A direct $Q_{\mathrm{EC}}$-value measurement of the superallowed ${\beta }^{+}$ emitter ${}^{22}\mathrm{Mg}$ was performed using TRIUMF's Ion Trap for Atomic and Nuclear Science. The direct ground-state to ground-state atomic mass difference between ${}^{22}\mathrm{Mg}$ and ${}^{22}\mathrm{Na}$ was determined to be $Q_{\mathrm{EC}}=4781.40\left(22\right)$ keV, representing the most precise single measurement of this quantity to date. In a continued push toward calculating superallowed isospin-symmetry-breaking corrections from first principles, ab initio shell-model calculations of the $A=22$ isobaric multiplet mass equation are also presented for the first time using the valence-space in-medium similarity renormalization group formalism. With particular starting two- and three-nucleon forces, this approach demonstrates good agreement with the experimental data.

In this paper, we investigate the $\gamma p\to p\eta \eta$ reaction within an effective Lagrangian approach and isobar model. We consider the contributions from the intermediate $N^{*}\left(1535\right)$, $N^{*}\left(1650\right)$, $N^{*}\left(1710\right)$, and $N^{*}\left(1720\right)$ isobars which finally decay to the $N\eta$ state. It is found that the excitation of the $N^{*}\left(1535\right)$ dominates this reaction close to threshold and $\rho$ meson exchange plays the most important role for the excitation of nucleon resonances. Therefore, this reaction offers a potentially good place to study the properties of nucleon resonances and their couplings to the $N\rho$ channel. Predictions for angular distributions and invariant mass spectra of final particles are also presented for future comparison with data.

Quadrupole and octupole deformation energy surfaces, low-energy excitation spectra, and transition rates in 14 isotopic chains: Xe, Ba, Ce, Nd, Sm, Gd, Rn, Ra, Th, U, Pu, Cm, Cf, and Fm, are systematically analyzed using a theoretical framework based on a quadrupole-octupole collective Hamiltonian (QOCH), with parameters determined by constrained reflection-asymmetric and axially symmetric relativistic mean-field calculations. The microscopic QOCH model based on the PC-PK1 energy density functional and $\delta$-interaction pairing is shown to accurately describe the empirical trend of low-energy quadrupole and octupole collective states, and predicted spectroscopic properties are consistent with recent microscopic calculations based on both relativistic and nonrelativistic energy density functionals. Low-energy negative-parity bands, average octupole deformations, and transition rates show evidence for octupole collectivity in both mass regions, for which a microscopic mechanism is discussed in terms of evolution of single-nucleon orbitals with deformation.

Background: Interest in the behavior of nucleon electromagnetic form factors at large momentum transfers has steadily increased since the discovery, using polarization observables, of the rapid decrease of the ratio $G_E^p/G_M^p$ of the proton's electric and magnetic form factors for momentum transfers $Q^2\gtrsim 1$ ${\mathrm{GeV}}^2$, in strong disagreement with previous extractions of this ratio using the traditional Rosenbluth separation technique.

Purpose: The GEp-III and $\mathrm{GEp}\text{−}2\gamma$ experiments were carried out in Jefferson Laboratory's (JLab's) Hall C from 2007 to 2008, to extend the knowledge of $G_E^p/G_M^p$ to the highest practically achievable $Q^2$ given the maximum beam energy of 6 GeV and to search for effects beyond the Born approximation in polarization transfer observables of elastic $\vec{e}p$ scattering. This article provides an expanded description of the common experimental apparatus and data analysis procedures, and reports the results of a final reanalysis of the data from both experiments, including the previously unpublished results of the full-acceptance dataset of the $\mathrm{GEp}\text{−}2\gamma$ experiment.

Methods: Polarization transfer observables in elastic $\vec{e}p\to e\vec{p}$ scattering were measured at central $Q^2$ values of 2.5, 5.2, 6.8, and 8.54 ${\mathrm{GeV}}^2$. At $Q^2=2.5{\mathrm{GeV}}^2$, data were obtained for central values of the virtual photon polarization parameter $\epsilon$ of 0.149, 0.632, and 0.783. The Hall C High Momentum Spectrometer detected and measured the polarization of protons recoiling elastically from collisions of JLab's polarized electron beam with a liquid hydrogen target. A large-acceptance electromagnetic calorimeter detected the elastically scattered electrons in coincidence to suppress inelastic backgrounds.

