Showing papers in "Physical Review C in 2009"

Systematic measurements of identified particle spectra in pp, d+Au, and Au+Au collisions at the star detector.

Abstract: Identified charged-particle spectra of pi(+/-), K(+/-), p, and (p) over bar at midrapidity (vertical bar y vertical bar < 0.1) measured by the dE/dx method in the STAR (solenoidal tracker at the BNL Relativistic Heavy Ion Collider) time projection chamber are reported for pp and d + Au collisions at root s(NN) = 200 GeV and for Au + Au collisions at 62.4, 130, and 200 GeV. Average transverse momenta, total particle production, particle yield ratios, strangeness, and baryon production rates are investigated as a function of the collision system and centrality. The transverse momentum spectra are found to be flatter for heavy particles than for light particles in all collision systems; the effect is more prominent for more central collisions. The extracted average transverse momentum of each particle species follows a trend determined by the total charged-particle multiplicity density. The Bjorken energy density estimate is at least several GeV/fm(3) for a formation time less than 1 fm/c. A significantly larger net-baryon density and a stronger increase of the net-baryon density with centrality are found in Au + Au collisions at 62.4 GeV than at the two higher energies. Antibaryon production relative to total particle multiplicity is found to be constant over centrality, but increases with the collision energy. Strangeness production relative to total particle multiplicity is similar at the three measured RHIC energies. Relative strangeness production increases quickly with centrality in peripheral Au + Au collisions, to a value about 50% above the pp value, and remains rather constant in more central collisions. Bulk freeze-out properties are extracted from thermal equilibrium model and hydrodynamics-motivated blast-wave model fits to the data. Resonance decays are found to have little effect on the extracted kinetic freeze-out parameters because of the transverse momentum range of our measurements. The extracted chemical freeze-out temperature is constant, independent of collision system or centrality; its value is close to the predicted phase-transition temperature, suggesting that chemical freeze-out happens in the vicinity of hadronization and the chemical freeze-out temperature is universal despite the vastly different initial conditions in the collision systems. The extracted kinetic freeze-out temperature, while similar to the chemical freeze-out temperature in pp, d + Au, and peripheral Au + Au collisions, drops significantly with centrality in Au + Au collisions, whereas the extracted transverse radial flow velocity increases rapidly with centrality. There appears to be a prolonged period of particle elastic scatterings from chemical to kinetic freeze-out in central Au + Au collisions. The bulk properties extracted at chemical and kinetic freeze-out are observed to evolve smoothly over the measured energy range, collision systems, and collision centralities.

Measurement of the solar neutrino capture rate with gallium metal. III: Results for the 2002--2007 data-taking period

Abstract: The Russian-American experiment SAGE began to measure the solar neutrino capture rate with a target of gallium metal in December 1989. Measurements have continued with only a few brief interruptions since that time. In this article we present the experimental improvements in SAGE since its last published data summary in December 2001. Assuming the solar neutrino production rate was constant during the period of data collection, combined analysis of 168 extractions through December 2007 gives a capture rate of solar neutrinos with energy more than 233 keV of $65.{4}_{\ensuremath{-}3.0}^{+3.1}$ (stat) ${}_{\ensuremath{-}2.8}^{+2.6}$ (syst) SNU. The weighted average of the results of all three Ga solar neutrino experiments, SAGE, Gallex, and GNO, is now $66.1\ifmmode\pm\else\textpm\fi{}3.1$ SNU, where statistical and systematic uncertainties have been combined in quadrature. During the recent period of data collection a new test of SAGE was made with a reactor-produced $^{37}\mathrm{Ar}$ neutrino source. The ratio of observed to calculated rates in this experiment, combined with the measured rates in the three prior $^{51}\mathrm{Cr}$ neutrino-source experiments with Ga, is $0.87\ifmmode\pm\else\textpm\fi{}0.05$. A probable explanation for this low result is that the cross section for neutrino capture by the two lowest-lying excited states in $^{71}\mathrm{Ge}$ has been overestimated. If we assume these cross sections are zero, then the standard solar model including neutrino oscillations predicts a total capture rate in Ga in the range of 63 SNU to 66 SNU with an uncertainty of about 4%, in good agreement with experiment. We derive the current value of the neutrino flux produced in the Sun by the proton-proton fusion reaction to be ${\ensuremath{\phi}}_{\mathit{pp}}^{\ensuremath{\bigodot}}=(6.0\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{10}/({\mathrm{cm}}^{2} \mathrm{s})$, which agrees well with the $\mathit{pp}$ flux predicted by the standard solar model. Finally, we make several tests and show that the data are consistent with the assumption that the solar neutrino production rate is constant in time.

