Showing papers in "Physical Review C in 2010"

Composition and thermodynamics of nuclear matter with light clusters

Abstract: We investigate nuclear matter at a finite temperature and density, including the formation of light clusters up to the $\ensuremath{\alpha}$ particle ($1\ensuremath{\leqslant}A\ensuremath{\leqslant}4$). The novel feature of this work is to include the formation of clusters as well as their dissolution due to medium effects in a systematic way using two many-body theories: a microscopic quantum statistical (QS) approach and a generalized relativistic mean-field (RMF) model. Nucleons and clusters are modified by medium effects. While the nucleon quasiparticle properties are determined within the RMF model from the scalar and vector self-energies, the cluster binding energies are reduced because of Pauli blocking shifts calculated in the QS approach. Both approaches reproduce the limiting cases of nuclear statistical equilibrium (NSE) at low densities and cluster-free nuclear matter at high densities. The treatment of the cluster dissociation is based on the Mott effect due to Pauli blocking, implemented in slightly different ways in the QS and the generalized RMF approaches. This leads to somewhat different results in the intermediate density range of about ${10}^{\ensuremath{-}3}$ to ${10}^{\ensuremath{-}1} \phantom{\rule{0.3em}{0ex}}{\mathrm{fm}}^{\ensuremath{-}3}$, which gives an estimate of the present accuracy of the theoretical predictions. We compare the numerical results of these models for cluster abundances and thermodynamics in the region of medium excitation energies with temperatures $T\ensuremath{\leqslant}20$ MeV and baryon number densities from zero to a few times saturation density. The effects of cluster formation on the liquid-gas phase transition and on the density dependence of the symmetry energy are studied. It is demonstrated that the parabolic approximation for the asymmetry dependence of the nuclear equation of state breaks down at low temperatures and at subsaturation densities because of cluster formation. Comparison is made with other theoretical approaches, in particular, those that are commonly used in astrophysical calculations. The results are relevant for heavy-ion collisions and astrophysical applications.

Collision geometry fluctuations and triangular flow in heavy-ion collisions

Abstract: We introduce the concepts of participant triangularity and triangular flow in heavy-ion collisions, analogous to the definitions of participant eccentricity and elliptic flow. The participant triangularity characterizes the triangular anisotropy of the initial nuclear overlap geometry and arises from event-by-event fluctuations in the participant-nucleon collision points. In studies using a multiphase transport model (AMPT), a triangular flow signal is observed that is proportional to the participant triangularity and corresponds to a large third Fourier coefficient in two-particle azimuthal correlation functions. Using two-particle azimuthal correlations at large pseudorapidity separations measured by the PHOBOS and STAR experiments, we show that this Fourier component is also present in data. Ratios of the second and third Fourier coefficients in data exhibit similar trends as a function of centrality and transverse momentum as in AMPT calculations. These findings suggest a significant contribution of triangular flow to the ridge and broad away-side features observed in data. Triangular flow provides a new handle on the initial collision geometry and collective expansion dynamics in heavy-ion collisions.

Nuclear Energy Density Optimization

Abstract: We carry out state-of-the-art optimization of a nuclear energy density of Skyrme type in the framework of the Hartree-Fock-Bogoliubov theory. The particle-hole and particle-particle channels are optimized simultaneously, and the experimental data set includes both spherical and deformed nuclei. The new model-based, derivative-free optimization algorithm used in this work has been found to be significantly better than standard optimization methods in terms of reliability, speed, accuracy, and precision. The resulting parameter set unedf0 results in good agreement with experimental masses, radii, and deformations and seems to be free of finite-size instabilities. An estimate of the reliability of the obtained parameterization is given, based on standard statistical methods. We discuss new physics insights offered by the advanced covariance analysis.

Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XII. Stiffness and stability of neutron-star matter

Abstract: We construct three new Hartree-Fock-Bogoliubov (HFB) mass models, labeled HFB-19, HFB20, and HFB-21, with unconventional Skyrme forces containing t4 and t5 terms, i.e., densitydependent generalizations of the usual t1 and t2 terms, respectively. The new forces underlying these models are fitted respectively to three different realistic equations of state of neutron matter for which the density dependence of the symmetry energy ranges from the very soft to the very stiff, reflecting thereby our present lack of complete knowledge of the high-density behavior of nuclear matter. All unphysical instabilities of nuclear matter, including the transition to a polarized state in neutron-star matter, are eliminated with the new forces. At the same time the new models fit essentially all the available mass data with rms deviations of 0.58 MeV and give the same high quality fits to measured charge radii that we obtained in earlier models with conventional Skyrme forces. Being constrained by neutron matter, these new mass models, which all give similar extrapolations out to the neutron drip line, are highly appropriate for studies of the r-process and the outer crust of neutron stars. Moreover, the underlying forces, labeled BSk19, BSk20 and BSk21, respectively, are well adapted to the study of the inner crust and core of neutron stars. The new family of Skyrme forces thus opens the way to a unified description of all regions of neutron stars.

New parametrization for the nuclear covariant energy density functional with a point-coupling interaction

Abstract: A new parametrization PC-PK1 for the nuclear covariant energy density functional with nonlinear point-coupling interaction is proposed by fitting to observables of 60 selected spherical nuclei, including the binding energies, charge radii, and empirical pairing gaps. The success of PC-PK1 is illustrated in the description of infinite nuclear matter and finite nuclei including the ground-state and low-lying excited states. In particular, PC-PK1 provides a good description for the isospin dependence of binding energy along either the isotopic or the isotonic chain, which makes it reliable for application in exotic nuclei. The predictive power of PC-PK1 is also illustrated for the nuclear low-lying excitation states in a five-dimensional collective Hamiltonian in which the parameters are determined by constrained calculations for triaxial shapes.

(3+1)D hydrodynamic simulation of relativistic heavy-ion collisions

Abstract: We present music, an implementation of the Kurganov-Tadmor algorithm for relativistic 3+1 dimensional fluid dynamics in heavy-ion collision scenarios. This Riemann-solver-free, second-order, high-resolution scheme is characterized by a very small numerical viscosity and its ability to treat shocks and discontinuities very well. We also incorporate a sophisticated algorithm for the determination of the freeze-out surface using a three dimensional triangulation of the hypersurface. Implementing a recent lattice based equation of state, we compute ${p}_{T}$-spectra and pseudorapidity distributions for Au+Au collisions at $\sqrt{s}=200 \mathrm{GeV}$ and present results for the anisotropic flow coefficients ${v}_{2}$ and ${v}_{4}$ as a function of both ${p}_{T}$ and pseudorapidity $\ensuremath{\eta}$. We were able to determine ${v}_{4}$ with high numerical precision, finding that it does not strongly depend on the choice of initial condition or equation of state.

Structure of even-even nuclei using a mapped collective Hamiltonian and the D1S Gogny interaction

