We use the finite-amplitude method for computing charge-changing Skyrme–quasiparticle random-phase approximation (QRPA) transition strengths in axially-deformed nuclei together with a modern Skyrme energy-density functional to fit several previously unconstrained parameters in the charge-changing time-odd part of the functional. With the modified functional we then calculate rates of ${\beta }^{-}$ decay for all medium-mass and heavy even-even nuclei between the valley of stability and the neutron drip line. We fit the Skyrme parameters to a limited set of $\beta$-decay rates, a set of Gamow-Teller resonance energies, and a set of spin-dipole resonance energies, in both spherical and deformed nuclei. Comparison to available experimental $\beta$-decay rates shows agreement at roughly the same level as in other global QRPA calculations. We estimate the uncertainty in our rates all the way to the neutron drip line through a construction that extrapolates the errors of known $\beta$-decay rates in nuclei with intermediate $Q$ values to less stable isotopes with higher $Q$ values.

We present a new measurement of the branching ratio for the decay of ${}^{14}\mathrm{O}$ to the ground state of ${}^{14}\mathrm{N}$. The experimental result, ${\lambda }_0/{\lambda }_{\mathrm{total}}=(4.934\pm 0.040(\mathrm{stat}.)\pm 0.061(\mathrm{syst}.))\times {10}^{-3}$, is significantly smaller than previous determinations of this quantity. The new measurement allows an improved determination of the partial half-life for the superallowed $0^{+}\to 0^{+}$ Fermi decay to the ${}^{14}\mathrm{N}$ first excited state, which impacts the determination of the $V_{ud}$ element of the CKM matrix. With the new measurement in place, the corrected ${}^{14}\mathrm{O}\mathcal{F}t$ value is in good agreement with the average $\mathcal{F}t$ for other superallowed $0^{+}\to 0^{+}$ Fermi decays.

We address the problem of the post-prior equivalence in inclusive breakup reactions induced by weakly bound nuclei. The problem is studied within the distorted-wave Born approximation (DWBA) model of Ichimura, Austern, and Vincent [Phys. Rev. C 32, 431 (1985)]. The post and prior formulas obtained in this model are briefly recalled and applied to several breakup reactions induced by deuterons and ${}^6\mathrm{Li}$ projectiles, to test their actual numerical equivalence. The different contributions of the prior-form formula are also discussed. A critical comparison with the prior-form DWBA model of Udagawa and Tamura [Phys. Rev. C 24, 1348 (1981)] is also provided.

We develop an effective field theory (EFT) for nuclear vibrations. The key ingredients—quadrupole degrees of freedom, rotational invariance, and a breakdown scale around the three-phonon level—are taken from data. The EFT is developed for spectra and electromagnetic moments and transitions. We employ tools from Bayesian statistics for the quantification of theoretical uncertainties. The EFT consistently describes spectra and electromagnetic transitions for ${}^{62}\mathrm{Ni},{}^{98,100}\mathrm{Ru},{}^{106,108}\mathrm{Pd},{}^{110,112,114}\mathrm{Cd}$, and ${}^{118,120,122}\mathrm{Te}$ within the theoretical uncertainties. This suggests that these nuclei can be viewed as anharmonic vibrators.

The information on the symmetry energy and its density dependence is deduced by comparing the available data on the electric dipole polarizability ${\alpha }_D$ of ${}^{68}\text{Ni}$, ${}^{120}\text{Sn}$, and ${}^{208}\text{Pb}$ with the predictions of the random-phase approximation, using a representative set of nuclear energy density functionals. The calculated values of ${\alpha }_D$ are used to validate different correlations involving ${\alpha }_D$, the symmetry energy at the saturation density $J$, the corresponding slope parameter $L$, and the neutron skin thickness $\mathrm{\Delta }{r}_{np}$, as suggested by the droplet model. A subset of models that reproduce simultaneously the measured polarizabilities in ${}^{68}\text{Ni}$, ${}^{120}\text{Sn}$, and ${}^{208}\text{Pb}$ are employed to predict the values of the symmetry energy parameters at saturation density and $\mathrm{\Delta }{r}_{np}$. The resulting intervals are $J=30–35$ MeV, $L=20–66$ MeV; and the values for $\mathrm{\Delta }{r}_{np}$ in ${}^{68}\text{Ni}$, ${}^{120}\text{Sn}$, and ${}^{208}\text{Pb}$ are in the ranges 0.15–0.19, 0.12–0.16, and 0.13–0.19 fm, respectively. The strong correlation between the electric dipole polarizabilities of two nuclei is instrumental to predict the values of electric dipole polarizabilities in other nuclei.

