We calculate the charged-current cross sections obtained at the T2K near detector for ${\nu }_{\mu }$-induced events without pions in the final state. The method used is quantum-kinetic transport theory. Results are shown first, as a benchmark, for electron-inclusive cross sections on ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ to be followed with a detailed comparison with the data measured by the T2K Collaboration on ${\mathrm{C}}_8{\mathrm{H}}_8$ and ${\mathrm{H}}_2\mathrm{O}$ targets. The contribution of 2p2h processes is found to be relevant mostly for backward angles; their theoretical uncertainties are within the experimental uncertainties. Particular emphasis is then put on a discussion of events in which pions are first created but then reabsorbed. Their contribution is found to be essential at forward angles.

We present a probable experimental signature of collective enhancement in the nuclear level density (NLD) by measuring the neutron and the giant dipole resonance (GDR) $\gamma$ rays emitted from the rare-earth ${}^{169}\mathrm{Tm}$ compound nucleus populated at 26.1 MeV excitation energy. An enhanced yield is observed in both neutron and $\gamma$-ray spectra corresponding to the same excitation energy in the daughter nuclei. The enhancement could only be reproduced by including a collective enhancement factor in the Fermi gas model of NLD to explain the neutron and GDR spectra simultaneously. The experimental results show that the relative enhancement factor is of the order of 10 and the fadeout occurs at $\sim 14$ MeV excitation energy, much before the commonly accepted transition from deformed to spherical shape. We also explain how the collective enhancement contribution changes the inverse level density parameter $k$ from 8 to 9.5 MeV observed recently in several deformed nuclei.

The isobaric collisions of ${}_{44}{}^{96}\mathrm{Ru}+{}_{44}{}^{96}\mathrm{Ru}$ and ${}_{40}{}^{96}\mathrm{Zr}+{}_{40}{}^{96}\mathrm{Zr}$ have recently been proposed to discern the charge separation signal of the chiral magnetic effect (CME). In this article, we employ the string melting version of a multiphase transport model to predict various charged-particle observables, including $dN/d\eta ,p_T$ spectra, elliptic flow $\left(v_2\right)$, and particularly possible CME signals in Ru + Ru and Zr + Zr collisions at $\sqrt{s_{{}_{NN}}}=200\mathrm{GeV}$. Two sets of the nuclear structure parametrization have been explored, and the difference between the two isobaric collisions appears to be small, in terms of $dN/d\eta ,p_T$ spectra, and $v_2$ for charged particles. We mimic the CME by introducing an initial charge separation that is proportional to the magnetic field produced in the collision, and study how the final-state interactions affect the CME observables. The relative difference in the CME signal between the two isobaric collisions is found to be robust, insensitive to the final-state interactions.

Background: Angular anisotropy has been observed between prompt neutrons emitted during the fission process. Such an anisotropy arises because the emitted neutrons are boosted along the direction of the parent fragment.

Purpose: To measure the neutron-neutron angular correlations from the spontaneous fission of ${}^{252}\mathrm{Cf}$ and ${}^{240}\mathrm{Pu}$ oxide samples using a liquid scintillator array capable of pulse-shape discrimination. To compare these correlations to simulations combining the Monte Carlo radiation transport code MCNPX with the fission event generator FREYA.

Method: Two different analysis methods were used to study the neutron-neutron correlations with varying energy thresholds. The first is based on setting a light output threshold while the second imposes a time-of-flight cutoff. The second method has the advantage of being truly detector independent.

Results: The neutron-neutron correlation modeled by FREYA depends strongly on the sharing of the excitation energy between the two fragments. The measured asymmetry enabled us to adjust the FREYA parameter $x$ in ${}^{240}\mathrm{Pu}$, which controls the energy partition between the fragments and is so far inaccessible in other measurements. The ${}^{240}\mathrm{Pu}$ data in this analysis was the first available to quantify the energy partition for this isotope. The agreement between data and simulation is overall very good for ${}^{252}\mathrm{Cf}\left(\mathrm{sf}\right)$ and ${}^{240}\mathrm{Pu}\left(\mathrm{sf}\right)$.

