A semimicroscopic model (particle-hole dispersive optical model) is formulated to describe the main relaxation modes of high-energy particle-hole-type excitations in medium-heavy mass nuclei. Within this model, Landau damping and the single-particle continuum are considered microscopically, while the spreading effect is treated phenomenologically, employing a statistical assumption. Description of direct nucleon decay of the above-mentioned excitations (including giant resonances) is a unique feature of the proposed model, which in applying to closed-shell nuclei is arranged for practical implementations. The methodical similarity of formulations of the single-quasiparticle and particle-hole optical models is emphasized.

We investigate the effects of secondary (knockout) protons, which constitute about $20\%$ of the observed protons at the solenoidal tracker detector (STAR) at the BNL Relativistic Heavy Ion Collider, on the higher order cumulants of proton and baryon numbers measured by event-by-event analyses in relativistic heavy-ion collisions. We argue that the contribution of this background effect on the cumulants is expressed by a simple formula and that hence their effects can be removed in the experimental analysis. It is discussed that this background effect has a non-negligible contribution to recently observed proton number cumulants at STAR, especially the third-order one, and that the removal of this effect is crucial to investigate the thermodynamical properties of the primordial hot medium appropriately.

Recent work has shown that a finite harmonic oscillator basis in nuclear many-body calculations effectively imposes a hard-wall boundary condition in coordinate space, motivating infrared extrapolation formulas for the energy and other observables. Here we further refine these formulas by studying two-body models and the deuteron. We accurately determine the box size as a function of the model space parameters, and compute scattering phase shifts in the harmonic oscillator basis. We show that the energy shift can be well approximated in terms of the asymptotic normalization coefficient and the bound-state momentum, discuss higher-order corrections for weakly bound systems, and illustrate this universal property using unitarily equivalent calculations of the deuteron.

Large-scale shell model calculations are performed within the $fp{g}_{9/2}$ valence space to study the odd-proton ${}^{57-62}$Mn isotopes of the neutron-rich region. The study emphasizes the importance of neutron $g_{9/2}$ excitations, which make it possible to extend the calculation to high-spin states, up to $J=27/2\hslash$ for the odd-mass ${}^{57,59,61}$Mn and $J=16\hslash$ for the odd-odd ${}^{58,60,62}$Mn, for both positive and negative parities. It is demonstrated that the extended pairing-plus-quadrupole interaction with monopole corrections captures main structure properties of these nuclei. We quantitatively compare the calculated levels with existing experimental data, and pay attention especially to those tentatively assigned states by experiment. Rotational features of the states involving neutron $g_{9/2}$ excitations are discussed.

Linear polarization measurements have been performed for $\gamma$ rays in ${}^{91}$Ru produced with the ${}^{58}$Ni(${}^{36}$Ar, $2p1n$$\gamma$)${}^{91}$Ru reaction at a beam energy of 111 MeV. The EXOGAM Ge clover array has been used to measure the $\gamma$-$\gamma$ coincidences, $\gamma$-ray linear polarization, and $\gamma$-ray angular distributions. The polarization sensitivity of the EXOGAM clover detectors acting as Compton polarimeters has been determined in the energy range 0.3–1.3 MeV. Several transitions have been observed for the first time. Measurements of linear polarization and angular distribution have led to the firm assignments of spin differences and parity of high-spin states in ${}^{91}$Ru. More specifically, calculations using a semiempirical shell model were performed to understand the structures of the first and second (21/2${}^{+}$) and (17/2${}^{+}$) levels. The results are in good agreement with the experimental data, supporting the interpretation of the nonyrast (21/2${}^{+}$) and (17/2${}^{+}$) states in terms of the $J_{\max }$ and $J_{\max }-2$ members of the seniority-three $\nu {\left(g_{9/2}\right)}^{-3}$ multiplet.

We study the effects of the tensor force, present in modern effective nucleon-nucleon interactions, in the spin instability of nuclear and neutron matter. Stability conditions of the system against certain very low energy excitation modes are expressed in terms of Landau parameters. It is shown that in the spin case, the stability conditions are equivalent to the condition derived from the spin susceptibility, which is obtained as the zero-frequency and long-wavelength limit of the spin response function calculated in the random phase approximation. Zero-range forces of the Skyrme type and finite-range forces of M3Y and Gogny type are analyzed. It is shown that for the Skyrme forces considered, the tensor effects are sizable and tend to increase the spin instability, which appears at smaller densities than in the case that the tensor is not taken into account. On the contrary, the tensor contribution of finite-range forces to the spin susceptibility is small or negligible for both isospin channels of symmetric nuclear matter as well as for neutron matter. A comparison with the spin susceptibility provided by realistic interactions is also presented.

