The excitation function for the $\mathit{pp}\to \mathit{pp}{K}^{+}{K}^{-}$ reaction revealed a significant enhancement close to threshold that may plausibly be assigned to the influence of the ${\mathit{pK}}^{-}$ and $K^{+}{K}^{-}$ final-state interactions. In an improved reanalysis of COSY-$11$ data for the $\mathit{pp}\to \mathit{pp}{K}^{+}{K}^{-}$ reaction at excess energies of $Q=10$ and 28 MeV, including the proton-$K^{-}$ interaction, the enhancement is confirmed. Invariant mass distributions for the two- and three-particle subsystems allow us to test at low excess energies the ansatz and parameters for the description of the interaction in the $\mathit{pp}{K}^{+}{K}^{-}$ system as derived from the COSY-ANKE data. Finally, based for the first time on the low-energy $K^{+}{K}^{-}$ invariant mass distributions and the generalized Dalitz plot analysis, we estimate the scattering length for the $K^{+}{K}^{-}$ interaction to be $|\mathrm{Re}(a_{K^{+}{K}^{-}})|={0.5}_{-0.5}^{+4.0}$ fm and $\mathrm{Im}(a_{K^{+}{K}^{-}})=3.0\pm 3.0$ fm.

We report the first lattice QCD results of the scattering amplitudes of the $K\pi$ system for $I=1/2$ channel together with the $I=3/2$ case. We investigate all quark diagrams contributing to these isospin states, and find that the scattering amplitudes are expressed as combinations of only three diagrams after setting the masses of $u$-quark and $d$-quark to be the same. The lattice simulations are performed in the quenched approximation at $\beta =2.23$ on a ${12}^3\times 24$ lattice with an improved Iwasaki gauge action. We employ a new dilution-type noise method to get an accuracy of data with reasonable CPU time. A simple method is proposed and applied to eliminate lattice artefact due to the finite extent of the lattice along the time direction. A clear difference in the quark mass dependence between the $I=3/2$ and $I=1/2$ channels is observed. Although the chiral extrapolation is subtle, we assume $E_{K\pi }^2\propto m_{u,d}^2$, and obtain the $S$-wave scattering lengths as $a_0(I=3/2)m_{\pi }=-{0.084}_{-0.064}^{+0.051}$ and $a_0(I=1/2)m_{\pi }=-0.625\pm 0.012$. We show all necessary formulas which make the calculation possible. We argue that $\Lambda N$ is the most appropriate target of Lüscher's formula for the baryonic system because it has no $\pi$ exchange diagrams and has a scattering length suitable for a lattice QCD simulation.

The $({\beta }^{+}{\beta }^{+}){}_{0\nu }$ and $(\varepsilon {\beta }^{+}){}_{0\nu }$ modes of ${}^{96}\mathrm{Ru}$, ${}^{102}\mathrm{Pd}$, ${}^{106}\mathrm{Cd}$, ${}^{124}\mathrm{Xe}$, ${}^{130}\mathrm{Ba}$, and ${}^{156}\mathrm{Dy}$ isotopes are studied in the projected Hartree-Fock-Bogoliubov framework for the $0^{+}\to 0^{+}$ transition. The reliability of the intrinsic wave functions required to study these decay modes has been established in our earlier works by obtaining an overall agreement between the theoretically calculated spectroscopic properties, namely yrast spectra, reduced $B(E2:0^{+}\to 2^{+})$ transition probabilities, quadrupole moments $Q(2^{+})$ and gyromagnetic factors $g(2^{+})$, and the available experimental data in the parent and daughter even-even nuclei. In the present work, the required nuclear transition matrix elements are calculated in the Majorana neutrino mass mechanism using the same set of intrinsic wave functions as used to study the two neutrino positron double-$\beta$ decay modes. Limits on effective light neutrino mass $\langle m_{\nu }\rangle$ and effective heavy neutrino mass $\langle M_N\rangle$ are extracted from the observed limits on half-lives $T_{1/2}^{0\nu }(0^{+}\to 0^{+})$ of $({\beta }^{+}{\beta }^{+}){}_{0\nu }$ and $(\varepsilon {\beta }^{+}){}_{0\nu }$ modes. We also investigate the effect of quadrupolar correlations vis-a-vis deformation on nuclear transition matrix elements (NTMEs) required to study the $({\beta }^{+}{\beta }^{+}){}_{0\nu }$ and $(\varepsilon {\beta }^{+}){}_{0\nu }$ modes.

