We have performed continuum-discretized coupled channels (CDCC) calculations of the breakup of ${}^8\mathrm{B}$ on ${}^{58}\mathrm{Ni}$ and direct proton transfer for the ${}^8\mathrm{B}+{}^{58}\mathrm{Ni}$ system at laboratory energies of $20–28.4$ MeV. The influence of the ${}^7\mathrm{Be}$ core-target optical potential (OP) on the breakup cross section was investigated. Elastic scattering angular distributions for the ${}^7\mathrm{Be}+{}^{58}\mathrm{Ni}$ and ${}^8\mathrm{B}+{}^{58}\mathrm{Ni}$ systems at five different energies around the Coulomb barrier were studied, and a reasonable energy-independent OP for each system was obtained. Using these OPs and two different ${}^7\mathrm{Be}$-$p$ relative motion wave functions, and summing breakup and direct proton transfer contributions, we were able to fit the experimental cross section at a ${}^8\mathrm{B}$ laboratory energy of $25.75$ MeV. We calculated the excitation function for the ${}^7\mathrm{Be}$ emission in the ${}^8\mathrm{B}+{}^{58}\mathrm{Ni}$ reaction, where ${}^7\mathrm{Be}$ products were measured at the forward angle ${\theta }_{\mathrm{lab}}={45}^{°}$ in the energy interval $E_{\mathrm{lab}}=20–28.4$ MeV. In view of the peripheral character of the ${}^8\mathrm{B}$ breakup reaction at near-barrier energies, we could extract the asymptotic normalization coefficient for the ${}^7\mathrm{Be}$-$p$ system, which was found to be $C_{\mathrm{Be}–p,p_{3/2}}^2=0.543\pm 0.027$ fm${}^{-1}$. Finally, the astrophysical $S_{17}$(0) factor was found to be $S_{17}(0)=20.8\pm 1.1$ eV b.

We present an unquenched quark model for baryons in which the effects of the quark-antiquark pairs ($u\overline{u}$, $d\overline{d}$, and $s\overline{s}$) are taken into account in an explicit form via a microscopic, QCD-inspired, quark-antiquark creation mechanism. In the present approach, the contribution of the quark-antiquark pairs can be studied for any inital baryon and for any flavor of the $q\overline{q}$ pairs. It is shown that, while the inclusion of the $q\overline{q}$ pairs does not affect the baryon magnetic moments, it leads to a sizable contribution of the orbital angular momentum to the spin of the proton and the $\Lambda$ hyperon.

We directly measure the ${}^{17}\mathrm{F}$($p$,$\gamma$)${}^{18}\mathrm{Ne}$ resonant reaction using a mixed beam of ${}^{17}\mathrm{F}$ and ${}^{17}\mathrm{O}$ at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory (ORNL). The astrophysically important $3^{+}$ resonance at $~600$ keV above the proton threshold in ${}^{18}\mathrm{Ne}$ is found to have a partial width ${\Gamma }_{\gamma }=56\pm 24(\mathrm{stat})\pm 30(\mathrm{sys})$ meV, in reasonable agreement with the theoretically predicted width. A $2\sigma$ upper limit on the direct capture of $S(E)⩽65$ keV b is determined at an energy of 800 keV. Experimental techniques and astrophysical implications are discussed.

We present a new effective interaction for shell-model calculations in the model space consisting of the single-particle orbits $1p_{3/2}$, $0f_{5/2}$, $1p_{1/2}$, and $0g_{9/2}$. Starting with a realistic interaction based on the Bonn-C potential, 133 two-body matrix elements and four single-particle energies are modified empirically so as to fit $400$ experimental energy data out of $69$ nuclei with mass numbers $A=63~96$. The systematics of binding energies, electromagnetic moments and transitions, and low-lying energy levels are described. The soft $Z=28$ closed core is observed, in contrast to the stable $N=50$ shell closure. The new interaction is applied to systematic studies of three different chains of nuclei, Ge isotopes around $N=40$, $N=Z$ nuclei with $A=64~70$, and $N=49$ odd-odd nuclei, focusing especially on the role of the $g_{9/2}$ orbit. The irregular behavior of the $0_2^{+}$ state in Ge isotopes is understood as a result of detailed balance between the $N=40$ single-particle energy gap and the collective effects. The development of the band structure in $N=Z$ nuclei is interpreted in terms of successive excitations of nucleons into the $g_{9/2}$ orbit. The triaxial/$\gamma$-soft structure in ${}^{64}\mathrm{Ge}$ and the prolate/oblate shape coexistence in ${}^{68}\mathrm{Se}$ are predicted, showing a good correspondence with the experimental data. The isomeric states in ${}^{66}\mathrm{As}$ and ${}^{70}\mathrm{Br}$ are obtained with the structure of an aligned proton-neutron pair in the $g_{9/2}$ orbit. Low-lying energy levels in $N=49$ odd-odd nuclei can be classified as proton-neutron pair multiplets, implying that the obtained single-particle structure in this neutron-rich region appears to be appropriate. These results demonstrate that, in spite of the modest model space, the new interaction turns out to describe rather well properties related to the $g_{9/2}$ orbit in various cases, including moderately deformed nuclei.

