Low-energy excited states in ${}^{71,73}$Ni populated via the $\beta$ decay of ${}^{71,73}$Co were investigated in an experiment performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). Detailed analysis led to the construction of level schemes of ${}^{71,73}$Ni, which are interpreted using systematics and analyzed using shell-model calculations. The 5/2${}^{-}$ states attributed to the the $f_{5/2}$ orbital and positive-parity 5/2${}^{+}$ and 7/2${}^{+}$ states from the $g_{9/2}$ orbital have been identified in both ${}^{71,73}$Ni. In ${}^{71}$Ni the location of a 1/2${}^{-}$ $\beta$-decaying isomer is proposed, and limits are suggested as to the location of the isomer in ${}^{73}$Ni. The location of positive-parity cluster states are also identified in ${}^{71,73}$Ni. Beta-delayed neutron branching ratios obtained from this data are given for both ${}^{71,73}$Co.

The ground state of ${}^{28}\text{F}$ has been observed as an unbound resonance $2\underline{2}0$ keV above the ground state of ${}^{27}$F. A comparison of this result with USDA/USDB shell model predictions leads to the conclusion that the ${}^{28}$F ground state is primarily dominated by $sd$-shell configurations. Here we present a detailed report on the experiment in which the ground state resonance of ${}^{28}$F was first observed. Additionally, we report the first observation of a neutron-unbound excited state in ${}^{27}$F at an excitation energy of $25\underline{0}0\left(2\underline{2}0\right)$ keV.

The large body of experimental data on the fission fragments anisotropies is analyzed in several heavy-ion-induced fission reaction systems. The entrance channel mass asymmetry parameters of these systems are put on both sides of the Businaro-Gallone mass asymmetry parameters. The role of the mass numbers of the projectile and the target in the prediction of a normal or an anomalous behavior in angular anisotropy as well as the validity of the standard saddle-point statistical model are considered. The average contribution of non-compound-nucleus fission for the systems with an anomalous behavior in anisotropy are also determined.

The reactions $\gamma p\to K^{+}\Lambda$ and $ep\to e^{\prime }{K}^{+}\Lambda$ have been investigated in a tree-level effective Lagrangian model that incorporates most of the well-established baryon resonances with spins up to $\frac{5}{2}$, four less well-established nucleon resonances with larger mass, and the $K^{☆}\left(892\right)$ and $K1\left(1270\right)$ resonances in the $t$ channel. The off-shell structure of the electromagnetic vertices in electroproduction is incorporated by the addition of electromagnetic form factors. To achieve a good fit to the electroproduction data, it was found necessary to treat the ground-state hyperon form factors as adjustable parameters rather than simply equating them with the neutron form factors as was done in past studies. Photoproduction data consisting of unpolarized differential cross sections from the CLAS Collaboration, hyperon polarization asymmetries from CLAS, GRAAL, and SAPHIR, photon beam asymmetries from GRAAL and LEPS, and double polarization observables from CLAS were fit over the c.m. energy range from threshold up to 2.3 GeV. Electroproduction data for the virtual photoproduction structure functions ${\sigma }_U$, ${\sigma }_T$, ${\sigma }_L$, ${\sigma }_{TT}$, and ${\sigma }_{LT}$ from the CLAS collaboration were fit over the $\Sigma K$ c.m. energy range from threshold up to 2.3 Gev and for several values of $q^2$, the square of the virtual photon 4-momentum. For each intermediate resonance included, the fitted parameters in the photoproduction fit consist of the products of the coupling strengths at the electromagnetic and strong interaction vertices. In the electroproduction fit, there were, in addition, two form-factor parameters for each intermediate baryon in the $s$ and $u$ channels and one form factor parameter for each kaon resonance in the $t$ channel. Results are presented for the fitted photoproduction and electroproduction observables and compared with the data for several sets of kinematical variables.

We report on a theoretical study of the $K^{-}p\to \eta \Lambda$ reaction near threshold by using an effective Lagrangian approach. The role of $s$-channel $\Lambda \left(1670\right)$, $t$-channel $K^{*}$, and $u$-channel proton pole diagrams are considered. We show that the total cross section data are well reproduced. However, only including the $s$-wave $\Lambda \left(1670\right)$ state and the background contribution from $t$ and $u$ channels is not enough to describe the bowl structures in the angular distribution of the $K^{-}p\to \eta \Lambda$ reaction, which indicates that there should be higher partial waves contributing to this reaction in some energy region. Indeed, if we considered the contributions from a $D_{03}$ resonance, we could describe the bowl structures; however, a rather small width ($\sim$2 MeV) of this resonance would be needed.

