Using an axisymmetric numerical code, we perform an extensive study of the magnetic-field configurations in nonrotating neutron stars, varying the mass, magnetic-field strength and the equation of state. We find that the monopolar (spherically symmetric) part of the norm of the magnetic field can be described by a single profile, which we fit by a simple eighth-order polynomial, as a function of the star's radius. This new generic profile applies remarkably well to all magnetized neutron star configurations built on hadronic equations of state. We then apply this profile to build magnetized neutron stars in spherical symmetry, using a modified Tolman–Oppenheimer–Volkoff system of equations. This new formalism produces slightly better results in terms of mass-radius diagrams than previous attempts to add magnetic terms to these equations. However, we show that such approaches are less accurate than the usual, nonmagnetized TOV models, and that consistent models must depart from spherical symmetry. Thus, our “universal” magnetic-field profile is intended to serve as a tool for nuclear physicists to obtain estimates of the magnetic field inside neutron stars as a function of radial depth to deduce its influence on composition and related properties. It possesses the advantage of being based on magnetic-field distributions from realistic self-consistent computations which are solutions of Maxwell's equations.

Background: Microscopic calculations of the electromagnetic response of light and medium-mass nuclei are now feasible thanks to the availability of realistic nuclear interactions with accurate saturation and spectroscopic properties, and the development of large-scale computing methods for many-body physics.

Purpose: To compute isovector dipole electromagnetic (E1) response and related quantities, i.e., integrated dipole cross section and polarizability, and compare with data from photoabsorption and Coulomb excitation experiments. To investigate the evolution pattern of the E1 response towards the neutron drip line with calculations of neutron-rich nuclei within a given isotopic chain.

Methods: The single-particle propagator is obtained by solving the Dyson equation, where the self-energy includes correlations nonperturbatively through the algebraic diagrammatic construction (ADC) method. The particle-hole ($ph$) polarization propagator is treated in the dressed random phase approximation (DRPA), based on an effective correlated propagator that includes some $2p2h$ effects but keeps the same computation scaling as the standard Hartree-Fock propagator.

Results: The E1 responses for ${}^{14,16,22,24}\mathrm{O}$, ${}^{36,40,48,52,54,70}\mathrm{Ca}$, and ${}^{68}\mathrm{Ni}$ have been computed: The presence of a soft dipole mode of excitation for neutron-rich nuclei is found, and there is a fair reproduction of the low-energy part of the experimental excitation spectrum. This is reflected in a good agreement with the empirical dipole polarizability values. The impact of different approximations to the correlated propagator used as input in the E1 response calculation is assessed.

Conclusion: For a realistic interaction that accurately reproduces masses and radii, an effective propagator of the mean-field type computed by the self-consistent Green's function provides a good description of the empirical E1 response, especially in the low-energy part of the excitation spectrum and around the giant dipole resonance. The high-energy part of the spectrum improves and displays an enhancement of the strength when quasiparticle fragmentation is added to the reference propagator. However, this fragmentation (without a proper restoration of dynamical self-consistency) spoils the predictions of the energy centroid of the giant dipole resonance.

We have measured a precise quasielastic excitation function for the ${}^{16}\mathrm{O}+{}^{65}\mathrm{Cu}$ system, at ${\theta }_{\mathrm{LAB}}={161}^{\circ }$, and at bombarding energies near the Coulomb barrier. A quasielastic barrier distribution for this system was deduced from the experimental quasielastic excitation function. An $\alpha$-stripping excitation function has also been measured at the same experimental conditions. These new data have been used to investigate the relative importance of several reaction channels in the reaction mechanism of the ${}^{16}\mathrm{O}+{}^{65}\mathrm{Cu}$ system. Large-scale coupled-channel calculations and coupled-reaction-channel calculations have been performed. No imaginary potential was used at the barrier region because many channels have been explicitly included in the calculations. Only an inner short-range potential was used to account for the fusion process. We did not fit data by varying potential parameters, and our theoretical results were compared directly to data. Good agreement was found between data and calculations. Owing to the high sensitivity of the barrier distribution, important results have been obtained. The first excited state ($1/2^{-}$) of ${}^{65}\mathrm{Cu}$ has less influence in the reaction mechanism than the second ($5/2^{-}$) and third ($7/2^{-}$) states, which are the most relevant among all the investigated ones. We have also observed a striking influence of the reorientation of the ground-state spin of the ${}^{65}\mathrm{Cu}$ nucleus on the elastic scattering at backward angles. In addition, calculations have shown that the excitation of the states $3^{-},2^{+},1^{-}$, and $2^{-}$ of the projectile ${}^{16}\mathrm{O}$ are also important for excellent agreement obtained with both the excitation function and the distribution of barriers. The $\alpha$-stripping data have been compared to the results of coupled-reaction-channel calculations and good agreement was obtained with the inclusion of the first excited state of ${}^{12}\mathrm{C}$ in the coupling scheme. However, the $\alpha$-transfer process has a small influence on the reaction dynamics of this system at the investigated energies.

