The deuteron quadrupole moment is calculated using two covariant spectator theory model wave functions obtained from the 2007 high-precision fits to $np$ scattering data. Included in the calculation are a new class of isoscalar $np$ interaction currents automatically generated by the nuclear force model used in these fits. The prediction for model WJC-1, with larger relativistic $P$-state components, is $2.5\%$ smaller than the experimental result, in common with the inability of models prior to 2014 to predict this important quantity. However, model WJC-2, with very small $P$-state components, gives agreement to better than 1%, similar to the results obtained recently from chiral effective field theory predictions to next-to-next-to-next-to-leading order.

Antineutrino spectra following the neutron induced fission of ${}^{235}\mathrm{U},{}^{238}\mathrm{U},{}^{239}\mathrm{Pu}$, and ${}^{241}\mathrm{Pu}$ are calculated using the summation approach. While each system involves the decay of more than 800 fission products, the energy region of the spectra most relevant to neutrino oscillations and the reactor antineutrino anomaly is dominated by fewer than 20 nuclei, for which we provide a priority list to drive new measurements. The very-high-energy portion of the spectrum is mainly due to the decay of just two nuclides, ${}^{92}\mathrm{Rb}$ and ${}^{96}\mathrm{Y}$. The integral of the signal measured by antineutrino experiments is found to have a dependence on the mass and proton numbers of the fissioning system. In addition, we observe that $\sim 70\%$ of the signal originates from the light fission fragment group and about $50\%$ from the decay of odd-$Z,$ odd-$N$ nuclides.

Measurements of the neutron radiative-capture cross section of ${}^{124}\mathrm{Xe}$ have been performed for the first time for neutron energies above 100 keV. In addition, data for the ${}^{124}\mathrm{Xe}\left(n,2n\right){}^{123}\mathrm{Xe}$ reaction cross section have been obtained from threshold to 14.8 MeV to cover the entire energy range of interest, while previous data existed only at around 14 MeV. The results of these measurements provide the basis for an alternative and sensitive diagnostic tool for investigating properties of the inertial confinement fusion plasma in deuterium-tritium (DT) capsules at the National Ignition Facility located at Lawrence Livermore National Laboratory. Here, areal density $\rho R$ (density $\times$ radius) of the fuel, burn asymmetry, and fuel-ablator mix are of special interest. The ${}^{124}\mathrm{Xe}\left(n,\gamma \right){}^{125}\mathrm{Xe}$ reaction probes the down-scattered neutrons, while the ${}^{124}\mathrm{Xe}\left(n,2n\right){}^{123}\mathrm{Xe}$ reaction provides a measure of the 14 MeV direct neutrons.

We present the two- and three-pion-exchange contributions to the nucleon-nucleon interaction which occur at next-to–next-to–next-to–next-to–leading order (${\mathrm{N}}^4\mathrm{LO}$, fifth order) of chiral effective field theory and calculate nucleon-nucleon scattering in peripheral partial waves with $L\ge 3$ by using low-energy constants that were extracted from $\pi N$ analysis at fourth order. While the net three-pion-exchange contribution is moderate, the two-pion exchanges turn out to be sizable and prevailingly repulsive, thus compensating the excessive attraction characteristic for next-to–next-to–leading order and ${\mathrm{N}}^3\mathrm{LO}$. As a result, the ${\mathrm{N}}^4\mathrm{LO}$ predictions for the phase shifts of peripheral partial waves are in very good agreement with the data (with the only exception being the ${}^1{F}_3$ wave). We also discuss the issue of the order-by-order convergence of the chiral expansion for the $NN$ interaction.

Background: Neutron emission is correlated in fission events because, on average, more than one neutron is emitted per fission. Measurements of these correlations, coupled with studies of more inclusive observables such as neutron multiplicity, provide sensitive information about the fission mechanism. Neutron-neutron angular correlations have been studied in both spontaneous fission of ${}^{252}\mathrm{Cf}$ and neutron-induced fission of ${}^{235}\mathrm{U}$. These correlations, until recently incalculable in most available simulations of fission, can now be calculated in event-by-event simulations of fission.

Purpose: Phenomenological studies of fission are of interest both for basic science and for practical applications. Neutron-neutron angular correlations are characteristic of the fissioning isotope and could be used in material identification.

Method: We use our model of complete fission events, freya, to first study the sensitivity of two-neutron angular correlations to the model inputs and then compare to available data. We also compare our simulations to neutron-fragment angular correlations.