Levels in ${}^{17}\text{O}$ affect the astrophysical $s$ process in two opposite ways. The neutron production is enhanced by resonances in the ${}^{13}\text{C}(\alpha ,n){}^{16}\text{O}$ reaction at excitation energies around 7 MeV in ${}^{17}\text{O}$, and the number of available neutrons is reduced by low-lying resonances in the ${}^{16}\text{O}(n,\gamma ){}^{17}\text{O}$ reaction corresponding to levels in ${}^{17}\text{O}$ with excitation energies of $4–5\text{MeV}$. The present work uses the ${}^{19}\text{F}(d,\alpha ){}^{17}\text{O}$ reaction to determine absolute widths of the relevant levels in ${}^{17}\text{O}$. The results improve the uncertainties of the previously adopted values and resolve a discrepancy between recent studies for the $1/2^{+}$ level close to the threshold of the ${}^{13}\text{C}(\alpha ,n){}^{16}\text{O}$ reaction. In addition, improved excitation energies and widths are provided for several states in ${}^{17}\text{O}$ up to excitation energies close to 8 MeV.

Background: Nuclear pasta phases, present in the inner crust of neutron stars, are associated with nucleonic matter at subsaturation densities arranged in regular shapes. Those complex phases, residing in a layer which is approximately 100-m thick, impact many features of neutron stars. Theoretical quantum-mechanical simulations of nuclear pasta are usually carried out in finite three-dimensional boxes assuming periodic boundary conditions. The resulting solutions are affected by spurious finite-size effects.

Purpose: To remove spurious finite-size effects, it is convenient to employ twist-averaged boundary conditions (TABC) used in condensed matter, nuclear matter, and lattice quantum chromodynamics applications. In this work, we study the effectiveness of TABC in the context of pasta phase simulations within nuclear density functional theory.

Methods: We perform Skyrme-Hartree-Fock calculations in three dimensions by implementing Bloch boundary conditions. The TABC averages are obtained by means of Gauss-Legendre integration over twist angles.

Results: We benchmark the TABC for a free nucleonic gas and apply it to simple cases such as the rod and slab phases, as well as to more elaborate P-surface and gyroidal phases.

Conclusions: We demonstrate that by applying TABC reliable results can be obtained from calculations performed in relatively small volumes. By studying various contributions to the total energy, we gain insights into pasta phases in mid-density range.

A quantum reaction approach to low-energy collisions of weakly bound few-body nuclei, based on the time-dependent wave-packet method, is presented in detail. In contrast to existing models that use this perspective, the approach separates the complete and incomplete fusion from the total fusion. Calculations performed within a one-dimensional model with two degrees of freedom for ${}^6\text{Li}+{}^{209}\text{Bi}$ at energies around the Coulomb barrier demonstrate that converged reliable excitation functions for total, incomplete, and complete fusion can be obtained with this type of approach.

A novel theory of radiative electron capture in second forbidden non-unique transition is applied to reanalyze experimental data obtained previously for the decay of ${}^{59}\mathrm{Ni}$. The measured $\gamma$ spectrum is shown to be distorted at the high-energy end, presenting the first direct evidence for the virtual $\beta \text{−}\gamma$ transition through the excited state in ${}^{59}\mathrm{Co}$. The complete theoretical predictions, including both the direct and the virtual decay channels, as well as the interference between them, reproduce very well the experimental spectrum. The virtual nuclear component amounts to about 4% of the total $\gamma$ intensity.