Results: The final GEp-III data are largely unchanged relative to the originally published results. The statistical uncertainties of the final $\mathrm{GEp}\text{−}2\gamma$ data are significantly reduced at $\epsilon =0.632$ and 0.783 relative to the original publication.

Conclusions: The final GEp-III results show that the decrease with $Q^2$ of $G_E^p/G_M^p$ continues to $Q^2=8.5{\mathrm{GeV}}^2$, but at a slowing rate relative to the approximately linear decrease observed in earlier Hall A measurements. At $Q^2=8.5{\mathrm{GeV}}^2$, $G_E^p/G_M^p$ remains positive but is consistent with zero. At $Q^2=2.5{\mathrm{GeV}}^2$, $G_E^p/G_M^p$ derived from the polarization component ratio $R\propto P_t/P_{\ell }$ shows no statistically significant $\epsilon$ dependence, as expected in the Born approximation. On the other hand, the ratio $P_{\ell }/P_{\ell }^{\mathrm{Born}}$ of the longitudinal polarization transfer component to its Born value shows an enhancement of roughly 1.7% at $\epsilon =0.783$ relative to $\epsilon =0.149$, with $\approx 2.2\sigma$ significance based on the total uncertainty, implying a similar effect in the transverse component $P_t$ that cancels in the ratio $R$.

The angular distributions of ${}^8\mathrm{Be}$ states in the excitation energy region $E_x\sim \left(16.5\text{–}18.2\right)$ MeV produced in the ${}^7\mathrm{Li}({}^3\mathrm{He},d){}^8\mathrm{Be}$ proton transfer reaction have been measured at the Orsay $14.8-\mathrm{MV}$ tandem accelerator for ${}^3\mathrm{He}^{2+}$ ion bombarding energy, $E_{\text{lab}}=20$ MeV, and forward angular range, ${\theta }_{\text{lab}}=5{}^{\circ }\text{–}50{}^{\circ }$. A high energy resolution detection system composed of a split-pole magnetic spectrometer and a $\mathrm{\Delta }E-E$, position-sensitive drift chamber was used to record the energy spectra of outgoing deuterons. The measured cross section data for the direct reaction component have been separated from the compound nucleus one, then analyzed in the framework of the nonlocal, finite-range (FR)–distorted-wave Born approximation (DWBA) theory. New values of the $C^{2}S$ and ($S_{p1/2},S_{p3/2})$ proton absolute and partial spectroscopic factors and related ${\gamma }_p^2\left(a\right)$ proton reduced widths versus the $p+{}^7\mathrm{Li}$ channel radius have been extracted for the $2^{+}\left(16.626\right)$ and $2^{+}\left(16.922\right),T=0+1$ isospin-mixed loosely bound states of astrophysical interest and the $1^{+}\left(17.640\right)$, $T=1$ unbound state of ${}^8\mathrm{Be}$. They are compared to sparse earlier experimental values and to shell-model-predicted ones from the literature, and are discussed. In particular, the status of the spectroscopic information on the $2^{+}$ isospin-mixed doublet is reviewed and updated. The application in nuclear astrophysics of the DWBA derived results is emphasized.

The production of ground-state and excited bottomonia in ultrarelativistic heavy-ion collisions is investigated within a kinetic-rate equation approach including regeneration. We augment our previous calculations by an improved treatment of medium effects, with temperature-dependent binding energies and pertinent reaction rates, $B$-meson resonance states in the equilibrium limit near the hadronization temperature, and a lattice-QCD based equation of state for the bulk medium. In addition to the centrality dependence of the bottomonium yields, we compute their transverse-momentum ($p_T$) spectra and elliptic flow with momentum-dependent reaction rates and a regeneration component based on $b$-quark spectra from a nonperturbative transport model of heavy-quark diffusion. The latter has noticeable consequences for the shape of the bottomonium $p_T$ spectra. We quantify how uncertainties in the various modeling components affect the predictions for observables. Based on this we argue that the $\mathrm{{\rm Y}}\left(1S\right)$ suppression is a promising observable for mapping out the in-medium properties of the QCD force, while $\mathrm{{\rm Y}}\left(2S\right)$ production can help to quantify the role of regeneration from partially thermalized $b$ quarks.

