Quantum Monte Carlo calculations of electromagnetic moments and transitions are reported for $A\le 9$ nuclei. The realistic Argonne $v_{18}$ two-nucleon and Illinois-7 three-nucleon potentials are used to generate the nuclear wave functions. Contributions of two-body meson-exchange current (MEC) operators are included for magnetic moments and $M1$ transitions. The MEC operators have been derived in both a standard nuclear physics approach and a chiral effective field theory formulation with pions and nucleons including up to one-loop corrections. The two-body MEC contributions provide significant corrections and lead to very good agreement with experiment. Their effect is particularly pronounced in the $A=9$, $T=3/2$ systems, in which they provide up to $\sim 20\%$ ($\sim 40\%$) of the total predicted value for the ${}^9$Li (${}^9$C) magnetic moment.

We have performed shell-model calculations for the two one-valence-neutron isotones ${}^{135}$Te and ${}^{137}$Xe and the two one-valence-proton isotopes ${}^{135,137}$Sb. The main aim of our study has been to investigate the evolution of single-particle states with increasing nucleon number. To this end, we have focused attention on the spectroscopic factors and the effective single-particle energies. In our calculations, we have employed a realistic low-momentum two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential that has already proved quite successful in describing the spectroscopic properties of nuclei in the ${}^{132}$Sn region. Comparison shows that our results reproduce very well the available experimental data. This gives confidence in the evolution of the single-particle states predicted by the present study.

Problems of production and study of new neutron-enriched heavy nuclei are discussed. Low-energy multinucleon transfer reactions are shown to be quite appropriate for this purpose. Reactions with actinide beams and targets are of special interest for synthesis of new neutron-enriched transfermium nuclei and not-yet-known nuclei with closed neutron shell $N=126$ having the largest impact on the astrophysical r-process. The estimated cross sections for the production of these nuclei look very promising for planning such experiments at currently available accelerators. These experiments, however, are rather expensive and difficult to perform because of low intensities of the massive projectile beams and problems of separating and detecting the heavy reaction products. Thus, realistic predictions of the corresponding cross sections for different projectile-target combinations are definitely required. Some uncertainty still remains in the values of several parameters used for describing the low-energy nuclear dynamics. This uncertainty does not allow one to perform very accurate predictions for the productions of new heavier-than-target (trans-target) nuclei in multinucleon transfer reactions. Most of these parameters (nucleon transfer rate, nuclear viscosity, and fission barriers) are fundamental characteristics of low-energy nuclear dynamics. Determination of the values of these parameters (as well as their temperature dependence) is of significance in its own right. The available experimental data on the production of heavy nuclei in low-energy multinucleon transfer reactions are still insufficient and fragmentary. Several new experiments are proposed, these include those in which the role of shell effects in reaction dynamics can be better clarified.

Our earlier Faddeev three-body study in the $K^{-}$-deuteron scattering length, $A_{K^{-}d}$, is revisited here in light of the recent developments on two fronts: (i) the improved chiral unitary approach to the theoretical description of the coupled $\overline{K}N$ related channels at low energies, and (ii) the new and improved measurement from SIDDHARTA Collaboration of the strong interaction energy shift and width in the lowest $K^{-}$-hydrogen atomic level. Those two, in combination, have allowed us to produce a reliable two-body input to the three-body calculation. All available low-energy $K^{-}p$ observables are well reproduced and predictions for the $\overline{K}N$ scattering lengths and amplitudes, ${\left(\pi \Sigma \right)}^{\circ }$ invariant-mass spectra, as well as for $A_{K^{-}d}$ are put forward and compared with results from other sources. The findings of the present work are expected to be useful in interpreting the forthcoming data from CLAS, HADES, LEPS, and SIDDHARTA Collaborations.