The two-stage dynamical stochastic model developed earlier for the description of fusion-fission reactions is applied to the calculation of mass and energy distributions of fission fragments of platinum isotopes in the reaction ${}^{36}\mathrm{Ar}+{}^{142}\mathrm{Nd}\to {}^{178-x}\mathrm{Pt}+xn$. The first stage of this model is the calculation of the approaching of the projectile nucleus to the target nucleus. In the second stage, the evolution of the system formed after the touching of the projectile and target nuclei is considered. The evolution of the system in both stages is described by three-dimensional Langevin equations for the shape parameters of the system. The mutual orientation of the colliding ions and tunneling through the Coulomb barrier in the entrance channel are also taken into account. The potential energy of the system is calculated within the macroscopic-microscopic approach. The calculated mass-energy distributions of fission fragments are compared with the available experimental data. The impact of shell effects, rotation of the system, and neutron evaporation on the calculated results is discussed.

Background: Modern nuclear structure models suggest that the shell structure near the valley of stability, with well-established shell closures at $N=50$, for example, changes in very neutron-rich nuclei far from stability. Single-particle properties of nuclei away from stability can be probed in single-neutron $(d,p)$ transfer reactions with beams of rare isotopes. The interpretation of these data requires reaction theories with various effective interactions. Often, approximations made to the final bound-state potential introduce a large uncertainty in the extracted single-particle properties, in particular the spectroscopic factor.

Purpose: Mitigate this uncertainty using a combined measurement method to constrain the shape of the bound-state potential and to reliably extract the spectroscopic factor.

Methods: The ${}^2\mathrm{H}({}^{86}\mathrm{Kr},p){}^{87}\mathrm{Kr}$ reaction was measured at 33 MeV/u at the National Superconducting Cyclotron Laboratory (NSCL) as a test of the combined method. The reaction protons were detected with the Oak Ridge Rutgers University Barrel Array (ORRUBA) of position sensitive silicon strip detectors, the first implementation of ORRUBA coupled to the S800 spectrograph with fast beams at NSCL.

Results: These measurements at 33 MeV/u are combined with previous studies of the ${}^{86}\mathrm{Kr}(d,p)$ reaction at 5.5 MeV/u to demonstrate a successful case of the combined method to constrain the shape of the single-particle potential and deduce asymptotic normalization coefficients and spectroscopic factors. In particular, the single-particle asymptotic normalization coefficient for the ground state of ${}^{87}\mathrm{Kr}$ was constrained to $b_{d5/2}=6.{46}_{-0.57}^{+1.12}{\mathrm{fm}}^{-1/2}$, and therefore the deduced spectroscopic factor is $S=0.{44}_{-0.13}^{+0.09}$ with uncertainties dominated by experimental statistics.

Conclusions: By combining measurements at two very different beam energies, single-particle asymptotic normalization coefficients, at least for low angular momentum transfers, can be constrained. Therefore, spectroscopic factors can be deduced with uncertainties dominated by experimental uncertainties, rather than limited knowledge of bound-state potential parameters.

The neutron-rich isotopes ${}^{211,213}\mathrm{Tl}$, beyond the $N=126$ shell closure, have been studied for the first time in isomer $\gamma$-ray decay, exploiting the fragmentation of a primary uranium beam at the Fragment Separator-Rare Isotopes Investigation at GSI setup. The observed isomeric states in ${}^{211,213}\mathrm{Tl}$ show a deviation from the seniority-like scheme of ${}^{209}\mathrm{Tl}$. The possible interpretation of the data is discussed on the basis of energy-level systematics and shell-model calculations.

