A measurement was performed at the white neutron source Geel Linear Accelerator (GELINA) of the Institute for Reference Materials and Measurements to determine the cross sections for the ($n$, $n^{\prime }\gamma$) and ($n$, $2n^{\prime }\gamma$) reactions on ${}^{56}\mathrm{Fe}$. The Gamma Array for Inelastic Neutron Scattering (GAINS) was used. The results are scaled to the neutron-induced fission cross section of ${}^{235}\mathrm{U}$. The paper emphasizes the multiple checks performed to assure the consistency of the results. $\gamma$ production cross sections, total inelastic cross sections, and level production cross sections were determined. A good agreement exists with previous measurements. Theoretical calculations were performed with the talys 1.6 reaction code using default parameters, but also using a microscopic approach. These calculations are discussed in comparison to the experimental data.

High-energy proton- and deuteron-nucleus collisions provide an excellent tool for studying a wide array of physics effects, including modifications of parton distribution functions in nuclei, gluon saturation, and color neutralization and hadronization in a nuclear environment, among others. All of these effects are expected to have a significant dependence on the size of the nuclear target and the impact parameter of the collision, also known as the collision centrality. In this article, we detail a method for determining centrality classes in $p\left(d\right)+A$ collisions via cuts on the multiplicity at backward rapidity (i.e., the nucleus-going direction) and for determining systematic uncertainties in this procedure. For $d+\text{Au}$ collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV we find that the connection to geometry is confirmed by measuring the fraction of events in which a neutron from the deuteron does not interact with the nucleus. As an application, we consider the nuclear modification factors $R_{p\left(d\right)+A}$, for which there is a bias in the measured centrality-dependent yields owing to auto correlations between the process of interest and the backward-rapidity multiplicity. We determine the bias-correction factors within this framework. This method is further tested using the hijing Monte Carlo generator. We find that for $d+\text{Au}$ collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV, these bias corrections are small and vary by less than 5% (10%) up to $p_T=10$ (20) GeV/$c$. In contrast, for $p+\text{Pb}$ collisions at $\sqrt{s_{{}_{NN}}}=5.02$ TeV we find that these bias factors are an order of magnitude larger and strongly $p_T$ dependent, likely attributable to the larger effect of multiparton interactions.

The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open-heavy-flavor production in $\mathrm{Cu}+\mathrm{Cu}$ collisions at $\sqrt{s_{NN}}=200$ GeV through the measurement of electrons at midrapidity that originate from semileptonic decays of charm and bottom hadrons. In peripheral $\mathrm{Cu}+\mathrm{Cu}$ collisions an enhanced production of electrons is observed relative to $p+p$ collisions scaled by the number of binary collisions. In the transverse momentum range from 1 to 5 GeV/$c$ the nuclear modification factor is $R_{AA}\sim 1.4$. As the system size increases to more central $\mathrm{Cu}+\mathrm{Cu}$ collisions, the enhancement gradually disappears and turns into a suppression. For $p_T>3$ GeV/$c$, the suppression reaches $R_{AA}\sim 0.8$ in the most central collisions. The $p_T$ and centrality dependence of $R_{AA}$ in $\mathrm{Cu}+\mathrm{Cu}$ collisions agree quantitatively with $R_{AA}$ in $d+\text{Au}$ and $\mathrm{Au}+\mathrm{Au}$ collisions, if compared at a similar number of participating nucleons $\langle N_{\mathrm{part}}\rangle$.

At low stellar temperatures the energy release due to the CN cycle is regulated by its slowest reaction ${}^{14}\mathrm{N}(p,\gamma ){}^{15}\mathrm{O}$, the rate of which strongly depends on the subthreshold resonance at $E_{\mathrm{c}}.\mathrm{m}.=-504\mathrm{keV}$, which corresponds to the 6.79 MeV state in ${}^{15}\mathrm{O}$. By using the Doppler-shift attenuation method and the ${}^3\mathrm{He}({}^{16}\mathrm{O},\alpha ){}^{15}\mathrm{O}$ reaction to populate the state, we obtained an upper limit on the lifetime of this state of $\tau <1.8\mathrm{fs}$ [68.3% confidence level (C.L.)]. In addition we measured the lifetimes of the 6.18 and 6.86 MeV states to be $\tau <2.5$ and $\tau =13.3_{-1.2}^{+0.9}\mathrm{fs}$, respectively (68.3% C.L.), in good agreement with the literature.

