A measurement of the inelastic component of the key astrophysical resonance in the ${}^{14}\mathrm{O}$$(\alpha ,p)$${}^{17}\mathrm{F}$ reaction for burning and breakout from hot carbon-nitrogen-oxygen (CNO) cycles is reported. The inelastic component is found to be comparable to the ground-state branch and will enhance the ${}^{14}\mathrm{O}$$(\alpha ,p)$${}^{17}\mathrm{F}$ reaction rate. The current results for the reaction rate confirm that the ${}^{14}\mathrm{O}$$(\alpha ,p)$${}^{17}\mathrm{F}$ reaction is unlikely to contribute substantially to burning and breakout from the CNO cycles under novae conditions. The reaction can, however, contribute strongly to the breakout from the hot CNO cycles under the more extreme conditions found in x-ray bursters.

We use the method of gauging equations to construct the electromagnetic current operator for the two-nucleon system in a theory with a finite cutoff. The employed formulation ensures that the two-nucleon $T$-matrix and corresponding five-point function, in the cutoff theory, are identical to the ones formally defined by a reference theory without a cutoff. A feature of our approach is that it effectively introduces a cutoff into the reference theory in a way that maintains the long-range part of the exchange current operator; for applications to effective field theory (EFT), this property is usually sufficient to guarantee the predictive power of the resulting cutoff theory. In addition, our approach leads to Ward-Takahashi (WT) identities that are linear in the interactions. From the point of view of EFT's where such a WT identity is satisfied in the reference theory, this ensures that gauge invariance in the cutoff theory is maintained order by order in the expansion.

Pairing interactions with various density dependencies (surface/volume mixing) are constrained with the two-neutron separation energy in the tin isotopic chain. The response associated with pairing vibrations in very neutron-rich nuclei is sensitive to the density dependence of the pairing interaction. Using the same pairing interaction in nuclear matter and in tin nuclei, the optimal range of densities relevant for the pairing channel is also studied.

The pairing effect plays a very important role in nuclear phenomena. We analyze the influence of pairing interaction on angular momentum alignments and backbending frequencies near the ultrahigh spin $\hslash \omega \approx 0.8$ MeV. Although the moment of inertia of rotational bands tends to be the same with or without pairing interaction, their angular momentum alignments and backbending frequencies still have large differences even at the ultrahigh spin region. For the normal orbitals, the alignment difference keeps almost constant from the larger spin region to the ultrahigh spin region. The high-$j$orbitals always cause drastic changes of alignment and lead to changes of backbending frequencies. Therefore, even at the ultrahigh spin region, to understand some nuclear phenomena, the pairing correlations should be included in some theoretical models.

Recently, it has been observed that events with the same total transverse energy of light charged particles (LCP) in the quasitarget region, $E_{\perp 12}^{\mathrm{QT}}$, show two quite distinct reaction scenarios in the projectile domain: multifragmentation and residue production. This phenomenon has been dubbed “bimodality.” Using quantum molecular dynamics calculations we demonstrate that this observation is very general. It appears in collisions of all symmetric systems larger than Ca and at beam energies between $50A$ MeV and $600A$ MeV and is due to large fluctuations of the impact parameter for a given $E_{\perp 12}^{\mathrm{QT}}$. Investigating in detail the $E_{\perp 12}^{\mathrm{QT}}$ bin in which both scenarios are present, we find that neither the average fragment momenta nor the average transverse and longitudinal energies of fragments show the behavior expected from a system in statistical equilibrium, in experiment as well as in QMD simulations. On the contrary, the experimental as well as the theoretical results point toward a fast process. This observation questions the conjecture that the observed bimodality is due to the coexistence of two phases at a given temperature in finite systems.

Recent CLAS data on the $p{\pi }^{+}{\pi }^{-}$ electroproduction off protons at $1.3<W<1.57$ GeV and $0.25<Q^2<0.6\hspace{0.5em}{\mathrm{GeV}}^2$ have been analyzed using a meson-baryon phenomenological model. By fitting nine onefold differential cross-section data for each $W$ and $Q^2$ bin, the charged double-pion electroproduction mechanisms are identified from their manifestations in the observables. We have extracted the cross sections from amplitudes of each of the considered isobar channels as well as from their coherent sum. We also obtained nonresonant partial wave amplitudes of all contributing isobar channels that could be useful for advancing a complete coupled-channels analysis of all meson electroproduction data.

