Background: Collective motions in quantum many-body systems are described as bosonic excitations. Multi-phonon excitations in atomic nuclei, however, were observed very rarely. In particular, the first two-phonon $\gamma$ vibrational $\left(2\gamma \right)$ excitation in odd-$A$ nuclei was reported in 2006 and only a few have been known so far. Two theoretical calculations for the data on ${}^{103}\mathrm{Nb}$ were performed, one of which was done by the present author within a limited model space up to $2\gamma$ basis states. Quite recently, conspicuously enhanced $B\left(E2\right)\mathrm{s}$, reduced $E2$ transition probabilities, feeding $2\gamma$ states were observed in ${}^{105}\mathrm{Nb}$ and conjectured that their parent states, called band (4), are candidates of $3\gamma$ states.

Purpose: In the present work, the model space is enlarged up to $4\gamma$ basis states. The purpose is twofold: One is to see how the description of $2\gamma$ eigenstates in the previous work is improved, and the other is to examine the existence of collective $3\gamma$ eigenstates, and when they exist, study their collectivity through calculating interband $B\left(E2\right)\mathrm{s}$.

Method: The particle-vibration coupling model based on the cranking model and the random-phase approximation is used to calculate the vibrational states in rotating odd-$A$ nuclei. Interband $B\left(E2\right)\mathrm{s}$ are calculated by adopting the method of the generalized intensity relation.

Results: The present model reproduces well the energy spectra and $B\left(E2\right)\mathrm{s}$ of $0\gamma \text{−}2\gamma$ states in ${}^{103}\mathrm{Nb}$ and ${}^{105}\mathrm{Nb}$. For $3\gamma$ states, calculated spectra indicate that the most collective state with the highest $K$ at zero rotation feels strong Coriolis force after rotation sets in and consequently is observed with lowered $K$, where $K$ is the projection of the angular momentum to the $z$ axis. The calculated states account for the observed enhanced $B\left(E2\right)\mathrm{s}$ within factors of 2–3.

Conclusions: The present calculation with the enlarged model space reproduces the observed $0\gamma \text{−}2\gamma$ states well and predicts properties of collective $3\gamma$ states. The most collective one is thought to be the main component of the observed band (4) from the analyses of the energy spectra and interband $B\left(E2\right)\mathrm{s}$ although some mixing with states that are not included in the present model would be possible.

Low-energy $\beta$-delayed fission of ${}^{194,196}\mathrm{At}$ and ${}^{200,202}\mathrm{Fr}$ was studied in detail at the mass separator ISOLDE at CERN. The fission-fragment mass distributions of daughter nuclei ${}^{194,196}\mathrm{Po}$ and ${}^{202}\mathrm{Rn}$ indicate a triple-humped structure, marking the transition between asymmetric fission of ${}^{178,180}\mathrm{Hg}$ and symmetric fission in the light Ra-Rn nuclei. Comparison with the macroscopic-microscopic finite-range liquid-drop model and the self-consistent approach employing the Gogny D1S energy density functional yields discrepancies. This demonstrates once more the need for dynamical fission calculations, because for both models the potential-energy surfaces lack pronounced structures, in contrast to those for the actinide region.

Background: Many important $\alpha$-particle induced reactions for nuclear astrophysics may only be measured using indirect techniques due to the small cross sections at the energy of interest. One such indirect technique is to determine the asymptotic normalization coefficients (ANCs) for near-threshold resonances extracted from sub-Coulomb $\alpha$-transfer reactions. This approach provides a very valuable tool for studies of astrophysically important reaction rates since the results are practically model independent. However, the validity of the method has not been directly verified.

Purpose: The aim of this Rapid Communication is to verify the technique using the ${}^{16}\mathrm{O}({}^6\mathrm{Li},d){}^{20}\mathrm{Ne}$ reaction as a benchmark. The ${}^{20}\mathrm{Ne}$ nucleus has a well-known $1^{-}$ state at an excitation energy of 5.79 MeV with a width of 28 eV. Reproducing the known value with this technique is an ideal opportunity to verify the method.