Abstract: A systematic study of low energy nuclear structure at normal deformation is carried out using the Hartree-Fock-Bogoliubov theory extended by the generator coordinate method and mapped onto a five-dimensional collective quadrupole Hamiltonian. Results obtained with the Gogny D1S interaction are presented from drip line to drip line for even-even nuclei with proton numbers $Z=10$ to $Z=110$ and neutron numbers $N\ensuremath{\leqslant}200$. The properties calculated for the ground states are their charge radii, two-particle separation energies, correlation energies, and the intrinsic quadrupole shape parameters. For the excited spectroscopy, the observables calculated are the excitation energies and quadrupole as well as monopole transition matrix elements. We examine in this work the yrast levels up to $J=6$, the lowest excited ${0}^{+}$ states, and the two next yrare ${2}^{+}$ states. The theory is applicable to more than $90%$ of the nuclei that have tabulated measurements. We assess its accuracy by comparison with experiments on all applicable nuclei where the systematic tabulations of the data are available. We find that the predicted radii have an accuracy of $0.6%$, much better than can be achieved with a smooth phenomenological description. The correlation energy obtained from the collective Hamiltonian gives a significant improvement to the accuracy of the two-particle separation energies and to their differences, the two-particle gaps. Many of the properties depend strongly on the intrinsic deformation and we find that the theory is especially reliable for strongly deformed nuclei. The distribution of values of the collective structure indicator ${R}_{42}=E({4}_{1}^{+})/E({2}_{1}^{+})$ has a very sharp peak at the value 10/3, in agreement with the existing data. On average, the predicted excitation energy and transition strength of the first ${2}^{+}$ excitation are $12%$ and $22%$ higher than experiment, respectively, with variances of the order of $40--50%$. The theory gives a good qualitative account of the range of variation of the excitation energy of the first excited ${0}^{+}$ state, but the predicted energies are systematically $50%$ high. The calculated yrare ${2}^{+}$ states show a clear separation between $\ensuremath{\gamma}$ and $\ensuremath{\beta}$ excitations, and the energies of the ${2}^{+}$ $\ensuremath{\gamma}$ vibrations accord well with experiment. The character of the ${0}_{2}^{+}$ state is interpreted as shape coexistence or $\ensuremath{\beta}$-vibrational excitations on the basis of relative quadrupole transition strengths. Bands are predicted with the properties of $\ensuremath{\beta}$ vibrations for many nuclei having ${R}_{42}$ values corresponding to axial rotors, but the shape coexistence phenomenon is more prevalent. The data set of the calculated properties of 1712 even-even nuclei, including spectroscopic properties for 1693 of them, are provided in CEA Web site and EPAPS repository with this article [1].

Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy-ion collisions

Abstract: Parity (P)-odd domains, corresponding to nontrivial topological solutions of the QCD vacuum, might be created during relativistic heavy-ion collisions. These domains are predicted to lead to charge separation of quarks along the orbital momentum of the system created in noncentral collisions. To study this effect, we investigate a three-particle mixed-harmonics azimuthal correlator which is a P-even observable, but directly sensitive to the charge-separation effect. We report measurements of this observable using the STAR detector in Au + Au and Cu + Cu collisions at root s(NN) = 200 and 62 GeV. The results are presented as a function of collision centrality, particle separation in rapidity, and particle transverse momentum. A signal consistent with several of the theoretical expectations is detected in all four data sets. We compare our results to the predictions of existing event generators and discuss in detail possible contributions from other effects that are not related to P violation.

Chiral three-nucleon forces and neutron matter

Abstract: We calculate the properties of neutron matter and highlight the physics of chiral three-nucleon forces. For neutrons, only the long-range $2\ensuremath{\pi}$-exchange interactions of the leading chiral three-nucleon forces contribute, and we derive density-dependent two-body interactions by summing the third particle over occupied states in the Fermi sea. Our results for the energy suggest that neutron matter is perturbative at nuclear densities. We study in detail the theoretical uncertainties of the neutron matter energy, provide constraints for the symmetry energy and its density dependence, and explore the impact of chiral three-nucleon forces on the $S$-wave superfluid pairing gap.

Detailed measurement of the e+e- pair continuum in p+p and Au+Au collisions at √sNN = 200 GeV and implications for direct photon production

Abstract: PHENIX has measured the e(+)e(-) pair continuum in root s(NN) = 200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e(+)e(-) yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the phi and the J/psi meson, the yield is consistent with expectations from correlated c (c) over bar production, although other mechanisms are not ruled out. In the low-mass region, below the phi, the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7 +/- 0.4(stat) +/- 1.5(syst) +/- 0.9(model). At low mass (m(ee) < 0.3 GeV/c(2)) and high p(T) (1 < p(T) < 5 GeV/c) an enhanced e(+)e(-) pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central Au+Au collisions, the excess of the direct photon yield over the p+p is exponential in p(T), with inverse slope T = 221 +/- 19(stat) +/- 19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T-init similar or equal to 300-600 MeV at times of 0.6-0.15 fm/c after the collision are in qualitative agreement with the direct photon data in Au+Au. For low p(T) < 1 GeV/c the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of T similar or equal to 100 MeV. Theoretical models underpredict the low-mass, low-p(T) enhancement.