Results: We find that the correlations calculated with freya are fairly robust with respect to the input parameters. Any strong deviations in the correlations result in poor agreement with measured inclusive neutron observables such as neutron multiplicity as a function of fragment mass and the neutron multiplicity distribution. The agreement of freya with the present set of correlation data is found to be good.

Conclusions: freya can be used to reliably predict neutron-neutron angular correlations and could then be used to identify materials.

Time reversal invariance violating (TRIV) effects in neutron transmission through a nuclear target are discussed. We demonstrate the existence of a class of experiments that are free from false asymmetries. We discuss the enhancement of TRIV effects for neutron energies corresponding to $p$-wave resonances in the compound nuclear system. We analyze a model experiment and show that such tests can have a discovery potential of ${10}^2–{10}^4$ compared to current limits.

We develop a dynamical coupled-channels model of $K^{-}p$ reactions, aiming at extracting the parameters associated with hyperon resonances and providing the elementary antikaon-nucleon scattering amplitudes that can be used for investigating various phenomena in the strangeness sector such as the production of hypernuclei from kaon-nucleus reactions. The model consists of (a) meson-baryon $\left(MB\right)$ potentials $v_{M^{\prime }{B}^{\prime },MB}$ derived from the phenomenological SU(3) Lagrangian, and (b) vertex interactions ${\Gamma }_{MB,Y^{*}}$ for describing the decays of the bare excited hyperon states $\left(Y^{*}\right)$ into $MB$ states. The model is defined in a channel space spanned by the two-body $\overline{K}N,\pi \Sigma ,\pi \Lambda ,\eta \Lambda$, and $K\Xi$ states and also the three-body $\pi \pi \Lambda$ and $\pi \overline{K}N$ states that have the resonant $\pi {\Sigma }^{*}$ and ${\overline{K}}^{*}N$ components, respectively. The resulting coupled-channels scattering equations satisfy the multichannel unitarity conditions and account for the dynamical effects arising from the off-shell rescattering processes. The model parameters are determined by fitting the available data of the unpolarized and polarized observables of the $K^{-}p\to \overline{K}N,\pi \Sigma ,\pi \Lambda ,\eta \Lambda ,K\Xi$ reactions in the energy region from the threshold to invariant mass $W=2.1$ GeV. Two models with equally good ${\chi }^2$ fits to the data have been constructed. The partial-wave amplitudes obtained from the constructed models are compared with the results from a recent partial-wave analysis by the Kent State University group. We discuss the differences between these three analysis results. Our results at energies near the threshold suggest that the higher partial waves should be treated on the same footing as the $S$ wave if one wants to understand the nature of $\Lambda \left(1405\right)1/2^{-}$ using the data below the $\overline{K}N$ threshold, as will be provided by the J-PARC E31 experiment.

We study the phase diagram of isospin-asymmetrical nuclear matter in the density-temperature plane, allowing for four competing phases of nuclear matter: (i) the unpaired phase; (ii) the translationally and rotationally symmetric, but isospin-asymmetrical BCS condensate; (iii) the current-carrying Larkin-Ovchinnikov-Fulde-Ferrell phase; and (iv) the heterogeneous phase-separated phase. The phase diagram of nuclear matter composed of these phases features two tricritical points, in general, as well as crossovers from the asymmetrical BCS phase to a Bose-Einstein condensate (BEC) of deuterons plus a neutron gas, for both the homogeneous superfluid phase (at high temperatures) and the heterogeneous phase (at low temperatures). The BCS-BEC-type crossover in the condensate occurs as the density is reduced. We analyze in detail some intrinsic properties of these phases, including the Cooper-pair wave function, the coherence length, the occupation numbers of majority and minority nucleonic components, and the dispersion relations of quasiparticle excitations about the ground state. We show by explicit examples that the physics of the individual phases and the transition from weak to strong coupling can be well understood by tracing the behavior of these quantities.

The world data on elastic electron scattering on ${}^3\mathrm{He}$ and ${}^4\mathrm{He}$ is used to determine the Zemach moments ${\langle r\rangle }_{\left(2\right)}$ and ${\langle r^3\rangle }_{\left(2\right)}$. These quantities are required to interpret the Lamb shift and hyperfine splitting data of muonic helium presently being measured at the Paul Scherrer Institute by the CREMA Collaboration. The rms radii are determined as well.

