We study odd-even mass staggering of nuclei, also called pairing gaps, using a Skyrme self-consistent mean-field theory and a numerically exact treatment of the pairing Hamiltonian. We find that the configuration-space Monte Carlo method proposed by Cerf and Martin [Phys. Rev. C 47, 2610 (1993)] offers a practical computational procedure to carry out the numerical solutions in large-dimensional model spaces. Refitting the global strength of the pairing interaction for 443 neutron pairing gaps in our number-conserving treatment, we find the correction to the pairing correlation energies and pairing gaps to have rms values of 0.6 and 0.12 MeV, respectively. The exact treatment provides a significant improvement in the fit to experimental gaps, although it is partially masked by a larger rms error due to deficiencies in other aspects of the theory, such as the mean-field energy functional.

The microscopic structure of neutron-rich $\mathit{sd}$-shell nuclei is investigated by using the spherical-shell model in the $\mathit{sd}$-$\mathit{pf}$ valence space with the extended pairing plus quadrupole-quadrupole forces accompanied by the monopole interaction (EPQQM). The calculation reproduces systematically the known energy levels for even-even and odd-mass nuclei including the recent data for ${}^{43}\mathrm{S}$, ${}^{46}\mathrm{S}$, and ${}^{47}\mathrm{Ar}$. In particular, the erosion of the $N=28$ shell closure in ${}^{42}\mathrm{Si}$ can be explained. Our EPQQM results are compared with other shell-model calculations with the SDPF-NR and SDPF-U effective interactions.

Large-amplitude dynamics of axial and triaxial quadrupole deformation in ${}^{24,26}\mathrm{Mg}$, ${}^{24}\mathrm{Ne}$, and ${}^{28}\mathrm{Si}$ is investigated on the basis of the quadrupole collective Hamiltonian constructed with the use of the constrained Hartree-Fock-Bogoliubov plus the local quasiparticle random-phase approximation method. The calculation reproduces well properties of the ground rotational bands, and $\beta$ and $\gamma$ vibrations in ${}^{24}\mathrm{Mg}$ and ${}^{28}\mathrm{Si}$. The $\gamma$ softness in the collective states of ${}^{26}\mathrm{Mg}$ and ${}^{24}\mathrm{Ne}$ are discussed. Contributions of the neutrons and protons to the transition properties are also analyzed in connection with the large-amplitude quadrupole dynamics.

The $\beta$ decay of ${}^{75}\mathrm{Cu}$ [$t_{1/2}=1.222(8)$s] to levels in ${}^{75}\mathrm{Zn}$ was studied at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory. The $\gamma \gamma$ and $\beta \gamma$ data were collected at the Low-energy Radioactive Ion Beam Spectroscopy Station using the high-resolution isobar separator to obtain a purified ${}^{75}\mathrm{Cu}$ beam with a rate of over 2000 ions per second. The excited states in ${}^{75}\mathrm{Zn}$ have been identified for the first time. A total of 120 $\gamma$-ray transitions were placed in a level scheme containing 59 levels including two states above the neutron separation energy and a previously unknown $1/2^{-}$ isomeric state at 127 keV. Spins and parities of several states were deduced and interpreted based on the observed $\beta$ feeding and $\gamma$-decay pattern.

Heavy-ion collisions at intermediate energies are studied by the isospin-dependent quantum molecular dynamics model in the company of the GEMINI model. The isospin-dependent quantum molecular dynamics model is applied to describe the violent stage of the collisions, while the GEMINI model is applied to simulate the decays of the prefragments. The present study mainly focuses on the odd-even effect in the yields of the final fragments. We find that the odd-even effect appears in the deexcitation process of the excited prefragments, and is affected by the excitation energies and the isotope distributions of the prefragments. Both the projectile-isospin-dependent odd-even effect in the region of $-4⩽T_Z⩽1$ and the role of the symmetry energy on the odd-even effect are studied. We find that the odd-even effect depends sensitively on the symmetry energy.