The pygmy dipole resonance in neutron-rich nuclei is studied within the framework of the Vlasov equation, which is solved numerically. The interaction used in the Thomas-Fermi ground state and in the Vlasov equation is derived from an energy functional that correctly describes the equation of state of nuclear matter and neutron matter. It is found that the pygmy resonance appears in the electric dipole response of all nuclei with strong neutron excess, the energies and transition probabilities being in reasonable agreement with experimental results. Since the Vlasov equation does not account for any shell effects, this indicates that the existence of the pygmy resonance is a generic phenomenon and does not rely on the specific shell structure. Besides the electric dipole response, the isoscalar toroidal response is calculated. The transition densities and velocity fields are discussed. A comparison of the peak positions and velocity fields suggests that the pygmy resonance can be identified with one of the low-lying modes excited by the isoscalar toroidal operator.

The excitation of the $1^{+}$, $2^{-}$, and $3^{+}$ modes in ${}^{16}$O, ${}^{22}$O, ${}^{24}$O, ${}^{28}$O, ${}^{40}$Ca, ${}^{48}$Ca, ${}^{52}$Ca, and ${}^{60}$Ca nuclei is studied with self-consistent random-phase approximation calculations. Finite-range interactions of the Gogny type, also containing tensor-isospin terms, are used. We analyze the evolution of the magnetic resonances with an increasing number of neutrons, the relevance of collective effects, the need for a correct treatment of the continuum, and the role of the tensor force.

The generalized seniority scheme has long been proposed as a means of dramatically reducing the dimensionality of nuclear shell-model calculations, when strong pairing correlations are present. However, systematic benchmark calculations, comparing results obtained in a model space truncated according to generalized seniority with those obtained in the full shell-model space, are required to assess the viability of this scheme. Here, a detailed comparison is carried out, for semimagic nuclei taken in a full major shell and with realistic interactions. The even-mass and odd-mass Ca isotopes are treated in the generalized seniority scheme, for generalized seniority $v⩽3$. Results for level energies, orbital occupations, and electromagnetic observables are compared with those obtained in the full shell-model space.

We derive an expression that allows for the unambiguous evaluation of the overlap between two arbitrary quasiparticle vacua, including its sign. Our expression is based on the Pfaffian of a skew-symmetric matrix, extending the overlap formula recently proposed by Robledo [Phys. Rev. C 79, 021302(R) (2009)] to the most general case of quasiparticle vacua, including the one of the overlap between two different blocked $n$-quasiparticle states for either even or odd systems. The powerfulness of the method is illustrated for a few typical matrix elements that appear in realistic angular-momentum-restored generator coordinate method calculations when breaking time-reversal invariance and using the full model space of occupied single-particle states.

We study pre-equilibrium giant dipole resonance (GDR) excitation and fusion in the neutron-rich system ${}^{132}$Sn $+$ ${}^{48}$Ca at energies near the Coulomb barrier, and we compare photon yields and total fusion cross sections to those of the stable system ${}^{124}$Sn $+$ ${}^{40}$Ca. The dynamic microscopic calculations are carried out on a three-dimensional lattice using both the time-dependent Hartree-Fock (TDHF) method and the density-constrained TDHF method. We demonstrate that the peak of the GDR excitation spectrum occurs at a substantially lower energy than expected for an equilibrated system, thus reflecting the very large prolate elongation of the dinuclear complex during the early stages of fusion. Our theoretical fusion cross sections for both systems agree reasonably well with recent data measured at the Holifield Radioactive Ion Beam Facility.