The relationship between the quasi-elastic excitation function and the capture cross section is derived. The quasi-elastic data is shown to be a useful tool to extract the capture cross sections and the angular momenta of the captured systems for the reactions ${}^{16}$O+${}^{144,154}$Sm,${}^{208}$Pb, ${}^{20}$Ne+${}^{208}$Pb, and ${}^{32}$S+${}^{90,96}$Zr near and above the Coulomb barrier energies.

Background: The ratio between the rates of the reactions ${}^{17}$O${(\alpha ,n)}^{20}$Ne and ${}^{17}$O${(\alpha ,\gamma )}^{21}$Ne determines whether ${}^{16}$O is an efficient neutron poison for the $s$ process in massive stars, or if most of the neutrons captured by ${}^{16}$O$(n,\gamma )$ are recycled into the stellar environment. This ratio is of particular relevance to constrain the $s$ process yields of fast rotating massive stars at low metallicity.

Purpose: Recent results on the $(\alpha ,\gamma )$ channel have made it necessary to measure the $(\alpha ,n)$ reaction more precisely and investigate the effect of the new data on $s$ process nucleosynthesis in massive stars.

Method: The ${}^{17}$O$(\alpha ,n_{(0+1)})$ reaction has been measured with a moderating neutron detector. In addition, the $(\alpha ,n_1)$ channel has been measured independently by observation of the characteristic 1633 keV $\gamma$ transition in ${}^{20}$Ne. The reaction cross section was determined with a simultaneous R-matrix fit to both channels. $(\alpha ,n)$ and $(\alpha ,\gamma )$ resonance strengths of states lying below the covered energy range were estimated using their known properties from the literature.

Result: The reaction channels ${}^{17}$O${(\alpha ,n_0)}^{20}$Ne and ${}^{17}$O${(\alpha ,n_1\gamma )}^{20}$Ne were measured in the energy range $E_{\alpha }=800$ keV to 2300 keV. A new ${}^{17}$O$(\alpha ,n)$ reaction rate was deduced for the temperature range 0.1 GK to 10 GK. At typical He burning temperatures, the combination of the new $(\alpha ,n)$ rate with a previously measured $(\alpha ,\gamma )$ rate gives approximately the same ratio as current compilations. The influence on the nucleosynthesis of the $s$ process in massive stars at low metallicity is discussed.

Conclusions: It was found that in He burning conditions the $(\alpha ,\gamma )$ channel is strong enough to compete with the neutron channel. This leads to a less efficient neutron recycling compared to a previous suggestion of a very weak $(\alpha ,\gamma )$ channel. $S$ process calculations using our rates confirm that massive rotating stars do play a significant role in the production of elements up to Sr, but they strongly reduce the $s$ process contribution to heavier elements.

Nucleon flow in the process of evolution from dinucleus to mononucleus is studied by means of the coupled Langevin equations in the three-dimensional collective space of the radial, neck, and asymmetry degrees of freedom for the systems ${}^{48}\mathrm{Ca}+{}^{238}\mathrm{U}$ and ${}^{58}\mathrm{Fe}+{}^{248}\mathrm{Cm}$. For a comparison, the dynamic evolution of the neck is also investigated with the Langevin equations in the two-dimensional collective space of the radial and neck for these two reaction systems. The results show that nucleon flow is strongly damped in the stage of the dinuclear system due to the large dissipation associated with the mass asymmetry degree of freedom. The evaporation residue (ER) cross sections for the ${}^{48}\mathrm{Ca}+{}^{238}\mathrm{U}$ and ${}^{58}\mathrm{Fe}+{}^{248}\mathrm{Cm}$ reactions are evaluated by means of the modified fusion-by-diffusion (FBD) model, in which the injection distance distributions in the asymmetric fission valley obtained from the dynamic calculations are integrated. The theoretical excitation functions of the ${}^{48}\mathrm{Ca}+{}^{238}\mathrm{U}$ reaction are in good agreement with the experimental data. For the ${}^{58}\mathrm{Fe}+{}^{248}\mathrm{Cm}$ reaction, the maximum ER cross sections in 3$n$- and 4$n$-evaporation channels calculated with the three-dimensional Langevin equations are, respectively, $0.008$ and $0.020$ fb. We have demonstrated that the effect of drift and diffusion towards a more symmetric configuration on the ER cross sections is counterbalanced by that of diffusion towards a more asymmetric one. The ER excitation functions calculated with the two approaches are similar, which means that the impact of the nucleon flow during the process of neck evolution on the formation probability of superheavy nuclei is small in the framework of the dynamic model. In this sense, the frozen approximation of mass asymmetry in the FBD model should be reasonable in the hot fusion reactions.