Conclusions: The asymmetry in the measured neutron-neutron angular distributions can be predicted by FREYA. The shape of the correlation function depends on how the excitation energy is partitioned between the two fission fragments. Experimental data suggest that the lighter fragment is disproportionately excited.

Herein, we investigated the channel coupling (CC) effect on the elastic scatterings of lithium (Li) isotopes ($A=6$–9) for ${}^{12}\mathrm{C}$ and ${}^{28}\mathrm{Si}$ targets at $E/A=50$–60 MeV. The wave functions of the Li isotopes were obtained using the stochastic multi-configuration mixing method based on the microscopic-cluster model. The proton radii of the ${}^7\mathrm{Li}$, ${}^8\mathrm{Li}$, and ${}^9\mathrm{Li}$ nuclei became smaller as the number of valence neutrons increased. The valence neutrons in the ${}^8\mathrm{Li}$ and ${}^9\mathrm{Li}$ nuclei exhibited a glue-like behavior, thereby attracting the $\alpha$ and $t$ clusters. Based on the transition densities derived from these microscopic wave functions, the elastic-scattering cross section was calculated using a microscopic coupled-channel method with a complex $G$-matrix interaction. The existing experimental data for the elastic scatterings of the Li isotopes and ${}^{10}\mathrm{Be}$ nuclei were well reproduced. The Li isotope elastic cross sections were demonstrated for the ${}^{12}\mathrm{C}$ and ${}^{28}\mathrm{Si}$ targets at $E/A=53$ MeV. The glue-like effect of the valence neutrons on the Li isotope was clearly demonstrated by the CC effect on elastic scattering. Finally, we realize that the valence neutrons stabilized the bindings of the core parts and the CC effect related to core excitation was indeed reduced.

High-spin level structures of ${}^{199}\mathrm{Tl}$ have been studied by in-beam $\gamma$-ray spectroscopic methods using the ${}^{196}\mathrm{Pt}({}^7\mathrm{Li}, 4n){}^{199}\mathrm{Tl}$ reaction at 40 MeV of beam energy. A large number of new states have been found, resulting in a significant extension of the previously known level scheme with the observation of 44 new transitions and 33 new levels. By comparing with the level structures in the odd-mass Tl isotopes and the even-even core Hg nuclei, configurations are proposed for the newly observed rotational bands and states in ${}^{199}\mathrm{Tl}$. The properties of the strongly coupled positive- and negative-parity bands can be interpreted in terms of the cranked Nilsson-Strutinsky-Bogoliubov model calculations, which show that the observed bands are built on the oblate shapes.

We realize the treatment of bound and continuum nuclear systems in the proximity of a three-body breakup threshold within the ab initio framework of the no-core shell model with continuum. Many-body eigenstates obtained from the diagonalization of the Hamiltonian within the harmonic-oscillator expansion of the no-core shell model are coupled with continuous microscopic three-cluster states to correctly describe the nuclear wave function both in the interior and asymptotic regions. We discuss the formalism in detail and give algebraic expressions for the case of core + $n+n$ systems. Using similarity-renormalization-group evolved nucleon-nucleon interactions, we analyze the role of ${}^4\mathrm{He}+n+n$ clustering and many-body correlations in the ground and low-lying continuum states of the Borromean ${}^6\mathrm{He}$ nucleus, and study the dependence of the energy spectrum on the resolution scale of the interaction. We show that ${}^6\mathrm{He}$ small binding energy and extended radii compatible with experiment can be obtained simultaneously, without resorting to extrapolations. We also find that a significant portion of the ground-state energy and the narrow width of the first $2^{+}$ resonance stem from many-body correlations that can be interpreted as core-excitation effects.