Method: The $1^{-}$ state at 5.79 MeV is studied using the $\alpha$-transfer reaction ${}^{16}\mathrm{O}({}^6\mathrm{Li},d){}^{20}\mathrm{Ne}$ at sub-Coulomb energies.

Results: The partial $\alpha$ width for the $1^{-}$ state at excitation energy of 5.79 MeV is extracted and compared with the known value, allowing the accuracy of the method to be evaluated.

Conclusions: This study demonstrates that extracting the ANCs using sub-Coulomb $\alpha$-transfer reactions is a powerful tool that can be used to determine the partial $\alpha$ width of near-threshold states that may dominate astrophysically important nuclear reaction rates.

Particle-$\gamma$ coincidences from the ${}^{89}\mathrm{Y}(p,p^{\prime }\gamma ){}^{89}\mathrm{Y}$ and ${}^{89}\mathrm{Y}(d,p\gamma ){}^{90}\mathrm{Y}$ reactions were utilized to obtain $\gamma$-ray spectra as function of excitation energy. The Oslo method was used to extract the level density from the particle-$\gamma$ coincidence matrices. The impact of the $N=50$ shell closure on the level densities is discussed within the framework of a combinatorial quasiparticle model.

A mapping from a triaxial rotor Hamiltonian to that of the SU(3) limit description in the interacting boson model (IBM) is established, which is achieved by the SU(3) realization of the triaxial rotor. A detailed comparison between the triaxial dynamics generated from the quadrupole-deformed rotor and those from the IBM image is made. The results indicate that the mapping can be well realized. A preliminary test for ${}^{128}\mathrm{Ba}$ further confirms the finite-$N$ effect of the mapping. It thus provides an alternative way to understand the triaxiality in the finite-$N$ system and additional insight into understanding the SU(3) IBM theory from microscopic point of view via the SU(3) shell model.

Background: An unexpected enhancement in the $\gamma$-ray strength function, as compared to the low-energy tail of the giant dipole resonance (GDR), has been observed for Sc, Ti, V, Fe, and Mo isotopes for $E_{\gamma }<4$ MeV. This enhancement was not observed in subsequent analyses on Sn isotopes, but a pygmy dipole resonance (PDR) centered at $E_{\gamma }\approx 8$ MeV was however detected. The $\gamma$-ray strength functions measured for Cd isotopes exhibit both features over the range of isotopes, with the low-energy enhancement decreasing and PDR strength increasing as a function of neutron number. This suggests a transitional region for the onset of low-energy enhancement, and also that the PDR strength depends on the number of neutrons.

Purpose: The $\gamma$-ray strength functions of ${}^{105–108}\mathrm{Pd}$ have been measured in order to further explore the proposed transitional region.

Method: Experimental data were obtained at the Oslo Cyclotron Laboratory by using the charged particle reactions $({}^3\mathrm{He},{}^3\mathrm{He}{}^{\prime }\gamma )$ and (${}^3\mathrm{He},\alpha \gamma$) on ${}^{106,108}\mathrm{Pd}$ target foils. Particle-$\gamma$ coincidence measurements provided information on initial excitation energies and the corresponding $\gamma$-ray spectra, which were used to extract the level densities and $\gamma$-ray strength functions according to the Oslo method.

Results: The $\gamma$-ray strength functions indicate a sudden increase in magnitude for $E_{\gamma }>4$ MeV, which is interpreted as a PDR centered at $E_{\gamma }\approx 8$ MeV. An enhanced $\gamma$-ray strength at low energies is also observed for ${}^{105}\mathrm{Pd}$, which is the lightest isotope measured in this work.

Conclusions: A PDR is clearly identified in the $\gamma$-ray strength functions of ${}^{105–108}\mathrm{Pd}$, and a low-energy enhancement is observed for ${}^{105}\mathrm{Pd}$. Further, the results correspond and agree very well with the observations from the Cd isotopes, and support the suggested transitional region for the onset of low-energy enhancement with decreasing mass number. The neutron number dependency of the PDR strength is also evident.