The low-lying states of $\mathit{sd}$-boson systems in the presence of random two-body interactions are studied in the proton-neutron interacting boson model (IBM-2). The predominance of spin-zero ground states is confirmed, and a very prominent maximum $F$-spin dominance in ground states is found. It turns out that the requirement of random interactions with $F$-spin conservation intensifies the above predominance. Collective motion in the low-lying states is discussed.

By using the statistical theory for neutron-induced light nucleus reaction, the calculation of the neutron double-differential cross sections for $n$$+$${}^9\mathrm{Be}$ reactions is performed. The secondary outgoing neutrons only coming from the $(n,2n)2\alpha$ reaction channel through six different emission processes are illustrated in detail in this article. Based on the theoretical analysis of neutron double-differential cross sections at $E_n=14.1$ and $18$ MeV, two predicted levels of ${}^9\mathrm{Be}$, i.e., $E(J^{\pi })\Gamma =9({\frac{5}{2}}^{+})1000$ and $10({\frac{5}{2}}^{+})1000$, have been recommended. The calculated results indicate that the fittings would be improved obviously while the predicted levels have been employed.

$\alpha$ decaying states of ${}^{44,46,52}\mathrm{Ti}$ were investigated with angular correlation functions between $t$ and $\alpha$ with the ${}^{40,42,48}\mathrm{Ca}({}^7\mathrm{Li},t\alpha ){}^{40,42,48}\mathrm{Ca}$ reactions at $E=26.0$ MeV. Many $\alpha$ cluster states were newly observed in the $10–15$ MeV excitation energy of ${}^{44}\mathrm{Ti}$ and their spin-parities were assigned, in which $J^{\pi }=7^{-}$ state was found at $11.95$ MeV as a candidate for the member of the $K=0_1^{-}$ negative parity band. In ${}^{46}\mathrm{Ti}$ many $\alpha$ cluster states were also found in the $11–17$ MeV excitation energy with the ${}^{42}\mathrm{Ca}({}^7\mathrm{Li},t\alpha ){}^{42}\mathrm{Ca}$ reaction, though its strength is weak compared with ${}^{44}\mathrm{Ti}$. No $\alpha$ cluster states were detected for the ${}^{48}\mathrm{Ca}({}^7\mathrm{Li},t\alpha ){}^{48}\mathrm{Ca}$ reaction, in which the number of coincidence events decaying from ${}^{48}\mathrm{Ca}$ was very small.

Recent interest in the elastic and quasielastic barrier distributions of systems involving weakly bound light projectiles has concentrated on the influence of coupling to breakup. We show that, for light neutron-rich radioactive beams, single-neutron stripping also has an important effect on the calculated barrier distribution. We also show that the recent suggestion that for such systems the quasielastic barrier distribution will not be exactly equivalent to the true fusion barrier distribution seems to hold true, although in the particular case investigated here the discrepancy in the barrier peak position, $0.25$ MeV, is considerably smaller than that found experimentally for the ${}^6\mathrm{Li}+{}^{144}\mathrm{Sm}$ system, $1.5$ MeV, where breakup is considered to be most important.

Pre- and post-scission neutron multiplicities are measured at different excitation energies of the compound nucleus ${}^{228}\mathrm{U}$ populated using the ${}^{19}\mathrm{F}+{}^{209}\mathrm{Bi}$ reaction. The measured yield of pre-scission and total neutrons are compared with the statistical model calculation for the decay of a compound nucleus. The statistical model calculations are performed using the Bohr-Wheeler transition state fission width as well as the dissipative dynamical fission width due to Kramers. Comparison between the measured and the calculated values shows that, while the Bohr-Wheeler fission width grossly underestimates the pre-scission neutron yield, a large amount of dissipation is required in the Kramers width to fit the experimental pre-scission multiplicities. Various factors contributing to the large excitation energy dependence of the fitted values of the dissipation coefficient are discussed.

