The $\mathit{pp}\to \mathit{pp}\gamma$ reaction has been studied at a beam energy of 310 MeV by detecting both final protons at the PROMICE-WASA facility and identifying the photon through the resulting missing-mass peak. The photon angular distribution in the center-of-mass system and those of the proton-proton relative momentum with respect to the beam direction and to that of the recoil photon were determined reliably up to a final $\mathit{pp}$ excitation energy of $E_{\mathit{pp}}~30$ MeV. Except for very small $E_{\mathit{pp}}$ values, the behavior of these distributions with excitation energy is well reproduced by a new refined model of the hard bremsstrahlung process. The model reproduces absolutely the total cross section and its energy dependence to within the experimental and theoretical uncertainties.

In the framework of the Hartree-Fock-Bogoliubov approach with the Skyrme interactions SLy5, SLy5$+$T, SLy5$+$T${}_w$, and several sets of the TIJ parametrizations (Skyrme effective interaction parametrizations including the tensor terms), the effect of the tensor force on the shell evolution at $Z,N=8$, 20, and 28 is investigated. It is shown that the evolution of the gap (defined as the energy difference between the last occupied and first unoccupied single-particle orbits) with SLy5$+$T is similar to that with SLy5$+$T${}_w$, and the gap values with SLy5$+$T are smaller than those with SLy5$+$T${}_w$ in the cases of $Z,N=8$, 20. At Z, N $=$ 28, the gap values with SLy5 are smaller than those with SLy5$+$T and larger than those with SLy5$+$T${}_w$. To understand these features, we analyze the spin-orbit potentials with and without the tensor contributions and the radial wave functions of relevant orbits. Meanwhile, we find that the deviation of the calculated gaps with SLy5$+$T${}_w$ from the experimental ones is larger than that with SLy5$+$T. This indicates that SLy5$+$T${}_w$ is not suitable for investigating the properties of the ground-state gap evolution. Finally, it is seen that the gap evolutions with different sets of the TIJ parametrizations are similar to each other except for the ones with T22, and there is almost no difference between the tensor effect in gap evolution with the perturbative method and the one with the complete fitting method.

We develop a method based on equation-of-motion coupled-cluster theory to describe properties of open-shell nuclei with $A\pm 2$ nucleons outside a closed shell. We perform proof-of-principle calculations for the ground states of the helium isotopes ${}^{3-6}\mathrm{He}$ and the first excited $2^{+}$ state in ${}^6\mathrm{He}$. The comparison with exact results from matrix diagonalization in small model spaces demonstrates the accuracy of the coupled-cluster methods. Three-particle–one-hole excitations of ${}^4\mathrm{He}$ play an important role for the accurate description of ${}^6\mathrm{He}$. For the open-shell nucleus ${}^6\mathrm{He}$, the computational cost of the method is comparable with the coupled-cluster singles-and-doubles approximation while its accuracy is similar to the coupled-cluster with singles, doubles, and triples excitations.

The most recent electron-proton elastic scattering data were re-analyzed using an empirical parametrization of the two-photon-exchange (TPE) effect contributions to ${\sigma }_R$. The TPE effect contribution $F(Q^2,\varepsilon )$ was double Taylor series expanded as a polynomial of order $n$ keeping only terms linear in $\varepsilon$ to account for the experimentally observed and verified linearity of the Rosenbluth plots. We fix the ratio $R=G_{\mathit{Ep}}/G_{\mathit{Mp}}$ to be that obtained from a fit to the recoil-polarization data and parametrize ${\sigma }_R$ first by a three-parameter formula (fit I) and then by a two-parameter formula (fit III). In contrast to previous analyses, the fit parameter $G_{\mathit{Mp}}^2$ as obtained from these fits is either smaller or equal to the values obtained from our conventional Rosenbluth fit (fit II) but never larger. The ratio $g(Q^2)/G_{\mathit{Mp}}^2$ which represents the ratio of the TPE and one-photon-exchange (OPE) effect contributions to the intercept of ${\sigma }_R$ is large and it ranges 3%$-$88%. The ratio $R_{1\gamma \otimes 2\gamma }=\tau f(Q^2)/G_{\mathit{Ep}}^2$ which represents the ratio of the TPE and OPE effect contributions to the slope of ${\sigma }_R$ is also large, reaching a value of 12.0$-$14.4 at $Q^2=$ 5.25 (GeV/c)${}^2$. The ratio $R_{1\gamma \otimes 2\gamma }$ as obtained from fits I and III is consistent, within error, with those obtained from previous analyses. Our formulas seem to explain the linearity of ${\sigma }_R$. Moreover, our analysis shows that the extracted $G_{\mathit{Ep}}^2$ and $G_{\mathit{Mp}}^2$ using the conventional Rosenbluth separation method can in fact be broken into the usual OPE and TPE contributions. Therefore, ${\sigma }_R$ can in fact be derived under weaker conditions than those imposed by the Born approximation. Our results show that the TPE amplitudes, $g(Q^2)/G_{\mathit{Mp}}^2$ and $f(Q^2)/G_{\mathit{Mp}}^2$, are sizable and grow with $Q^2$ value up to $Q^2~$ 6 (GeV/c)${}^2$ in agreement with previous studies. A revision of and comparison to previous analyses are also presented.