Triangular flow in hydrodynamics and transport theory

Abstract: In ultrarelativistic heavy-ion collisions, the Fourier decomposition of the relative azimuthal angle, $\ensuremath{\Delta}\ensuremath{\phi}$, distribution of particle pairs yields a large $\mathrm{cos}(3\ensuremath{\Delta}\ensuremath{\phi})$ component, extending to large rapidity separations $\ensuremath{\Delta}\ensuremath{\eta}g1$. This component captures a significant portion of the ridge and shoulder structures in the $\ensuremath{\Delta}\ensuremath{\phi}$ distribution, which have been observed after contributions from elliptic flow are subtracted. An average finite triangularity owing to event-by-event fluctuations in the initial matter distribution, followed by collective flow, naturally produces a $\mathrm{cos}(3\ensuremath{\Delta}\ensuremath{\phi})$ correlation. Using ideal and viscous hydrodynamics and transport theory, we study the physics of triangular (${v}_{3}$) flow in comparison to elliptic (${v}_{2}$), quadrangular (${v}_{4}$), and pentagonal (${v}_{5}$) flow. We make quantitative predictions for ${v}_{3}$ at RHIC and LHC as a function of centrality and transverse momentum. Our results for the centrality dependence of ${v}_{3}$ show a quantitative agreement with data extracted from previous correlation measurements by the STAR collaboration. This study supports previous results on the importance of triangular flow in the understanding of ridge and shoulder structures. Triangular flow is found to be a sensitive probe of initial geometry fluctuations and viscosity.

Information content of a new observable: The case of the nuclear neutron skin

Abstract: We address two questions pertaining to the uniqueness and usefulness of a new observable: (i) Considering the current theoretical knowledge, what novel information does new measurement bring in? (ii) How can new data reduce uncertainties of current theoretical models? We illustrate these points by studying the radius of the neutron distribution of a heavy nucleus, a quantity related to the equation of state for neutron matter that determines properties of nuclei and neutron stars. By systematically varying the parameters of two theoretical models and studying the resulting confidence ellipsoid, we quantify the relationships between the neutron skin and various properties of finite nuclei and infinite nuclear matter. Using the covariance analysis, we identify observables and pseudo-observables that correlate, and do not correlate, with the neutron skin. By adding the information on the neutron radius to the pool of observables determining the energy functional, we show how precise experimental determination of the neutron radius in $^{208}\mathrm{Pb}$ would reduce theoretical uncertainties on the neutron matter equation of state.

Low-energy-threshold analysis of the Phase I and Phase II data sets of the Sudbury Neutrino Observatory

Abstract: Results are reported from a joint analysis of Phase I and Phase II data from the Sudbury Neutrino Observatory. The effective electron kinetic energy threshold used is Teff=3.5 MeV, the lowest analysis threshold yet achieved with water Cherenkov detector data. In units of 106 cm-2 s-1, the total flux of active-flavor neutrinos from 8B decay in the Sun measured using the neutral current (NC) reaction of neutrinos on deuterons, with no constraint on the 8B neutrino energy spectrum, is found to be FNC=5.140-0.158+0.160(stat)-0.117+0.132(syst). These uncertainties are more than a factor of 2 smaller than previously published results. Also presented are the spectra of recoil electrons from the charged current reaction of neutrinos on deuterons and the elastic scattering of electrons. A fit to the Sudbury Neutrino Observatory data in which the free parameters directly describe the total 8B neutrino flux and the energy-dependent e survival probability provides a measure of the total 8B neutrino flux F8B=5.046-0.152+0.159(stat)-0.123+0.107(syst). Combining these new results with results of all other solar experiments and the KamLAND reactor experiment yields best-fit values of the mixing parameters of 12=34.06-0.84+1.16 degrees and m212=7.59-0.21+0.2010-5 eV2. The global value of 8B is extracted to a precision of -2.95+2.38%. In a three-flavor analysis the best fit value of sin213 is 2.00-1.63+2.0910-2. This implies an upper bound of sin213<0.057 (95% C.L.).