We present the first ab initio coupled-cluster calculations of medium-mass nuclei with explicit chiral three-nucleon (3$N$) interactions. Using a spherical formulation of coupled cluster with singles and doubles excitations including explicit 3$N$ contributions, we study ground states of ${}^{16,24}\text{O}$, ${}^{40,48}\text{Ca,}$ and ${}^{56}\text{Ni}$. We employ chiral nucleon-nucleon ($\mathit{\text{NN}}$) plus 3$N$ interactions softened through a similarity renormalization group (SRG) transformation at the three-body level. We investigate the impact of all truncations and quantify the resulting uncertainties—this includes the contributions from triple excitations, the truncation of the set of three-body matrix elements, and the omission of SRG-induced four-body interactions. Furthermore, we assess the quality of a normal-ordering approximation of the 3$N$ interaction beyond light nuclei. Our study points towards the predictive power of chiral Hamiltonians in the medium-mass regime.

The ground state of neutron-rich unbound ${}^{13}$Li was observed for the first time in a one-proton removal reaction from ${}^{14}$Be at a beam energy of 53.6 MeV/u. The ${}^{13}$Li ground state was reconstructed from ${}^{11}$Li and two neutrons giving a resonance energy of 120${}_{-80}^{+60}$ keV. All events involving single- and double-neutron interactions in the Modular Neutron Array (MoNA) were analyzed, simulated, and fitted self-consistently. The three-body (${}^{11}\text{Li}+n+n$) correlations within Jacobi coordinates showed strong dineutron characteristics. The decay energy spectrum of the intermediate ${}^{12}$Li system (${}^{11}\text{Li}+n$) was described with an $s$-wave scattering length of greater than $-4$ fm, which is a smaller absolute value than reported in a previous measurement.

We present a microscopic calculation of the complete quasiparticle interaction, including central as well as noncentral components, in neutron matter from high-precision two- and three-body forces derived within the framework of chiral effective-field theory. The contributions from two-nucleon forces are computed in many-body perturbation theory to first and second order (without any simplifying approximations). In addition we include the leading-order one-loop diagrams from the next-to next-to leading order (N${}^2$LO) chiral three-nucleon force, which contribute to all Fermi liquid parameters except those associated with the center-of-mass tensor interaction. The relative-momentum dependence of the quasiparticle interaction is expanded in Legendre polynomials up to $L=2$. Second-order Pauli blocking and medium polarization effects act coherently in specific channels; namely, for the Landau parameters $f_1$, $h_0$, and $g_0$, which results in a dramatic increase in the quasiparticle effective mass as well as a decrease in both the effective tensor force and the neutron matter spin susceptibility. For densities greater than about half the nuclear matter saturation density ${\rho }_0$, the contributions to the Fermi liquid parameters from the leading-order chiral three-nucleon force scale in all cases approximately linearly with the nucleon density. The largest effect of the three-nucleon force is to generate a strongly repulsive effective interaction in the isotropic spin-independent channel. We show that the leading-order chiral three-nucleon force leads to an increase in the spin susceptibility of neutron matter, but we observe no evidence for a ferromagnetic spin instability in the vicinity of the saturation density ${\rho }_0$. This work sets the foundation for future studies of neutron matter response to weak and electromagnetic probes with applications to neutron star structure and evolution.

The prompt neutron and $\gamma$ emission from primary fission fragments are calculated for thermal neutron induced fission of ${}^{235}$U and ${}^{239}$Pu and for spontaneous fission of ${}^{252}$Cf using a Monte Carlo Hauser-Feshbach approach for the evaporation of the excited fission fragments. Remaining free model parameters, such as excitation energy sharing and initial spin distribution, are determined by comparison of the neutron emission characteristics with experimental data. Using the obtained parameters the $\gamma$-ray characteristics, e.g., $\gamma$ spectrum, multiplicity distribution, average multiplicity and energy, and multiplicity distribution, are calculated and compared with available experimental data.