Chiral vibrations in the $A=135$ region are studied in the framework of a RPA plus self-consistent tilted axis cranking formalism. In this model chiral vibrations appear as a precursor toward the static chiral regime. The properties of the RPA phonons are discussed and compared to experimental data. We discuss the limits of the chiral region and the transition to the nonharmonic regime.

The thermodynamics and phase structure of the Polyakov loop-extended two-flavor chiral quark-meson (PQM) model are explored beyond the mean-field approximation. The analysis of the PQM model is based on the functional renormalization group (FRG) method. We formulate and solve the renormalization group flow equation for the scale-dependent thermodynamic potential in the presence of the gluonic background field at finite temperature and density. We determine the phase diagram of the PQM model in the FRG approach and discuss its modification compared to the mean-field approximation. We focus on the fluctuations of the net-quark number density, including higher cumulants, and discuss the influence of nonperturbative effects near the chiral crossover transition. We find that, with increasing net-quark number density, the higher-order cumulants exhibit a characteristic structure near the transition. We also consider ratios of different cumulants of the net-quark number density and discuss their role as probes of the deconfinement and chiral phase transitions.

The possibility that particle production in high-energy collisions is a result of two asymmetric hydrodynamic flows is investigated using the Khalatnikov form of the (1$+$1)-dimensional approximation of hydrodynamic equations. The general solution is discussed and applied to the physically appealing “generalized in-out cascade” where the space-time and energy-momentum rapidities are equal at initial temperature but boost invariance is not imposed. It is demonstrated that the two-bump structure of the entropy density, characteristic of the asymmetric input, changes easily into a single broad maximum compatible with data on particle production in symmetric processes. A possible microscopic QCD interpretation of asymmetric hydrodynamics is proposed.

The internal structure of the resonant $\Lambda \text{(1405)}$ state is investigated based on meson-baryon coupled-channels chiral dynamics by evaluating density distributions obtained from the form factors of the $\Lambda \text{(1405)}$ state. The form factors are defined as an extension of the ordinary stable particles and are directly evaluated from the current-coupled meson-baryon scattering amplitude, paying attention to the charge conservation of the probe interactions. For the resonant $\Lambda \text{(1405)}$ state we calculate the density distributions in two ways. One is on the pole position of the $\Lambda \text{(1405)}$ in the complex energy plane, which evaluates the resonant $\Lambda \text{(1405)}$ structure without contamination from nonresonant backgrounds, and another is on the real energy axis around the $\Lambda \text{(1405)}$ resonance energy, which may be achieved in experiments. Using several probe interactions and channel decomposition, we separate the various contributions to the internal structure of the $\Lambda \text{(1405)}$. As a result, we find that the resonant $\Lambda \text{(1405)}$ state is composed of widely spread $\mathrm{K̄}$ around $N$, which gives dominant component inside the $\Lambda \text{(1405)}$, with escaping $\pi \Sigma$ component. Furthermore, we consider $\mathrm{K̄}N$ bound state without decay channels, with which we can observe the internal structure of the bound state within real numbers. We also study the dependence of the form factors on the binding energy and meson mass. This verifies that the form factor defined through the current-coupled scattering amplitude serves as a natural generalization of the form factor for the resonance state. The relation between the interaction strength and the meson mass shows that the physical kaon mass appears to be within the suitable range to form a molecular bound state with the nucleon through the chiral SU(3) interaction.