We present a formalism to solve the Bethe-Goldstone scattering equation without the use of partial wave expansion which is alternative to the one we developed in a previous work. The present approach is more suitable for the calculation of in-medium nucleon-nucleon cross sections, which are the focal point of this paper. The impact of removing the spherical approximation on the angle and energy dependence of, particularly, in-medium proton-proton and proton-neutron differential cross sections is discussed along with its potential implication.

We study the effects of the symmetry energy on the neutron drip density and properties of nuclei in neutron star crusts. The nonuniform matter around the neutron drip point is calculated by using the Thomas-Fermi approximation with the relativistic mean-field model. The neutron drip density and the composition of the crust are found to be correlated with the symmetry energy and its slope. We compare the self-consistent Thomas-Fermi approximation with other treatments of surface and Coulomb energies and find that these finite-size effects play an essential role in determining the equilibrium state at low density.

Background: Single-particle occupancies for a wide range of magic and near-magic nuclei are significantly below the values predicted by independent-particle shell-model calculations.

Purpose: We aim in this paper to address the question: To what extent does the extracted structure information have uncertainties due to approximations involved in the reaction formalism and assumed dynamic model?

Method: The proton knockout reaction ${}^{12}\mathrm{C}{(p,2p)}^{11}\mathrm{B}$ at 400 MeV/u incident energy is analyzed using the few-body Faddeev–Alt-Grassberger-Sandhas reaction framework. A two-body model is used for ${}^{12}\mathrm{C}$ which involves an inert ${}^{11}\mathrm{B}\left({\frac{3}{2}}^{-}\right)$ core and a valence proton. The contributions of higher order terms beyond the single scattering approximation are studied, in particular the ones corresponding to the rescattering between ${}^{12}\mathrm{C}$ constituents.

Results: Total cross section and core transverse momentum distribution are calculated. We have found that rescattering terms between the composite nucleus constituents contribute dominantly to the absorptive distortion.

Conclusions: The accurate treatment of these rescattering terms in the reaction formalism is crucial if one aims to extract reliable structure information from the data. We have also found that work needs to be performed in the reaction theory in order to incorporate a complete structure description of the projectile nucleus and to bridge the proton knockout results with those obtained from electron scattering.

Based on the stochastic Langevin model, we study the effects of angular momentum ($\ell$) on the multiplicities of postsaddle neutrons, protons, and $\alpha$ particles as a function of postsaddle friction strength ($\beta$) for ${}^{200}\mathrm{Pb}$ nucleus. It is shown that with increasing $\ell$ the sensitivity of these particles to $\beta$ is significantly enhanced. Moreover, we find that neutrons (charged particles) evaporated from light ${}^{200}\mathrm{Pb}$ having high $\ell$ and high excitation energy $E^{*}$ exhibit a similar (greater) sensitivity to $\beta$ as compared to the case of heavy ${}^{251}\mathrm{Es}$ having low $\ell$ and low $E^{*}$. Our findings suggest that on the experimental side, to accurately probe information of postsaddle dissipation with particle multiplicity, in particular with the multiplicity of charged particles, it is optimal to populate light fissioning systems with large angular momentum and high excitation energy.

Updated constraints from neutron star masses and radii impose stronger restrictions on the equation of state for baryonic matter at high densities and low temperatures. The existence of $2M_{\odot }$ neutron stars rules out many soft equations of state with prominent “exotic” compositions. The present work reviews the conditions required for the pressure as a function of baryon density to satisfy these constraints. Several scenarios for sufficiently stiff equations of state are evaluated. The common starting point is a realistic description of both nuclear and neutron matter based on a chiral effective field theory approach to the nuclear many-body problem. Possible forms of hybrid matter featuring a quark core in the center of the star are discussed using a three-flavor Polyakov–Nambu–Jona-Lasinio model. It is found that a conventional equation of state based on nuclear chiral dynamics meets the astrophysical constraints. Hybrid matter generally turns out to be too soft unless additional strongly repulsive correlations, e.g., through vector current interactions between quarks, are introduced. The extent to which strangeness can accumulate in the equation of state is also discussed.