The similarity renormalization group (SRG) has been successfully applied to soften interactions for ab initio nuclear calculations. In almost all practical applications in nuclear physics, an SRG generator with the kinetic energy operator is used. With this choice, a fast convergence of many-body calculations can be achieved, but at the same time substantial three-body interactions are induced even if one starts from a purely two-nucleon ($\mathit{NN}$) Hamiltonian. Three-nucleon ($3N$) interactions can be handled by modern many-body methods. However, it has been observed that when including initial chiral $3N$ forces in the Hamiltonian, the SRG transformations induce a non-negligible four-nucleon interaction that cannot be currently included in the calculations for technical reasons. Consequently, it is essential to investigate alternative SRG generators that might suppress the induction of many-body forces while at the same time might preserve the good convergence. In this work we test two alternative generators with operators of block structure in the harmonic oscillator basis. In the no-core shell model calculations for ${}^3\mathrm{H}$, ${}^4\mathrm{He}$, and ${}^6\mathrm{Li}$ with chiral $\mathit{NN}$ force, we demonstrate that their performances appear quite promising.

We discuss a role of diproton correlation in two-proton emission from the ground state of a proton-rich nucleus, ${}^6\mathrm{Be}$. Assuming the three-body structure of $\alpha +p+p$ configuration, we develop a time-dependent approach in which the two-proton emission is described as a time evolution of a three-body metastable state. With this method, the dynamics of the two-proton emission can be intuitively discussed by monitoring the time dependence of the two-particle density distribution. With a model Hamiltonian which well reproduces the experimental two-proton decay width, we show that a strongly correlated diproton emission is a dominant process in the early stage of the two-proton emission. When the diproton correlation is absent, the sequential two-proton emission competes with the diproton emission, and the decay width is underestimated. These results suggest that the two-proton emission decays provide a good opportunity to probe the diproton correlation in proton-rich nuclei beyond the proton dripline.

The structure of the neutron-rich silicon isotopes ${}^{36,38,40}\mathrm{Si}$ was studied by one-neutron and one-proton knockout reactions at intermediate beam energies. We construct level schemes for the knockout residues ${}^{35,37,39}\mathrm{Si}$ and ${}^{35,37,39}\mathrm{Al}$ and compare knockout cross sections to the predictions of an eikonal model in conjunction with large-scale shell-model calculations. The agreement of these calculations with the present experiment lends support to the microscopic explanation of the enhanced collectivity in the region of ${}^{42}\mathrm{Si}$. We also present an empirical method for reproducing the observed low-momentum tails in the parallel momentum distributions of knockout residues.

The stability of the $\beta$-equilibrated dense nuclear matter is analyzed with respect to the thermodynamic stability conditions. Based on the density dependent M3Y effective nucleon-nucleon interaction, the effects of the nuclear incompressibility on the proton fraction in neutron stars and the location of the inner edge of their crusts and core-crust transition density and pressure are investigated. The high-density behavior of symmetric and asymmetric nuclear matter satisfies the constraints from the observed flow data of heavy-ion collisions. The neutron star properties studied using $\beta$-equilibrated neutron star matter obtained from this effective interaction for a pure hadronic model agree with the recent observations of the massive compact stars. The density, pressure, and proton fraction at the inner edge separating the liquid core from the solid crust of neutron stars are determined to be ${\rho }_t=0.0938 {\mathrm{fm}}^{-3}$, ${\mathrm{P}}_t=0.5006 \mathrm{MeV} {\mathrm{fm}}^{-3}$, and ${\mathrm{x}}_{p\left(t\right)}=0.0308$, respectively.

A method for calculating the occupation probability of the number of harmonic-oscillator (HO) quanta is developed for a precise few-body wave function obtained in a correlated Gaussian basis. The probability distributions of two- to four-nucleon wave functions obtained by using different nucleon-nucleon ($NN$) interactions are analyzed to gain insight into the characteristic behavior of the various interactions. Tensor correlations as well as short-range correlations play a crucial role in enhancing the probability of high HO excitations. For the excited states of ${}^4\mathrm{He}$, the interaction dependence is much less because high HO quanta are mainly responsible for describing the relative-motion function between the $3N+N$ (${}^3\mathrm{H}+p$ and ${}^3\mathrm{He}+n$) clusters.