For nearly forty years, the Galster parametrization has been employed to fit existing data for the neutron electric form factor, $G_{\mathrm{E}}^n$, vs the square of the four-momentum transfer, $Q^2$. Typically this parametrization is constrained to be consistent with experimental data for the neutron charge radius. However, we find that the Galster form does not have sufficient freedom to accommodate reasonable values of the radius without constraining or compromising the fit. In addition, the $G_{\mathrm{E}}^n$ data are now at sufficient precision to motivate a two-parameter fit (or three parameters if we include thermal neutron data). Here we present a modified form of a two-dipole parametrization that allows this freedom and fits both $G_{\mathrm{E}}^n$ (including recent data at both low and high four-momentum transfer) and the charge radius well with simple, well-defined parameters. Analysis reveals that the Galster form is essentially a two-parameter approximation to the two-dipole form but becomes degenerate if we try to extend it naturally to three parameters.

From a Faddeev calculation for the $\pi$-$(\Delta \rho ){}_{N_{5/2^{-}}(1675)}$ system we show the plausible existence of three dynamically generated $I(J^P)=3/2(5/2^{+})$ baryon states below 2.3 GeV, whereas only two resonances, ${\Delta }_{5/2^{+}}(1905)(****)$ and ${\Delta }_{5/2^{+}}(2000)(**),$ are cataloged in the Particle Data Book Review. Our results give theoretical support to data analyses extracting two distinctive resonances, ${\Delta }_{5/2^{+}}(~$1740) and ${\Delta }_{5/2^{+}}(~$2200), from which the mass of ${\Delta }_{5/2^{+}}(2000)(**)$ is estimated. We propose that these two resonances should be cataloged instead of ${\Delta }_{5/2^{+}}(2000).$ This proposal gets further support from the possible assignment of the other baryon states found in the approach in the $I=1/2,3/2$ with $J^P=1/2^{+},3/2^{+},5/2^{+}$ sectors to known baryonic resonances. In particular, ${\Delta }_{1/2^{+}}(1750)(*)$ is naturally interpreted as a $\pi N_{1/2^{-}}(1650)$ bound state.

The low-lying states of ${}_{\hspace{0.5em}\Lambda }^{21}$Ne are studied with antisymmetrized molecular dynamics for hypernuclei. We have obtained ten rotational bands where the number of bands are increased compared to ${}^{20}\mathrm{Ne}$ by adding a $\Lambda$ hyperon. Among them, we focus on the $K^{\pi }=0_1^{+}\otimes {\Lambda }_s$ and $K^{\pi }=0_1^{-}\otimes {\Lambda }_s$ bands. The former has a shell-model-like structure that has $\Lambda$ in an $s$ wave coupled to the ground band of ${}^{20}\mathrm{Ne}$. The latter is a cluster state that has a $\alpha +{}_{\hspace{0.5em}\Lambda }^{17}$O dicluster structure. The difference between their structures leads to the binding energy of $\Lambda$ particle $B_{\Lambda }$ and reduction of the $E2$ transition probabilities $B(E2)$.

Structural evolution in neutron-rich Os and W isotopes is investigated in terms of the interacting boson model (IBM) Hamiltonian determined by (constrained) Hartree-Fock-Bogoliubov calculations with the Gogny-D1S energy density functional (EDF). The interaction strengths of the IBM Hamiltonian are produced by mapping the potential energy surface (PES) of the Gogny-EDF with quadrupole degrees of freedom onto the corresponding PES of the IBM system. We examine the prolate-to-oblate shape/phase transition which is predicted to take place in this region as a function of neutron number $N$ within the considered Os and W isotopic chains. The onset of this transition is found to be more rapid compared to the neighboring Pt isotopes. The calculations also allow the prediction of spectroscopic variables (excited state energies and reduced transition probabilities) which are presented for the neutron-rich ${}^{192,194,196}\mathrm{W}$ nuclei, for which there is only very limited experimental data available to date.