Superallowed 0 + →0 + nuclear β decays: A new survey with precision tests of the conserved vector current hypothesis and the standard model

Abstract: A new critical survey is presented of all half-life, decay-energy, and branching-ratio measurements related to 20 superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}\ensuremath{\beta}$ decays. Compared with our last review, there are numerous improvements: First, we have added 27 recently published measurements and eliminated 9 references, either because they have been superseded by much more precise modern results or because there are now reasons to consider them fatally flawed; of particular importance, the new data include a number of high-precision Penning-trap measurements of decay energies. Second, we have used the recently improved isospin symmetry-breaking corrections, which were motivated by these new Penning-trap results. Third, our calculation of the statistical rate function $f$ now accounts for possible excitation in the daughter atom, a small effect but one that merits inclusion at the present level of experimental precision. Finally, we have re-examined the systematic uncertainty associated with the isospin symmetry-breaking corrections by evaluating the radial-overlap correction using Hartree-Fock radial wave functions and comparing the results with our earlier calculations, which used Saxon-Woods wave functions; the provision for systematic uncertainty has been changed as a consequence. The new ``corrected'' $\mathcal{F}t$ values are impressively constant and their average, when combined with the muon lifetime, yields the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, ${V}_{\mathit{ud}}=0.97425\ifmmode\pm\else\textpm\fi{}0.00022$. The unitarity test on the top row of the matrix becomes $|{V}_{\mathit{ud}}|{}^{2}+|{V}_{\mathit{us}}|{}^{2}+|{V}_{\mathit{ub}}|{}^{2}=0.99995\ifmmode\pm\else\textpm\fi{}0.00061$. Both ${V}_{\mathit{ud}}$ and the unitarity sum have significantly reduced uncertainties compared with our previous survey, although the new value of ${V}_{\mathit{ud}}$ is statistically consistent with the old one. From these data we also set limits on the possible existence of scalar interactions, right-hand currents, and extra $Z$ bosons. Finally, we discuss the priorities for future theoretical and experimental work with the goal of making the CKM unitarity test even more definitive.

Variations on a theme by Skyrme: A systematic study of adjustments of model parameters

Abstract: We present a survey of the phenomenological adjustment of the parameters of the Skyrme-Hartree-Fock (SHF) model for a self-consistent description of nuclear structure and low-energy excitations. A large sample of reliable input data from nuclear bulk properties (energy, radii, surface thickness) is selected guided by the criterion that ground-state correlations should remain small. Least-squares fitting techniques are used to determine the SHF parameters that accommodate best the given input data. The question of the predictive value of the adjustment is scrutinized by performing systematic variations with respect to chosen nuclear matter properties (incompressibility, effective mass, symmetry energy, and sum-rule enhancement factor). We find that the ground-state data, although representing a large sample, leave a broad range of choices, i.e., a broad range of nuclear matter properties. Information from giant resonances is added to pin down more precisely the open features. We then apply the set of newly adjusted parametrizations to several more detailed observables such as neutron skin, isotope shifts, and super-heavy elements. The techniques of least-squares fitting provide safe estimates for the uncertainties of such extrapolations. The systematic variation of forces allows to disentangle the various influences on a given observable and to estimate the predictive value of the SHF model. The results depend very much on the observable under consideration.