A particle-core Hamiltonian is used to describe the lowest parity partner bands, $K^{\pi }=1/2^{\pm }$, in ${}^{219}\mathrm{Ra}$, ${}^{237}\mathrm{U}$, and ${}^{239}\mathrm{Pu}$ and three pairs of parity partner bands, $K^{\pi }=1/2^{\pm },3/2^{\pm },$ and $5/2^{\pm }$, in ${}^{227}\mathrm{Ra}$. The core is described by a quadrupole and octupole boson Hamiltonian. The particle-core Hamiltonian consists of four terms: a quadrupole-quadrupole, an octupole-octupole, a spin-spin, and a rotational ${\widehat{I}}^2$ interaction, with $\widehat{I}$ denoting the total angular momentum. The model Hamiltonian is treated within a projected spherical particle-core basis. The calculated excitation energies are compared with the corresponding experimental data as well as with those obtained using other approaches. For ${}^{219}\mathrm{Ra}$, we also calculated the $E1$ and $E2$ branching ratios. Also, we searched for some signatures for static octupole deformation in the considered odd isotopes.

The effect of the three-body force (TBF) is studied in nucleus-nucleus elastic scattering on the basis of Brueckner theory for nucleon-nucleon $(\mathit{NN})$ effective interaction (complex $G$ matrix) in the nuclear matter. A new $G$ matrix called CEG07 proposed recently by the present authors includes the TBF effect and reproduces a realistic saturation curve in the nuclear matter, and it is shown to well reproduce proton-nucleus elastic scattering. The microscopic optical potential for the nucleus-nucleus system is obtained by folding the $G$ matrix with nucleon density distributions in colliding nuclei. We first analyze in detail the ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ elastic scattering at $E/A=70$ MeV. The observed cross sections are nicely reproduced up to the most backward scattering angles only when the TBF effect is included. The use of the frozen-density approximation (FDA) is essentially important to properly estimate the effect of the TBF in nucleus-nucleus scattering. Other prescriptions for defining the local density have also been tested, but only the FDA prescription gives a proper description of the experimental cross sections as well as the effect of the TBF. The effects of the three-body attraction and the $\omega$-rearrangement term are also analyzed. The CEG07 interaction is compared with CDM3Y6, which is a reliable and successful effective density-dependent $\mathit{NN}$ interaction used in the double-folding model. The CEG07 $G$ matrix is also tested in the elastic scattering of ${}^{16}\mathrm{O}$ by the ${}^{12}\mathrm{C}$, ${}^{28}\mathrm{Si}$, and ${}^{40}\mathrm{Ca}$ targets at $E/A=93.9$ MeV, and in the elastic scattering of ${}^{12}\mathrm{C}$ by the ${}^{12}\mathrm{C}$ target at $E/A=135$ MeV with great success. The decisive effect of the TBF is clearly seen also in those systems. Finally, we have tested CEG07a, CEG07b, and CEG07c for the ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ system at various energies.

The spectral density of the $\varphi$ meson in a hot bath of nucleons and pions is calculated by relating the vector meson self-energy to the forward scattering amplitude (FSA), which is constrained by experimental data. Dispersion techniques are used to verify the relationship between the real and the imaginary parts of the in-medium self-energy. The position of the spectral peak of the $\varphi$ meson is found to be shifted from its vacuum position by only a small amount, but its width is considerably increased.

The collective wobbling mode, the strongest signature for the rotation of a triaxial nucleus, has previously been seen only in a few Lu isotopes in spite of extensive searches in nearby isotopes. A sequence of transitions in the $N=94$ ${}^{167}\mathrm{Ta}$ nucleus exhibiting features similar to those attributed to the wobbling bands in the Lu nuclei has now been found. This band feeds into the $\pi i_{13/2}$ band at a relative energy similar to that seen in the established wobbling bands and its dynamic moment of inertia and alignment properties are nearly identical to the $i_{13/2}$ structure over a significant frequency range. Given these characteristics, it is likely that the wobbling mode has been observed for the first time in a nucleus other than Lu, making this collective motion a more general phenomenon.