We study energy-weighted sum rules of the pion and kaon propagator in nuclear matter at finite temperature. The sum rules are obtained from matching the Dyson form of the meson propagator with its spectral Lehmann representation at low and high energies. We calculate the sum rules for specific models of the kaon and pion self-energy. The in-medium spectral densities of the $K$ and $\overline{K}$ mesons are obtained from a chiral unitary approach in coupled channels that incorporates the $S$ and $P$ waves of the kaon-nucleon interaction. The pion self-energy is determined from the $P$-wave coupling to particle-hole and Δ-hole excitations, modified by short-range correlations. The sum rules for the lower-energy weights are fulfilled satisfactorily and reflect the contributions from the different quasiparticle and collective modes of the meson spectral function. We discuss the sensitivity of the sum rules to the distribution of spectral strength and their usefulness as quality tests of model calculations.

We investigate the influence of couplings among continuum states in collisions of weakly bound nuclei. For this purpose, we compare cross sections for complete fusion, breakup, and elastic scattering evaluated by continuum discretized coupled channel (CDCC) calculations, including and not including these couplings. In our study, we discuss this influence in terms of the polarization potentials that reproduces the elastic wave function of the coupled channel method in single channel calculations. We find that the inclusion of couplings among continuum states renders the real part of the polarization potential more repulsive, whereas it leads to weaker absorption to the breakup channel. We show that the noninclusion of continuum-continuum couplings in CDCC calculations may lead to qualitative and quantitative wrong conclusions.

$\beta$-decay spectroscopy of the proton-rich nucleus ${}^{24}\mathrm{Si}$ was performed. The decay scheme was reconstructed from results of delayed $\gamma$-ray and proton measurements. We observed two $\beta$ branches to bound states in ${}^{24}\mathrm{Al}$ for the first time. The branching ratios were determined to be $31(4)\%$ and $23.9(15)\%$ for the $1_1^{+}$ state at $0.426$ MeV and the state at $1.090$ MeV, respectively. The observation of an allowed transition to the $1.090$-MeV state enabled us to firmly determine its spin-parity as $1^{+}$. In the proton measurements performed with the $\Delta E\text{−}E$ method, we observed a new unbound level at $6.735$ MeV. The branching ratios to three unbound states, including the new level, were also determined for the first time. Based on the decay scheme, the $B(\mathrm{GT})$ values of ${}^{24}\mathrm{Si}$ were deduced. The $B(\mathrm{GT})$ values were smaller than those of the mirror nucleus ${}^{24}\mathrm{Ne}$ by $22\%$ and $10\%$ for the $1_1^{+}$ and $1_2^{+}$ states, respectively. The mirror asymmetries of $B(\mathrm{GT})$, observed in both the $1_1^{+}$ and the $1_2^{+}$ states, indicate changes in configuration in the wave function associated with the Thomas-Ehrman shift. To clarify the mechanism of this asymmetry, a comparison with shell-model calculations is also discussed. The calculations attribute the changes in configuration to the lowering of the $1s_{1/2}$ orbital.