Heavy-element fission barriers

Abstract: We present calculations of fission properties for heavy elements. The calculations are based on the macroscopic-microscopic finite-range liquid-drop model with a 2002 parameter set. For each nucleus we have calculated the potential energy in three different shape parametrizations: (1) for 5 009 325 different shapes in a five-dimensional deformation space given by the three-quadratic-surface parametrization, (2) for 10 850 different shapes in a three-dimensional deformation space spanned by epsilon(2), epsilon(4), and gamma in the Nilsson perturbed-spheroid parametrization, supplemented by a densely spaced grid in epsilon(2), epsilon(3), epsilon(4), and epsilon(6) for axially symmetric deformations in the neighborhood of the ground state, and (3) an axially symmetric multipole expansion of the shape of the nuclear surface using beta(2), beta(3), beta(4), and beta(6) for intermediate deformations. For a fissioning system, it is always possible to define uniquely one saddle or fission threshold on the optimum trajectory between the ground state and separated fission fragments. We present such calculated barrier heights for 1585 nuclei from Z=78 to Z=125. Traditionally, actinide barriers have been characterized in terms of a "double-humped" structure. Following this custom we present calculated energies of the first peak, second minimum, and second peak in the barrier for 135 actinide nuclei from Th to Es. However, for some of these nuclei which exhibit a more complex barrier structure, there is no unique way to extract a double-humped structure from the calculations. We give examples of such more complex structures, in particular the structure of the outer barrier region near Th-232 and the occurrence of multiple fission modes. Because our complete results are too extensive to present in a paper of this type, our aim here is limited: (1) to fully present our model and the methods for determining the structure of the potential-energy surface, (2) to present fission thresholds for a large number of heavy elements, (3) to compare our results with the two-humped barrier structure deduced from experiment for actinide nuclei, and (4) to compare to additional fission-related data and other fission models. . (Less)

Neutrinoless double- β decay in the microscopic interacting boson model

Abstract: We present a formalism for calculating nuclear matrix elements of double-$\ensuremath{\beta}$ decay within the framework of the microscopic interacting boson model. We calculate Fermi, Gamow-Teller, and tensor matrix elements in the decay of Ge-Se-Mo-Te-Xe-Nd-Sm and compare our results with those of the shell-model (SM) and of the quasiparticle random-phase approximation (QRPA). Our results are in agreement with QRPA. We discuss simple features of the matrix elements and give a formula that allows one to estimate matrix elements in terms of the number of valence proton and neutron pairs.

Unified approach for nucleon knock-out and coherent and incoherent pion production in neutrino interactions with nuclei

Abstract: We present a theory of neutrino interactions with nuclei aimed at the description of the partial cross sections, namely quasielastic and multinucleon emission, coherent and incoherent single-pion production. For this purpose, we use the theory of nuclear responses treated in the random-phase approximation, which allows a unified description of these channels. It is particularly suited for the coherent pion production where collective effects are important, whereas they are moderate in the other channels. We also study the evolution of the neutrino cross sections with the mass number from carbon to calcium. We compare our approach to the available neutrino experimental data on carbon. We put a particular emphasis on the multinucleon channel, which at present is not easily distinguishable from the quasielastic events. This component turns out to be quite relevant for the interpretation of experiments (K2K, MiniBooNE, SciBooNE). It can account in particular for the unexpected behavior of the quasielastic cross section.

Long range rapidity correlations and jet production in high energy nuclear collisions

Abstract: The STAR Collaboration at the Relativistic Heavy Ion Collider presents a systematic study of high-transverse-momentum charged-di-hadron correlations at small azimuthal pair separation Delta phi in d+Au and central Au+Au collisions at s(NN)=200 GeV. Significant correlated yield for pairs with large longitudinal separation Delta eta is observed in central Au+Au collisions, in contrast to d+Au collisions. The associated yield distribution in Delta eta x Delta phi can be decomposed into a narrow jet-like peak at small angular separation which has a similar shape to that found in d+Au collisions, and a component that is narrow in Delta phi and depends only weakly on Delta eta, the "ridge." Using two systematically independent determinations of the background normalization and shape, finite ridge yield is found to persist for trigger p(t)>6 GeV/c, indicating that it is correlated with jet production. The transverse-momentum spectrum of hadrons comprising the ridge is found to be similar to that of bulk particle production in the measured range (2 < p(t)< 4 GeV/c).