This work presents a direct measurement of the ${}^{96}\mathrm{Ru}(p,\gamma ){}^{97}\mathrm{Rh}$ cross section via a novel technique using a storage ring, which opens opportunities for reaction measurements on unstable nuclei. A proof-of-principle experiment was performed at the storage ring ESR at GSI in Darmstadt, where circulating ${}^{96}\mathrm{Ru}$ ions interacted repeatedly with a hydrogen target. The ${}^{96}\mathrm{Ru}(p,\gamma ){}^{97}\mathrm{Rh}$ cross section between 9 and 11 MeV has been determined using two independent normalization methods. As key ingredients in Hauser-Feshbach calculations, the $\gamma$-ray strength function as well as the level density model can be pinned down with the measured ($p,\gamma$) cross section. Furthermore, the proton optical potential can be optimized after the uncertainties from the $\gamma$-ray strength function and the level density have been removed. As a result, a constrained ${}^{96}\mathrm{Ru}(p,\gamma ){}^{97}\mathrm{Rh}$ reaction rate over a wide temperature range is recommended for $p$-process network calculations.

We demonstrate the damping of quantum octupole vibrations near the touching point when two colliding nuclei approach each other in the mass-asymmetric ${}^{16}\mathrm{O}$ + ${}^{208}\mathrm{Pb}$ system, for which the strong fusion hindrance was clearly observed. We, for the first time, apply the random-phase approximation method to the heavy-mass asymmetric dinuclear system to calculate the transition strength $B$($E3)$ as a function of the center-of-mass distance. The obtained $B(E3)$ strengths are substantially damped near the touching point, because the single-particle wave functions of the two nuclei strongly mix with each other and a neck is formed. The energy-weighted sums of $B(E3)$ are also strongly correlated with the damping factor, which is phenomenologically introduced in the standard coupled-channel calculations to reproduce the fusion hindrance. This strongly indicates that the damping of the quantum vibrations universally occurs in the deep sub-barrier fusion reactions.

Isoscalar giant resonances have been measured in the unstable ${}^{68}\mathrm{Ni}$ nucleus using inelastic alpha and deuteron scattering at $50A$ MeV in inverse kinematics with the active target MAYA at GANIL. Using alpha scattering, the extracted isoscalar giant monopole resonance (ISGMR) centroid was determined to be $21.1\pm 1.9$ MeV and the isoscalar giant quadrupole resonance (ISGQR) to be $15.9\pm 1.3$ MeV. Indications for soft isoscalar monopole and dipole modes are provided. Results obtained with both $\left(\alpha ,{\alpha }^{\prime }\right)$ and $\left(d,d^{\prime }\right)$ probes are compatible. The evolution of isoscalar giant resonances along the Ni isotopic chain from ${}^{56}\mathrm{Ni}$ to ${}^{68}\mathrm{Ni}$ is discussed.

Fully converged calculations of deuteron-deuteron elastic scattering observables are performed at energies above three- and four-body breakup threshold. Differential cross sections and analyzing powers are obtained using realistic nucleon-nucleon force models together with the Coulomb repulsion between protons. For all observables we find a very reasonable agreement with the available experimental data limited to deuteron beam energies up to 25.3 MeV.

Background: The ground state neutron density of a medium mass nucleus contains fundamental nuclear structure information and is at present relatively poorly known.

Purpose: We explore if parity violating elastic electron scattering can provide a feasible and model independent way to determine not just the neutron radius but the full radial shape of the neutron density ${\rho }_n\left(r\right)$ and the weak charge density ${\rho }_W\left(r\right)$ of a nucleus.

Methods: We expand the weak charge density of ${}^{48}\mathrm{Ca}$ in a model independent Fourier Bessel series and calculate the statistical errors in the individual coefficients that might be obtainable in a model parity violating electron scattering experiment.