Minimum-bias fragment distributions (FDs) are calculated by folding a power-law parton energy spectrum with parametrized fragmentation functions (FFs) derived from $e^{+}$-$e^{-}$ and $p$-$\overline{p}$ collisions. Substantial differences between measured $e^{+}$-$e^{-}$ and $p$-$\overline{p}$ FFs suggest that FF “universality” may not be a valid assumption. The common parton spectrum is constrained by comparison with a $p$-$p$ $p_t$ spectrum hard component. Changes in FFs due to parton “energy loss” or “medium modification” are modeled by altering FF parametrizations consistent with rescaling QCD splitting functions. In-vacuum and in-medium FDs are compared with spectrum hard components from $200$-GeV Au-Au collisions for several centralities. The reference for all nuclear collisions is the FD derived from in-vacuum $e^{+}$-$e^{-}$ FFs. The hard component for $p$-$p$ and peripheral Au-Au collisions is found to be strongly suppressed for smaller fragment momenta, consistent with the FD derived from in-vacuum $p$-$\overline{p}$ FFs. At a particular centrality the Au-Au hard component transitions to enhancement at smaller momenta and suppression at larger momenta, consistent with FDs derived from in-medium $e^{+}$-$e^{-}$ FFs. Fragmentation systematics suggest that QCD color connections change dramatically in more-central $A$-$A$ collisions. Observed parton and hadron spectrum systematics are inconsistent with saturation-scale arguments used to support assumptions of parton thermalization.

We investigate the applicability of the finite temperature random phase approximation (RPA) using a solvable Lipkin model. We show that the finite temperature RPA reproduces reasonably well the temperature dependence of total strength, both for the positive energy (i.e., the excitation) and the negative energy (i.e., the de-excitation) parts. This is the case even at very low temperatures, which may be relevant to astrophysical purposes.

We investigate the importance of accounting for the transient time within the framework of the statistical approach (SA) for describing the fission process beginning from the quasistationary nuclear configuration. Two arguments are given in favor of the positive point of view on this problem. First, the average scission time is shown to be always larger than the inverse quasistationary fission rate by the value that is close to the transient time ${\tau }_r$. Second, comparing the SA and the combined dynamical statistical approach (CDSA), we have found that suppressing the fission process for some delay time in the framework of the SA significantly reduces the amount of disagreement between the values of proper observables calculated using the SA and the CDSA.

Cross sections and forward/backward ratios in the laboratory reference system were measured for the ${}^{143}\mathrm{Nd}(n,\alpha ){}^{140}\mathrm{Ce}$ reaction at 4.0, 5.0, and 6.0 MeV and for the ${}^{147}\mathrm{Sm}(n,\alpha ){}^{144}\mathrm{Nd}$ reaction at 5.0 and 6.0 MeV. A twin-gridded ionization chamber and large-area back-to-back ${}^{143}\mathrm{Nd}{}_2{\mathrm{O}}_3$ samples and ${}^{147}\mathrm{Sm}{}_2{\mathrm{O}}_3$ samples were employed. Experiments were performed at the 4.5 MV Van de Graaff accelerator of Peking University, China. Fast neutrons were produced through the ${}^2\mathrm{H}(d,n){}^3\mathrm{He}$ reaction by using a deuterium gas target. A small ${}^{238}\mathrm{U}$ fission chamber was employed for absolute neutron flux determination, and a ${\mathrm{BF}}_3$ long counter was used as the neutron flux monitor. Present experimental data are compared with previous measurements, evaluations, and model calculations.

The finite amplitude method (FAM), which we have recently proposed [T. Nakatsukasa, T. Inakura, and K. Yabana, Phys. Rev. C 76, 024318 (2007)], significantly simplifies the fully self-consistent calculation of the random-phase approximation (RPA). This article presents a computational scheme of FAM suitable for systematic investigation and shows its performance for realistic Skyrme energy functionals. We adopt the mixed representation in which the forward and backward RPA amplitudes are represented by index of hole orbitals and of the spatial grid points for the three-dimensional real space. We solve a linear algebraic problem with a sparse non-Hermitian matrix, using an iterative method. We show results of the dipole response for selected spherical and deformed nuclei. The calculated peak energies of the giant dipole resonance well agree with experiments for heavy nuclei. However, they are systematically underestimated for light nuclei. We also discuss the width of the giant dipole resonance in the fully self-consistent RPA calculation.