Relativistic heavy ion collisions provide laboratory environments from which one can study the creation of a novel state of matter, the quark-gluon plasma. The existence of such a state is postulated to alter the mechanism and evolution of charge production, which then becomes manifest in charge correlations. We study the separation of balancing charges at kinetic freeze-out by analyzing recent results on balancing charge correlations for Au + Au collisions at $\sqrt{s_{\mathrm{NN}}}=200\hspace{0.5em}\text{GeV}$. We find that in central collisions, the spatial points from which balancing charges are emitted are characterized by smaller relative angles. These results are consistent with the expectation that charge production occurred later in the collision, as would be expected for delayed hadronization. An alternative explanation would be that the charges were produced early, perhaps with a different mechanism where the charge production mechanism was altered from string breaking which tends to separate the charges in relative rapidity. The alternative explanation would also rely on the diffusion of charges being small. In addition we calculate the contributions from charge-balance correlations to STAR’s local parity violation observable. We find that local charge conservation, when combined with elliptic flow, explains the bulk of STAR’s measurement.

Using the two-component model for charmonium production, which includes contributions from both initial hard nucleon-nucleon scattering and from regeneration in the quark-gluon plasma, we study the nuclear modification factor $R_{\mathit{AA}}$ and elliptic flow $v_2$ of $J/\psi$ in relativistic heavy-ion collisions. For the expansion dynamics of produced hot, dense matter, we introduce a schematic fireball model with its transverse acceleration determined from the pressure gradient inside the fireball and azimuthally anisotropic expansion parametrized to reproduce measured $v_2$ of light hadrons. We assume that light hadrons freeze out at the temperature of 120 MeV while charmonia freeze out at 160 MeV, similar to the kinetic and chemical freeze-out temperatures in the statistical model, respectively. For the properties of charmonia in the quark-gluon plasma, we use the screening mass between their charm and anticharm quarks and their dissociation cross sections given by the perturbative quantum chromodynamical (pQCD) calculations in the leading order and up to the next-to-leading order, respectively. For the relaxation time of charm and anticharm quarks in the quark-gluon plasma, we also use the one calculated in the leading-order pQCD. Modeling the effect of higher-order corrections in pQCD by introducing multiplicative factors to the dissociation cross sections of charmonia and the elastic scattering cross sections of charm and anticharm quarks, we find that this effect is small for the $R_{\mathit{AA}}$ of $J/\psi$ as they suppress the number of initially produced $J/\psi$ but enhance the number of regenerated ones. The higher-order corrections increase, however, the $v_2$ of $J/\psi$. Our results suggest that the $v_2$ of $J/\psi$ can play an important role in discriminating between $J/\psi$ production from initial hard collisions and from regeneration in the quark-gluon plasma.

The Heavy-Ion Jet Interaction Generator (hijing) Monte Carlo model is updated with the latest parton distributions functions and a new set of the parameters in the two-component minijet model that controls the total $p+p$ cross section and the central pseudorapity density. We study hadron spectra and multiplicity distributions using the hijing$2.0$ model and compare to recent experimental data from $p+p$ collisions at the Large Hadron Collider (LHC) energies. We also give predictions of hadron production in $p+p$, $p+\text{Pb}$, and $\text{Pb}+\text{Pb}$ collisions at the full LHC energy.

We investigate the contribution of medium-modified jets and initial state fluctuations to the asymmetry in charged-particle production with respect to the reaction plane. This asymmetry has been suggested as a compelling signature for the chiral magnetic effect in QCD and makes the study of conventional scenarios for the creation of such charged-particle multiplicity fluctuations a timely endeavor. The different path-length combinations of jets through the medium in noncentral heavy ion collisions result in finite correlations of like and different charged particles emitted in the different hemispheres. Our calculation is based on the combination of jet events from Yet another Jet Energy-Loss Model (YaJEM) and a bulk-medium evolution. It is found that the jet production probabilities are too small to observe this effect. The influence of initial state fluctuations on this observable is explored by using an event-by-event (3+1)-dimensional hybrid approach that is based on Ultra-relativistic Quantum Molecular Dynamics (UrQMD) with an ideal hydrodynamic evolution. In this calculation, momentum conservation and elliptic flow are explicitly taken into account. The asymmetries in the initial state are translated to a final state momentum asymmetry by the hydrodynamic flow profile. Dependent on the size of the initial state fluctuations, the resulting charged-particle asymmetries are in qualitative agreement with the preliminary STAR (solenoid tracker at the Relativistic Heavy Ion Collider) results. The multiparticle correlation as proposed by the PHENIX Collaboration can, in principle, be used to disentangle the different contributions, however, in practice, is affected substantially by the procedure to subtract trivial resonance decay contributions.