New effective interaction for f 5 pg 9 -shell nuclei

Abstract: We present a new effective interaction for shell-model calculations in the model space consisting of the single-particle orbits $1{p}_{3/2}$, $0{f}_{5/2}$, $1{p}_{1/2}$, and $0{g}_{9/2}$. Starting with a realistic interaction based on the Bonn-C potential, 133 two-body matrix elements and four single-particle energies are modified empirically so as to fit $400$ experimental energy data out of $69$ nuclei with mass numbers $A=63~96$. The systematics of binding energies, electromagnetic moments and transitions, and low-lying energy levels are described. The soft $Z=28$ closed core is observed, in contrast to the stable $N=50$ shell closure. The new interaction is applied to systematic studies of three different chains of nuclei, Ge isotopes around $N=40$, $N=Z$ nuclei with $A=64~70$, and $N=49$ odd-odd nuclei, focusing especially on the role of the ${g}_{9/2}$ orbit. The irregular behavior of the ${0}_{2}^{+}$ state in Ge isotopes is understood as a result of detailed balance between the $N=40$ single-particle energy gap and the collective effects. The development of the band structure in $N=Z$ nuclei is interpreted in terms of successive excitations of nucleons into the ${g}_{9/2}$ orbit. The triaxial/$\ensuremath{\gamma}$-soft structure in $^{64}\mathrm{Ge}$ and the prolate/oblate shape coexistence in $^{68}\mathrm{Se}$ are predicted, showing a good correspondence with the experimental data. The isomeric states in $^{66}\mathrm{As}$ and $^{70}\mathrm{Br}$ are obtained with the structure of an aligned proton-neutron pair in the ${g}_{9/2}$ orbit. Low-lying energy levels in $N=49$ odd-odd nuclei can be classified as proton-neutron pair multiplets, implying that the obtained single-particle structure in this neutron-rich region appears to be appropriate. These results demonstrate that, in spite of the modest model space, the new interaction turns out to describe rather well properties related to the ${g}_{9/2}$ orbit in various cases, including moderately deformed nuclei.

MARTINI: An event generator for relativistic heavy-ion collisions

Abstract: We introduce the modular algorithm for relativistic treatment of heavy ion interactions (MARTINI), a comprehensive event generator for the hard and penetrating probes in high-energy nucleus-nucleus collisions. Its main components are a time-evolution model for the soft background, PYTHIA 8.1, and the McGill-Arnold, Moore, and Yaffe (AMY) parton-evolution scheme, including radiative as well as elastic processes. This allows us to generate full event configurations in the high ${p}_{T}$ region that take into account thermal quantum chromodynamic (QCD) and quantum electrodynamic (QED) effects as well as effects of the evolving medium. We present results for the neutral pion nuclear modification factor in $\mathrm{Au}+\mathrm{Au}$ collisions at the BNL Relativistic Heavy Ion Collider as a function of ${p}_{T}$ for different centralities and also as a function of the angle with respect to the reaction plane for noncentral collisions. Furthermore, we study the production of high-transverse-momentum photons, incorporating a complete set of photon-production channels.