Results: We find that it is feasible to determine roughly six Fourier Bessel coefficients of the weak charge density of ${}^{48}\mathrm{Ca}$ within a reasonable amount of beam time. However, it would likely be much harder to determine the full weak density of a significantly heavier nucleus such as ${}^{208}\mathrm{Pb}$.

Conclusions: Parity violating elastic electron scattering can determine the full weak charge density of a medium mass nucleus in a model independent way. This weak density contains fundamental information on the size, surface thickness, shell oscillations, and saturation density of the neutron distribution in a nucleus. The measured ${\rho }_W\left(r\right)$, combined with the previously known charge density ${\rho }_{ch}\left(r\right)$, will literally provide a detailed textbook picture of where the neutrons and protons are located in an atomic nucleus.

Background: Dynamic core-excitation effects have been found to be of importance in breakup reactions and may be of relevance when obtaining spectroscopic information from transfer reactions.

Purpose: In this paper we extend the distorted-wave Born approximation (DWBA) formalism in order to allow for noncentral components in the core-core term appearing in the transition operator, which allows for dynamic core-excitation effects. Then we study these effects by applying the formalism to different $(d,p)$ reactions.

Methods: The expression of the nonlocal kernels required for the evaluation of the DWBA amplitudes has been extended so as to include noncentral parts in the core-core interaction. The DWBA scattering amplitude is then obtained by solving the corresponding inhomogeneous equation, with the new computed kernels, and the usual outgoing boundary conditions. A new DWBA code has been developed for this purpose.

Results: For ${}^{10}\mathrm{Be}(d,p){}^{11}\mathrm{Be}$, core-excitation effects are found to be almost negligible $(<3\%)$. The importance of this effect has been found to depend to a large extent on the excitation energy of the core. This has been confirmed in the ${}^{30}\mathrm{Ne}(d,p){}^{31}\mathrm{Ne}$ case, for which the excitation energy of the first $2^{+}$ state is 0.8 MeV, and the effect of core excitation increases to $\approx 10\%$.

Conclusions: We find dynamic core-excitation effects in transfer reactions to have small contributions to cross sections, in general. However, they should not be neglected, since they may modify the spectroscopic information obtained from these reactions and may become of importance in reactions with nuclei with a core with high deformation and low excitation energy.

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{\mathit{N}N}}}=200 \mathrm{GeV}$ down to $p_T=0.4 \mathrm{GeV}/c$. Photons are detected via photon conversions to $e^{+}{e}^{-}$ pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low $p_T$. We find an excess of direct photons above the $N_{\mathrm{coll}}$-scaled yield measured in $p+p$ collisions. This excess yield is well described by an exponential distribution with an inverse slope of about $240\mathrm{MeV}/c$ in the $p_T$ range $0.6–2.0 \mathrm{GeV}/c$. While the shape of the $p_T$ distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with $N_{\mathrm{part}}^{\alpha }$, where $\alpha =1.38\pm 0.03\left(\mathrm{stat}\right)\pm 0.07\left(\mathrm{syst}\right)$.

Background: A major goal of nuclear theory is to understand the strong interaction in nuclei as it manifests itself in terms of two- and many-body forces among the nuclear constituents, the protons and neutrons, and the interactions of these constituents with external electroweak probes via one- and many-body currents.

Purpose: The objective of the present work is to calculate the quasielastic electroweak response functions in light nuclei within the realistic dynamical framework outlined above. These response functions determine the inclusive cross section as function of the lepton momentum and energy transfers.

Methods: Their ab initio calculation is a very challenging quantum many-body problem, since it requires summation over the entire excitation spectrum of the nucleus and inclusion in the electroweak currents of one- and many-body terms. Green's functions Monte Carlo methods allow one to circumvent both difficulties by computing the response in imaginary time (the so-called Euclidean response) and hence summing implicitly over the bound and continuum states of the nucleus, and by implementing specific algorithms designed to deal with the complicated spin-isospin structure of nuclear many-body operators.