The information about sizes and nuclear density distributions in unstable (radioactive) nuclei is usually extracted from the data on interaction of radioactive nuclear beams with a nuclear target. We show that in the case of nucleus-nucleus collisions the values of the parameters depend somewhat strongly on the considered theoretical approach and on the assumption about the parametrization of the nuclear density distribution. The obtained values of root-mean-square radii ($R_{\mathrm{rms}}$) for stable nuclei with atomic weights $A=12–40$ vary by approximately 0.1 fm when calculated in the optical approximation, in the rigid target approximation, and using the exact expression of the Glauber theory. We present several examples of $R_{\mathrm{rms}}$ radii calculations using these three theoretical approaches and compare these results with the data obtained from electron-nucleus scattering.

High-statistics differential cross sections and spin-density matrix elements for the reaction $\gamma p\to p\omega$ have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass (c.m.) energies from threshold up to $2.84$ GeV. Results are reported in $112\hspace{0.5em}10$-MeV wide c.m. energy bins, each subdivided into $\cos {\theta }_{\mathrm{c}.\mathrm{m}.}^{\omega }$ bins of width $0.1$. These are the most precise and extensive $\omega$ photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.

An event-based partial wave analysis (PWA) of the reaction $\gamma p\to p\omega$ has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world’s first high-precision spin-density matrix element measurements, available to the event-based PWA through the decay distribution of $\omega \to {\pi }^{+}{\pi }^{-}{\pi }^0$. The data confirm the dominance of the $t$-channel ${\pi }^0$ exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states $F_{15}(1680)$ and $D_{13}(1700)$ near threshold, as well as the $G_{17}(2190)$ at higher energies. Suggestive evidence for the presence of a $J^P=5/2^{+}$ state around $2$ GeV, a “missing” state, has also been found. Evidence for other states is inconclusive.

Three weakly populated high-spin rotational bands associated with the $\gamma$ decay of ${}^{159}\mathrm{Er}$ and ${}^{160}\mathrm{Er}$ were observed in fusion-evaporation reactions involving a beam of ${}^{48}\mathrm{Ca}$ at an energy of $215$ MeV incident on a ${}^{116}\mathrm{Cd}$ target. The $\gamma$ decays were detected using the highly efficient Gammasphere spectrometer. The discovery of these bands, which extend discrete-line spectroscopy in these nuclei to ultrahigh spin of $~60\hslash$, is consistent with recent observations of high-spin collective structures in isotopes of Er, Yb, and Tm around $N=90$. Cranked Nilsson-Strutinsky calculations suggest that these bands may arise from well-deformed triaxial configurations with either positive or negative $\gamma$ deformation.

Ternary breakup of an excited projectile-like fragment produced in mid-peripheral collisions of ${}^{124}\mathrm{Xe}$ projectiles with ${}^{112}\mathrm{Sn}$ nuclei at $E/A=50$ MeV is examined. Charge correlations reveal that symmetric breakups occur with significant probability. By selecting on the parallel velocity of the heaviest fragment we minimize the entrance channel dynamics. Calculations with the statistical decay code GEMINI failed to reproduce the experimental charge correlations for any suitable combination of excitation energy and spin considered. A statistical multifragmentation model (SMM) in which breakup of low-density nuclear matter is assumed was able to reproduce the observed charge correlations. The $\langle N\rangle /Z$ and isotope distributions of fragments were compared to the results of the SMM calculations. Describing the $\langle N\rangle /Z$ of heavy fragments ($Z>6$) within SMM suggests that a reduction of the symmetry energy parameter from $\gamma =25$ to $14$ MeV is necessary. We observe that the yield of neutron-rich isotopes of heavy fragments is particularly sensitive to the symmetry energy.

The STAR Collaboration at the Relativistic Heavy Ion Collider presents a systematic study of high-transverse-momentum charged-di-hadron correlations at small azimuthal pair separation $\Delta \varphi$ in $d+\mathrm{Au}$ and central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV. Significant correlated yield for pairs with large longitudinal separation $\Delta \eta$ is observed in central $\mathrm{Au}+\mathrm{Au}$ collisions, in contrast to $d+\mathrm{Au}$ collisions. The associated yield distribution in $\Delta \eta$$\times$$\Delta \varphi$ can be decomposed into a narrow jet-like peak at small angular separation which has a similar shape to that found in $d+\mathrm{Au}$ collisions, and a component that is narrow in $\Delta \varphi$ and depends only weakly on $\Delta \eta$, the “ridge.” Using two systematically independent determinations of the background normalization and shape, finite ridge yield is found to persist for trigger $p_t>6$ $\mathrm{GeV}/c$, indicating that it is correlated with jet production. The transverse-momentum spectrum of hadrons comprising the ridge is found to be similar to that of bulk particle production in the measured range ($2<p_t<4\hspace{0.5em}\mathrm{GeV}/c$).