This paper details the solar neutrino analysis of the 385.17-day phase-III data set acquired by the Sudbury Neutrino Observatory (SNO). An array of ${}^3$He proportional counters was installed in the heavy-water target to measure precisely the rate of neutrino-deuteron neutral-current interactions. This technique to determine the total active ${}^8$B solar neutrino flux was largely independent of the methods employed in previous phases. The total flux of active neutrinos was measured to be $5.{54}_{-0.31}^{+0.33}{\text{(stat.)}}_{-0.34}^{+0.36}\text{(syst.)}\times {10}^6$ cm${}^{-2}$ s${}^{-1}$, consistent with previous measurements and standard solar models. A global analysis of solar and reactor neutrino mixing parameters yielded the best-fit values of $\Delta m^2=7.{59}_{-0.21}^{+0.19}\times {10}^{-5}{\text{eV}}^2$ and $\theta =34.4_{-1.2}^{+1.3}\text{degrees}$.

The single-neutron properties of $N$ $=$ 51 nuclei have been studied with the ($d$,$p$) and ($\alpha$,${}^3$He) reactions, at beam energies of 15 and 50 MeV respectively, on ${}^{88}$Sr, ${}^{90}$Zr, and ${}^{92}$Mo targets. The light reaction products were momentum analyzed using a conventional magnetic spectrometer. Additionally, the ${}^2{\mathrm{H}(}^{86}\mathrm{Kr},p$) reaction was measured at a beam energy of 10 MeV/u, where outgoing light ions were analyzed using a helical-orbit spectrometer. Absolute cross sections and angular distributions corresponding to the population of different final states in the heavy product were obtained for each reaction. Spectroscopic factors were extracted and centroids of the single-particle strength were deduced. The observations appear consistent with calculations based on an evolution of single-particle structure driven by the nucleon-nucleon forces acting between valence protons and neutrons.

We present a model of electron-positron pair production in pion-nucleon collisions in the exclusive reaction $\pi N\to N{e}^{+}{e}^{-}$. The model is based on an effective field theory approach, incorporating 16 baryon resonances below 2 GeV. Parameters of the model are fitted to pion photoproduction data. We present the resulting dilepton invariant mass spectra for ${\pi }^{-}p$ collisions up to $\sqrt{s}=1.9$ GeV center-of-mass collision energy. These results are meant to give predictions for the planned experiments at the HADES spectrometer in GSI, Darmstadt.

We calculate the electromagnetic form factors of the nucleon to third chiral order in manifestly Lorentz-invariant effective field theory. The $\rho$ and $\omega$ mesons as well as the $\Delta \left(1232\right)$ resonance are included as explicit dynamical degrees of freedom. To obtain a self-consistent theory with respect to constraints we consider the proper relations among the couplings of the effective Lagrangian. For the purpose of generating a systematic power counting, the extended on-mass-shell renormalization scheme is applied in combination with the small-scale expansion. The results for the electric and magnetic Sachs form factors are analyzed in terms of experimental data and compared to previous findings in the framework of chiral perturbation theory. The pion-mass dependence of the form factors is briefly discussed.

Background: The density of the nucleus has been important in explaining the nuclear dependence of the quark distributions, also known as the EMC effect, as well as the presence of high-momentum nucleons arising from short-range correlations (SRCs). Recent measurements of both of these effects on light nuclei have shown a clear deviation from simple density-dependent models.

Purpose: A better understanding of the nuclear quark distributions and short-range correlations requires a careful examination of the experimental data on these effects to constrain models that attempt to describe these phenomena.

Methods: We present a detailed analysis of the nuclear dependence of the EMC effect and the contribution of SRCs in nuclei, comparing to predictions and simple scaling models based on different pictures of the underlying physics. We also make a direct, quantitative comparison of the two effects to further examine the connection between these two observables related to nuclear structure.

Results: We find that, with the inclusion of the new data on light nuclei, neither of these observables can be well explained by common assumptions for the nuclear dependence. The anomalous behavior of both effects in light nuclei is consistent with the idea that the EMC effect is driven by either the presence of high-density configurations in nuclei or the large virtuality of the high-momentum nucleons associated with these configurations.