We argue that the traditional event-plane method, which is still widely used to analyze anisotropic flow in ultrarelativistic heavy-ion collisions, should be abandoned because flow fluctuations introduce an uncontrolled bias in the measurement. Instead, one should use an alternative, such as the scalar-product method or cumulant method, which always measures an unambiguous property of the underlying anisotropic flow and therefore eliminates this bias, and does so without any disadvantages. It is known that this correction is important for precision comparisons of traditional $v_n$ measurements requiring better than a few-percent accuracy. However, we show that it is absolutely essential for correlations between different harmonics, such as those that have been recently measured by the ATLAS Collaboration, which can differ from the nominally measured quantity by a factor two or more. We also describe how, using the corrected analysis method, the information from different subevents can be combined in order to optimize the precision of analyses.

In the framework of the Glauber approach we investigate the influence of the initial fluctuations on various measures of the initial-state geometry in ${}^{63}\mathrm{Cu}+{}^{197}\mathrm{Au}$ and ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$ relativistic ion collisions. Comparing variants of the Glauber model (the wounded-nucleon model, the mixed model, and the hot-spot model) we indicate sensitivity of certain observables, in particular for the azimuthal eccentricity parameters as well as for the correlation of directions of the principal axes associated with the Fourier components. The effects of the nuclear deformation for the initial geometry are investigated. We apply glissando in our analysis.

Experimental results on the ${\Sigma }^{+}\left(1189\right)$ hyperon transverse polarization in photoproduction on a hydrogen target using the CLAS detector at Jefferson Laboratory are presented. The ${\Sigma }^{+}\left(1189\right)$ was reconstructed in the exclusive reaction $\gamma +p\to K_S^0+{\Sigma }^{+}\left(1189\right)$ via the ${\Sigma }^{+}\to p{\pi }^0$ decay mode. The $K_S^0$ was reconstructed in the invariant mass of two oppositely charged pions with the ${\pi }^0$ identified in the missing mass of the detected $p{\pi }^{+}{\pi }^{-}$ final state. Experimental data were collected in the photon energy range $E_{\gamma }=1.0$–3.5 GeV ($\sqrt{s}$ range 1.66–2.73 GeV). We observe a large negative polarization of up to 95$\%$. As the mechanism of transverse polarization of hyperons produced in unpolarized photoproduction experiments is still not well understood, these results will help to distinguish between different theoretical models on hyperon production and provide valuable information for the searches of missing baryon resonances.

We study the response of a single-component pair-correlated baryonic Fermi-liquid to density, spin, and their current perturbations. A complete set of response functions is derived in the low-temperature regime both within an effective theory based on a small momentum transfer expansion and within a numerical scheme valid for arbitrary momentum transfers. A comparison of these two approaches validates the perturbative approximation within the domain of its convergence. We derive the spectral functions of collective excitations associated with the density, density-current, spin, and spin-current perturbations. The dispersion relations of density and spin fluctuations are derived and it is shown that the density fluctuations lead to exciton-like undamped bound states, whereas the spin excitations correspond to diffusive modes above the pair-breaking threshold. The contribution of the collective pair-breaking modes to the specific heat of neutron matter at subnuclear densities is computed and is shown to be comparable to that of the degenerate electron gas at not too low temperatures.