In a previous paper, we proposed a projected configuration interaction method that uses sets of axially deformed single-particle states to build up the many-body basis. We show that the choice of the basis set is essential to the efficiency of the method, and we propose a newly improved algorithm for selecting the projected basis states. We also extend our method to model spaces that can accommodate both parities and can include odd-multipole terms in the effective interaction, such as the octupole contributions. Examples of ${}^{56}\mathrm{Ni}$, ${}^{68}\mathrm{Se}$, ${}^{70}\mathrm{Se}$, and ${}^{76}\mathrm{Se}$ are calculated showing good agreement with the full configuration interaction results.

We report the observation of high-spin states in nuclei in the vicinity of the “island of inversion,” populated via the ${}^{18}\mathrm{O}+{}^{18}\mathrm{O}$ fusion reaction at an incident beam energy of $34$ MeV. The fusion reaction mechanism circumvents the limitations of other reactions used so far to populate excited states in these nuclei. The level structures of ${}^{33,34}\mathrm{P}$ and ${}^{33}\mathrm{S}$ have been investigated and their level schemes were substantially extended. The intensities and branching ratios of the $\gamma$ transitions were measured. The observed $\gamma$ coincidence intensity anisotropy and polarization asymmetry were analyzed for a consistent assignment of the spins and parities of the nuclear levels. The $1876$-keV transition in ${}^{34}\mathrm{P}$ that had an ambiguous multipolarity assignment has been confirmed to be a mixed transition. Truncated (1p-1h) shell model calculations within the “$\mathit{sdpf}$” valence space were performed. These calculations reproduce the experimental excitation energies of ${}^{34}\mathrm{P}$ but fail to explain the observed mixing ratio for the $1876$-keV transition.

The elastic-scattering angular distribution for ${}^8\mathrm{Li}$ on ${}^{12}\mathrm{C}$ has been measured at $E_{\mathrm{LAB}}=23.9$ MeV with ${}^8\mathrm{Li}$ radioactive nuclear beam produced by the Radioactive Ion Beams in Brazil facility. This angular distribution was analyzed in terms of optical-model with Woods-Saxon and double-folding São Paulo potential. The roles of the breakup and inelastic channels were also investigated with cluster folding and deformed potentials, respectively, through coupled-channels calculations. The angular distribution for the proton-transfer ${}^{12}\mathrm{C}({}^8\mathrm{Li},{}^9\mathrm{Be}){}^{11}\mathrm{B}$ reaction was also measured at the same energy. The spectroscopic factor for the $\langle {}^9\mathrm{Be}|{}^8\mathrm{Li}+p\rangle$ bound system was obtained and compared with shell-model calculations and with other experimental values. Total reaction cross sections for the present system were also extracted from the elastic-scattering analysis. A systematic of the reduced reaction cross sections obtained from the present and published data on ${}^{6,7,8}\mathrm{Li}$ isotopes on ${}^{12}\mathrm{C}$ was performed as a function of energy.

Using the capture cross-section data from ${}^{48}\mathrm{Ca}+{}^{238}\mathrm{U}$, ${}^{48}\mathrm{Ca}+{}^{244}\mathrm{Pu}$, and ${}^{48}\mathrm{Ca}+{}^{248}\mathrm{Cm}$ reactions in the superheavy mass region, and fusion-evaporation cross sections from ${}^{58}\mathrm{Ni}+{}^{58}\mathrm{Ni}$, ${}^{64}\mathrm{Ni}+{}^{64}\mathrm{Ni}$, and ${}^{64}\mathrm{Ni}+{}^{100}\mathrm{Mo}$ reactions known for fusion hindrance phenomenon in coupled-channels calculations, the Wong formula is assessed for its angular momentum and barrier-modification effects at sub-barrier energies. The simple, $\ell =0$ barrier-based Wong formula is shown to ignore the modifications of the barrier due to its inbuilt $\ell$ dependence via $\ell$ summation, which is found to be adequate enough to explain the capture cross sections for all the three above-mentioned ${}^{48}\mathrm{Ca}$-based reactions forming superheavy systems. For the capture (equivalently, quasifission) reactions, the complete $\ell$-summed Wong formula is shown to be the same as the dynamical cluster-decay model expression, of one of us (R.K.G.) and collaborators, with the condition of fragment preformation probability $P_0^{\ell }=1$ for all the angular momentum $\ell$ values. In the case of fusion-evaporation cross sections, however, a further modification of barriers is required for below-barrier energies, affected in terms of either the barrier “lowering” or barrier “narrowing” via the curvature constant. Calculations are made for use of nuclear proximity potential, with effects of multipole deformations included up to hexadecapole, and orientation degrees of freedom integrated for both the coplanar and noncoplanar configurations.

