A theoretical study of the $\overline{p}p\to \overline{p}n{\pi }^{+}$ reaction for antiproton beam energy from $1$ to $4$ GeV is made by including contributions from various known $N^{*}$  and ${\Delta }^{*}$ resonances. It is found that for the beam energy around $1.5$ GeV, the contribution of the Roper resonance $N_{(1440)}^{*}$ produced by the $t$-channel $\sigma$ exchange dominates over all other contributions. Since such a reaction can be studied in the forthcoming PANDA experiment at the GSI Facility of Antiproton and Ion Research (FAIR), the reaction will be realistically the cleanest place for studying the properties of the Roper resonance and the best place for looking for other “missing” $N^{*}$ resonances with large coupling to $N\sigma$.

The ${}^{14}\mathrm{C}$$(\alpha ,\gamma )$ reaction rate at temperatures below $0.3$ GK depends on the properties of two near threshold resonances in ${}^{18}\mathrm{O}$, the $1^{-}$ at $6.198$ MeV and the $3^{-}$ at $6.404$ MeV. The $\alpha +$${}^{14}\mathrm{C}$ asymptotic normalization coefficients for these resonances were determined using the $\alpha$-transfer reactions ${}^{14}\mathrm{C}$(${}^7\mathrm{Li}$, $t$) and ${}^{14}\mathrm{C}$(${}^6\mathrm{Li}$, $d$) at sub-Coulomb energies. The ${}^{14}\mathrm{C}$$(\alpha ,\gamma )$ reaction rate at low temperatures has been evaluated. Implications of the new reaction rate on the evolution of accreting helium white dwarfs and on the nucleosynthesis of low mass stars during the asymptotic giant branch phase are discussed.

With the double Penning-trap mass spectrometer ISOLTRAP at ISOLDE/CERN the masses of the neutron-rich isotopes ${}^{136-146}\mathrm{Xe}$ were measured with a relative uncertainty of the order of ${10}^{-8}$ to ${10}^{-7}$. In particular, the masses of ${}^{144-146}\mathrm{Xe}$ were measured for the first time. These new mass values allow one to extend calculations of the mass surface in this region. Proton-Neutron interaction strength, obtained from double differences of binding energies, relate to subtle structural effects, such as the onset of octupole correlations, the growth of collectivity, and its relation to the underlying shell model levels. In addition, they provide a test of density functional calculations.

We investigate the microscopic structure of the low-lying isovector-dipole excitation mode in neutron-rich ${}^{36,38,40}\mathrm{Mg}$ close to the drip line by means of the deformed quasiparticle random-phase approximation employing the Skyrme and the local pairing energy-density functionals. It is found that the low-lying bump structure above the neutron emission-threshold energy develops when the drip line is approached, and that the isovector dipole strength at $E_x<10$ MeV exhausts about $6.0\%$ of the classical Thomas-Reiche-Kuhn dipole sum rule in ${}^{40}\mathrm{Mg}$. We obtained the collective dipole modes at around $8\text{−}10$ MeV in Mg isotopes, that consist of many two-quasiparticle excitations of the neutron. The transition density clearly shows an oscillation of the neutron skin against the isoscalar core. We found significant coupling effects between the dipole and octupole excitation modes due to the nuclear deformation. It is also found that the responses for the compressional dipole and isoscalar octupole excitations are much enhanced in the lower energy region.

The $\beta$-delayed $\alpha$ decay of ${}^{16}\mathrm{N}$ has been used to restrict the $E1$ fraction of the ground state $\gamma$ transition in the astrophysically important ${}^{12}\mathrm{C}$$(\alpha ,\gamma )$${}^{16}\mathrm{O}$ reaction in several experiments. A review of the published measurements is given, and GEANT4 simulations and $R$-matrix calculations are presented to further clarify the observed $\alpha$ spectra. A clear response function, in the form of a low-energy tail from the scattering of $\alpha$ particles in the catcher foil, is observed in these simulations for any foil thickness. Contrary to claims in the literature, the simulations show that the TRIUMF measurement and those performed at Yale and Mainz originate from the same underlying spectrum. The simulations suggest that the discrepancies between the Yale and TRIUMF final results can be attributed to incorrect deconvolution methods applied in the former case. The simulations show in general that the form (width) of the spectrum is very sensitive to the catcher foil thickness. It is concluded that the TRIUMF measurement most likely represents the currently closest approximation to the true $\beta$-delayed $\alpha$-decay spectrum of ${}^{16}\mathrm{N}$.

The effects of a strong magnetic field in the dynamical response of a pure neutron system to a weak neutrino probe are studied within the framework of the Landau Fermi liquid theory in the nonrelativistic Hartree-Fock approximation at zero temperature. We use Skyrme forces to parametrize the partially magnetized nuclear interacting plasma and describe its collective modes. We study the vector and vector-axial matter response functions and the neutrino mean free path in this two-component fermion system with net spin polarization and density-dependent in-medium correlations. We find a decrease in the neutrino opacity of magnetized matter with respect to the nonmagnetized case for fields $\log {}_{10}\hspace{0.5em}B(G)\gtrsim 17$.