Incomplete fusion of ${}^{20}\mathrm{Ne}$ with ${}^{59}\mathrm{Co}$ has been investigated at 3–7 MeV/nucleon using the measurement and analysis of excitation functions. The recoil-catcher technique followed by offline gamma-ray spectroscopy has been employed. Evaporation residues are found to have contributions from precursor decays, which have been separated out from the measured cumulative cross sections of evaporation residues. Measured independent cross sections are compared with PACE-2 predictions. The PACE-2 calculations are carried out for evaporation residues formed in complete fusion (CF), and the parameters are optimized so as to reproduce the cross section of evaporation residues produced exclusively in CF, e.g., $\mathit{xn}$ and pxn products. With these parameters, the predicted CF cross sections for alpha emission products are calculated. Any substantial enhancement in the experimental cross section over the PACE-2 prediction is taken as a signature of incomplete fusion (ICF). The analysis indicates the occurrence of incomplete fusion involving the breakup of ${}^{20}\mathrm{Ne}$ into ${}^{16}\mathrm{O}$ $+$ ${}^4\mathrm{He}$ and/or ${}^{12}\mathrm{C}$ $+$ ${}^8\mathrm{Be}$(2α) followed by fusion of one of the fragments with the target nucleus ${}^{59}\mathrm{Co}$. These data also suggest that the probability of incomplete fusion increases with the projectile energy. Moreover, the ICF probability is found to increase with entrance-channel mass-asymmetry of the projectile-target systems.

The properties of warm dilute $\alpha$-nucleon matter are studied in a variational approach in the Thomas-Fermi approximation starting from an effective two-body nucleon-nucleon interaction. The equation of state, symmetry energy, incompressibility of the said matter, and $\alpha$ fraction are in consonance with those evaluated from the virial approach, which sets the benchmark for such calculations at low densities.

The linear response of a superfluid neutron liquid onto external vector field is studied for the case of ${}^3{P}_2$-${}^3{F}_2$ pairing. In particular, we analyze the case of neutron condensation into the state with $m_j=0$, which is conventionally considered as the preferable one in the bulk matter of neutron stars. Consideration is limited to the case when the wavelength of a perturbation is large as compared to the coherence length in the superfluid matter and the transferred energy is small in comparison with the gap amplitude. The obtained results are used to analyze collisionless soundlike excitations of the superfluid condensate. Zero sound (if it exists) is found to be anisotropic and undergoes a strong decrement below some temperature threshold depending substantially on the intensity of Fermi-liquid interactions.

We address the issue of whether quasifree single-nucleon knockout measurements carry sufficient information about the nuclear interior. To this end, we present comparisons of the reaction probability densities for $A(e,e^{\text{'}}p)$ and $A(p,2p)$ in quasifree kinematics for the target nuclei ${}^4\mathrm{He}$, ${}^{12}\mathrm{C}$, ${}^{56}\mathrm{Fe}$, and ${}^{208}\mathrm{Pb}$. We adopt a comprehensive framework based on the impulse approximation and on a relativized extension of Glauber multiple-scattering reaction theory in which the medium effects related to short-range correlations (SRCs) are implemented. It is demonstrated that SRCs weaken the effect of attenuation. For light target nuclei, both the quasifree $(p,2p)$ and $(e,e^{\text{'}}p)$ can probe average densities of the same order as nuclear saturation density ${\rho }_0$. For heavy nuclei such as ${}^{208}\mathrm{Pb}$, the probed average densities are smaller than $0.1{\rho }_0$ and the $(e,e^{\text{'}}p)$ reaction is far more efficient in probing the bulk regions than $(p,2p)$.