0νββ-decay nuclear matrix elements with self-consistent short-range correlations

Abstract: A self-consistent calculation of nuclear matrix elements of the neutrinoless double-beta decays ($0\ensuremath{ u}\ensuremath{\beta}\ensuremath{\beta}$) of $^{76}\mathrm{Ge}$, $^{82}\mathrm{Se}$, $^{96}\mathrm{Zr}$, $^{100}\mathrm{Mo}$, $^{116}\mathrm{Cd}$, $^{128}\mathrm{Te}$, $^{130}\mathrm{Te}$, and $^{136}\mathrm{Xe}$ is presented in the framework of the renormalized quasiparticle random phase approximation (RQRPA) and the standard QRPA. The pairing and residual interactions as well as the two-nucleon short-range correlations are for the first time derived from the same modern realistic nucleon-nucleon potentials, namely, from the charge-dependent Bonn potential (CD-Bonn) and the Argonne V18 potential. In a comparison with the traditional approach of using the Miller-Spencer Jastrow correlations, matrix elements for the $0\ensuremath{ u}\ensuremath{\beta}\ensuremath{\beta}$ decay are obtained that are larger in magnitude. We analyze the differences among various two-nucleon correlations including those of the unitary correlation operator method (UCOM) and quantify the uncertainties in the calculated $0\ensuremath{ u}\ensuremath{\beta}\ensuremath{\beta}$-decay matrix elements.

Electroexcitation of Nucleon Resonances from CLAS Data on Single Pion Electroproduction

Abstract: We present results on the electroexcitation of the low mass resonances $\ensuremath{\Delta}(1232){P}_{33}$, $N(1440){P}_{11}$, $N(1520){D}_{13}$, and $N(1535){S}_{11}$ in a wide range of ${Q}^{2}$. The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for $\ensuremath{\pi}$ electroproduction off the proton. The data were analyzed using two conceptually different approaches---fixed-$t$ dispersion relations and a unitary isobar model---allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the $\ensuremath{\Delta}(1232){P}_{33}$ show the importance of a meson-cloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for ${Q}^{2}\ensuremath{\leqslant}6$ GeV${}^{2}$. For the Roper resonance, $N(1440){P}_{11}$, the data provide strong evidence that this state is a predominantly radial excitation of a three-quark ($3q$) ground state. Measured in pion electroproduction, the transverse helicity amplitude for the $N(1535){S}_{11}$ allowed us to obtain the branching ratios of this state to the $\ensuremath{\pi}N$ and $\ensuremath{\eta}N$ channels via comparison with the results extracted from $\ensuremath{\eta}$ electroproduction. The extensive CLAS data also enabled the extraction of the ${\ensuremath{\gamma}}^{*}p\ensuremath{\rightarrow}N(1520){D}_{13}$ and $N(1535){S}_{11}$ longitudinal helicity amplitudes with good precision. For the $N(1535){S}_{11}$, these results became a challenge for quark models and may be indicative of large meson-cloud contributions or of representations of this state that differ from a $3q$ excitation. The transverse amplitudes for the $N(1520){D}_{13}$ clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at ${Q}^{2}g1$ GeV${}^{2}$, confirming a long-standing prediction of the constituent quark model.

Light-cone wave function approach to open heavy flavor dynamics in QCD matter

Abstract: We calculate the lowest-order charm and beauty parton distribution functions in and fragmentation functions into $D$ and $B$ mesons using the operator definitions of factorized perturbative quantum chromodynamics (QCD). In the vacuum, we find the leading corrections that arise from the structure of the final-state hadrons. Quark-antiquark potentials extracted from the lattice are employed to demonstrate the existence of open heavy flavor bound-state solutions in the quark-gluon plasma in the vicinity of the critical temperature. We provide first results for the in-medium modification of the heavy-quark distribution and decay probabilities in a comoving plasma. In an improved perturbative QCD description of heavy-flavor dynamics in the thermal medium, we combine $D$- and $B$-meson formation and dissociation with parton-level charm and beauty quark quenching to obtain predictions for the heavy-meson and nonphotonic-electron suppression in $\mathrm{Cu}+\mathrm{Cu}$ and $\mathrm{Pb}+\mathrm{Pb}$ collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider, respectively.