We study the variation of elliptic flow of thermal dileptons with a transverse momentum ($p_T$) and invariant mass ($M$) for Pb+Pb collisions at $\sqrt{s_{\text{NN}}}=2.76$ TeV for 30$\%$–40$\%$ centrality. The dilepton productions from a quark gluon plasma and hot hadrons have been considered, including the spectral change of light vector mesons in the thermal bath. The space-time evolution has been carried out within the framework of (2+1)-dimensional ideal hydrodynamics with a lattice+hadron resonance gas equation of state. We find that a judicious selection of $M$ windows can be used to extract the collective properties of quark matter and hadronic matter, and also obtain a distinct signature of medium effects on vector mesons. Results within the ambit of the present work for nuclear collisions at the Large Hadron Collider (LHC) indicate a reduction of elliptic flow ($v_2$) for $M$ beyond $\phi$ mass, which, if observed experimentally, would imitate the small momentum anisotropy in the early stage of the collective motion of the partons. We also observe that the magnitude of the elliptic flow is significantly larger at LHC than at Relativistic Heavy Ion Collider (RHIC) collision conditions.

High-spin states in ${}^{123}$I have been populated in the ${}^{80}$Se(${}^{48}$Ca,$p4n$)${}^{123}$I reaction at 207 MeV and $\gamma$-ray coincidence events have been recorded with the Gammasphere spectrometer. The level scheme of ${}^{123}$I has been extended up to spin $I=63/2$. The nucleus undergoes a shape transition from moderately deformed states with collective rotation at low spins to noncollective oblate configurations at higher spins. Maximally aligned terminating states involving all nine particles outside the ${}^{114}$Sn core and states with one particle antialigned are identified. A large number of weak transitions feed the terminating states. Cranked Nilsson-Strutinsky calculations have been performed to determine possible configurations for the observed energy levels.

Excited states of the $N=Z=33$ nucleus ${}^{66}$As have been populated in a fusion-evaporation reaction and studied using $\gamma$-ray spectroscopic techniques. Special emphasis was put into the search for candidates for the $T=1$ states. A new 3${}^{+}$ isomer has been observed with a lifetime of 1.1(3) ns. This is believed to be the predicted oblate shape isomer. The excited levels are discussed in terms of the shell model and of the complex excited Vampir approaches. Coulomb energy differences are determined from the comparison of the $T=1$ states with their analog partners. The unusual behavior of the Coulomb energy differences in the $A=70$ mass region is explained through different shape components (oblate and prolate) within the members of the same isospin multiplets. This breaking of the isospin symmetry is attributed to the correlations induced by the Coulomb interaction.

The rapid structural change in low-lying collective excitation states of neutron-rich Sr and Zr isotopes is studied by solving a five-dimensional collective Hamiltonian with parameters determined from both relativistic mean-field and nonrelativistic Skyrme-Hartree-Fock calculations using the PC-PK1 and SLy4 forces, respectively. Pair correlations are treated in the BCS method with either a separable pairing force or a density-dependent zero-range force. The isotope shifts, excitation energies, and electric monopole and quadrupole transition strengths are calculated and compared with corresponding experimental data. The calculated results with both the PC-PK1 and the SLy4 forces exhibit a picture of spherical-oblate-prolate shape transition in neutron-rich Sr and Zr isotopes. However, compared with the experimental data, the PC-PK1 (or SLy4) force predicts a more moderate (or dramatic) change in most of the collective properties around $N=60$. The underlying microscopic mechanism responsible for the rapid transition is discussed.