A truncated partial wave analysis for the photoproduction of two pseudoscalar mesons on a nucleon is discussed with respect to the determination of a complete set of observables. For the selection of such a set we have applied a criterion previously developed for photo- and electrodisintegration of a deuteron, which allows one to find a ‘minimal’ set of observables for determining the partial wave amplitudes up to possible discrete ambiguities. The question of resolving the remaining ambiguities by invoking additional observables is discussed for the simplest case, when the partial wave expansion is truncated at the lowest total angular momentum of the final state $J_{\max }=1/2$. The resulting ‘fully’ complete set, allowing an unambiguous determination of the partial wave amplitudes, is presented.

Fission product mass distributions were measured in ${}^{20}$Ne + ${}^{232}$Th reaction at $E_{\mathrm{lab}}$ = 142.5 and 114 MeV using recoil catcher technique followed by off-line γ-ray spectrometry. Fission products formed predominantly in complete fusion fission (CFF) or transfer-induced fusion fission (TF) were distinguished based on their $A/Z$. Two groups of fission products that centered around $A/Z$ for CFF and TF were observed. Mass distributions for CFF and TF were obtained after applying corrections for charge distribution using parameters appropriate for CFF and TF. A symmetric mass distribution was observed for CFF. For TF, mass distribution was observed to be asymmetric, indicating a significant role of shell effect owing to the lower excitation energy of the fissioning system. Variance of mass distribution at $E_{\mathrm{lab}}$ = 142.5 MeV was calculated using the random neck rupture model (RNRM). The scission-point elongation parameter obtained by RNRM calculations was higher compared to that obtained from the liquid drop model.

Lattice QCD models predict the presence of a critical point in the QCD phase diagram where the first-order phase transition from a system of quark-gluon plasma to hadron gas ceases to exist. Higher moments of conserved quantities, such as net-charge, net-baryon number, and net-strangeness, are proposed to be sensitive probes for locating the critical point. The moments of net-charge distributions have been studied as a function of centrality for Au+Au collisions at $\sqrt{s_{NN}}=7.7$ to 200 GeV using three event generators, viz., UrQMD, HIJING, and THERMINATOR-2. The effect of centrality selection, resonance production, as well as contributions from particle species to the net-charge moments and their products have been studied. It is observed that mean of the net-charge distributions are dominated by net-protons, whereas standard deviation, skewness, and kurtosis closely follow net-pion distributions. These results, along with the predictions from the hadron resonance gas model, are presented.

The first systematic study of the correlation between the experimental giant dipole resonance (GDR) width and the average deformation $\langle \beta \rangle$ of the nucleus at finite excitation is presented for the mass region $A\sim 59$ to 208. We show that the width of the GDR ($\Gamma$) and the quadrupole deformation of the nucleus do not follow a linear relation, as predicted earlier, owing to the GDR-induced quadrupole moment, and the correlation also depends on the mass of the nuclei. The different empirical values of $\langle \beta \rangle$ extracted from the experimental GDR width match exceptionally well with the thermal shape fluctuation model. As a result, this universal correlation between $\langle \beta \rangle$ and $\Gamma$ provides a direct experimental probe to determine the nuclear deformation at finite temperature and angular momentum over the entire mass region.

We compare a set of equations of state derived within microscopic many-body approaches, and study their predictions as far as phenomenological data on nuclei from heavy ion collisions, and astrophysical observations on neutron stars are concerned. We find that all the data, taken together, put strong constraints not easy to be fulfilled accurately. Although no major discrepancies are found among the considered microscopic equations of state and with respect to the data, it turns out that, if one takes strictly the phenomenological constraints, the selection reduces to only one equation of state. The results provide an estimate of the uncertainty on the theoretical prediction at a microscopic level of the nuclear equation of state.

The photofission cross section of ${}^{238}$U was measured at sub-barrier energies as a function of the $\gamma$-ray energy using a monochromatic, high-brilliance, Compton-backscattered $\gamma$-ray beam. The experiment was performed at the High Intensity $\gamma$-ray Source (HI$\gamma$S) facility at beam energies between $E_{\gamma }=4.7$ MeV and 6.0 MeV and with $\sim 3\%$ energy resolution. Indications of transmission resonances have been observed at $\gamma$-ray beam energies of $E_{\gamma }=5.1$ MeV and 5.6 MeV with moderate amplitudes. The triple-humped fission barrier parameters of ${}^{238}$U have been determined by fitting empire-3.1 nuclear reaction code calculations to the experimental photofission cross section.