This paper discusses the impact of finite particle losses associated with instrumental effects in measurements of moments of produced multiplicities with the identity method towards the evaluation of fluctuation measures such as ${\nu }_{\mathrm{dyn}}$. One finds that the identity method remains applicable provided it is modified to determine factorial moments $\langle N(N-1)\rangle$, rather than moments $\langle N^2\rangle$. It is further demonstrated that ${\nu }_{\mathrm{dyn}}$ remains robust if detection efficiencies are uniform across the measurement's acceptance. The robustness is lost, however, if detection efficiencies are momentum dependent, although the identity method remains applicable provided detection efficiencies can be determined with sufficient accuracy.

The helicity amplitudes for the photoproduction of nucleon resonances excited from neutrons are determined in the Bonn-Gatchina coupled-channel partial wave analysis. Upper limits for the decay fraction of the pentaquark candidate $N\left(1685\right)\to K^0\mathrm{\Lambda }$ are given. The electric and magnetic couplings at the pole positions are also tabulated, and these are used to suggest candidates for possible multiplets with quark-spin-1/2 and -3/2 content.

Spectroscopic factors, extracted from one-neutron knockout and Coulomb dissociation reactions, for transitions from the ground state of ${}^{33}\mathrm{Mg}$ to the ground-state rotational band in ${}^{32}\mathrm{Mg}$, and from ${}^{32}\mathrm{Mg}$ to low-lying negative-parity states in ${}^{31}\mathrm{Mg}$, are interpreted within the rotational model. Associating the ground state of ${}^{33}\mathrm{Mg}$ and the negative-parity states in ${}^{31}\mathrm{Mg}$ with the $\frac{3}{2}\left[321\right]$ Nilsson level, the strong coupling limit gives simple expressions that relate the amplitudes ($C_{j\ell }$) of this wave function with the measured cross sections and derived spectroscopic factors ($S_{j\ell }$). To obtain a consistent agreement with the data within this framework, we find that one requires a modified $\frac{3}{2}\left[321\right]$ wave function with an increased contribution from the spherical $2p_{3/2}$ orbit as compared to a standard Nilsson calculation. This is consistent with the findings of large-scale shell model calculations and can be traced to weak binding effects that lower the energy of low-$\ell$ orbitals.

I study two-photon contribution to the elastic lepton-proton scattering, associated with $\sigma$ meson exchange, with special attention paid to the low-$Q^2$ region. It is shown that the corresponding amplitude grows sharply but remains finite at $Q^2\to 0$. The analytical formula for the amplitude at $Q^2=0$ is obtained. I also estimate the shift of the muonic hydrogen energy levels, induced by $\sigma$ meson exchange. For the $2S$ level the shift is approximately 30 times smaller than needed to resolve the proton radius puzzle, but still exceeds the precision of the muonic hydrogen measurements.

The finite-temperature Hartree-Fock-Bogoliubov (HFB) approximation often breaks symmetries of the underlying many-body Hamiltonian. Restricting the calculation of the HFB partition function to a subspace with good quantum numbers through projection after variation restores some of the correlations lost in breaking these symmetries, although effects of the broken symmetries such as sharp kinks at phase transitions remain. However, the most general projection after variation formula in the finite-temperature HFB approximation is limited by a sign ambiguity. Here, I extend the Pfaffian formula for the many-body traces of HFB density operators introduced by Robledo [L. M. Robledo, Phys. Rev. C. 79, 021302(R) (2009)] to eliminate this sign ambiguity and evaluate the more complicated many-body traces required in projection after variation in the most general HFB case. The method is validated through a proof-of-principle calculation of the particle-number-projected HFB thermal energy in a simple model.

An updated and improved version of the effective interaction based on the Argonne-Urbana nuclear Hamiltonian, derived using the formalism of correlated basis functions and the cluster expansion technique, is employed to obtain a number of properties of cold nuclear matter at arbitrary neutron excess within the formalism of many-body perturbation theory. The numerical results, including the ground-state energy per nucleon, the symmetry energy, the pressure, the compressibility, and the single-particle spectrum, are discussed in the context of the available empirical information, obtained from measured nuclear properties and heavy-ion collisions.