Dihadron azimuthal angle correlations relative to the reaction plane have been investigated in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV using a multiphase transport model (AMPT). Such reaction plane azimuthal-angle-dependent correlations can shed light on the path-length effect of energy loss of high-transverse-momentum particles propagating through a hot dense medium. The correlations vary with the trigger particle azimuthal angle with respect to the reaction plane direction, ${\varphi }_s={\varphi }_T-{\Psi }_{\mathrm{EP}}$, which is consistent with the experimental observation by the STAR Collaboration. The dihadron azimuthal angle correlation functions on the away side of the trigger particle present a distinct evolution from a single-peak to a broad, possibly double-peak structure when the trigger particle direction goes from in-plane to out-of-plane with the reaction plane. The away-side angular correlation functions are asymmetric with respect to the back-to-back direction in some regions of ${\varphi }_s$, which could provide insight into the testing $v_1$ method for reconstructing the reaction plane. In addition, both the root-mean-square width ($W_{\mathrm{rms}}$) of the away-side correlation distribution and the splitting parameter $(D)$ between the away-side double peaks increase slightly with ${\varphi }_s$, and the average transverse momentum of away-side-associated hadrons shows a strong ${\varphi }_s$ dependence. Our results indicate that a strong parton cascade and resultant energy loss could play an important role in the appearance of a double-peak structure in the dihadron azimuthal angular correlation function on the away side of the trigger particle.

Measurements of the double-differential ${\pi }^{\pm }$ production cross section in the range of momentum $100⩽p⩽800$ MeV/$c$ and angle $0.35⩽\theta ⩽2.15$ rad using ${\pi }^{\pm }$ beams incident on beryllium, aluminum, carbon, copper, tin, tantalum, and lead targets are presented. The data were taken with the large-acceptance hadron production (HARP) detector in the T9 beam line of the CERN Proton Synchrotron. The secondary pions were produced by beams in a momentum range from 3 to $12.9\mathrm{GeV}/c$ hitting a solid target with a thickness of $5\%$ of a nuclear interaction length. The tracking and identification of the produced particles was performed using a small-radius cylindrical time projection chamber placed inside a solenoidal magnet. Incident particles were identified by an elaborate system of beam detectors. Results are obtained for the double-differential cross sections $d^2\sigma /\mathit{dp}\hspace{0.5em}d\theta$ at six incident-beam momenta. Data at $3,5,8$, and $12\mathrm{GeV}/c$ are available for all targets, while additional data at $8.9$ and $12.9\mathrm{GeV}/c$ were taken in positive particle beams on Be and Al targets, respectively. The measurements are compared with several generators of GEANT4 and the MARS Monte Carlo simulation.

The one- and the two-particle propagators for an infinite noninteracting Fermi system are studied as functions of space-time coordinates. Their behavior at the origin and in the asymptotic region is discussed, as is their scaling in the Fermi momentum. Both propagators are shown to have a divergence at equal times. The impact of the interaction among the fermions on their momentum distribution, on their pair correlation function, and, hence, on the Coulomb sum rule is explored using a phenomenological model. Finally, the problem of how the confinement is reflected in the momentum distribution of the system’s constituents is briefly addressed.

Direct mass measurements of the neutron-rich ${}^{40-44}\mathrm{S}$ isotopes were performed at the Low Energy Beam and Ion Trap facility at the National Superconducting Cyclotron Laboratory. The resulting mass excesses (MEs) are $\mathrm{ME}({}^{40}\mathrm{S})=-22\mathrm{\hspace{1em}}837.8(3.9)$ keV, $\mathrm{ME}({}^{41}\mathrm{S})=-19\mathrm{\hspace{1em}}008.6(4.1)$ keV, $\mathrm{ME}({}^{42}\mathrm{S})=-17\mathrm{\hspace{1em}}637.9(2.7)$ keV, $\mathrm{ME}({}^{43}\mathrm{S})=-12\mathrm{\hspace{1em}}195.5(4.9)$ keV, and $\mathrm{ME}({}^{44}\mathrm{S})=-9\mathrm{\hspace{1em}}204.2(5.2)$ keV, and they represent improvements by factors of 20 to 50 in the precision of previous mass measurements of these isotopes.

We present the formalism for calculating the femtoscopic correlation function directly in spherical harmonics. The numerator and denominator are stored as a set of one-dimensional histograms representing the spherical harmonic decompositions of each. We present the formalism to calculate the correlation function from them directly, without going to any three-dimensional histogram. We discuss the practical implementation of the method and we provide an example of its use. We also discuss the stability of the method in the presence of angular holes in the underlying data (e.g., from experimental acceptance).