A linear relation for charged-particle emissions is presented starting from the microscopic mechanism of the radioactive decay. It relates the logarithms of the decay half-lives with two variables, called ${\chi }^{\text{'}}$ and ${\rho }^{\text{'}}$, which depend upon the $Q$ values of the outgoing clusters as well as the masses and charges of the nuclei involved in the decay. This relation explains well all known cluster decays. It is found to be a generalization of the Geiger-Nuttall law in $\alpha$ radioactivity, and therefore we call it the universal decay law. Predictions of the most likely emissions of various clusters are presented by applying the law over the whole nuclear chart. It is seen that the decays of heavier clusters with nonequal proton and neutron numbers are mostly located in the trans-lead region. The emissions of clusters with equal protons and neutrons, like ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$, are possible in some neutron-deficient nuclei with $Z⩾54$.

Excited states in ${}^{191}\mathrm{Ir}$, ${}^{193}\mathrm{Ir}$, and ${}^{197}\mathrm{Au}$ were studied and absolute partial $\gamma$-ray cross sections were measured using the ($n,n^{\text{'}}\gamma$) reaction. A Compton-suppressed germanium-detector array (GEANIE) for $\gamma$-ray spectroscopy was used for the measurement and the broad-spectrum pulsed neutron source of the Los Alamos Neutron Science Center’s WNR facility provided energetic neutrons. The energy of the incident neutrons was determined using the time-of-flight technique. Absolute partial $\gamma$-ray cross sections were measured up to incident neutron energy of 20 MeV for several transitions feeding directly the $11/2^{-}$ isomers and ground states in ${}^{191}\mathrm{Ir}$, ${}^{193}\mathrm{Ir}$, and ${}^{197}\mathrm{Au}$. The feeding of the $11/2^{-}$ isomers, which originate from the odd proton occupying the $h_{11/2}$ orbital, was found for the three targets to be very similar and increasing relative to the feeding of the corresponding ground state with increasing neutron energy up to $E_n~10$ MeV. Above this neutron energy the opening of the $(n,2n)$ reaction channel strongly affects the population of the isomers and leads to a decrease of their relative population compared to the population of the ground states. The experimental results are compared with theoretical predictions from the GNASH reaction model calculation implementing a version of the spin distribution for the pre-equilibrium reaction piece with either a compound nucleus spin distribution (CN-GNASH) or a Feshbach-Kerman-Koonin (FKK-GNASH) quantum mechanical spin distribution. The effects of the spin cutoff parameter values on the population of states are examined. Evidence is presented that FKK-GNASH provides a description of the experimental data that mitigates the need for adjustment of the level density parameter to fit the data.

Measurements of (${}^3\mathrm{He}$,$d$) reactions can provide information on the proton widths of states that play a role in astrophysically important ($p,\gamma$) reactions. We report on the first study of the (${}^3\mathrm{He}$,$d$) reaction in inverse kinematics with a ${}^{56}\mathrm{Ni}$$\hspace{0.5em}(T_{1/2}=6.1\hspace{0.5em}\mathrm{d})$ ion beam. The $Q$-value resolution of $~$ keV achieved in this experiment was sufficient to separate the transitions populating the ground state and the $1/2^{-}\text{−}5/2^{-}$ doublet at $E_x~1.1$ MeV in ${}^{57}\mathrm{Cu}$. Prospects for similar (${}^3\mathrm{He}$,$d$) experiments with improved energy resolution are also discussed.