We have performed shell-model calculations for the even- and odd-mass $N=82$ isotones, focusing attention on low-energy states. The single-particle energies and effective two-body interaction both have been determined within the framework of the time-dependent degenerate linked-diagram perturbation theory, starting from a low-momentum interaction derived from the CD-Bonn nucleon-nucleon potential. In this way, no phenomenological input enters our effective Hamiltonian, whose reliability is evidenced by the good agreement between theory and experiment.

We study ${}^1{S}_0$ pairing gaps in neutron and nuclear matter as well as $T=1$ pairing in finite nuclei on the basis of microscopic two-nucleon interactions. Special attention is paid to the consistency of the pairing interaction and normal self-energy contributions. We find that pairing gaps obtained from low-momentum interactions depend only weakly on approximation schemes for the normal self-energy, required in present energy-density functional calculations, while pairing gaps from hard potentials are very sensitive to the effective-mass approximation scheme.

We reexamine effects of the $\rho$-$\omega$ meson mixing mediated by nucleon polarizations on the symmetry energy in isospin-asymmetric nuclear matter. Taking into account the rearrangement term neglected in previous studies by others, we evaluate the $\rho$-$\omega$ mixing angle in a novel way within the relativistic mean-field models with and without chiral limits. It is found that the symmetry energy is significantly softened at high densities contrary to the finding in earlier studies. As the first step of going beyond the lowest-order calculations, we also solve the Dyson equation for the $\rho$-$\omega$ mixing. In this case, it is found that the symmetry energy is not only significantly softened by the $\rho$-$\omega$ mixing at suprasaturation densities, similar to the lowest-order $\rho$-$\omega$ mixing, but interestingly also softened at subsaturation densities. In addition, the softening of the symmetry energy at subsaturation densities can be partly suppressed by the nonlinear self-interaction of the $\sigma$ meson.

We calculate the nucleon parameters in nuclear matter using the QCD sum rules method. The radiative corrections to only the leading operator product expansion terms are included, with the corrections of the order ${\alpha }_s$ beyond the logarithmic approximation taken into account. The density dependence of the influence of radiative corrections on the nucleon parameters is obtained. At saturation density, the radiative corrections increase the values of vector and scalar self-energies by about $40$ and $30$ MeV, respectively, which is much smaller than the result of a straightforward naive estimation. The results appear to be stable with respect to possible variations of the value of ${\Lambda }_{\mathrm{QCD}}$.

Unintegrated parton distributions in the proton and nucleus are predicted by a modified Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equation incorporating the shadowing corrections, which include exact energy-momentum conservation in each splitting and fusion vertices. We find that the nuclear shadowing effects are obvious, although they are far from the saturation limit. On the other hand, we point out that the suppression of the unintegrated gluon distribution toward lower $k_t^2$ may arise from the valence-like input rather than the saturation effects.

A high-energy-resolution magnetic spectrometer has been used to measure the ${}^{12}\mathrm{C}$ excitation energy spectrum to search for the $2^{+}$ excitation of the 7.65 MeV, $0^{+}$ Hoyle state. By measuring in the diffractive minimum of the angular distribution for the broad $0^{+}$ background, evidence is found for a possible $2^{+}$ state at 9.6(1) MeV with a width of 600(100) keV. The implications for the ${}^8\mathrm{Be}+{}^4\mathrm{He}$ reaction rate in stellar environments are discussed.

We investigate $p$-wave pion production in nucleon-nucleon collisions up to next-to-next-to-leading order in chiral effective field theory. In particular, we show that it is possible to describe simultaneously the $p$-wave amplitudes in the $\mathit{pn}\to \mathit{pp}{\pi }^{-}$, $\mathit{pp}\to \mathit{pn}{\pi }^{+}$, $\mathit{pp}\to d{\pi }^{+}$ channels by adjusting a single low-energy constant accompanying the short-range operator that is available at this order. This study provides a nontrivial test of the applicability of chiral effective field theory to reactions of the type $\mathit{NN}\to \mathit{NN}\pi$.

Employing a recently developed Monte Carlo model, we study the fission of ${}^{240}\mathrm{Pu}$ induced by neutrons with energies from thermal to just below the threshold for second-chance fission. Current measurements of the mean number of prompt neutrons emitted in fission, together with less accurate measurements of the neutron energy spectra, place remarkably fine constraints on predictions of microscopic calculations. In particular, the total excitation energy of the nascent fragments must be specified to within 1 MeV to avoid disagreement with measurements of the mean neutron multiplicity. The combination of the Monte Carlo fission model with a statistical likelihood analysis also presents a powerful tool for the evaluation of fission neutron data. Of particular importance is the the fission spectrum, which plays a key role in determining reactor criticality. We show that our approach can be used to develop an estimate of the fission spectrum with uncertainties several times smaller than current experimental uncertainties for outgoing neutron energies of less than 2 MeV.

