Prompt fission neutron spectrum (PFNS) measurements for the neutron-induced fission of ${}^{238}\mathrm{U}$ are carried out at incident neutron energies of 2.0, 2.5, and 3.0 MeV, respectively. The time-of-flight technique is employed to determine the energy of fission neutrons. The prompt fission neutron energy spectra so obtained are analyzed using Watt parametrization to derive the neutron multiplicity and average prompt fission neutron energy. The present experimental PFNS data are compared with the evaluated spectra taken from the ENDF/B-VII.1 library and the predictive calculations carried out using the empire-3.2 (Malta) code with built-in Los Alamos (LA) and Kornilov PFNS models. The sensitivity of the empire-3.2 LA model–calculated PFNS to the nuclear level density parameter of the average fission fragment and to the total kinetic energy is investigated. empire-3.2 LA model PFNS calculations that use Madland 2006–recommended values [D. G. Madland, Nucl. Phys. A 772, 113 (2006)] of the total kinetic energy and the level density parameter $a=A/(10\pm 0.5)$ compare very well to measured data at all incident neutron incident energies.

The quantum statistics (QS) correlations of identical bosons are well known to be sensitive to the space-time extent and dynamics of the particle emitting source in high-energy collisions. While two-pion correlations are most often experimentally measured, the QS correlations of three pions and higher are rarely explored. A set of techniques to isolate and analyze three- and four-pion QS correlations is presented. In particular, the technique of built correlation functions allows one to more easily study the effects of quantum coherence at finite relative momenta instead of at the unmeasured intercept of correlation functions.

In this work, the role of the ${\mathrm{\Delta }}^{*}$ resonances in the process of $pp\to n{K}^{+}{\mathrm{\Sigma }}^{+}$ are systematically investigated with the effective Lagrangian approach and the isobar model. We find that a $P_{31}$ state, either ${\mathrm{\Delta }}^{*}\left(1750\right)$ or ${\mathrm{\Delta }}^{*}\left(1910\right)$ is favored by the data while the $P_{33}$ state, namely ${\mathrm{\Delta }}^{*}\left(1920\right)$, has small contribution. Besides, either the subthreshold $S_{31}{\mathrm{\Delta }}^{*}\left(1620\right)$ resonance or strong $n\mathrm{\Sigma }$ final state interaction or both have a possible contribution at near threshold region, depending on the measured cross sections. We demonstrate the invariant mass distributions and the Dalitz plots in order to investigate whether it is possible to distinguish the controversial $K\mathrm{\Sigma }$ production mechanism in these observables.

We generalize the notion of partial dynamical symmetry (PDS) to a system of interacting bosons and fermions. In a PDS, selected states of the Hamiltonian are solvable and preserve the symmetry exactly, while other states are mixed. As a first example of such novel symmetry construction, spectral features of the odd-mass nucleus ${}^{195}\mathrm{Pt}$ are analyzed.

We demonstrate that the prolate shape of the uranium nucleus generates anticorrelation between spectator asymmetry and initial-state ellipticity of the collision zone, providing a way to constrain the initial event shape in U $+$ U collisions. As an application, we show that this can be used to separate the background contribution due to flow from the signals of the chiral magnetic effect.

The longest-range part of the nuclear force from the one-pion exchange governs the energy dependence of the scattering amplitude in the near-threshold region and imposes correlations between the coefficients in the effective range expansion. These correlations may be regarded as low-energy theorems and are known to hold to a high accuracy in the neutron-proton ${}^3{S}_1$ partial wave. We generalize the low-energy theorems to the case of unphysical pion masses and provide results for the correlations between the coefficients in the effective range expansion in this partial wave for pion masses up to $M_{\pi }\sim 400\text{MeV}$. We discuss the implications of our findings for the available and upcoming lattice-quantum-chromodynamics simulations of two-nucleon observables.

Experimental giant monopole resonance energies are now known to constrain nuclear incompressibility of symmetric nuclear matter $K$ and its density slope $M$ at a particular value of subsaturation density, the crossing density ${\rho }_c$. Consistent with these constraints, we propose a reasonable way to construct a plausible equation of state of symmetric nuclear matter in a broad density region around the saturation density ${\rho }_0$. Help of two additional empirical inputs, the value of ${\rho }_0$ and that of the energy per nucleon $e\left({\rho }_0\right)$ are needed. The value of $K\left({\rho }_0\right)$ comes out to be $211.9\pm 24.5$ MeV.