The results of midrapidity $(0<y<0.8)$ neutral pion spectra over an extended transverse momentum range $(1<p_T<12\hspace{0.5em}\mathrm{GeV}/c)$ in $\sqrt{s_{\mathit{NN}}}=200\hspace{0.5em}\mathrm{GeV}\hspace{0.5em}\mathrm{Au}+\mathrm{Au}$ collisions, measured by the STAR experiment, are presented. The neutral pions are reconstructed from photons measured either by the STAR Barrel Electro-Magnetic Calorimeter or by the Time Projection Chamber via tracking of conversion electron-positron pairs. Our measurements are compared to previously published ${\pi }^{\pm }$ and ${\pi }^0$ results. The nuclear modification factors $R_{\mathrm{CP}}$ and $R_{\mathrm{AA}}$ of ${\pi }^0$ are also presented as a function of $p_T$. In the most central $\mathrm{Au}+\mathrm{Au}$ collisions, the binary collision scaled ${\pi }^0$ yield at high $p_T$ is suppressed by a factor of about 5 compared to the expectation from the yield of $p+p$ collisions. Such a large suppression is in agreement with previous observations for light quark mesons and is consistent with the scenario that partons suffer considerable energy loss in the dense medium formed in central nucleus-nucleus collisions at the Relativistic Heavy Ion Collider.

We investigate the collisional energy losses of the fast gluons and light quarks in quark-gluon plasma produced in central $(\mathrm{Au}+\mathrm{Au})$ collisions at at energies currently available at the BNL Relativistic Heavy Ion Collider (RHIC) $(\sqrt{s_{\mathit{NN}}}=200\hspace{0.5em}\mathrm{GeV})$. We use the effective quasiparticle model for investigation of physical characteristic of expanding plasma. We take into account the possibility of hot glue production at the first stage. We calculate these energy losses and compare them with radiative energy losses of gluons and quarks in an analogous model. We show that radiative energy losses exceed considerably the collisional energy losses.

We perform a systematic analysis of the density dependence of nuclear symmetry energy within the microscopic Brueckner-Hartree-Fock (BHF) approach using the realistic Argonne V18 nucleon-nucleon potential plus a phenomenological three-body force of Urbana type. Our results are compared thoroughly with those arising from several Skyrme and relativistic effective models. The values of the parameters characterizing the BHF equation of state of isospin asymmetric nuclear matter fall within the trends predicted by those models and are compatible with recent constraints coming from heavy ion collisions, giant monopole resonances, or isobaric analog states. In particular we find a value of the slope parameter $L=66.5$ MeV, compatible with recent experimental constraints from isospin diffusion, $L=88\pm 25$ MeV. The correlation between the neutron skin thickness of neutron-rich isotopes and the slope $L$ and curvature $K_{\mathrm{sym}}$ parameters of the symmetry energy is studied. Our BHF results are in very good agreement with the correlations already predicted by other authors using nonrelativistic and relativistic effective models. The correlations of these two parameters and the neutron skin thickness with the transition density from nonuniform to $\beta$-stable matter in neutron stars are also analyzed. Our results confirm that there is an inverse correlation between the neutron skin thickness and the transition density.

Elastic scattering cross sections of the ${}^{89}\mathrm{Y}$$(\alpha ,\alpha )$${}^{89}\mathrm{Y}$ reaction have been measured at energies $E_{\mathrm{c}.\mathrm{m}.}=15.51$ and $18.63$ MeV. The high-precision data for the semimagic $N=50$ nucleus ${}^{89}\mathrm{Y}$ are used to derive a local potential and to evaluate the predictions of global and regional $\alpha$-nucleus potentials. The variation of the elastic $\alpha$-scattering cross sections along the $N=50$ isotonic chain is investigated by a study of the ratios of angular distributions for ${}^{89}\mathrm{Y}$$(\alpha ,\alpha )$${}^{89}\mathrm{Y}$ and ${}^{92}\mathrm{Mo}$$(\alpha ,\alpha )$${}^{92}\mathrm{Mo}$ at $E_{\mathrm{c}.\mathrm{m}.}\approx 15.51$ and $18.63$ MeV. This ratio is a very sensitive probe at energies close to the Coulomb barrier, where scattering data alone is usually not enough to characterize the different potentials. Furthermore, $\alpha$-cluster states in ${}^{93}\mathrm{Nb}$$=$${}^{89}\mathrm{Y}$$\otimes \alpha$ are investigated.