Background: Formation of a fully equilibrated compound nucleus is a critical step in the heavy-ion fusion reaction mechanism but can be hindered by orders of magnitude by quasifission, a process in which the dinuclear system breaks apart prior to full equilibration. To provide a complete description of heavy-ion fusion it is important to characterize the quasifission process. In particular, the impact of changing the neutron richness on the quasifission process is not well known. A previous study of Cr + W reactions at a constant $13\%$ above the Coulomb barrier concluded that an increase in neutron richness leads to a decrease in the prominence of the quasifission reaction channel.

Purpose: The dynamics of quasifission for reactions with varying neutron richness was explored at a constant excitation energy, closer to the interaction barrier than the previous work, to see if the correlation between neutron richness and quasifission is valid at lower energies.

Methods: Mass distributions were measured at the Australian National University for eight different combinations of Cr + W reactions, using the kinematic coincidence method. To eliminate the effect of differing excitation energies, measurements were made at beam energies chosen to give 52 MeV of excitation energy in all the compound nuclei.

Results: A curvature parameter, describing the shape of the mass distributions, was determined for the fission-like fragment mass distributions for each reaction, and compared to various reaction parameters known to influence quasifission.

Conclusions: The present work demonstrates that, at energies near the interaction barrier, the beam energy with respect to the barrier is as important as neutron-richness effects in determining the quasifission characteristics in these Cr + W reactions involving statically deformed target nuclei, and both are important considerations for future heavy and superheavy element production reactions.

Background: Nucleon knockout reactions have been previously used to extract single particle information from nuclei. The analysis of nucleon knockout from a stable projectile in the collision with a proton target and the comparison with the experimental data is a key test for the reaction and structure models used to evaluate the reaction observables.

Purpose: We analyze $p$ and $n$ knockout from ${}^{12}\mathrm{C}$, assuming that only the heavy fragment or core $C$ (taken as inert), the knockout particle $N$, and the proton target $p$ participate in the collision process with the aim of (i) getting insight to the dominant kinematic conditions of the emitted particles; (ii) clarifying the dynamics of the reaction; (iii) exploring the isospin dependence (here $p$ and $n$ knockout) of the calculated reaction cross sections.

Method: We solve three-body Faddeev/Alt-Grassberger-Sandhas (Faddeev/AGS) equations for transition operators and calculate kinematically fully exclusive, semi-inclusive, and inclusive cross sections.

Results: We show that (i) the dominant final-state kinematic conditions are consistent with the assumption of quasifree scattering reaction mechanism; (ii) the distortions due to higher order multiple scattering terms depend on the final-state kinematics, and the $N-C$ and $p-C$ final state interaction provide significant effects in the calculated observables; (iii) the twofold energy–polar angle and polar angle–polar angle cross sections exhibit distinct $p$- and $n$-knockout behaviors. Finally we also show that the Faddeev/AGS formalism is able to a certain extent to reproduce the available experimental data for the $p$ knockout.

Conclusions: Kinematically fully exclusive measurements of $p$ and $n$ knockout are needed to rigorously assess the role of the distortion, as it cannot be taken into account as an overall reduction factor. This is a prerequisite for a reliable understanding of the structure of the projectile and the reaction mechanism. In addition, realistic interactions inferred from ab initio structure models are needed for analyzing experimental data.

The Deep Underground Neutrino Experiment (DUNE) could be revolutionary for MeV neutrino astrophysics, because of its huge detector volume, unique event reconstruction capabilities, and excellent sensitivity to the ${\nu }_e$ flavor. However, its backgrounds are not yet known. A major background is expected due to muon spallation of argon, which produces unstable isotopes that later $\beta$ decay. We present the first comprehensive study of MeV spallation backgrounds in argon, detailing isotope production mechanisms and decay properties, analyzing $\beta$ energy and time distributions, and proposing experimental cuts. We show that above a nominal detection threshold of 5-MeV electron energy, the most important backgrounds are—surprisingly—due to low-$A$ isotopes, such as Li, Be, and B, even though high-$A$ isotopes near argon are abundantly produced. We show that spallation backgrounds can be powerfully rejected by simple cuts, with clear paths for improvements. We compare these background rates to rates of possible MeV astrophysical neutrino signals in DUNE, including solar neutrinos (detailed in a companion paper [Capozzi et al. arXiv:1808.08232 [hep-ph]], supernova burst neutrinos, and the diffuse supernova neutrino background. Further, to aid trigger strategies, in the Appendixes we quantify the rates of single and multiple MeV events due to spallation, radiogenic neutron capture, and other backgrounds, including through pileup. Our overall conclusion is that DUNE has high potential for MeV neutrino astrophysics, but reaching this potential requires new experimental initiatives.