We investigate ultrarelativistic collisions of the ${}^{12}\mathrm{C}$ nucleus with heavy targets and show that harmonic flow measures based on ratios of cumulant moments are particularly suited for study of the intrinsic deformation of the ${}^{12}\mathrm{C}$ wave function. In this way one can probe the expected $\alpha$ clusterization in the ground state, which leads to a large initial triangularity in the shape of the fireball in the transverse plane. We show that the clusterization effect results in very characteristic behavior of the ratios of the cumulant moments as functions of the number of participant nucleons, for both elliptic and triangular deformations. Thus experimental event-by-event studies of harmonic flow in ultrarelativistic light-heavy collisions may offer a new window through which to look at the ground-state structure of light nuclei.

Background: By looking specifically at free nucleons (here protons), we present for the first time a comprehensive body of experimental results concerning the mean free path, the nucleon-nucleon cross-section and in-medium effects in nuclear matter.

Purpose: Using the large dataset of exclusive measurements provided by the $4\pi$ array INDRA, we determine the relative degree of stopping as a function of system mass and bombarding energy. We show that the stopping can be directly related to the transport properties in the nuclear medium.

Methods: We perform a systematic study of protons nuclear stopping in central collisions for heavy-ion induced reactions in the Fermi-energy domain, between $15A$ and $100A$ MeV.

Results: It is found that the mean free path exhibits a maximum at ${\lambda }_{NN}=9.5\pm 2$ fm, around $E_{\mathrm{inc}}=35A-40A$ MeV incident energy and decreases toward an asymptotic value ${\lambda }_{NN}=4.5\pm 1$ fm at $E_{\mathrm{inc}}=100A$ MeV.

Conclusions: After accounting for Pauli blocking of elastic nucleon-nucleon collisions, it is shown that the effective in-medium $NN$ cross section is further reduced compared to the free value in this energy range. Therefore, in-medium effects cannot be neglected in the Fermi-energy range. These results bring new fundamental inputs for microscopic descriptions of nuclear reactions in the Fermi-energy domain.

Background: Double-$\beta$ decay is a rare nuclear process in which two neutrons in the nucleus are converted to two protons with the emission of two electrons and two electron antineutrinos.

Purpose: We measured the half-life of the two-neutrino double-$\beta$ decay of ${}^{150}\mathrm{Nd}$ to excited final states of ${}^{150}\mathrm{Sm}$ by detecting the deexcitation $\gamma$ rays of the daughter nucleus.

Method: This study yields the first detection of the coincidence $\gamma$ rays from the $0{}_1^{+}$ excited state of ${}^{150}\mathrm{Sm}$. These $\gamma$ rays have energies of 333.97 and 406.52 keV and are emitted in coincidence through a $0_1^{+}\to 2_1^{+}\to 0_{\mathrm{gs}}^{+}$ transition.

Results: The enriched ${\mathrm{Nd}}_2{\mathrm{O}}_3$ sample consisted of 40.13 g ${}^{150}\mathrm{Nd}$ and was observed for 642.8 days at the Kimballton Underground Research Facility, producing 21.6 net events in the region of interest. This count rate gives a half-life of $T_{1/2}=[1.{07}_{-0.25}^{+0.45}\left(\mathrm{stat}\right)\pm 0.07\left(\mathrm{syst}\right)]\times {10}^{20}$ yr. The effective nuclear matrix element was found to be $0.0465{}_{-0.0054}^{+0.0098}$. Finally, lower limits were obtained for decays to higher excited final states.

Conclusions: Our half-life measurement agrees within uncertainties with another recent measurement in which no coincidence was employed. Our nuclear matrix element calculation may have an impact on a recent neutrinoless double-$\beta$ decay nuclear matrix element calculation which implies that the decay to the first excited state in ${}^{150}\mathrm{Sm}$ is favored over that to the ground state.

Background: The two-flavor color superconducting (2SC) phase of quark matter is a possible constituent of the core of neutron stars. To assess its impact on the observable behavior of the star one must analyze transport properties, which in 2SC matter are controlled by the scattering of gapless fermionic modes by each other and possibly also by color-magnetic flux tubes.

Purpose: We determine the electrical and thermal conductivities and the shear viscosity of 2SC matter.

Methods: We use a variational formulation of transport theory, treating the strong and electromagnetic interactions via a weak coupling expansion.

Results: We provide the leading order scaling of the transport coefficients with temperature and chemical potential as well as accurate fits to our numerical results. We also find that the scattering of fermions by color-magnetic flux tubes is insignificant for thermal conductivity, but may contribute to the electrical conductivity and shear viscosity in the limit of very low temperature or high magnetic field. We also estimate the transport coefficients in unpaired quark matter.

Conclusions: Our calculation has set the stage for exploration of possible signatures of the presence of 2SC quark matter in neutron stars.