Employing the quantum molecular dynamics (QMD) approach for nucleus-nucleus collisions, we test the predictive power of the energy-based clusterization algorithm, i.e., the simulating annealing clusterization algorithm (SACA), to describe the experimental data of charge distribution and various event-by-event correlations among fragments. The calculations are constrained into the Fermi-energy domain and/or mildly excited nuclear matter. Our detailed study spans over different system masses, and system-mass asymmetries of colliding partners show the importance of the energy-based clusterization algorithm for understanding multifragmentation. The present calculations are also compared with the other available calculations, which use one-body models, statistical models, and/or hybrid models.

Simulations by transport codes are indispensable to extract valuable physical information from heavy-ion collisions. In order to understand the origins of discrepancies among different widely used transport codes, we compare 15 such codes under controlled conditions of a system confined to a box with periodic boundary, initialized with Fermi-Dirac distributions at saturation density and temperatures of either 0 or 5 MeV. In such calculations, one is able to check separately the different ingredients of a transport code. In this second publication of the code evaluation project, we only consider the two-body collision term; i.e., we perform cascade calculations. When the Pauli blocking is artificially suppressed, the collision rates are found to be consistent for most codes (to within $1\%$ or better) with analytical results, or completely controlled results of a basic cascade code. In orderto reach that goal, it was necessary to eliminate correlations within the same pair of colliding particles that can be present depending on the adopted collision prescription. In calculations with active Pauli blocking, the blocking probability was found to deviate from the expected reference values. The reason is found in substantial phase-space fluctuations and smearing tied to numerical algorithms and model assumptions in the representation of phase space. This results in the reduction of the blocking probability in most transport codes, so that the simulated system gradually evolves away from the Fermi-Dirac toward a Boltzmann distribution. Since the numerical fluctuations are weaker in the Boltzmann-Uehling-Uhlenbeck codes, the Fermi-Dirac statistics is maintained there for a longer time than in the quantum molecular dynamics codes. As a result of this investigation, we are able to make judgements about the most effective strategies in transport simulations for determining the collision probabilities and the Pauli blocking. Investigation in a similar vein of other ingredients in transport calculations, like the mean-field propagation or the production of nucleon resonances and mesons, will be discussed in the future publications.

We calculate the contribution of absorption effects to the correlation function of two identical particles emitted by a fixed source. These effects result from the successive collisions undergone by the emitted particles before they leave the source of emission.

In a mean-field description of superfluidity, particle number and gauge angle are treated as quasiclassical conjugated variables. This level of description was recently used to describe nuclear reactions around the Coulomb barrier. Important effects of the relative gauge angle between two identical superfluid nuclei (symmetric collisions) on transfer probabilities and fusion barrier have been uncovered. A theory making contact with experiments should at least average over different initial relative gauge-angles. In the present work, we propose a new approach to obtain the multiple pair transfer probabilities between superfluid systems. This method, called phase-space combinatorial (PSC) technique, relies both on phase-space averaging and combinatorial arguments to infer the full pair transfer probability distribution at the cost of multiple mean-field calculations only. After benchmarking this approach in a schematic model, we apply it to the collision ${}^{20}\mathrm{O}+{}^{20}\mathrm{O}$ at various energies below the Coulomb barrier. The predictions for one pair transfer are similar to results obtained with an approximated projection method, whereas significant differences are found for two pairs transfer. Finally, we investigated the applicability of the PSC method to the contact between nonidentical superfluid systems. A generalization of the method is proposed and applied to the schematic model showing that the pair transfer probabilities are reasonably reproduced. The applicability of the PSC method to asymmetric nuclear collisions is investigated for the ${}^{14}\mathrm{O}+{}^{20}\mathrm{O}$ collision and it turns out that unrealistically small single- and multiple pair transfer probabilities are obtained. This is explained by the fact that relative gauge angle play in this case a minor role in the particle transfer process compared to other mechanisms, such as equilibration of the charge/mass ratio. We conclude that the best ground for probing gauge-angle effects in nuclear reaction and/or for applying the proposed PSC approach on pair transfer is the collisions of identical open-shell spherical nuclei.