Event-by-Event Simulation of the Three-Dimensional Hydrodynamic Evolution from Flux Tube Initial Conditions in Ultrarelativistic Heavy Ion Collisions

Abstract: We present a sophisticated treatment of the hydrodynamic evolution of ultrarelativistic heavy ion collisions, based on the following features: initial conditions obtained from a flux tube approach, compatible with the string model and the color glass condensate picture; an event-by-event procedure, taking into the account the highly irregular space structure of single events, being experimentally visible via so-called ridge structures in two-particle correlations; the use of an efficient code for solving the hydrodynamic equations in $3+1$ dimensions, including the conservation of baryon number, strangeness, and electric charge; the employment of a realistic equation of state, compatible with lattice gauge results; the use of a complete hadron resonance table, making our calculations compatible with the results from statistical models; and a hadronic cascade procedure after hadronization from the thermal matter at an early time.

Identified particle production, azimuthal anisotropy, and interferometry measurements in Au plus Au collisions at root s(NN)=9.2 GeV

Abstract: We present the first measurements of identified hadron production, azimuthal anisotropy, and pion interferometry from Au + Au collisions below the nominal injection energy at the BNL Relativistic Heavy-Ion Collider (RHIC) facility. The data were collected using the large acceptance solenoidal tracker at RHIC (STAR) detector at root s(NN) = 9.2 GeV from a test run of the collider in the year 2008. Midrapidity results on multiplicity density dN/dy in rapidity y, average transverse momentum , particle ratios, elliptic flow, and Hanbury-Brown-Twiss (HBT) radii are consistent with the corresponding results at similar root s(NN) from fixed-target experiments. Directed flow measurements are presented for both midrapidity and forward-rapidity regions. Furthermore the collision centrality dependence of identified particle dN/dy, , and particle ratios are discussed. These results also demonstrate that the capabilities of the STAR detector, although optimized for root s(NN) = 200 GeV, are suitable for the proposed QCD critical-point search and exploration of the QCD phase diagram at RHIC.

Equation of state of a dense and magnetized fermion system

Abstract: The equation of state of a system of fermions in a uniform magnetic field is obtained in terms of the thermodynamic quantities of the theory by using functional methods. It is shown that the breaking of the O(3) rotational symmetry by the magnetic field results in a pressure anisotropy, which leads to the distinction between longitudinal- and transverse-to-the-field pressures. A criterion to find the threshold field at which the asymmetric regime becomes significant is discussed. This threshold magnetic field is shown to be the same as the one required for the pure field contribution to the energy and pressures to be of the same order as the matter contribution. A graphical representation of the field-dependent anisotropic equation of state of the fermion system is given. Estimates of the upper limit for the inner magnetic field in self-bound stars, as well as in gravitationally bound stars with inhomogeneous distributions of mass and magnetic fields, are also found.

Relativistic effective interaction for nuclei, giant resonances, and neutron stars