The ${}^{240}\mathrm{Am}(n,f$) cross section has been measured for the first time above 4 MeV, using the surrogate-ratio method over the neutron energy range of 200 keV to 14 MeV. The reactions ${}^{243}\mathrm{Am}(p,tf$) and ${}^{238}\mathrm{U}(p,tf$), which proceed through the fissioning excited nuclei ${}^{241}\mathrm{Am}$* and ${}^{236}\mathrm{U}$*, were used as surrogates for the desired ${}^{240}\mathrm{Am}(n,f$) and ${}^{235}\mathrm{U}(n,f$) reactions. The experiment was fielded using the STARLiTeR detector system with a recently commissioned VME-based data acquisition system. The 38.4-MeV proton beam used in these measurements was provided by the K150 cyclotron at the Texas A&M Cyclotron Institute. The measured ${}^{240}\mathrm{Am}(n,f$) cross section disagrees with many of the most recent evaluations, and a reevaluation is recommended.

Using the light-front pion wave function based on a Bethe-Salpeter amplitude model, we study the properties of the pion in symmetric nuclear matter. The pion model we adopt is well constrained by previous studies to explain the pion properties in vacuum. In order to consistently incorporate the constituent up and down quarks of the pion immersed in symmetric nuclear matter, we use the quark-meson coupling model, which has been widely applied to various hadronic and nuclear phenomena in a nuclear medium with success. We predict the in-medium modifications of the pion electromagnetic form factor, charge radius, and weak decay constant in symmetric nuclear matter.

The ${}^{10}\mathrm{B}\left(p,{\alpha }_0\right){}^7\mathrm{Be}$ bare nucleus astrophysical $S\left(E\right)$ factor has been measured for the first time at energies from about 100 keV down to about 5 keV by means of the Trojan Horse method (THM). In this energy region, the $S\left(E\right)$ factor is strongly dominated by the 8.699 MeV ${}^{11}\mathrm{C}$ level ($J^{\pi }={\frac{5}{2}}^{+}$), producing an $s$-wave resonance centered at about 10 keV in the entrance channel. Up to now, only the high–energy tail of this resonance has been measured, while the low-energy trend is extrapolated from the available direct data. The THM has been applied to the quasifree ${}^2\mathrm{H}({}^{10}\mathrm{B},{\alpha }_0$ ${}^7\mathrm{Be}$)n reaction induced at a boron-beam energy of 24.5 MeV. An accurate analysis leads to the determination of the ${}^{10}\mathrm{B}\left(p,{\alpha }_0\right){}^7\mathrm{Be}$ $S\left(E\right)$ factor and of the corresponding electron screening potential $U_e$, thus giving for the first time an independent evaluation of it.

Background: Recent experiments on $\beta$-delayed fission reported an asymmetric mass yield in the neutron-deficient nucleus ${}^{180}\mathrm{Hg}$. Earlier experiments in the mass region $A=190–200$ close to the $\beta$-stability line, using the $(p,f)$ and $(\alpha ,f)$ reactions, observed a more symmetric distribution of fission fragments. While the $\beta$-delayed fission of ${}^{180}\mathrm{Hg}$ can be associated with relatively low excitation energy, this is not the case for light-ion reactions, which result in warm compound nuclei. The low-energy fission of ${}^{180,198}\mathrm{Hg}$ has been successfully described by theory in terms of strong shell effects in pre-scission configurations associated with dinuclear structures.

Purpose: To elucidate the roles of proton and neutron numbers and excitation energy in determining symmetric- and asymmetric-fission yields, we compute and analyze the isentropic potential energy surfaces of ${}^{174,180,198}\mathrm{Hg}$ and ${}^{196,210}\mathrm{Po}$.

Methods: We use the finite-temperature superfluid nuclear density functional theory for excitation energies up to $E^{*}=30$ MeV and zero angular momentum. For our theoretical framework, we consider the Skyrme energy density functional ${\mathrm{SkM}}^{*}$ and a density-dependent pairing interaction.

Results: For ${}^{174,180}\mathrm{Hg}$, we predict fission pathways consistent with asymmetric fission at low excitation energies, with the symmetric-fission pathway opening very gradually as excitation energy is increased. For ${}^{198}\mathrm{Hg}$ and ${}^{196}\mathrm{Po}$, we expect the nearly symmetric-fission channel to dominate. ${}^{210}\mathrm{Po}$ shows a preference for a slightly asymmetric pathway at low energies, and a preference for a symmetric pathway at high energies.