Using a multiphase transport (AMPT) model that includes the implementation of deformed uranium nuclei, we have studied the centrality dependence of the charged particle multiplicity ($N_{\mathrm{ch}}$, $d{N}_{\mathrm{ch}}/d\eta$), average transverse momentum ($\langle p_{\mathrm{T}}\rangle$), eccentricity (${\varepsilon }_2$), triangularity (${\varepsilon }_3$), their fluctuations, elliptic flow ($v_2$), and triangular flow ($v_3$) for different configurations of $\mathrm{U}+\mathrm{U}$ collisions at midrapidity for $\sqrt{s_{NN}}$ $=$ 200 GeV. The calculations have been done for both the default and string-melting versions of the AMPT model. The results are compared to the corresponding observations from $\mathrm{Au}+\mathrm{Au}$ collisions. We find that for the $\mathrm{U}+\mathrm{U}$ collisions $d{N}_{\mathrm{ch}}/d\eta$ at midrapidity is enhanced by about 15$\%$–40$\%$ depending on the collision and model configuration chosen, compared to $\mathrm{Au}+\mathrm{Au}$ collisions. Within the several configurations studied, the tip-to-tip collisions lead to the largest values of $N_{\mathrm{ch}}$, transverse energy ($E_{\mathrm{T}}$), and $\langle p_{\mathrm{T}}\rangle$. Both $\langle {\varepsilon }_2\rangle$ and its fluctuation show a rich centrality dependence, whereas little variation is observed for $\langle {\varepsilon }_3\rangle$ and its fluctuations. The $\mathrm{U}+\mathrm{U}$ side-on-side collision configuration provides maximum values of $\langle {\varepsilon }_2\rangle$ and minimum values of eccentricity fluctuations, whereas for peripheral collisions and mid-central collisions minimum values of $\langle {\varepsilon }_2\rangle$ and the maximum value of eccentricity fluctuations are observed for the body-to-body configuration and the tip-to-tip configuration has a minimum value of $\langle {\varepsilon }_2\rangle$ and a maximum value of eccentricity fluctuations for central collisions. The calculated $v_2$ value closely correlates with the eccentricity in the model. It is smallest for the body-to-body configuration in peripheral and mid-central collisions while it is minimum for the tip-to-tip configuration in central collisions. For peripheral collisions $v_2$ in $\mathrm{U}+\mathrm{U}$ can be about 40$\%$ larger than in $\mathrm{Au}+\mathrm{Au}$ whereas for central collisions it can be a factor of 2 higher depending on the collision configuration. It is also observed that $v_3$($p_{\mathrm{T}}$) is higher for tip-to-tip and body-to-body configurations compared to other systems for the collision centrality studied.

We study the centrality dependence to be expected if only charmonium production in the corona survives in high-energy nuclear collisions, with full suppression in the hot, deconfined core. To eliminate cold nuclear matter effects as far as possible, we consider the ratio of charmonium to open charm production. The centrality dependence of this ratio is found to follow a universal geometric form, applicable to both the Large Hadron Collider (LHC) and the Relativistic Heavy-Ion Collider (RHIC) in collisions at both central and forward rapidities.

The in-medium mass of the ${\eta }^{\prime }$ meson is discussed in a context of partial restoration of chiral symmetry in nuclear medium. The ${\eta }^{\prime }$ mass is expected to be reduced by an order of 100 MeV at the saturation density. The reduction is a consequence of the suppression of the anomaly effect on the ${\eta }^{\prime }$ mass induced by partial restoration of chiral symmetry. This strong attraction in ${\eta }^{\prime }$ nuclear systems does not accompany large absorption of ${\eta }^{\prime }$ into nuclear matter. This leads to the possibility of so narrow bound states of the ${\eta }^{\prime }$ meson in nuclei to be seen in hadronic reactions with light nuclear targets.

Isoscalar monopole strength function in ${}^{16}$O up to $E_x\simeq 40$ MeV is discussed. We found that the fine structures at the low-energy region up to $E_x\simeq 16$ MeV in the experimental monopole strength function obtained by the ${}^{16}$O$(\alpha ,{\alpha }^{\prime })$ reaction can be rather satisfactorily reproduced within the framework of the $4\alpha$ cluster model, while the gross three bump structures observed at the higher energy region ($16\lesssim E_x\lesssim 40$ MeV) look likely to be approximately reconciled by the mean-field calculations such as random-phase approximation and quasirandom-phase approximation. In this paper, it is emphasized that two different types of monopole excitations exist in ${}^{16}$O; one is the monopole excitation to cluster states which is dominant in the lower-energy part ($E_x\lesssim 16$ MeV), and the other is the monopole excitation of the mean-field type such as one-particle, one-hole (1p1h), which is attributed mainly to the higher-energy part ($16\lesssim E_x\lesssim 40$ MeV). It is found that this character of the monopole excitations originates from the fact that the ground state of ${}^{16}$O with the dominant doubly closed shell structure has a duality of the mean-field type as well as $\alpha$-clustering character. This dual nature of the ground state seems to be a common feature in light nuclei.

A complete and improved calculation of phase-space factors for $2\nu \beta \beta$ and $0\nu \beta \beta$ decay is presented. The calculation makes use of exact Dirac wave functions with finite nuclear size and electron screening and includes lifetimes, single and summed electron spectra, and angular electron correlations.