We develop a technique, denoted as the finite radius approximation (FRA), that uses a two-dimensional version of the Nyquist-Shannon sampling theorem to determine transverse densities and their uncertainties from experimental quantities. Uncertainties arising from experimental uncertainties on the form factors and lack of measured data at high $Q^2$ are treated. A key feature of the FRA is that a form factor measured at a given value of $Q^2$ is related to a definite region in coordinate space. An exact relation between the FRA and the use of a Bessel series is derived. The proton Dirac form factor is sufficiently well known such that the transverse charge density is very accurately known except for transverse separations $b$ less than about 0.1 fm. The Pauli form factor is well known to $Q^2$ of about 10 GeV${}^2$, and this allows a reasonable, but improvable, determination of the anomalous magnetic moment density.

Chiral theories with spontaneous symmetry breaking such as the Nambu–Jona-Lasinio (NJL) model lead to the existence of a scalar mode. We present in a detailed manner how the corresponding low-momentum effective Lagrangian involving the scalar field can be constructed starting from the NJL model. We discuss the relevance of the scalar mode for the problem of nuclear binding and saturation. We show that it depends on the nucleon mass origin with two extreme cases. If this origin is entirely due to confinement, the coupling of this mode to the nucleons vanishes, making it irrelevant for the nuclear binding problem. If instead it is entirely due to spontaneous symmetry breaking, it couples to the nucleons but nuclear matter collapses. It is only in the case of a mixed origin with spontaneous breaking that nuclear matter can be stable and reach saturation. We describe models of nucleon structure where this balance is achieved. We also show how chiral constraints and confinement modify the QCD sum rules for mass evolution in nuclear matter.

The NPDGamma collaboration reports results from the first phase of a measurement of the parity violating up-down asymmetry $A_{\gamma }$ with respect to the neutron spin direction of $\gamma$ rays emitted in the reaction $\mathrm{n⃗}+p\to d+\gamma$ using the capture of polarized cold neutrons on the protons in a liquid parahydrogen target. One expects parity-odd effects in the hadronic weak interaction between nucleons to be induced by the weak interaction between quarks. $A_{\gamma }$ in $\mathrm{n⃗}+p\to d+\gamma$ is dominated by a $\Delta I=1$, ${}^3{S}_1$-${}^3{P}_1$ parity-odd transition amplitude in the n-p system. The first phase of the measurement was completed at the Los Alamos Neutron Science Center spallation source (LANSCE), with the result $A_{\gamma }=[-1.2\pm 2.1\hspace{0.5em}(\mathrm{stat}.)\pm 0.2\hspace{0.5em}(\mathrm{sys}.)]\times {10}^{-7}$. We also report the first measurement of an upper limit for the parity-allowed left-right asymmetry in this reaction, with the result $A_{\gamma ,\mathrm{LR}}=[-1.8\pm 1.9\hspace{0.5em}(\mathrm{stat}.)\pm 0.2\hspace{0.5em}(\mathrm{sys}.)]\times {10}^{-7}$. In this paper we give a detailed report on the theoretical background, experimental setup, measurements, extraction of parity-odd and parity-allowed asymmetries, analysis of potential systematic effects, and LANSCE results. The asymmetry has an estimated size of $5\times {10}^{-8}$ and the aim of the NPDGamma collaboration is to measure it to $1\times {10}^{-8}$. The second phase of the measurement will be performed at the Spallation Neutron Source at Oak Ridge National Laboratory.

We calculate the photon pair production rate in a strong magnetic field created in off-central heavy-ion collisions. Photon decay leads to depletion of the photon yield by a few percent at RHIC and by as much as 20% at the LHC. It also generates a substantial azimuthal asymmetry (“elliptic flow”) of the final photon distribution. We estimate $v_2\approx 2$% at RHIC and $v_2\approx 14$% at LHC. Photon decay measurements is an important tool for studying the magnetic fields in early stages of heavy-ion collisions.

An intranuclear cascade model for one-nucleon removal cross sections at intermediate energies beyond the sudden and inert-core assumptions is presented. Indirect processes are taken into account in the reaction mechanism via a Monte Carlo–based approach. The formalism is applied to a set of weakly bound nuclei for which data are available. Results are in correct agreement with experiment including the case of deeply bound nucleon removal. A comparison to eikonal predictions is performed.