Conclusions: Our self-consistent theory suggests that excitation energy weakly affects the fission pattern of the nuclei considered. The transition from the asymmetric fission in the proton-rich nuclei to a more symmetric fission in the heavier isotopes is governed by the shell structure of pre-scission configurations.

The flow vorticity development is studied in the reaction plane of peripheral relativistic heavy-ion reactions at energies just above the threshold of the transition to a quark-gluon plasma (QGP). Earlier calculations at higher energies with larger initial angular momentum predicted significant vorticity leading to measurable $\Lambda$ polarization. Here we discuss the possibility of vorticity and circulation in dense plasma at lower temperatures. In low-viscosity QGP this vorticity still remains significant.

Background: Clustering phenomena in $N\ne Z$ nuclei provide an opportunity to understand the interplay between cluster and nucleon degrees of freedom.

Purpose: To study resonances in the ${}^{18}\mathrm{O}$ spectrum, populated in ${}^{14}\mathrm{C}+\alpha$ elastic scattering.

Method: The thick target inverse kinematics technique was used to measure the excitation function for the ${}^{14}\mathrm{C}+\alpha$ elastic scattering. A 42-MeV ${}^{14}\mathrm{C}$ beam was used to populate states of excitation energy up to 14.9 MeV in ${}^{18}\mathrm{O}$. The analysis was performed using a multilevel, multichannel $R$-matrix approach.

Results: Detailed spectroscopic information, including spin parities, partial $\alpha$- and neutron-decay widths and dimensionless reduced widths, was obtained for excited states in ${}^{18}\mathrm{O}$ between 8 and 14.9 MeV in excitation energy. Cluster-nucleon configuration interaction model calculations of the same quantities are performed and compared to the experimental results.

Conclusions: Strong fragmentation of large $\alpha$-cluster strengths is observed in the spectrum of ${}^{18}\mathrm{O}$, making the $\alpha$-cluster structure of ${}^{18}\mathrm{O}$ quite different from the pattern of known quasirotational bands of alternating parity that are characteristic of $N=Z$, even-even nuclei like ${}^{16}\mathrm{O}$ and ${}^{20}\mathrm{Ne}$.

High spin states of ${}^{33}\mathrm{S}$ populated through ${}^{27}\mathrm{Al}{(}^{12}\mathrm{C},\alpha \mathrm{pn}){}^{33}\mathrm{S}$ reaction at E$\left({}^{12}\mathrm{C}\right)=40$ MeV have been studied using the Indian National Gamma Array (INGA) facility. The level scheme was extended and modified utilizing data from the $\gamma -\gamma$ coincidence, directional correlation, and linear polarization measurements. Three levels of the negative parity yrast sequence were found to be connected by strong E2 transitions. The lifetimes of these states determined by the Doppler shift attenuation method have been utilized to study the evolution of collectivity with spin. Large basis shell model calculations have been performed to understand the microscopic origin of these levels.

Complete and incomplete fusion cross sections for the ${}^9\mathrm{Be}$ $+{}^{181}\mathrm{Ta}$ system were measured at near barrier energies, using the offline gamma ray spectroscopy method. The results were compared with coupled channel calculations that do not take into account the coupling of the breakup channel, using a double folding potential as bare potential. A complete fusion suppression of the order of 35% was found, at energies above the barrier, whereas the total fusion cross sections are in agreement with the calculations. The ratio between incomplete fusion and total fusion at energies above the Coulomb barrier was found to be $32\pm 1\%$. At sub-barrier energies one observes some enhancement of total fusion cross section.

The ultrarelativistic quantum molecular dynamics (UrQMD) transport model is used to study a system-size and energy dependence of the pion production in high energy collisions. New data of the NA61/SHINE Collaboration on spectra of negatively charged pions in proton-proton interactions at Super Proton Synchrotron (SPS) energies are considered. These results are compared with the corresponding data of the NA49 Collaboration in central Pb + Pb collisions at the same collision energies per nucleon. Mean pion multiplicity per participant nucleon, inverse slope parameter of the transverse momentum spectra, and width of rapidity distribution are investigated. A role of isospin effects is discussed. We find that the UrQMD model predicts a nonmonotonous behavior of mean transverse mass with collision energy for positively charged pions at mid-rapidity in inelastic proton-proton interactions. This will be checked soon experimentally by the NA61/SHINE Collaboration.