abundance pattern.

An experiment using the ${}^{11}$B(${}^3$He,$d$)${}^{12}$C reaction was performed at iThemba LABS at an incident energy of 44 MeV and analyzed with a high energy-resolution magnetic spectrometer, to reinvestigate states in ${}^{12}$C published in 1971. The original investigation reported the existence of an 11.16 MeV state in ${}^{12}$C that displays a 2${}^{+}$ nature. In the present experiment, data were acquired at laboratory angles of 25${}^{\circ }$, 30${}^{\circ }$, and 35${}^{\circ }$, which is part of the center-of-mass (c.m.) angle range in the original measurements where a clear signature of such a state was observed. These new low-background measurements revealed no evidence of the previously reported state at 11.16 MeV in ${}^{12}$C.

Synthesis of element 120 in the ${}^{58}\mathrm{Fe}+{}^{244}$Pu hot fusion reaction has been evaluated by means of a modified “fusion by diffusion” (FBD) model. In the model, dynamic evolution from dinucleus to mononucleus is taken into account with the two-dimensional coupled Langenvin equations. The calculated maximum evaporation residue cross sections in 3$n$- and 4$n$-evaporation channels of ${}^{58}\mathrm{Fe}+{}^{244}$Pu reaction are $0.005$ and $0.016$ pb, which are far below the present experimental sensitivity for the detection of one decay. The fusion probability calculated with the modified FBD model clearly shows that fusion of the heavy system ${}^{58}\mathrm{Fe}+{}^{244}$Pu is severely hindered.

Within the framework of light-front field theory, we reassess the electromagnetic form factors of the pion and kaon. Comparison with experiment is made for the full range of momentum transfer, $q^2<0$, including recent data. The light-front model's single regulator mass, $m_R$, of the $\overline{q}q$ bound-state vertex function is initially adjusted to reproduce the weak decay constants, $f_{\pi }$ and $f_K$, and both mesons' charge radii, $\langle r_{\pi }\rangle$ and $\langle r_K\rangle$. We study the behavior of these observables under variation of the quark masses and find an optimized parameter set, $m_u=m_d$, $m_s$, and $m_R$, for which they are in sensibly better agreement with experiment than in a previous analysis, a feature also observed for the elastic form factors, in particular at small $q^2$. This model refinement is important in view of an extension to vector and heavy-light mesons.

Background: Four strong single-particle bound levels with strikingly similar level spacings have recently been measured in ${}^{131}$Sn and ${}^{133}$Sn. This similarity has not yet been addressed by a theoretical nuclear structure model. Information on these single-particle bound levels, as well as on resonant levels above the neutron capture threshold, is also needed to determine neutron capture cross sections—and corresponding capture reaction rates—on ${}^{130,132}$Sn. The ${}^{130}$Sn$(n,\gamma$) rate was shown in a recent sensitivity study to significantly impact the synthesis of heavy elements in the $r$-process in supernovae.

Purpose: Understand the structure of bound and resonant levels in ${}^{131,133}$Sn, and determine if the densities of unbound resonant levels are sufficiently high to warrant statistical model treatments of neutron capture on ${}^{130,132}$Sn.

Method: Single-particle bound and resonant levels for ${}^{131,133}$Sn are self-consistently calculated by the analytical continuation of the coupling constant (ACCC) method based on a relativistic mean field (RMF) theory with BCS approximation.

Results: We obtain four strong single-particle bound levels in both ${}^{131,133}$Sn with an ordering that agrees with experiments and spacings that, while differing from experiment, are consistent between the Sn isotopes. We also find at most one single-particle level in the effective energy range for neutron captures in the $r$-process.

Conclusions: Our RMF+ACCC+BCS model successfully reproduces observed single-particle bound levels in ${}^{131,133}$Sn and self-consistently predicts single-particle resonant levels with densities too low for widely used traditional statistical model treatments of neutron capture cross sections on ${}^{130,132}$Sn employing Fermi gas level density formulations.

We analyze the role played by long-distance symmetries within the context of the similarity renormalization group (SRG) approach, which is based on phase-shift-preserving continuous unitary transformations that evolve Hamiltonians with a cutoff on energy differences. We find that there is a SRG cutoff for which almost perfect fulfillment of Wigner symmetry is found. We discuss the possible consequences of such a finding.