Conclusions: The unexpected nuclear dependence in the measurements of the EMC effect and SRC contributions appear to suggest that the local environment of the struck nucleon is the most relevant quantity for explaining these results. The common behavior suggests a connection between the two seemingly disparate phenomena, but the data do not yet allow for a clear preference between models which aim to explain this connection.

Neutron star crusts are studied using a classical molecular dynamics model developed for heavy-ion reactions. After the model is shown to produce a plethora of the so-called pasta shapes, a series of techniques borrowed from nuclear physics, condensed matter physics, and topology is used to craft a method that can be used to characterize the shape of the pasta structures in an unequivocal way.

Background: Superallowed $\beta$-decay rates provide stringent constraints on physics beyond the standard model of particle physics. To extract crucial information about the electroweak force, small isospin-breaking corrections to the Fermi matrix element of superallowed transitions must be applied.

Purpose: We perform systematic calculations of isospin-breaking corrections to superallowed $\beta$ decays and estimate theoretical uncertainties related to the basis truncation, to time-odd polarization effects related to the intrinsic symmetry of the underlying Slater determinants, and to the functional parametrization.

Methods: We use the self-consistent isospin- and angular-momentum-projected nuclear density functional theory employing two density functionals derived from the density-independent Skyrme interaction. Pairing correlations are ignored. Our framework can simultaneously describe various effects that impact matrix elements of the Fermi decay: symmetry breaking, configuration mixing, and long-range Coulomb polarization.

Results: Isospin-breaking corrections to the $I=0^{+}$, $T=1\to I=0^{+}$, $T=1$ pure Fermi transitions are computed for nuclei from $A=10$ to $A=98$ and, for the first time, to the Fermi branch of the $I,T=1/2\to I$, $T=1/2$ transitions in mirror nuclei from $A=11$ to $A=49$. We carefully analyze various model assumptions impacting theoretical uncertainties of our calculations and provide theoretical error bars on our predictions.

Conclusions: The overall agreement with empirical isospin-breaking corrections is very satisfactory. Using computed isospin-breaking corrections we show that the unitarity of the CKM matrix is satisfied with a precision of better than 0.1$\%$.

High-$p_T$ hadrons produced in hard collisions and detected inclusively bear peculiar features: (i) they originate from jets whose initial virtuality and energy are of the same order and (ii) such jets are rare and have a very biased energy sharing among the particles, namely the detected hadron carries the main fraction of the jet energy. The former feature leads to an extremely intensive gluon radiation and energy dissipation at the early stage of hadronization, either in vacuum or in a medium. As a result, a leading hadron must be produced on a short length scale. Evaluation within a model of perturbative fragmentation confirms the shortness of the production length. This result is at variance with the unjustified assumption of long production length, made within the popular energy-loss scenario. Thus, we conclude that the main reason of suppression of high-$p_T$ hadrons in heavy-ion collisions is the controlled-by-color-transparency attenuation of a high-$p_T$ dipole propagating through the hot medium. Adjusting a single parameter, the transport coefficient, we describe quite well the data from the Large Hadron Collider and the Relativistic Heavy Ion Collider for the suppression factor $R_{AA}$ as function of $p_T$, collision energy, and centrality. We observe that the complementary effect of the initial-state interaction causes a flattening and even fall of $R_{AA}$ at large $p_T$. The azimuthal anisotropy of hadron production, calculated with no further adjustment, also agrees well with data at different energies and centralities.

Background: There has been much recent investigation into dijets at the Large Hadron Collider, but predictions for dijets at Relativistic Heavy Ion Collider (RHIC) scales are lacking.

Purpose: We present a systematic study of the dijet suppression at RHIC using the VNI/Bass-Müller-Srivastava parton cascade.

Methods: We examine the modification of the dijet asymmetry $A_j$ and the within-cone transverse energy distribution (jet shape) along with partonic fragmentation distributions $z$ and $j_t$ in terms of $\widehat{q}$, the path length of leading and subleading jets, cuts on the jet energy distributions, the jet cone angle, and the jet-medium interaction mechanism.