Nuclear fusion reactions are the most important processes in nature to power stars and produce new elements, and lie at the center of the understanding of nucleosynthesis in the universe. It is critically important to study the reactions in full plasma environments that are close to true astrophysical conditions. By using laser-driven counter-streaming collisionless plasmas, the fusion $d+d{\to }^3\mathrm{He}+n$ is studied in a Gamow-like window around 27 keV. The results give hints that astrophysical nuclear reaction yields can be modulated significantly by the self-generated electromagnetic fields and the collective motion of the plasma. This plasma-version minicollider may provide a novel tool for studies of astrophysics-interested nuclear reactions, as well as a useful tool to constrain the models of plasma colliding dynamic.

Background: The five-dimensional quadrupole collective model based on energy density functionals (EDFs) has often been employed to treat long-range correlations associated with shape fluctuations in nuclei. Our goal is to derive the collective inertial functions in the collective Hamiltonian by the local quasiparticle random-phase approximation (QRPA) that correctly takes into account time-odd mean-field effects. Currently, a practical framework to perform the QRPA calculation with the modern EDFs on the $(\beta ,\gamma )$ deformation space is not available.

Purpose: Toward this goal, we develop an efficient numerical method to perform the QRPA calculation on the $(\beta ,\gamma )$ deformation space based on the Skyrme EDF.

Methods: We use the finite amplitude method (FAM) for the efficient calculation of QRPA strength functions for multipole external fields. We construct a computational code of FAM-QRPA in the three-dimensional Cartesian coordinate space to handle triaxially deformed superfluid nuclei.

Results: We validate our new code by comparing our results with former QRPA calculations for axially symmetric nuclei. Isoscalar quadrupole strength functions in triaxial superfluid nuclei ${}^{110}\mathrm{Ru}$ and ${}^{190}\mathrm{Pt}$ are obtained within a reasonable computational cost.

Conclusions: QRPA calculations for triaxially deformed superfluid nuclei based on the Skyrme EDF are achieved with the help of the FAM. This is an important step toward the microscopic calculation of collective inertial functions of the local QRPA.

Multinucleon transfer processes in low-energy heavy ion reactions have attracted increasing interest in recent years aiming at the production of new neutron-rich isotopes. Clearly, it is an imperative task to further develop understanding of underlying reaction mechanisms to lead experiments to success. In this paper, from systematic time-dependent Hartree-Fock calculations for the ${}^{238}\mathrm{U}+{}^{124}\mathrm{Sn}$ reaction, it is demonstrated that transfer dynamics depend strongly on the orientations of ${}^{238}\mathrm{U}$, quantum shells, and collision energies. Two important conclusions are obtained: (i) Experimentally observed many-proton transfer from ${}^{238}\mathrm{U}$ to ${}^{124}\mathrm{Sn}$ can be explained by a multinucleon transfer mechanism governed by enhanced neck evolution in tip collisions; (ii) novel reaction dynamics are observed in tip collisions at energies substantially above the Coulomb barrier, where a number of nucleons are transferred from ${}^{124}\mathrm{Sn}$ to ${}^{238}\mathrm{U}$, producing transuranium nuclei as primary reaction products, which could be a means to synthesize superheavy nuclei. Both results indicate the importance of the neck (shape) evolution dynamics, which are sensitive to orientations, shell effects, and collision energies, for exploring possible pathways to produce new unstable nuclei.

Precision measurements of free-neutron $\beta$ decay have been used to precisely constrain our understanding of the weak interaction. However, the neutron Fierz interference term $b_n$, which is particularly sensitive to beyond-standard-model tensor currents at the TeV scale, has thus far eluded measurement. Here we report the first direct constraints on this term, finding $b_n=0.067\pm 0.{005}_{\text{stat}}{}_{-0.061}^{+0.090}{}_{\text{sys}}$, consistent with the standard model. The uncertainty is dominated by absolute energy reconstruction and the linearity of the $\beta$ spectrometer energy response.