Abstract: Nuclear effective interactions are useful tools in astrophysical applications especially if one can guide the extrapolations to the extremes regions of isospin and density that are required to simulate dense, neutron-rich systems. Isospin extrapolations may be constrained in the laboratory by measuring the neutron skin thickness of a heavy nucleus, such as $^{208}\mathrm{Pb}$. Similarly, future observations of massive neutron stars will constrain the extrapolations to the high-density domain. In this contribution we introduce a new relativistic effective interaction that is simultaneously constrained by the properties of finite nuclei, their collective excitations, and neutron-star properties. By adjusting two of the empirical parameters of the theory, one can efficiently tune the neutron skin thickness of $^{208}\mathrm{Pb}$ and the maximum neutron-star mass. We illustrate this procedure in response to the recent interpretation of x-ray observations by Steiner, Lattimer, and Brown that suggests that the FSUGold effective interaction predicts neutron-star radii that are too large and a maximum stellar mass that is too small. The new effective interaction is fitted to a neutron skin thickness in $^{208}\mathrm{Pb}$ of only ${R}_{n}\ensuremath{-}{R}_{p}=0.16$ fm and yields a moderately large maximum neutron-star mass of 1.94 ${M}_{\ensuremath{\bigodot}}$.

Density slope of the nuclear symmetry energy from the neutron skin thickness of heavy nuclei

Abstract: Expressing explicitly the parameters of the standard Skyrme interaction in terms of the macroscopic properties of asymmetric nuclear matter, we show in the Skyrme-Hartree-Fock approach that unambiguous correlations exist between observables of finite nuclei and nuclear matter properties. We find that existing data on neutron skin thickness $\ensuremath{\Delta}{r}_{\mathit{np}}$ of Sn isotopes give an important constraint on the symmetry energy ${E}_{\mathrm{sym}}({\ensuremath{\rho}}_{0})$ and its density slope $L$ at saturation density ${\ensuremath{\rho}}_{0}$. Combining these constraints with those from recent analyses of isospin diffusion and the double neutron/proton ratio in heavy-ion collisions at intermediate energies leads to a more stringent limit on $L$ approximately independent of ${E}_{\mathrm{sym}}({\ensuremath{\rho}}_{0})$. The implication of these new constraints on the $\ensuremath{\Delta}{r}_{\mathit{np}}$ of $^{208}\mathrm{Pb}$ as well as the core-crust transition density and pressure in neutron stars is discussed.

Constraints on the symmetry energy and on neutron skins from the pygmy resonances in 68Ni and 132Sn

Abstract: Correlations between the behavior of the nuclear symmetry energy, the neutron skins, and the percentage of energy-weighted sum rule (EWSR) exhausted by the pygmy dipole resonance (PDR) in $^{68}\mathrm{Ni}$ and $^{132}\mathrm{Sn}$ are investigated by using different random phase approximation (RPA) models for the dipole response, based on a representative set of Skyrme effective forces plus meson-exchange effective Lagrangians. A comparison with the experimental data has allowed us to constrain the value of the derivative of the symmetry energy at saturation. The neutron skin radius is deduced under this constraint.

Production of radioactive isotopes through cosmic muon spallation in KamLAND

Abstract: Radioactive isotopes produced through cosmic muon spallation are a background for rare-event detection in ν detectors, double-β-decay experiments, and dark-matter searches. Understanding the nature of cosmogenic backgrounds is particularly important for future experiments aiming to determine the pep and CNO solar neutrino fluxes, for which the background is dominated by the spallation production of ^(11)C. Data from the Kamioka liquid-scintillator antineutrino detector (KamLAND) provides valuable information for better understanding these backgrounds, especially in liquid scintillators, and for checking estimates from current simulations based upon MUSIC, FLUKA, and GEANT4. Using the time correlation between detected muons and neutron captures, the neutron production yield in the KamLAND liquid scintillator is measured to be Y_n=(2.8±0.3)×10^(-4) μ^(-1) g^(-1) cm^2. For other isotopes, the production yield is determined from the observed time correlation related to known isotope lifetimes. We find some yields are inconsistent with extrapolations based on an accelerator muon beam experiment.