The manifestation of exceptional points in the scattering continuum of an atomic nucleus is studied using the real-energy continuum shell model. It is shown that low-energy exceptional points appear for realistic values of coupling to the continuum and, hence, could be accessible experimentally. Experimental signatures are proposed which include the jump by $2\pi$ of the elastic scattering phase shift and a salient energy dependence of cross sections in the vicinity of the exceptional point.

Inclusive electron-proton and electron-deuteron inelastic cross sections have been measured at Jefferson Lab (JLab) in the resonance region, at large Bjorken $x$, up to $0.92$, and four-momentum transfer squared $Q^2$ up to $7.5\hspace{0.5em}{\mathrm{GeV}}^2$ in the experiment E00-116. These measurements are used to extend to larger $x$ and $Q^2$ precision, quantitative, studies of the phenomenon of quark-hadron duality. Our analysis confirms, both globally and locally, the apparent “violation” of quark-hadron duality previously observed at a $Q^2$ of $3.5\hspace{0.5em}{\mathrm{GeV}}^2$ when resonance data are compared to structure function data created from CTEQ6M and MRST2004 parton distribution functions (PDFs). More importantly, our new data show that this discrepancy saturates by $Q^2~4\hspace{0.5em}{\mathrm{GeV}}^2$, becoming $Q^2$ independent. This suggests only small violations of $Q^2$ evolution by contributions from the higher-twist terms in the resonance region that is confirmed by our comparisons to ALEKHIN and ALLM97. We conclude that the unconstrained strength of the CTEQ6M and MRST2004 PDFs at large $x$ is the major source of the disagreement between data and these parametrizations in the kinematic regime we study and that, in view of quark-hadron duality, properly averaged resonance region data could be used in global quantum chromodynamics fits to reduce PDF uncertainties at large $x$.

Measurements of the double-differential ${\pi }^{\pm }$ production cross section in the range of momentum $0.5⩽p⩽8.0$ GeV/$c$ and angle $0.025⩽\theta ⩽0.25\hspace{0.5em}\mathrm{rad}$ in collisions of protons on beryllium, carbon, nitrogen, oxygen, aluminum, copper, tin, tantalum, and lead are presented. The data were taken with the large-acceptance HAdRon Production (HARP) detector in the T9 beamline of the CERN Proton Synchrotron. Incident particles were identified by an elaborate system of beam detectors. Thin targets of 5% of a nuclear interaction length were used. The tracking and identification of the produced particles were performed using the forward system of the HARP experiment. Results are obtained for the double-differential cross sections $d^2\sigma /\mathit{dp}\hspace{0.5em}d\Omega$ mainly at four incident proton beam momenta (3, 5, 8, and 12 GeV/$c$). Measurements are compared with the GEANT4 and MARS Monte Carlo generators. A global parametrization is provided as an approximation of all the collected datasets, which can serve as a tool for quick yield estimates.

We examine possibilities of pion condensation with zero momentum ($s$-wave condensation) in neutron stars by using the pion-nucleus optical potential $U$ and the relativistic mean field (RMF) models. We use low-density phenomenological optical potentials parametrized to fit deeply bound pionic atoms or pion-nucleus elastic scatterings. The proton fraction $(Y_p)$ and electron chemical potential $({\mu }_e)$ in neutron star matter are evaluated in RMF models. We find that the $s$-wave pion condensation hardly takes place in neutron stars and especially has no chance if hyperons appear in neutron star matter and/or the $b_1$ parameter in $U$ has density dependence.