We present a high-resolution in-beam $\gamma$-ray spectroscopy study of excited states in the mirror nuclei ${}^{55}\mathrm{Co}$ and ${}^{55}\mathrm{Ni}$ following one-nucleon knockout from a projectile beam of ${}^{56}\mathrm{Ni}$. The newly determined partial cross sections and the $\gamma$-decay properties of excited states provide a test of state-of-the-art nuclear structure models and probe mirror symmetry in unique ways. The new experimental data are compared to large-scale shell-model calculations in the full $pf$ space which include charge-dependent contributions. A mirror asymmetry for the partial cross sections leading to the two lowest $3/2^{-}$ states in the $A=55$ mirror pair was identified as well as a significant difference in the $E1$ decays from the $1/2_1^{+}$ state to the same two $3/2^{-}$ states. The mirror asymmetry in the partial cross sections cannot be reconciled with the present shell-model picture or small mixing introduced in a two-state model. The observed mirror asymmetry in the $E1$ decay pattern, however, points at stronger mixing between the two lowest $3/2^{-}$ states in ${}^{55}\mathrm{Co}$ than in its mirror ${}^{55}\mathrm{Ni}$.

We present a global fit to all data on the suppression of high-energy jets and high-energy hadrons in the most central heavy-ion collisions at the CERN Large Hadron Collider (LHC) for two different collision energies, within a hybrid strong-weak coupling quenching model. Even though the measured suppression factors for hadrons and jets differ significantly from one another and appear to asymptote to different values in the high-energy limit, we obtain a simultaneous description of all these data after constraining the value of a single model parameter. We use our model to investigate the origin of the difference between the observed suppression of jets and hadrons and relate it, quantitatively, to the observed modification of the jet fragmentation function in jets that have been modified by passage through the medium produced in heavy-ion collisions. In particular, the observed increase in the fraction of hard fragments in medium-modified jets, which indicates that jets with the fewest hardest fragments lose the least energy, corresponds quantitatively to the observed difference between the suppression of hadrons and jets. We argue that a harder fragmentation pattern for jets with a given energy after quenching is a generic feature of any mechanism for the interaction between jets and the medium that they traverse that yields a larger suppression for wider jets. We also compare the results of our global fit to LHC data to measurements of the suppression of high-energy hadrons in BNL Relativistic Heavy Ion Collider (RHIC) collisions, and find that with its parameter chosen to fit the LHC data, our model is inconsistent with the RHIC data at the $3\sigma$ level, suggesting that hard probes interact more strongly with the less hot quark-gluon plasma produced at RHIC.

The first detection of gravitational waves from the binary neutron star merger event GW170817 has started to provide important new constraints on the nuclear equation of state at high density. The tidal deformability bound of GW170817 combined with the observed two solar mass neutron star poses a serious challenge to theoretical formulations of realistic equations of state. We analyze a fully comprehensive set of relativistic nuclear mean-field theories by confronting them with the observational bounds and the measured neutron-skin thickness. We find that only a few models can withstand these bounds which predict a stiff overall equation of state but with a soft neutron-proton symmetry energy. Two possible indications are proposed: Circumstantial evidence of hadron-quark phase transition inside the star and new parametrizations that are consistent with ground-state properties of finite nuclei and observational bounds. Based on extensive analysis of these sets, an upper limit on the radius of a $1.4M_{\odot }$ neutron star of $R_{1.4}\lesssim 12.9$ km is deduced.