Background: The systematic trend in mean-square charge radii as a function of proton or neutron number exhibits a discontinuity at the nucleon-shell closures. While the established $N=28$ shell closure is evident in the charge radii of the isotopic chains of K through Mn, a similar signature of the $N=20$ shell closure is absent in the Ca region.

Purpose: The isotope shift between neutron-deficient ${}^{36}\mathrm{K}$ and ${}^{37}\mathrm{K}$ was determined to investigate the change of the mean-square charge radii across $N=20$ in the K isotopic chain.

Methods: The $D1$ atomic hyperfine spectra of ${}^{36}\mathrm{K}$ and ${}^{37}\mathrm{K}$ were measured using an optical pumping and subsequent $\beta$-decay asymmetry detection technique. Atomic rate equations were solved to fit the resonant line shape. The result was compared to Skyrme energy-density functional and shell-model calculations.

Results: The isotope shift was obtained as $\delta {\nu }^{37,36}=-139\left(4\right)\left(3\right)$ MHz. Using a re-evaluated isotope shift, $\delta {\nu }^{39,37}=-264\left(2\right)\left(3\right)$ MHz, the isotope shift relative to ${}^{39}\mathrm{K}$ was determined to be $\delta {\nu }^{39,36}=-403\left(5\right)\left(4\right)$ MHz. The differential mean-square charge radius was then deduced as $\delta {\langle r^2\rangle }^{39,36}=-0.16\left(5\right)\left(8\right){\mathrm{fm}}^2$. The Skyrme energy-density functional and shell-model calculations overpredict the experimental values below $N=20$ and underpredict them above $N=20$, and their agreement is marginal.

Conclusions: The absence of the shell-closure signature at $N=20$ in the K isotopic chain is understood as a balance between the monopole and the quadrupole proton-core polarizations below and above $N=20$, respectively.

Cross sections for neutron-induced reactions of ${}^{241}\text{Am}$ in the resonance region have been evaluated. Results of time-of-flight cross section experiments carried out at the GELINA, LANSCE, ORELA and Saclay facilities have been combined with optical model calculations to derive consistent cross sections from the thermal energy region up to the continuum region. Resolved resonance parameters were derived from a resonance shape analysis of transmissions, capture yields, and fission yields in the energy region up to 150 eV using the refit code. From a statistical analysis of these parameters, a neutron strength function (${10}^4{S}_0=1.01\pm 0.12$), mean level spacing ($D_0=0.60\pm 0.01$ eV) and average radiation width ($\langle {\mathrm{\Gamma }}_{{\gamma }_0}\rangle =43.3\pm 1.1$ meV) for $s$-wave resonances were obtained. Neutron strength functions for higher partial waves ($l>0$) together with channel and effective scattering radii were deduced from calculations based on a complex mean-field optical model potential, applying an equivalent hard-sphere scattering radius approximation.

Intermediate-energy Coulomb excitation of ${}^{32}\mathrm{Mg}$ using in-beam $\gamma$-ray spectroscopy with a relatively thick lead target was studied at a beam energy of 195 MeV/nucleon at the RIKEN Radioactive Isotope Beam Factory (RIBF). The angular distribution of the inelastic scattering was analyzed with distorted-wave calculations taking into account both the Coulomb and the nuclear excitation contributions. A $B\left(E2\right)$ value of 432(51) $e^2{\mathrm{fm}}^4$ was extracted, which agrees with most of the previously reported results obtained at several tens of MeV/nucleon. Our investigation demonstrates that the electromagnetic properties of exotic nuclei can be studied with Coulomb excitation at beam energies of a few hundreds of MeV/nucleon, where a thicker target can be used to increase the excitation yields.