Low-density neutron matter

Abstract: The properties of low-density neutron matter are important for the understanding of neutron star crusts and the exterior of large neutron-rich nuclei. We examine various properties of dilute neutron matter using quantum Monte Carlo methods, with $s$- and $p$-wave terms in the interaction. Our results provide a smooth evolution of the equation of state and pairing gap from extremely small densities, where analytic expressions are available, up to the strongly interacting regime probed experimentally and described theoretically in cold atomic systems, where ${k}_{F}\ensuremath{\approx}0.5 {\text{fm}}^{\ensuremath{-}1}$ and the pairing gap becomes of the order of magnitude of the Fermi energy. We also present results for the momentum distribution and pair distributions, displaying the same evolution from weak to strong coupling. Combined with previous quantum Monte Carlo and other calculations at moderate densities, these results provide strong constraints on the neutron matter equation of state up to saturation densities.

Ab initio coupled-cluster approach to nuclear structure with modern nucleon-nucleon interactions

Abstract: We perform coupled-cluster calculations for the doubly magic nuclei $^{4}\mathrm{He}$, $^{16}\mathrm{O}$, $^{40,48}\mathrm{Ca}$, for neutron-rich isotopes of oxygen and fluorine, and employ ``bare'' and secondary renormalized nucleon-nucleon interactions. For the nucleon-nucleon interaction from chiral effective field theory at order next-to-next-to-next-to leading order, we find that the coupled-cluster approximation including triples corrections binds nuclei within 0.4 MeV per nucleon compared to data. We employ interactions from a resolution-scale dependent similarity renormalization group transformations and assess the validity of power counting estimates in medium-mass nuclei. We find that the missing contributions from three-nucleon forces are consistent with these estimates. For the unitary correlator model potential, we find a slow convergence with respect to increasing the size of the model space. For the $G$-matrix approach, we find a weak dependence of ground-state energies on the starting energy combined with a rather slow convergence with respect to increasing model spaces. We also analyze the center-of-mass problem and present a practical and efficient solution.

AZURE: An R-matrix code for nuclear astrophysics

Abstract: The paper describes a multilevel, multichannel R-matrix code, AZURE, for applications in nuclear astrophysics. The code allows simultaneous analysis and extrapolation of low-energy particle scattering, capture, and reaction cross sections of relevance to stellar hydrogen, helium, and carbon burning. The paper presents a summary of R-matrix theory, code description, and a number of applications to demonstrate the applicability and versatility of AZURE.

Neutrino and antineutrino quasielastic interactions with nuclei

Abstract: We investigate the interaction of neutrinos and antineutrinos with nuclei. We explore, in particular, the role played by multinucleon excitations, which can contaminate the quasielastic cross section. For neutrinos the multinucleon term produces a sizable increase in the quasielastic cross section. Part of the effect arises from tensor correlations. For antineutrinos this influence is smaller, owing to the axial-vector interference, which increases the relative importance of the terms that are not affected by these multinucleon excitations.

Precise half-life values for two-neutrino double- β decay

Abstract: All existing positive results on two-neutrino double-$\ensuremath{\beta}$ decay in different nuclei were analyzed. Using the procedure recommended by the Particle Data Group, weighted average values for half-lives of $^{48}\mathrm{Ca}$, $^{76}\mathrm{Ge}$, $^{82}\mathrm{Se}$, $^{96}\mathrm{Zr}$, $^{100}\mathrm{Mo}$, $^{100}\mathrm{Mo}$-$^{100}\mathrm{Ru}$ (${0}_{1}^{+}$), $^{116}\mathrm{Cd}$, $^{130}\mathrm{Te}$, $^{150}\mathrm{Nd}$, $^{150}\mathrm{Nd}$-$^{150}\mathrm{Sm}$ (${0}_{1}^{+}$), and $^{238}\mathrm{U}$ were obtained. Existing geochemical data were analyzed, and recommended values for half-lives of $^{128}\mathrm{Te}$, $^{130}\mathrm{Te}$, and $^{130}\mathrm{Ba}$ are proposed. Given the measured half-life values, nuclear matrix elements were calculated. I recommend the use of these results as the most currently reliable values for the half-lives and nuclear matrix elements.