Recoil-isomer tagging with the ${}^{54}\mathrm{Fe}$$+$${}^{92}\mathrm{Mo}$ reaction was used to establish a 10(2)-$\mu$s isomeric state in ${}^{139}\mathrm{Eu}$. Prompt versus delayed $\gamma$-ray coincidence data have revealed the presence of a prompt rotational band built upon the isomer. The alignment properties of the states in this band show that the isomer is based upon a proton $g_{7/2}$ configuration. The decay of the isomer takes place through a single 26-keV $E1$ transition. The $\gamma$-ray transition strength for this decay is consistent with those established in the neighboring isomeric gamma-soft nuclei. In these nuclei, isomers are expected to form as a consequence of differences in nuclear shapes or configurations, and the natural hindrance associated with configuration-changing $E1$ transitions. The isomeric nature of the state in ${}^{139}\mathrm{Eu}$ is reasoned to be because of difference in shape of the proton $g_{7/2}$ state and the proton $h_{11/2}$ ground state to which it decays.

The influence of the quadrupole shape fluctuations on the dipole vibrations in transitional nuclei is investigated in the framework of the instantaneous shape sampling model, which combines the interacting boson model for the slow collective quadrupole motion with the random phase approximation for the rapid dipole vibrations. Coupling to the complex background configurations is taken into account by folding the results with a Lorentzian with an energy-dependent width. The low-energy portion of the $\gamma$-absorption cross section, which is important for photonuclear processes, is studied for the isotopic series of Kr, Xe, Ba, and Sm. The experimental cross sections are well reproduced. The low-energy cross section is determined by the Landau fragmentation of the dipole strength and its redistribution caused by the shape fluctuations. Collisional damping only wipes out fluctuations of the absorption cross section, generating the smooth energy dependence observed in experiment. In the case of semimagic nuclei, shallow pygmy resonances are found, in agreement with experiment.

High-spin states in ${}^{157}\mathrm{Yb}$ have been populated in the ${}^{144}\mathrm{Sm}$(${}^{16}\mathrm{O}$,3$n$)${}^{157}\mathrm{Yb}$ fusion-evaporation reaction at a beam energy of 85 MeV. Two rotational bands built on the $\nu f_{7/2}$ and ν$h$${}_{9/2}$ intrinsic states, respectively, have been established for the first time. The newly observed ν$f$${}_{7/2}$ band and previously known ν$i$${}_{13/2}$ band in ${}^{157}\mathrm{Yb}$ are discussed in terms of total Routhian surface methods and compared with the structures in the neighboring $N$ $=$ 87 isotones. The structural characters observed in ${}^{157}\mathrm{Yb}$ provide evidence for shape coexistence of three distinct shapes: prolate, triaxial, and oblate. At higher spins, both the ν$f$${}_{7/2}$ band and ν$i$${}_{13/2}$ band in ${}^{157}\mathrm{Yb}$ undergo a shape evolution with sizable alignments occurring.

The thermodynamic properties of a dinuclear system are studied with the methods of statistical mechanics. A schematic model calculation shows that the excitation-energy transfer proceeds in energy steps of considerable amount which are subject to large fluctuations. As a consequence, thermal averaging is strong enough to assure the application of thermodynamical methods for describing the energy exchange between the two nuclei in contact. In particular, thermal averaging justifies the definition of a nuclear temperature. The division of excitation energy in thermal equilibrium is derived for several analytical descriptions of the level density.

Comparing four different (ideal and viscous) hydrodynamic models for the evolution of the medium created in $200A$ GeV Au-Au collisions, combined with two different models for the path-length dependence of parton energy loss, we study the effects of jet quenching on the emission-angle dependence of the nuclear suppression factor $R_{\mathit{AA}}(\varphi )$ and the away-side per-trigger yield $I_{\mathit{AA}}(\varphi )$. Each hydrodynamic model was tuned to provide a reasonable description of the single-particle transverse momentum spectra for all collision centralities, and the energy-loss models were adjusted to yield the same pion nuclear suppression factor in central Au-Au collisions. We find that the experimentally measured in-plane versus out-of-plane spread in $R_{\mathit{AA}}(\varphi )$ is better reproduced by models that shift the weight of the parton energy loss to later times along its path. Among the models studied here, this is best achieved by energy-loss models that suppress energy loss at early times, combined with hydrodynamic models that delay the dilution of the medium density due to hydrodynamic expansion by viscous heating. We were unable to identify a clear tomographic benefit of a measurement of $I_{\mathit{AA}}(\varphi )$ over that of $R_{\mathit{AA}}(\varphi )$.