Spectra and radial flow in relativistic heavy ion collisions with Tsallis statistics in a blast-wave description

Abstract: We have implemented the Tsallis statistics in a Blast-Wave model (TBW) and applied it to midrapidity transverse-momentum spectra of identified particles measured at BNL Relativistic Heavy Ion Collider (RHIC) This new TBW function fits the RHIC data very well for ${p}_{T}l3$ GeV/$c$ We observed that the collective flow velocity starts from zero in $p+p$ and peripheral $\mathrm{Au}+\mathrm{Au}$ collisions and grows to $0470\ifmmode\pm\else\textpm\fi{}0009c$ in central $\mathrm{Au}+\mathrm{Au}$ collisions The resulting $(q\ensuremath{-}1)$ parameter, which characterizes the degree of nonequilibrium in a system, indicates an evolution from a highly nonequilibrated system in $p+p$ collisions toward an almost thermalized system in central $\mathrm{Au}+\mathrm{Au}$ collisions The temperature and collective velocity are well described by a quadratic dependence on $(q\ensuremath{-}1)$ Two sets of parameters in our TBW are required to describe the meson and baryon groups separately in $p+p$ collisions while one set appears to fit all spectra in central $\mathrm{Au}+\mathrm{Au}$ collisions

Attempt to produce element 120 in the Pu 244 + Fe 58 reaction

Abstract: An experiment aimed at the synthesis of isotopes of element 120 has been performed using the $^{244}\mathrm{Pu}(^{58}\mathrm{Fe},\mathit{xn}){}^{302\ensuremath{-}x}120$ reaction. No decay chains consistent with fusion-evaporation reaction products were observed during an irradiation with a beam dose of $7.1\ifmmode\times\else\texttimes\fi{}{10}^{18} 330\text{\ensuremath{-}}\mathrm{MeV} {}^{58}\mathrm{Fe}$ projectiles. The sensitivity of the experiment corresponds to a cross section of 0.4 pb for the detection of one decay.

Density dependence of the nuclear symmetry energy: A microscopic perspective

Abstract: We perform a systematic analysis of the density dependence of nuclear symmetry energy within the microscopic Brueckner-Hartree-Fock (BHF) approach using the realistic Argonne V18 nucleon-nucleon potential plus a phenomenological three-body force of Urbana type. Our results are compared thoroughly with those arising from several Skyrme and relativistic effective models. The values of the parameters characterizing the BHF equation of state of isospin asymmetric nuclear matter fall within the trends predicted by those models and are compatible with recent constraints coming from heavy ion collisions, giant monopole resonances, or isobaric analog states. In particular we find a value of the slope parameter L=66.5 MeV, compatible with recent experimental constraints from isospin diffusion, L=88±25 MeV. The correlation between the neutron skin thickness of neutron-rich isotopes and the slope L and curvature Ksym parameters of the symmetry energy is studied. Our BHF results are in very good agreement with the correlations already predicted by other authors using nonrelativistic and relativistic effective models. The correlations of these two parameters and the neutron skin thickness with the transition density from nonuniform to β-stable matter in neutron stars are also analyzed. Our results confirm that there is an inverse correlation between the neutron skin thickness and the transition density.

Higher-order effects on the incompressibility of isospin asymmetric nuclear matter