Charge separation induced by the chiral magnetic effect has suggested that some $\mathcal{P}$- or $\mathcal{C}P$-odd metastable domains could be produced in a QCD vacuum in the early stage of relativistic heavy-ion collisions. Based on a multiphase transport model, our results suggest that a domain-based scenario with final state interactions can describe the solenoidal tracker at RHIC (STAR) detector measurements of both same- and opposite-charge azimuthal angle correlations, $\langle cos({\varphi }_{\alpha }+{\varphi }_{\beta })\rangle$, in Au + Au collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV. The occupancy factor of the total volume of domains over the fireball volume is small, which indicates that the size and number of metastable domains should be relatively small in the early stage of a quark-gluon plasma.

We investigate the $\overline{p}p\to \varphi \varphi$ reaction within an effective Lagrangian approach. We show that the inclusion of either a scalar meson $f_0$ or a tensor meson $f_2$ in the $s$-channel can lead to a fairly good description of the bump structure of the total cross section around the invariant $\overline{p}p$ mass $W\simeq 2.2$ GeV, which cannot be reproduced with only the “background” contributions from $t$- and $u$-channel $N^{*}\left(1535\right)$ resonance as studied in a previous work. From the fits, we infer the properties of the involved scalar or tensor resonances.

Background: Measurement of the energy dependence of the fusion cross section at sub-barrier energies provides an important test for theoretical models of fusion.

Purpose: The aim of the study is to extend the measurement of fusion cross sections in the sub-barrier domain for the ${}^{18}\mathrm{O}+{}^{12}\mathrm{C}$ system, and to use the new experimental data to confront microscopic calculations of fusion.

Method: Evaporation residues produced in fusion of ${}^{18}\mathrm{O}$ ions with ${}^{12}\mathrm{C}$ target nuclei were detected with good geometric efficiency and identified by measuring their energy and time-of-flight. Theoretical calculations with a density-constrained time-dependent Hartree-Fock (DC-TDHF) theory include for the first time the effect of pairing on the fusion cross section.

Results: Comparison of the measured fusion excitation function with the predictions of the DC-TDHF calculations reveal that the experimental data exhibit a smaller decrease in cross section with decreasing energy than is theoretically predicted.

Conclusion: The larger cross sections observed at the lowest energies measured indicate a larger tunneling probability for the fusion process. This larger probability can be associated with a smaller, narrower fusion barrier than presently included in the theoretical calculations.

Hagedorn states are characterized by being very massive hadron-like resonances and by not being limited to quantum numbers of known hadrons. To generate such a zoo of different Hagedorn states, a covariantly formulated bootstrap equation is solved by ensuring energy conservation and conservation of baryon number $B$, strangeness $S$, and electric charge $Q$. The numerical solution of this equation provides Hagedorn spectra, which also enable us to obtain the decay width for Hagedorn states needed in cascading decay simulations. A single Hagedorn state cascades by various two-body decay channels subsequently into final stable hadrons. All final hadronic observables such as masses, spectral functions, and decay branching ratios for hadronic feed-down are taken from a hadronic transport model. Strikingly, the final energy spectra of resulting hadrons are exponential, showing a thermal-like distribution with the characteristic Hagedorn temperature.

Rotational and electromagnetic properties of the yrast band in ${}^{102}\mathrm{Pd}$ are analyzed in terms of a phenomenological phonon model that includes anharmonic terms. Both the moment of inertia and $B\left(E2\right)$'s are well reproduced by the model, providing an independent confirmation of the multiphonon picture recently proposed. The (empirical) dependence of the phonon-phonon interaction on the phonon frequency, in Ru, Pd, and Ru isotopes, follows the expectations from particle-vibration coupling.

We present an approach that includes temperature-dependent shell effects and fluctuations of the pairing field in the thermal shape-fluctuation model (TSFM). We apply this approach to study the width of giant dipole resonance (GDR) in ${}^{97}\mathrm{Tc}$, ${}^{120}\mathrm{Sn}$, and ${}^{208}\mathrm{Pb}$. Our results demonstrate that the TSFM that includes pairing fluctuations can explain the recently observed quenching in the GDR width. We also show that to validate pairing prescriptions and the parameters involved, we require more and precise data.