The angular momentum basis method is introduced to solve the inclusive breakup problem within the model proposed by Ichimura, Austern, and Vincent [Phys. Rev. C 32, 431 (1985)]. This method is based on the geometric transformation between different Jacobi coordinates, in which the particle spins can be included in a natural and efficient way. To test the validity of this partial wave expansion method, a benchmark calculation is done comparing with the one given by Lei and Moro [Phys. Rev. C 92, 044616 (2015)]. In addition, using the distorted-wave Born approximation version of the IAV model, applications to ${}^7\mathrm{Li}+{}^{58}\mathrm{Ni}$ reactions at energies around Coulomb barrier are presented and compared with available data.

The ${}^{10}\mathrm{B}+{}^{120}\mathrm{Sn}$ reaction has been investigated at $E_{\mathrm{Lab}}=37.5$ MeV. The cross sections for different channels, such as the elastic scattering, the excitation of the $2^{+}$ and $3^{-}{}^{120}\mathrm{Sn}$ states, the excitation of the $1^{+}$ state of ${}^{10}\mathrm{B}$, and the $1n$ pick-up transfer, have been measured. One-step distorted-wave Born approximation and coupled-reaction-channels calculations have been performed in the context of the double-folding São Paulo potential. The effect of coupling the inelastic and transfer states on the angular distributions is discussed in the paper. In general, the theoretical calculations within the coupled-reaction-channels formalism yield a satisfactory agreement with the corresponding experimental angular distributions.

Inclusive $(p,dx)$ reactions at 42–392 MeV are investigated to understand quantitatively the roles of direct pickup and knockout. These two processes are formulated and introduced into the intranuclear cascade model. The calculated spectral shapes and magnitudes of the double-differential cross sections agree well with all experimental observations over the entire ranges of emission energy and laboratory angle. The model reveals the contributions of pickup and knockout in terms of incident-energy dependence. Direct pickup accounts for the highest energy domain of the spectra of not only discrete but also continuum regions with excitations up to around 45 MeV. Knockout becomes increasingly important with incident proton energy. It is negligible at 42 MeV, occupies the lower half of spectra at 90 MeV, and above 300 MeV is responsible for most of each energy spectrum except the part at highest energy. This trend is very similar to that of $(p,nx)$ cross sections. The indirect pickup component appears at these energies, as suggested in previous studies.

Background: Existing bound-state-type calculations of three-neutron resonances yield contradicting results.

Purpose: A direct study of the three-neutron continuum using rigorous scattering equations with realistic potentials and search for possible resonances is aimed.

Methods: Faddeev-type integral equations for three-neutron transition operators are solved in the momentum-space partial-wave framework. The evolution of resonances is studied by enhancing the strength of the two-neutron interaction in partial waves with nonzero orbital momentum.

Results: Calculated three-neutron transition operators exhibit resonant behavior for sufficiently large enhancement factors; pole trajectories in the complex energy plain are extracted from their energy dependence. However, the resonant behavior completely disappears for the physical interaction strength.

Conclusions: There are no physically observable three-neutron resonant states consistent with presently accepted interaction models.

Background: Triaxiality in nuclear low-lying states has attracted great interest for many years. Recently, reduced transition probabilities for levels near the ground state in ${}^{110}\mathrm{Ru}$ have been measured and provided strong evidence of a triaxial shape of this nucleus.

Purpose: The aim of this work is to provide a microscopic study of low-lying states for Ru isotopes with $A\approx 100$ and to examine in detail the role of triaxiality and the evolution of quadrupole shapes with the isospin and spin degrees of freedom.

Method: Low-lying excitation spectra and transition probabilities of even-even Ru isotopes are described at the beyond-mean-field level by solving a five-dimensional collective Hamiltonian with parameters determined by constrained self-consistent mean-field calculations based on the relativistic energy density functional PC-PK1.