Results: Theoretical predictions for ${}^4\mathrm{He}$ and ${}^{12}\mathrm{C}$, confirmed by experiment in the electromagnetic case, show that two-body currents generate excess transverse strength from threshold to the quasielastic to the dip region and beyond.

Conclusions: These results challenge the conventional picture of quasielastic inclusive scattering as being largely dominated by single-nucleon knockout processes.

We discuss the contributions to the equation of state for the $\text{N}\ell \text{LO}$ Skyrme pseudopotential $(\ell =2,3)$. We show that by adding fourth- and sixth-order gradient terms, it is possible to fairly reproduce the spin/isospin decomposition of an equation of state obtained from ab initio methods. Moreover, by inspecting the partial-wave decomposition of the equation of state, we show for the first time a possible way to add explicit constraints on the sign of the tensor terms of the Skyrme interaction.

Background: Polarized ${}^3\mathrm{He}$ targets have been used as effective polarized neutron targets for electron scattering experiments for over twenty years. Over the last ten years, the effective luminosity of polarized ${}^3\mathrm{He}$ targets based on spin-exchange optical pumping has increased by over an order of magnitude. This has come about because of improvements in commercially-available lasers and an improved understanding of the physics behind the polarization process.

Purpose: We present the development of high-performance polarized ${}^3\mathrm{He}$ targets for use in electron scattering experiments. Improvements in the performance of polarized ${}^3\mathrm{He}$ targets, target properties, and operating parameters are documented.

Methods: We utilize the technique of alkali-hybrid spin-exchange optical pumping to polarize the ${}^3\mathrm{He}$ targets. Spectrally narrowed diode lasers used for the optical pumping greatly improved the performance. A simulation of the alkali-hybrid spin-exchange optical pumping process was developed to provide guidance in the design of the targets. Data was collected during the characterization of 24 separate glass target cells, each of which was constructed while preparing for one of four experiments at Jefferson Laboratory in Newport News, Virginia.

Results: From the data obtained we made determinations of the so-called $X$-factors that quantify a temperature-dependent and as-yet poorly understood spin-relaxation mechanism that limits the maximum achievable ${}^3\mathrm{He}$ polarization to well under 100%. The presence of the $X$-factor spin-relaxation mechanism was clearly evident in our data. Good agreement between the simulation and the actual target performance was obtained by including details such as off-resonant optical pumping. Included in our results is a measurement of the $\mathrm{K}\text{−}{}^3\mathrm{He}$ spin-exchange rate coefficient $k_{\mathrm{se}}^{\mathrm{K}}=(7.46\pm 0.62)\times {10}^{-20}{\mathrm{cm}}^3/\mathrm{s}$ over the temperature range 503 K to 563 K.

Conclusions: In order to achieve high performance under the operating conditions described in this paper, the K to Rb alkali vapor density ratio should be about $5\pm 2$ and the line width of the optical pumping lasers should be no more than $0.3$ nm. Our measurements of the $X$-factors under these conditions seem to indicate the ${}^3\mathrm{He}$ polarization is limited to $\approx 90$%. The simulation results, now benchmarked against experimental data, are useful for the design of future targets. Further work is required to better understand the temperature dependence of the $X$-factor spin-relaxation mechanism and the limitations of our optical pumping simulation.

Recent work has shown that a temperature dependence of the shear-viscosity-to-entropy ratio $\eta /s$ influences the collective flow pattern in heavy-ion collisions in characteristic ways that can be measured by studying hadron transverse momentum spectra and their anisotropies. Here we point out that it also affects the pair momentum dependence of the Hanbury-Brown–Twiss (HBT) radii (the source size parameters extracted from two-particle intensity interferometry) and the variance of their event-by-event fluctuations. This observation establishes interferometric signatures as useful observables to complement the constraining power of single-particle spectra on the temperature dependence of $\eta /s$.