Results: We find that $A_j$ is most sensitive to $\widehat{q}$ and relatively insensitive to the nature of the jet-medium interaction mechanism. The jet profile is dominated by $\widehat{q}$ and the nature of the interaction mechanism. The partonic fragmentation distributions clearly show the jet modification and differentiate between elastic and radiative plus elastic modes.

Conclusions: Dijets at RHIC scales are strongly modified by a quark-gluon plasma medium; measurements of their suppression will provide a vital additional data point for understanding the modification of hard probes.

Background: There is a renewed experimental interest in antiproton-proton scattering with an intense, possibly polarized antiproton beam. On the theoretical side, significant progress has been made in the understanding of the nuclear force from chiral effective field theory.

Purpose: We provide a high-quality model-independent description of the available low-energy antiproton-proton scattering data.

Method: We perform a new energy-dependent partial-wave analysis of all antiproton-proton elastic ($\overline{p}p\to \overline{p}p$) and charge-exchange ($\overline{p}p\to \overline{n}n$) scattering data below 925 MeV/$c$ antiproton laboratory momentum. The Schrödinger equation is solved for the coupled $\overline{p}p$ and $\overline{n}n$ channels. The relevant long-range parts of the electromagnetic and the one- and two-pion exchange interactions are included exactly. The short-range interactions, including the coupling to the mesonic annihilation channels, are parametrized by a complex boundary condition at a radius of $r=1.2$ fm.

Results: The updated database, which includes significantly more high-quality charge-exchange data, contains 3749 scattering data. The fit gives ${\chi }_{\min }^2/N_{\mathrm{df}}=1.048$, where $N_{\mathrm{df}}=3578$ is the number of degrees of freedom. We discuss the description of the experimental data and we present the antiproton-proton phase-shift parameters.

Conclusions: Chiral effective field theory provides an excellent long-range antinucleon-nucleon interaction. The results of the PWA should serve as the starting point for future theoretical and experimental investigations of low-energy antiproton-proton scattering.

The Gamow-Teller (GT) strength distribution has been investigated in a high-resolution (${}^3$He,$t$) charge-exchange experiment on the double-beta ($\beta \beta$) decaying nucleus ${}^{100}$Mo. The experiment was carried out at the Osaka University Research Center for Nuclear Physics (RCNP) with a 420 MeV incident ${}^3$He beam and the Grand Raiden magnetic spectrometer. A final-state energy resolution of 33 keV was achieved. It was found that nearly the entire low-energy (up to $\approx 4$ MeV) ${\mathrm{GT}}^{-}$ strength is concentrated in the ground-state transition to ${}^{100}$Tc, which is interpreted as a result of the particular neutron and proton sub-shell occupancies. The impact on the matrix elements for the two-neutrino double-beta ($2\nu \beta \beta$) decay and the use of ${}^{100}$Mo as a neutrino detection material is discussed.

Background: The $\beta$ decays of ${}^3$H and ${}^6$He can play an important role in testing nuclear wave-function calculations and fixing low-energy constants in effective-field theory approaches. However, there exists a large discrepancy between previous measurements of the ${}^6$He half-life.

Purpose: Our measurement aims at resolving this long-standing discrepancy in the ${}^6$He half-life and providing a reliable $ft$ value and Gamow-Teller matrix element for comparison with theoretical ab initio calculations.

Method: We measured the ${}^6$He half-life by counting the $\beta$-decay electrons with two scintillator detectors operating in coincidence.

Results: The measured ${}^6$He half-life is $806.89\pm 0.{11}_{\mathrm{stat}}{}_{-0.19}^{+0.23}{}_{\mathrm{syst}}$ ms corresponding to a relative precision of $3\times {10}^{-4}$. Calculating the statistical rate function we determined the $ft$ value to be $803.{04}_{-0.23}^{+0.26}$ s.

Conclusions: Our result resolves the previous discrepancy by providing a higher-precision result with careful analysis of potential systematic uncertainties. The result provides a reliable basis for future precision comparisons with ab initio calculations.