In ultracentral heavy-ion collisions, anisotropic hydrodynamic flow is generated by density fluctuations in the initial state rather than by geometric overlap effects. For a given centrality class, the initial fluctuation spectrum is sensitive to the method chosen for binning the events into centrality classes. We show that sorting events by total initial entropy or by total final multiplicity yields event classes with equivalent statistical fluctuation properties, in spite of viscous entropy production during the fireball evolution. With this initial entropy-based centrality definition we generate several classes of ultracentral Pb + Pb collisions at Cern Large Hadron Collider energies and evolve the events using viscous hydrodynamics with nonzero shear but vanishing bulk viscosity. Comparing the predicted anisotropic flow coefficients for charged hadrons with CMS data we find that both the Monte Carlo Glauber (MC-Glb) and Monte Carlo Kharzeev-Levin-Nardi (MC-KLN) models produce initial fluctuation spectra that are incompatible with the measured final anisotropic flow power spectrum, for any choice of the specific shear viscosity. In spite of this failure, we show that the hydrodynamic model can qualitatively explain, in terms of event-by-event fluctuations of the anisotropic flow coefficients and flow angles, the breaking of flow factorization for elliptic, triangular, and quadrangular flow measured by the CMS experiment. For elliptic flow, this factorization breaking is large in ultracentral collisions. We conclude that the bulk of the experimentally observed flow factorization breaking effects are qualitatively explained by hydrodynamic evolution of initial-state fluctuations, but that their quantitative description requires a better understanding of the initial fluctuation spectrum.

For nucleus-nucleus collisions at energies currently available at the BNL Relativistic Heavy Ion Collider (RHIC), we calculate observables in two different transport approaches, i.e., the $n$-body molecular dynamical model “relativistic quantum molecular dynamics for strongly interacting matter with phase transition or crossover” (RSP) and the two-body parton hadron string dynamics (PHSD), starting out from the same distribution in the initial energy density at the quark gluon plasma (QGP) formation time. The RSP dynamics is based on the Nambu-Jona-Lasinio (NJL) Lagrangian, whereas in PHSD the partons are described by the dynamical quasiparticle model (DQPM). Despite the very different description of the parton properties and their interactions and of the hadronization in both approaches, the final transverse momentum distributions of pions turn out to be quite similar, which is less visible for the strange mesons owing to the large NJL cross sections involved. Our findings can be attributed, in part, to a partial thermalization of the quark degrees of freedom in central $\mathrm{Au}+\mathrm{Au}$ collisions for both approaches. The rapidity distribution of mesons shows a stronger sensitivity to the nature of the degrees of freedom involved and to their interaction strength in the QGP.

The critical densities and impact of forming $\mathrm{\Delta }\left(1232\right)$ resonances in neutron stars are investigated within an extended nonlinear relativistic mean-field (RMF) model. The critical densities for the formation of four different charge states of $\mathrm{\Delta }\left(1232\right)$ are found to depend differently on the separate kinetic and potential parts of nuclear symmetry energy, the first example of a microphysical property of neutron stars to do so. Moreover, they are sensitive to the in-medium $\mathrm{\Delta }$ mass $m_{\mathrm{\Delta }}$ and the completely unknown $\mathrm{\Delta }\text{−}\rho$ coupling strength $g_{\rho \mathrm{\Delta }}$. In the universal baryon-meson coupling scheme where the respective $\mathrm{\Delta }$-meson and nucleon-meson coupling constants are assumed to be the same, the critical density for the first ${\mathrm{\Delta }}^{-}\left(1232\right)$ to appear is found to be ${\rho }_{\mathrm{\Delta }}^{\mathrm{crit}}=(2.08\pm 0.02){\rho }_0$ using RMF model parameters consistent with current constraints on all seven macroscopic parameters usually used to characterize the equation of state of isospin-asymmetric nuclear matter at saturation density ${\rho }_0$. Moreover, the composition and the mass-radius relation of neutron stars are found to depend significantly on the values of the $g_{\rho \mathrm{\Delta }}$ and $m_{\mathrm{\Delta }}$.

We introduce a new parametric initial-condition model for high-energy nuclear collisions based on eikonal entropy deposition via a “reduced-thickness” function. The model simultaneously describes experimental proton-proton, proton-nucleus, and nucleus-nucleus multiplicity distributions and generates nucleus-nucleus eccentricity harmonics consistent with experimental flow constraints. In addition, the model is compatible with ultracentral uranium-uranium data unlike existing models that include binary collision terms.