Within the framework of $\mathtt{FREYA}$ event-by-event fission simulations, we study the sensitivity of various neutron observables to the input yield function $Y(A,Z,\mathrm{TKE})$ on which the fission event sampling is based. We first perform a statistical analysis of the available fission data in order to determine the distribution of possible yield functions $Y(A,Z,\mathrm{TKE})$ and we then construct a sample of 15 000 such yield functions. For each of these, $\mathtt{FREYA}$ is used to generate one million fission events, leading to a corresponding ensemble of fission observables, including the neutron multiplicity distribution and its factorial moments, the neutron energy spectrum, and the neutron-neutron angular correlation. This procedure allows us to study the sensitivity of those neutron observables to the uncertainty in the experimental data. Particular attention is given to the pronounced anticorrelation between the mean neutron multiplicity $\overline{\nu }$ and the mean total fragment kinetic energy $\overline{\mathrm{TKE}}$. Because the former observable is very well determined experimentally, it is possible to exploit that inherent anticorrelation to derive a significantly stricter tolerance on $\overline{\mathrm{TKE}}$. In addition, we study the sensitivity to the various $\mathtt{FREYA}$ parameters and we introduce a method for determining a $A$-dependent $x$ parameter, $x\left(A\right)$, based on the measured $A$-dependent neutron multiplicity, $\overline{\nu }\left(A\right)$.

Exothermal nuclear reactions that become forbidden due to Coulomb repulsion in the $\varepsilon \to 0$ limit $[{lim}_{\varepsilon \to 0}\sigma \left(\varepsilon \right)=0]$ are investigated. $[\sigma \left(\varepsilon \right)$ is the cross section and $\varepsilon$ is the center of mass energy.] It is found that any perturbation may mix states with small but finite amplitude to the initial state resulting in finite cross section (and rate) of the originally forbidden nuclear reaction in the $\varepsilon \to 0$ limit. The statement is illustrated by modification of nuclear reactions due to impurities in a gas mix of atomic state. The change of the wave function of reacting particles in nuclear range due to their Coulomb interaction with impurity is determined using standard time-independent perturbation calculation of quantum mechanics. As an example, cross section, rate and power densities of impurity-assisted nuclear $pd$ reaction are numerically calculated. With the aid of astrophysical factors cross section and power densities of the impurity-assisted $d(d,n){}_2{}^3\text{He}$, $d(d,p)t,d(t,n){}_2{}^4\text{He}$, ${}_2{}^3\text{He}(d,p){}_2{}^4\text{He}$, ${}_3{}^6\text{Li}(p,\alpha ){}_2{}^3\text{He}$, ${}_3{}^6\text{Li}(d,\alpha ){}_2{}^4\text{He}$, ${}_3{}^7\text{Li}(p,\alpha ){}_2{}^4\text{He}$, ${}_4{}^9\text{Be}(p,\alpha ){}_3{}^6\text{Li},{}_4{}^9\text{Be}(p,d){}_4{}^8\text{Be},{}_4{}^9\text{Be}(\alpha ,n){}_6{}^{12}\text{C},{}_5{}^{10}\text{B}(p,\alpha ){}_4{}^7\text{Be}$, and ${}_5{}^{11}\text{B}(p,\alpha ){}_4{}^8\text{Be}$ reactions are also given. The affect of gas mix-wall interaction on the process is considered too.

Electromagnetic fields produced in relativistic heavy-ion collisions are affected by the asymmetry of the projectile-target combination as well as the different initial configurations of the nucleus. In this study, the results of the electric and magnetic fields produced for different combinations of ions, namely ${}^{12}\mathrm{C}+{}^{197}\mathrm{Au}$, ${}^{24}\mathrm{Mg}+{}^{197}\mathrm{Au}$, ${}^{64}\mathrm{Cu}+{}^{197}\mathrm{Au}$, and ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ at $\sqrt{s_{NN}}=200$ GeV, are demonstrated with a multiphase transport model. The configuration of the distribution of nucleons of ${}^{12}\mathrm{C}$ is initialized by a Woods-Saxon spherical structure, a three-$\alpha$-clustering triangular structure or a three-$\alpha$-clustering chain structure. It was observed that the electric and magnetic fields display different behavioral patterns for asymmetric combinations of the projectile and target nuclei as well as for different initial configurations of the carbon nucleus. The major features of the process are discussed.