We present a modified version of the Fusion by Diffusion (FBD) model aimed at describing the synthesis of superheavy nuclei in cold fusion reactions, in which a low excited compound nucleus emits only one neutron. The modified FBD model accounts for the angular momentum dependence of three basic factors determining the evaporation residue cross section: the capture cross section ${\sigma }_{\text{cap}}(l)$, the fusion probability $P_{\text{fus}}(l)$, and the survival probability $P_{\text{surv}}(l)$. The fusion hindrance factor, the inverse of $P_{\text{fus}}(l)$, is treated in terms of thermal fluctuations in the shape degrees of freedom and is expressed as a solution of the Smoluchowski diffusion equation. The $l$ dependence of $P_{\text{fus}}(l)$ results from the $l$-dependent potential energy surface of the colliding system. A new parametrization of the distance of starting point of the diffusion process is introduced. An analysis of a complete set of 27 excitation functions for production of superheavy nuclei in cold fusion reactions, studied in experiments at GSI Darmstadt, RIKEN Tokyo, and LBNL Berkeley, is presented. The FBD model satisfactorily reproduces shapes and absolute cross sections of all the cold fusion excitation functions. It is shown that the peak position of the excitation function for a given 1$n$ reaction is determined by the $Q$ value of the reaction and the height of the fission barrier of the final nucleus. This fact could possibly be used in future experiments (with well-defined beam energy) for experimental determination of the fission barrier heights.

We have measured fission fragment-mass yields for neutron-induced fission of ${}^{232}\mathrm{Th}$ and ${}^{238}\mathrm{U}$ at energies 32.8, 45.3, and 59.9 MeV. The experiments were done at quasimonoenergetic neutron beams of the Cyclotron Research Center at Louvain-la-Neuve. To detect the fission fragments, a multisection Frisch-gridded ionization chamber was used. The measurement and data analysis techniques are discussed in detail. The obtained mass yields are compared to model calculations with the intermediate-energy nuclear reaction code MCFX. The MCFX code is used to calculate the fraction of fissioning nuclei after cascade, preequilibrium, and statistical reaction stages. The formation of mass distributions is considered as a result of oscillations of the mass-asymmetry degree of freedom in the potential well calculated with the temperature-dependent shell correction method. The experimental results as well as the results of the model calculations demonstrate that the probability of symmetric fission increases with incident neutron energy for both nuclei. The comparison also shows that the symmetric fission is more enhanced for thorium than for uranium with increasing neutron energy. We also compare ${}^{238}\mathrm{U}$ results with available experimental data; the ${}^{232}\mathrm{Th}$ data were measured for the first time.

In high-energy heavy ion collisions a hot and dense medium is formed, where the ${\mathrm{U}}_{\mathrm{A}}(1)$ or chiral symmetry may temporarily be restored. As a consequence, the mass of the ${\eta }^{\prime }$(958) mesons may be reduced to its quark model value, and the abundance of ${\eta }^{\prime }$ mesons at low $p_{\mathrm{T}}$ may be enhanced by more than a factor of 10. The intercept parameter ${\lambda }_{*}$ of the charged pion Bose Einstein correlations provides a sensitive observable of the possibly enhanced ${\eta }^{\prime }$ abundance. We have analyzed ${\lambda }_{*}(m_{\mathrm{T}})$ data from $\sqrt{s_{{}_{\mathit{NN}}}}=200\hspace{0.5em}\mathrm{GeV}$ central Au$+$Au reactions measured at the BNL Relativistic Heavy Ion Collider (RHIC), using extensive Monte Carlo simulations based on six popular models for hadronic multiplicities. Based on the combined STAR and PHENIX data set, and on various systematic investigations of resonance multiplicities and model parameters, we conclude that in $\sqrt{s_{{}_{\mathit{NN}}}}=200\hspace{0.5em}\mathrm{GeV}$ central Au$+$Au reactions the mass of the ${\eta }^{\prime }$ meson is reduced by $\Delta m_{{\eta }^{\prime }}^{*}>200\hspace{0.5em}\mathrm{MeV}$, at the 99.9% confidence level in the considered model class. Such a significant ${\eta }^{\prime }$ mass modification may indicate the restoration of the $U_A(1)$ symmetry in a hot and dense hadronic matter and the return of the ninth “prodigal” Goldstone boson. A similar analysis of NA44 S$+$Pb data at top CERN Super Proton Synchroton (SPS) energies showed no significant in-medium ${\eta }^{\prime }$ mass modification.