Hamiltonian Light-Front Field Theory in a Basis Function Approach

Abstract: Hamiltonian light-front quantum field theory constitutes a framework for the nonperturbative solution of invariant masses and correlated parton amplitudes of self-bound systems. By choosing the light-front gauge and adopting a basis function representation, a large, sparse, Hamiltonian matrix for mass eigenstates of gauge theories is obtained that is solvable by adapting the ab initio no-core methods of nuclear many-body theory. Full covariance is recovered in the continuum limit, the infinite matrix limit. There is considerable freedom in the choice of the orthonormal and complete set of basis functions with convenience and convergence rates providing key considerations. Here we use a two-dimensional harmonic oscillator basis for transverse modes that corresponds with eigensolutions of the soft-wall anti-de Sitter/quantum chromodynamics (AdS/QCD) model obtained from light-front holography. We outline our approach and present illustrative features of some noninteracting systems in a cavity. We illustrate the first steps toward solving quantum electrodynamics (QED) by obtaining the mass eigenstates of an electron in a cavity in small basis spaces and discuss the computational challenges.

Translation of collision geometry fluctuations into momentum anisotropies in relativistic heavy-ion collisions

Abstract: We develop a systematic framework for the study of the initial collision geometry fluctuations in relativistic heavy-ion collisions and investigate how they evolve through different stages of the fireball history and translate into final-particle momentum anisotropies. We find in our event-by-event analysis that only the few lowest momentum anisotropy parameters survive after the hydrodynamical evolution of the system. The geometry of the produced medium is found to be affected by the pre-equilibrium evolution of the medium and the thermal smearing of the discretized event-by-event initial conditions, both of which tend to smear out the spatial anisotropies. We find such effects to be more prominent for higher moments than for lower moments. The correlations between odd and even spatial anisotropy parameters during the pre-equilibrium expansion are quantitatively studied and found to be small. Our study provides a theoretical foundation for the understanding of initial-state fluctuations and the collective expansion dynamics in relativistic heavy-ion collisions.

Neutron halo in deformed nuclei

Abstract: Halo phenomena in deformed nuclei are investigated within a deformed relativistic Hartree Bogoliubov (DRHB) theory. These weakly bound quantum systems present interesting examples for the study of the interdependence between the deformation of the core and the particles in the halo. Contributions of the halo, deformation effects, and large spatial extensions of these systems are described in a fully self-consistent way by the DRHB equations in a spherical Woods-Saxon basis with the proper asymptotic behavior at a large distance from the nuclear center. Magnesium and neon isotopes are studied and detailed results are presented for the deformed neutron-rich and weakly bound nucleus (44)Mg. The core of this nucleus is prolate, but the halo has a slightly oblate shape. This indicates a decoupling of the halo orbitals from the deformation of the core. The generic conditions for the occurrence of this decoupling effects are discussed.

Neutron density distributions of Pb 204 , 206 , 208 deduced via proton elastic scattering at E p = 295 MeV

Abstract: Cross sections and analyzing powers for polarized proton elastic scattering from $^{58}\mathrm{Ni}$, and $^{204,206,208}\mathrm{Pb}$ were measured at intermediate energy ${E}_{p}=295$ MeV. An effective relativistic Love-Franey interaction is tuned to reproduce $^{58}\mathrm{Ni}$ scattering data within the framework of the relativistic impulse approximation. The neutron densities of the lead isotopes are deduced using model-independent sum-of-Gaussians distributions. Their error envelopes are estimated by a new ${\ensuremath{\chi}}^{2}$ criterion including uncertainties associated with the reaction model. The systematic behaviors of extracted error envelopes of the neutron density distributions in $^{204,206,208}\mathrm{Pb}$ are presented. The extracted neutron and proton density distribution of $^{208}\mathrm{Pb}$ gives a neutron skin thickness of $\ensuremath{\Delta}{r}_{\mathit{np}}={0.211}_{\ensuremath{-}0.063}^{+0.054}$ fm.