The density dependence of the nuclear symmetry energy is inspected using the statistical multifragmentation model with Skyrme effective interactions. The model consistently considers the expansion of the fragments’ volumes at finite temperature at the freeze-out stage. By selecting parametrizations of the Skyrme force that lead to very different equations of state for the symmetry energy, we investigate the sensitivity of the isoscaling parameter and the isotopic distributions to differences in the symmetry energy. Our results suggest that, in spite of being sensitive to the thermal dilation of the fragments’ volumes, it is difficult to distinguish among the Skyrme forces from the isoscaling analysis. On the other hand, the isotopic distribution of the emitted fragments turns out to be very sensitive to the force employed in the calculation.

The low-energy structure of the proton dripline nucleus ${}^{20}\mathrm{Na}$ has been studied using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. A $1.7$-MeV/nucleon ${}^{20}\mathrm{Na}$ beam of $~5\times {10}^6$ ions/s was Coulomb excited by a $0.5\text{−}\mathrm{mg}/{\mathrm{cm}}^{2\hspace{0.5em}\mathrm{nat}}$Ti target. Scattered beam and target particles were detected by the BAMBINO segmented Si detector while $\gamma$ rays were detected by two TIGRESS HPGe clover detectors set perpendicular to the beam axis. Coulomb excitation from the $2^{+}$ ground state to the first excited $3^{+}$ and $4^{+}$ states was observed, and $B(\lambda$L) values were determined using the $2^{+}\to 0^{+}$ de-excitation in ${}^{48}\mathrm{Ti}$ as a reference. The resulting $B(\lambda \mathrm{L})\downarrow$ values are $B(E2;3^{+}\to 2^{+})=55\pm 6\hspace{0.5em}{e}^2{\mathrm{fm}}^4$ ($17.0\pm 1.9$ W.u.), $B(E2;4^{+}\to 2^{+})=35.7\pm 5.7\hspace{0.5em}{e}^2{\mathrm{fm}}^4$ ($11.1\pm 1.8$ W.u.), and $B(M1;4^{+}\to 3^{+})=0.154\pm 0.030\hspace{0.5em}{{\mu }_N}^2$ ($0.086\pm 0.017$ W.u.). These measurements provide the first experimental determination of $B(\lambda L)$ values for this proton dripline nucleus of astrophysical interest.

A simple exact covariant model in which a scalar particle $\Psi$ is modeled as a bound state of two different particles is used to elucidate relativistic aspects of electromagnetic form factors $F(Q^2)$. The model form factor is computed using an exact covariant calculation of the lowest order triangle diagram. The light-front technique of integrating over the minus component of the virtual momentum gives the same result and is the same as the one obtained originally by Gunion et al. [Phys. Rev. D 8, 287 (1973)] by using time-ordered perturbation theory in the infinite-momentum frame. The meaning of the transverse density $\rho (b)$ is explained by providing a general derivation, using three spatial coordinates, of its relationship with the form factor. This allows us to identify a mean-square transverse size $\langle b^2\rangle =\int d^{2}b\hspace{0.5em}{b}^2\rho (b)=-4\frac{\mathit{dF}}{{\mathit{dQ}}^2}(Q^2=0)$. The quantity $\langle b^2\rangle$ is a true measure of hadronic size because of its direct relationship with the transverse density. We show that the rest-frame charge distribution is generally not observable by studying the explicit failure to uphold current conservation. Neutral systems of two charged constituents are shown to obey the conventional lore that the heavier one is generally closer to the transverse origin than the lighter one. It is argued that the negative central charge density of the neutron arises, in pion-cloud models, from pions of high longitudinal momentum that reside at the center. The nonrelativistic limit is defined precisely, and the ratio of the binding energy $B$ to the mass $\mathcal{M}$ of the lightest constituent is shown to govern the influence of relativistic effects. It is shown that the exact relativistic formula for $F(Q^2)$ is the same as the familiar one of the three-dimensional Fourier transform of a square of a wave function for very small values of $B/\mathcal{M}$, but this only occurs for values of $B/\mathcal{M}$ less than about $0.001$. For masses that mimic the quark-diquark model of the nucleon we find that there are substantial relativistic corrections to the form factor for any value of $Q^2$. A schematic model of the lowest $s$ states of nuclei is developed. Relativistic effects are found to decrease the form factor for light nuclei but to increase the form factor for heavy nuclei. Furthermore, these lowest $s$ states are likely to be strongly influenced by relativistic effects that are of the order of $15\%\text{−}20\%$.