Background: Neutrinoless double-$\beta \left(0\nu \beta \beta \right)$ decay is related to many fundamental concepts in nuclear and particle physics beyond the standard model. Currently there are many experiments searching for this weak process. An accurate knowledge of the nuclear matrix element for the $0\nu \beta \beta$ decay is essential for determining the effective neutrino mass once this process is eventually measured.

Purpose: We report the first full relativistic description of the $0\nu \beta \beta$ decay matrix element based on a state-of-the-art nuclear structure model.

Methods: We adopt the full relativistic transition operators which are derived with the charge-changing nucleonic currents composed of the vector coupling, axial-vector coupling, pseudoscalar coupling, and weak-magnetism coupling terms. The wave functions for the initial and final nuclei are determined by the multireference covariant density functional theory (MR-CDFT) based on the point-coupling functional PC-PK1. Correlations beyond the mean field are introduced by configuration mixing of both angular momentum and particle number projected quadrupole deformed mean-field wave functions.

Results: The low-energy spectra and electric quadrupole transitions in ${}^{150}\mathrm{Nd}$ and its daughter nucleus ${}^{150}\mathrm{Sm}$ are well reproduced by the MR-CDFT calculations. The $0\nu \beta \beta$ decay matrix elements for both the $0_1^{+}\to 0_1^{+}$ and $0_1^{+}\to 0_2^{+}$ decays of ${}^{150}\mathrm{Nd}$ are evaluated. The effects of particle number projection, static and dynamic deformations, and the full relativistic structure of the transition operators on the matrix elements are studied in detail.

Conclusions: The resulting $0\nu \beta \beta$ decay matrix element for the $0_1^{+}\to 0_1^{+}$ transition is $5.60$, which gives the most optimistic prediction for the next generation of experiments searching for the $0\nu \beta \beta$ decay in ${}^{150}\mathrm{Nd}$.

We study the nuclear parton distribution functions on the basis of our recently developed semimicroscopic model, which takes into account a number of nuclear effects including nuclear shadowing, Fermi motion and nuclear binding, nuclear meson-exchange currents, and off-shell corrections to bound nucleon distributions. We discuss in detail the dependencies of nuclear effects on the type of parton distribution (nuclear sea vs valence), as well as on the parton flavor (isospin). We apply the resulting nuclear parton distributions to calculate ratios of cross sections for proton-induced Drell-Yan production off different nuclear targets. We obtain a good agreement on the magnitude, target and projectile $x$, and the dimuon mass dependence of proton-nucleus Drell-Yan process data from the E772 and E866 experiments at Fermilab. We also provide nuclear corrections for the Drell-Yan data from the E605 experiment.

Background: Microscopic calculations of four-body collisions become very challenging in the energy regime above the threshold for four free particles. The neutron-${}^3\mathrm{He}$ scattering is an example of such processes with elastic, rearrangement, and breakup channels.

Purpose: We aim to calculate observables for elastic and inelastic neutron-${}^3\mathrm{He}$ reactions up to 30 MeV neutron energy using realistic nuclear force models.

Methods: We solve the Alt, Grassberger, and Sandhas (AGS) equations for the four-nucleon transition operators in the momentum-space framework. The complex-energy method with special integration weights is applied to deal with the complicated singularities in the kernel of AGS equations.

Results: We obtain fully converged results for the differential cross section and neutron analyzing power in the neutron-${}^3\mathrm{He}$ elastic scattering as well as the total cross sections for inelastic reactions. Several realistic potentials are used, including one with an explicit $\Delta$ isobar excitation.

Conclusions: There is reasonable agreement between the theoretical predictions and experimental data for the neutron-${}^3\mathrm{He}$ scattering in the considered energy regime. The most remarkable disagreements are seen around the minimum of the differential cross section and the extrema of the neutron analyzing power. The breakup cross section increases with energy exceeding rearrangement channels above 23 MeV.

Background: Theoretical approaches based on density functional theory provide the only tractable method to incorporate the wide range of densities and isospin asymmetries required to describe finite nuclei, infinite nuclear matter, and neutron stars.

Purpose: A relativistic energy density functional (EDF) is developed to address the complexity of such diverse nuclear systems. Moreover, a statistical perspective is adopted to describe the information content of various physical observables.

Methods: We implement the model optimization by minimizing a suitably constructed ${\chi }^2$ objective function using various properties of finite nuclei and neutron stars. The minimization is then supplemented by a covariance analysis that includes both uncertainty estimates and correlation coefficients.