Using the reduced-density-matrix formalism, the interaction time of two heavy nuclei is studied. In the reactions ${}^{136}\mathrm{Xe}+{}^{136}\mathrm{Xe}$ and ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$, the mean interaction time and variance of interaction time distribution are calculated and compared with those of other treatments.

We extend our subtractive-renormalization method to evaluate the ${}^1{\mathrm{S}}_0$ and ${}^3{\mathrm{S}}_1\text{−}{}^3{\mathrm{D}}_1\hspace{0.5em}\mathit{NN}$-scattering phase shifts up to next-to-next-to-leading order (NNLO) in chiral effective theory. We show that, if energy-dependent contact terms are employed in the $\mathit{NN}$ potential, the ${}^1{\mathrm{S}}_0$ phase shift can be obtained by carrying out two subtractions on the Lippmann-Schwinger equation. These subtractions use knowledge of the the scattering length and the ${}^1{\mathrm{S}}_0$ phase shift at a specific energy to eliminate the low-energy constants in the contact interaction from the scattering equation. For the $J=1$ coupled channel, a similar renormalization can be achieved by three subtractions that employ knowledge of the ${}^3{\mathrm{S}}_1$scattering length, the ${}^3{\mathrm{S}}_1$ phase shift at a specific energy, and the ${}^3{\mathrm{S}}_1\text{−}{}^3{\mathrm{D}}_1$ generalized scattering length. In both channels a similar method can be applied to a potential with momentum-dependent contact terms, except that in that case one of the subtractions must be replaced by a fit to one piece of experimental data. This method allows the use of arbitrarily high cutoffs in the Lippmann-Schwinger equation. We examine the NNLO $S$-wave phase shifts for cutoffs as large as $19$ GeV and show that the presence of linear energy dependence in the $\mathit{NN}$ potential creates spurious poles in the scattering amplitude. In consequence the results are in conflict with empirical data over appreciable portions of the considered cutoff range. We also identify problems with the use of cutoffs greater than 1 GeV when momentum-dependent contact interactions are employed. These problems are ameliorated, but not eliminated, by the use of spectral-function regularization for the two-pion exchange part of the $\mathit{NN}$ potential.

The Gamow-Teller strength distributions for the $\beta$ decay of the ground state and the predicted lowest two excited $0^{+}$ states of ${}^{68}\mathrm{Se}$ to ${}^{68}\mathrm{As}$ are obtained with the complex excited VAMPIR variational approach using two effective interactions and a rather large model space. The shape mixing is described consistently for both the $0^{+}$ states in the even-even ${}^{68}\mathrm{Se}$ and the $1^{+}$ states in the odd-odd ${}^{68}\mathrm{As}$. The influence of the shape mixing accounted by the different effective interactions used and a comparison with the available data are presented. The possible influence of the decay of the excited $0^{+}$ states in the astrophysical environment of x-ray bursts is discussed.

The measurement by the BES Collaboration of $J/\psi \to \gamma p\overline{p}$ decays indicates an enhancement at the $p\overline{p}$ threshold. In another experiment, BES finds a peak in the invariant mass of $\pi$ mesons produced in the possibly related decay $J/\psi \to \gamma {\pi }^{+}{\pi }^{-}{\eta }^{\text{'}}$. Using a semiphenomenological potential model that describes all the $N\overline{N}$ scattering data, we show that the explanation of both effects may be given by a broad quasibound state in the spin and isospin singlet $S$ wave. The structure of the observed peak is due to an interference of this quasibound state with a background amplitude and depends on the annihilation mechanism.

We have measured the half-life of the electron-capture (ec) decay of ${}^{97}\mathrm{Ru}$ in a metallic environment, both at low temperature $(19\hspace{0.5em}\mathrm{K})$, and also at room temperature. We find the half-lives at both temperatures to be the same within $0.1\%$. This demonstrates that a recent claim that the ec decay half-life for ${}^7\mathrm{Be}$ changes by $0.9\%\pm 0.2\%$ under similar circumstances certainly cannot be generalized to other ec decays. Our results for the half-life of ${}^{97}\mathrm{Ru}$, $2.8370(14)$ d at room temperature and $2.8382(14)$ d at $19$ K, are consistent with, but much more precise than, previous room-temperature measurements. In addition, we have also measured the half-lives of the ${\beta }^{-}$-emitters ${}^{103}\mathrm{Ru}$ and ${}^{105}\mathrm{Rh}$ at both temperatures, and found them also to be unchanged.