The first $3^{-}$ and $4^{-}$ states of ${}^{12}\mathrm{C}$ are studied in the present container model, in which the shift parameter is introduced to break the parity symmetry for projecting out the negative-parity states. Taking the limit as the shift parameter approaches zero and by variational calculations for one-deformed size parameter, the local energy minima are obtained for the $3^{-}$ and $4^{-}$ states. It is found that the obtained single Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave functions for $3^{-}$ and $4^{-}$ states are 96% and 92% equivalent to the corresponding generator coordinate method (GCM) wave functions, respectively. The calculated intrinsic densities further show that these negative-parity states of three clusters, different from the traditional understanding of a rigid triangle structure, are found to have nonlocalized clustering structure in the two-dimensional container picture.

We construct accurate models of the three-nucleon ($3N$) interaction by fitting, in a hybrid phenomenological approach, the low-energy constants parametrizing the subleading $3N$ contact operators to the triton binding energy, $n\text{−}d$ scattering lengths, cross section, and polarization observables of $p\text{−}d$ scattering at 2 MeV center-of-mass energy. These models lead to a satisfactory description of polarized $p\text{−}d$ scattering data in the whole energy range below the deuteron breakup threshold. In particular, the longstanding $A_y$ puzzle seems to be solved thanks to the new terms considered in the $3N$ force. Two types of hierarchies among the subleading contact operators are also derived, based on the large-$N_c$ counting and on a recently proposed relativistic counting. We test these hierarchies against the same experimental data and show that they are respected at a reasonable level.

Gamow-Teller (GT) transitions starting from the $T_z=+2$ nucleus ${}^{64}\mathrm{Zn}$ to the $T_z=+1$ nucleus ${}^{64}\mathrm{Ga}$ were studied in a ($p,n$)-type (${}^3\mathrm{He},t$) charge-exchange reaction at a beam energy of 140 MeV/nucleon and scattering angles close to $0^{\circ }$. Here, $T_z$ is the $z$ component of the isospin $T$. The experiment was conducted at the Research Center for Nuclear Physics (RCNP) in Osaka, Japan. An energy resolution of $\approx 34$ keV was achieved by applying beam matching techniques to the Grand Raiden magnetic spectrometer system. With our good resolution, we could observe GT strength fragmented in many states up to an excitation energy of $\approx 11$ MeV. By performing angular distribution analysis, we could identify states in ${}^{64}\mathrm{Ga}$ excited by GT transitions. The reduced GT transition strengths [$B$(GT) values] were calculated assuming the proportionality between the cross sections and the $B$(GT) values. Shell-model calculations using the GXPF1J interaction reproduced the $B$(GT) strength distribution throughout the spectrum. States with isospin $T=3$ were identified by comparing the ${}^{64}\mathrm{Zn}\text{(}{}^3\text{He,}t{\text{)}}^{64}\text{Ga}$ spectrum with a ${}^{64}\mathrm{Zn}(d,{}^2\mathrm{He}){}^{64}\mathrm{Cu}$ spectrum. Relative excitation energies of the corresponding structures are in good agreement, supporting the robustness of isospin symmetry in the mass number $A=64$ nuclei.

The generalized triaxial rotor model with independent variable moments of inertia is applied to describe the transitional behavior of staggering patterns observed in the $\gamma$ bands of ${}^{108,110,112}\mathrm{Ru}$. An oscillating behavior is introduced in the variations of the moments of inertia ${\mathcal{I}}_1$ and ${\mathcal{I}}_2$ to describe the $\gamma$-soft pattern in ${}^{108}\mathrm{Ru}$. Then the amplitude of the oscillating term is exponentially reduced as a function of spin in ${}^{110}\mathrm{Ru}$. The oscillating term is taken away completely in ${}^{112}\mathrm{Ru}$. A good agreement is obtained between the model calculation and the experimental data both in the phase and amplitude of the staggering pattern. Using the obtained eigenfunctions, effective $\gamma$ values are so determined to reproduce best the branching ratios of $\gamma$ decays from the $\gamma$ bands. The stable values of ${\gamma }_{\mathrm{eff}}\approx {20}^{\circ }$ are obtained for the lower-spin states in any of ${}^{108,110,112}\mathrm{Ru}$.