Results: The calculated energy surfaces, low-energy spectra, and intraband and interband transition rates, as well as some characteristic collective observables, such as $E\left(4_{\mathrm{g}.\mathrm{s}.}^{+}\right)/E\left(2_{\mathrm{g}.\mathrm{s}.}^{+}\right),E\left(2_{\gamma }^{+}\right)/E\left(4_{\mathrm{g}.\mathrm{s}.}^{+}\right)$, and $B(E2;2_{\mathrm{g}.\mathrm{s}.}^{+}\to 0_{\mathrm{g}.\mathrm{s}.}^{+})$ and $\gamma$-band staggerings, are in good agreement with the available experimental data.

Conclusions: The main features of the experimental low-lying excitation spectra and electric transition rates are well reproduced and, thus, strongly support the onset of triaxiality in the low-lying excited states of Ru isotopes around ${}^{110}\mathrm{Ru}$.

An important characterization of electromagnetic and weak transitions in atomic nuclei are sum rules. We focus on the non-energy-weighted sum rule (NEWSR), or total strength, and the energy-weighted sum rule (EWSR); the ratio of the EWSR to the NEWSR is the centroid or average energy of transition strengths from an nuclear initial state to all allowed final states. These sum rules can be expressed as expectation values of operators, which in the case of the EWSR is a double commutator. While most prior applications of the double commutator have been to special cases, we derive general formulas for matrix elements of both operators in a shell model framework (occupation space), given the input matrix elements for the nuclear Hamiltonian and for the transition operator. With these new formulas, we easily evaluate centroids of transition strength functions, with no need to calculate daughter states. We apply this simple tool to a number of nuclides and demonstrate the sum rules follow smooth secular behavior as a function of initial energy, as well as compare the electric dipole ($E1$) sum rule against the famous Thomas-Reiche-Kuhn version. We also find surprising systematic behaviors for ground-state electric quadrupole ($E2$) centroids in the $sd$ shell.

The hindrance phenomenon of heavy-ion fusion cross sections at deep subbarrier energies often accompanies a maximum of an astrophysical $S$ factor at a threshold energy for fusion hindrance. We argue that this phenomenon can naturally be explained when the fusion excitation function is fitted with two potentials, with a larger (smaller) logarithmic slope at energies lower (higher) than the threshold energy. This analysis clearly suggests that the astrophysical $S$ factor provides a convenient tool to analyze the deep subbarrier hindrance phenomenon, even though the $S$ factor may have a strong energy dependence for heavy-ion systems unlike that for astrophysical reactions.

A nonrelativistic quark coalescence model is formulated for polarized vector mesons and baryons of spin-1/2 octet and spin-3/2 decuplet. With the spin density matrix, one can compute in a uniform way the polarizations of vector mesons and baryons from those of quarks and antiquarks with explicit momentum dependence. The results are compared to those obtained from kinetic and statistical models for hadrons.

A self-consistent thermodynamic $T$-matrix approach is deployed to study the microscopic properties of the quark-gluon plasma (QGP), encompassing both light- and heavy-parton degrees of freedom in a unified framework. The starting point is a relativistic effective Hamiltonian with a universal color force. The input in-medium potential is quantitatively constrained by computing the heavy-quark (HQ) free energy from the static $T$-matrix and fitting it to pertinent lattice-QCD (lQCD) data. The corresponding $T$-matrix is then applied to compute the equation of state (EoS) of the QGP in a two-particle irreducible formalism, including the full off-shell properties of the selfconsistent single-parton spectral functions and their two-body interaction. In particular, the skeleton diagram functional is fully resummed to account for emerging bound and scattering states as the critical temperature is approached from above. We find that the solution satisfying three sets of lQCD data (EoS, HQ free energy, and quarkonium correlator ratios) is not unique. As limiting cases we discuss a weakly coupled solution, which features color potentials close to the free energy, relatively sharp quasiparticle spectral functions and weak hadronic resonances near $T_{\mathrm{c}}$, and a strongly coupled solution with a strong color potential (much larger than the free energy), resulting in broad nonquasiparticle parton spectral functions and strong hadronic resonance states which dominate the EoS when approaching $T_{\mathrm{c}}$.