Results: A new model, “FSUGold2,” is created that can well reproduce the ground-state properties of finite nuclei, their monopole response, and that accounts for the maximum neutron-star mass observed up to date. In particular, the model predicts both a stiff symmetry energy and a soft equation of state for symmetric nuclear matter, suggesting a fairly large neutron-skin thickness in ${}^{208}\mathrm{Pb}$ and a moderate value of the nuclear incompressibility.

Conclusions: We conclude that without any meaningful constraint on the isovector sector, relativistic EDFs will continue to predict significantly large neutron skins. However, the calibration scheme adopted here is flexible enough to create models with different assumptions on various observables. Such a scheme—properly supplemented by a covariance analysis—provides a powerful tool to identify the critical measurements required to place meaningful constraints on theoretical models.

Since the pioneering experiment E89-009 studying hypernuclear spectroscopy using the $(e,e^{\prime }{K}^{+})$ reaction was completed, two additional experiments, E01-011 and E05-115, were performed at Jefferson Lab. These later experiments used a modified experimental design, the “tilt method,” to dramatically suppress the large electromagnetic background, and allowed for a substantial increase in luminosity. Additionally, a new kaon spectrometer, HKS (E01-011), a new electron spectrometer, HES, and a new splitting magnet (E05-115) were added to produce new data sets of precision, high-resolution hypernuclear spectroscopy. All three experiments obtained a spectrum for ${}_{\Lambda }^{12}\mathrm{B}$, which is the most characteristic $p$-shell hypernucleus and is commonly used for calibration. Independent analyses of these different experiments demonstrate excellent consistency and provide the clearest level structure to date of this hypernucleus as produced by the $(e,e^{\prime }{K}^{+})$ reaction. This paper presents details of these experiments, and the extraction and analysis of the observed ${}_{\Lambda }^{12}\mathrm{B}$ spectrum.

Background: Precision measurements at low energy search for physics beyond the standard model in a way complementary to searches for new particles at colliders. In the weak sector the most general $\beta$-decay Hamiltonian contains, besides vector and axial-vector terms, also scalar, tensor, and pseudoscalar terms. Current limits on the scalar and tensor coupling constants from neutron and nuclear $\beta$ decay are on the level of several percent.

Purpose: Extracting new information on tensor coupling constants by measuring the $\beta$-asymmetry parameter in the pure Gamow-Teller decay of ${}^{67}\mathrm{Cu}$, thereby testing the V-A structure of the weak interaction.

Method: An iron sample foil into which the radioactive nuclei were implanted was cooled down to mK temperatures in a ${}^3\mathrm{He}{\text{−}}^4\mathrm{He}$ dilution refrigerator. An external magnetic field of 0.1 T, in combination with the internal hyperfine magnetic field, oriented the nuclei. The anisotropic $\beta$ radiation was observed with planar high-purity germanium detectors operating at a temperature of about 10 K. An on-line measurement of the $\beta$ asymmetry of ${}^{68}\mathrm{Cu}$ was performed as well for normalization purposes. Systematic effects were investigated using geant4 simulations.

Results: The experimental value, $\tilde{A}=0.587\left(14\right)$, is in agreement with the standard model value of 0.5991(2) and is interpreted in terms of physics beyond the standard model. The limits obtained on possible tensor-type charged currents in the weak interaction Hamiltonian are $-0.045<(C_T+C_T^{\prime })/C_A<0.159$ (90% C.L.).

Conclusions: The obtained limits are comparable to limits from other correlation measurements in nuclear $\beta$ decay and contribute to further constraining tensor coupling constants.

Suppressions of light- and heavy-flavor observables are considered to be excellent probes of QCD matter created in ultrarelativistic heavy ion collisions. Suppression predictions of quark and gluon jets appear to suggest a clear hierarchy according to which neutral pions should be more suppressed than $D$ mesons, which in turn should be more suppressed than single electrons. However, joint comparison of neutral pion (light probe) and nonphotonic single-electron (heavy probe) suppression data at the BNL Relativistic Heavy Ion Collider (RHIC) unexpectedly showed similar jet suppression for these two probes, which presents the well-known heavy-flavor puzzle at RHIC. We here analyze which effects are responsible for this unexpected result by using the dynamical energy-loss formalism. We find that the main effect is a surprising reversal in the suppression hierarchy between neutral pions and $D$ mesons, which is due to the deformation of the suppression patterns of light partons by fragmentation functions. Furthermore, we find that, due to the decay functions, the single-electron suppression approaches the $D$-meson suppression. Consequently, we propose that these two effects, taken together, provide a clear intuitive explanation of this longstanding puzzle.