Deuteron elastic cross sections, as well as neutron, proton, and $\alpha$-particle emission spectra, from $d+{}^{54,56,58}\text{Fe}$ reactions have been measured with deuteron beam energies of 5, 7, and 9 MeV. Optical model parameters have been tested against our experimental data. The fraction of total reaction cross section responsible for the formation of compound nuclei has been deduced from the angular distributions. The degree of discrepancy between calculated and experimental compound cross sections was found to increase with increasing neutron number. The nuclear level densities of the residual nuclei ${}^{55}\text{Co},{}^{57}\text{Co},{}^{55}\text{Fe},{}^{57}\text{Fe},{}^{52}\text{Mn}$, and ${}^{54}\text{Mn}$ have been deduced from the compound double differential cross sections. The Gilbert-Cameron model with Iljinov parameter systematics [A. S. Iljinov and M. V. Mebel, Nucl. Phys. A 543, 517 (1992)] was found to have a good agreement with our results.

We have analyzed elastic scattering angular distributions and total reaction cross sections of the exotic nuclei ${}^{9,11}\text{Li}$ on ${}^{208}\text{Pb}$, at energies below and above the Coulomb barrier. For this purpose, we have used an optical potential with no adjustable parameters, composed by the nuclear São Paulo potential, derived from the nonlocal nature of the interaction, and the Coulomb dipole polarization potential, derived from the semiclassical theory of Coulomb excitation. Within this formalism, we identified an unusual long-range absorption for the ${}^{11}\text{Li}+{}^{208}\text{Pb}$ system, which is dominated by the Coulomb interaction. We compare it to the absorption mechanisms observed for ${}^6\text{He}+{}^{208}\text{Pb}$ which, unlike those of ${}^{11}\text{Li}+{}^{208}\text{Pb}$, take place at small interacting distances, where both Coulomb and nuclear interactions are important. The proposed approach shows to be a fundamental basis to study reactions involving exotic nuclei.

The description of nucleons scattering off doubly closed-shell nuclei ${}^{16}\mathrm{O}$ and ${}^{208}\mathrm{Pb}$ at energies below 50 MeV is carried out in a fully self-consistent framework of the particle-vibration coupling approach. The applications are performed with commonly used Skyrme-type effective interactions. Nucleon-nucleus optical potentials are thus calculated without ad hoc adjusted parameters. These potentials are then solved with standard optical model codes (dwba98 in the present case). Empirical nucleon-nucleus elastic angular distributions are thus successfully reproduced.

Starting from state-by-state calculations of exclusive rates of the ordinary muon capture, we evaluated total ${\mu }^{-}$ capture rates for a set of light- and medium-weight nuclear isotopes. We employed a version of the proton-neutron quasiparticle random-phase approximation ($pn$-QRPA, for short) which uses as realistic nuclear forces the Bonn C-D one-boson exchange potential. Special attention was paid on the percentage contribution to the total ${\mu }^{-}$ capture rate of specific low-spin multipolarities resulting by summing over the corresponding multipole transitions. The nuclear method used offers the possibility of estimating separately the individual contributions to the total and partial rates of the polar-vector and axial-vector components of the weak-interaction Hamiltonian for each accessible final state of the daughter nucleus. One of our main goals is to provide a reliable description of the charge-changing transitions matrix elements entering the description of other similar semileptonic nuclear processes like the charged-current neutrino-nucleus reactions, the electron capture on nuclei, the single ${\beta }^{\pm }$-decay mode, etc., which play important role in currently interesting laboratory and astrophysical applications like the neutrino detection through lepton-nucleus interaction probes and neutrino nucleosynthesis. Such results can also be useful in various ongoing muon capture experiments at Paul Scherrer Institute (PSI), Fermilab, Japan Proton Accelerator Research Complex, and Research Center for Nuclear Physics, Osaka University.

The density and temperature dependence of the nuclear symmetry free energy is investigated using microscopic two- and three-body nuclear potentials constructed from chiral effective field theory. The nuclear force models and many-body methods are benchmarked to properties of isospin-symmetric nuclear matter in the vicinity of the saturation density as well as the virial expansion of the neutron matter equation of state at low fugacities. The free energy per particle of isospin-asymmetric nuclear matter is calculated assuming a quadratic dependence of the interaction contributions on the isospin asymmetry. The spinodal instability at subnuclear densities is examined in detail.