Excited states in ${}^{98}\mathrm{Y}$, populated in neutron-induced fission of ${}^{235}\mathrm{U}$ and in spontaneous fission of ${}^{248}\mathrm{Cm}$ and ${}^{252}\mathrm{Cf}$, have been studied by means of $\gamma$ spectroscopy using the Lohengrin fission-fragment separator at ILL Grenoble and the EXILL, Eurogam2, and Gammasphere Ge arrays. Two new isomers have been found in ${}^{98}\mathrm{Y}$: a deformed one with $T_{1/2}=180\left(7\right)$ ns and a rotational band on top of it, and a spherical one with $T_{1/2}=0.45\left(15\right)\mu \text{s}$, analogous to the $8^{+}$ isomer in ${}^{96}\mathrm{Y}$, corresponding to the ${(\nu g_{7/2},\pi g_{9/2})}_{8^{+}}$ spherical configuration. Using the JYFLTRAP Penning trap, an accurate excitation energy of 465.7(7) keV has been determined for the 2.36-s isomer in ${}^{98}\mathrm{Y}$. This result and the studies of excited levels in ${}^{98}\mathrm{Zr}$, populated in ${\beta }^{-}$ decay of the isomer, indicate a new spin-parity, $I^{\pi }={\left(7\right)}^{+}$ for the isomer. The high spin and the decay properties of this isomer suggest the presence of the $9/2^{+}\left[404\right]$ neutron extruder orbital in its structure. This is consistent with the large deformation of the isomer, reported recently. The present work does not provide arguments to support the special role of the $\nu g_{7/2}\text{−}\pi g_{9/2}$ interaction (the spin-orbit-partner, or SOP, mechanism).

Background: It is understood from the recent experimental studies that prompt/resonant breakup, and transfer followed by breakup in the weakly bound ${}^{6,7}\mathrm{Li}$-induced reactions play a significant role in the complete-incomplete fusion (CF-ICF), suppression/enhancement in the fusion cross section around the Coulomb barrier.

Purpose: Investigation of ICF over CF by measuring cross sections of the populated residues, produced via different channels in the ${}^7\mathrm{Li}$-induced reaction on a ${}^{\text{nat}}\mathrm{Nb}$ target within the 3–6.5 MeV/nucleon energy region.

Method: The ${}^7\mathrm{Li}$ beam was allowed to hit the self-supporting ${}^{93}\mathrm{Nb}$ targets, backed by the aluminium (Al) foil alternately, within 3–6.5 MeV/nucleon energy. Populated residues were identified by offline $\gamma$-ray spectrometry. Measured excitation functions of different channels were compared with different equilibrium and pre-equilibrium models.

Result: The enhancement in cross sections in the proton ($\sim 20-30$ MeV) and $\alpha$-emitting channels, which may be ascribed to ICF, was observed in the measured energy range when compared to the Hauser-Feshbach and exciton model calculations using empire, which satisfactorily reproduces the neutron channels, compared to the Weisskopf-Ewing model and hybrid Monte Carlo calculations. The increment of the incomplete fusion fraction was observed with rising projectile energy.

Conclusion: Contrary to the alice14, experimental results are well reproduced by the empire throughout the measured energy range. The signature of ICF over CF indicates that the breakup/transfer processes are involved in the weakly bound ${}^7\mathrm{Li}$-induced reaction on ${}^{93}\mathrm{Nb}$ slightly above the Coulomb barrier.

A high-precision half-life measurement for the superallowed Fermi ${\beta }^{+}$ emitter ${}^{22}\mathrm{Mg}$ was performed at the TRIUMF-ISAC facility using a $4\pi$ proportional gas counter. The result of $T_{1/2}=3.87400\pm 0.00079$ s is a factor of 3 more precise than the previously adopted world average and resolves a discrepancy between the two previously published ${}^{22}\mathrm{Mg}$ half-life measurements.

Direct mass measurements of the low-spin $3/2^{-}$ and high-spin $13/2^{+}$ states in the neutron-deficient isotopes ${}^{195}\mathrm{Po}$ and ${}^{197}\mathrm{Po}$ were performed with the Penning-trap mass spectrometer ISOLTRAP at ISOLDE-CERN. These measurements allow the determination of the excitation energy of the isomeric state arising from the $\nu i_{13/2}$ orbital in ${}^{195,197}\mathrm{Po}$. Additionally, the excitation energy of isomeric states of lead, radon, and radium isotopes in this region were obtained from $\alpha$-decay chains. These excitation energies complete the knowledge of the energy systematics in the region and confirm that the $13/2^{+}$ states remain isomeric, independent of the number of valence neutrons.