Abstract: Analytical expressions for the saturation density of asymmetric nuclear matter as well as its binding energy and incompressibility at saturation density are given up to fourth order in the isospin asymmetry $\ensuremath{\delta}=({\ensuremath{\rho}}_{n}\ensuremath{-}{\ensuremath{\rho}}_{p})/\ensuremath{\rho}$ using 11 characteristic parameters defined by the density derivatives of the binding energy per nucleon of symmetric nuclear matter, the symmetry energy ${E}_{\mathrm{sym}} (\ensuremath{\rho})$, and the fourth-order symmetry energy ${E}_{\mathrm{sym},4}(\ensuremath{\rho})$ at normal nuclear density ${\ensuremath{\rho}}_{0}$. Using an isospin- and momentum-dependent modified Gogny interaction (MDI) and the Skyrme-Hartree-Fock (SHF) approach with 63 popular Skyrme interactions, we have systematically studied the isospin dependence of the saturation properties of asymmetric nuclear matter, particularly the incompressibility ${K}_{\mathrm{sat}}(\ensuremath{\delta})={K}_{0}+{K}_{\mathrm{sat},2}{\ensuremath{\delta}}^{2}+{K}_{\mathrm{sat},4}{\ensuremath{\delta}}^{4}+O({\ensuremath{\delta}}^{6})$ at saturation density. Our results show that the magnitude of the higher order ${K}_{\mathrm{sat},4}$ parameter is generally small compared to that of the ${K}_{\mathrm{sat},2}$ parameter. The latter essentially characterizes the isospin dependence of the incompressibility at saturation density and can be expressed as ${K}_{\mathrm{sat},2}={K}_{\mathrm{sym}}\ensuremath{-}6L\ensuremath{-}\frac{{J}_{0}}{{K}_{0}}L$, where $L$ and ${K}_{\mathrm{sym}}$ represent, respectively, the slope and curvature parameters of the symmetry energy at ${\ensuremath{\rho}}_{0}$ and ${J}_{0}$ is the third-order derivative parameter of symmetric nuclear matter at ${\ensuremath{\rho}}_{0}$. Furthermore, we have constructed a phenomenological modified Skyrme-like (MSL) model that can reasonably describe the general properties of symmetric nuclear matter and the symmetry energy predicted by both the MDI model and the SHF approach. The results indicate that the higher order ${J}_{0}$ contribution to ${K}_{\mathrm{sat},2}$ generally cannot be neglected. In addition, it is found that there exists a nicely linear correlation between ${K}_{\mathrm{sym}}$ and $L$ as well as between ${J}_{0}/{K}_{0}$ and ${K}_{0}$. These correlations together with the empirical constraints on ${K}_{0},L,{E}_{\mathrm{sym}} ({\ensuremath{\rho}}_{0})$, and the nucleon effective mass lead to an estimate of ${K}_{\mathrm{sat},2}=\ensuremath{-}370\ifmmode\pm\else\textpm\fi{}120$ MeV.

Ab initio no-core full configuration calculations of light nuclei

Abstract: We perform no-core full configuration calculations for a set of light nuclei including $^{16}\mathrm{O}$ with a realistic $\mathit{NN}$ interaction, JISP16. We obtain ground-state energies and their uncertainties through exponential extrapolations that we demonstrate are reliable in $^{2}\mathrm{H}$, $^{3}\mathrm{H}$, and $^{4}\mathrm{He}$ test cases where fully converged results are obtained directly. We find that $^{6}\mathrm{He}$, $^{6}\mathrm{Li}$, and $^{8}\mathrm{He}$ are underbound by about 600 keV, 560 keV, and $1.7$ MeV, respectively. $^{12}\mathrm{C}$ is overbound by about $1.7$ MeV and $^{16}\mathrm{O}$ is overbound by about 16 MeV. The first excited ${0}^{+}$ states in $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ are also evaluated but their uncertainties are significantly larger than the uncertainties for the ground states.

Variational calculation of the ppK- system based on chiral SU(3) dynamics

Abstract: The ${\mathit{ppK}}^{\ensuremath{-}}$ system, as a prototype for possible quasibound $\overline{K}$ nuclei, is investigated using a variational approach. Several versions of energy-dependent effective $\overline{K}N$ interactions derived from chiral SU(3) dynamics are employed as input, together with a realistic $\mathit{NN}$ potential (Av18). Taking into account theoretical uncertainties in the extrapolations below the $\overline{K}N$ threshold, we find that the antikaonic dibaryon ${\mathit{ppK}}^{\ensuremath{-}}$ is not deeply bound. With the driving $s$-wave $\overline{K}N$ interaction the resulting total binding energy is $B({\mathit{ppK}}^{\ensuremath{-}})=20\ifmmode\pm\else\textpm\fi{}3$ MeV and the mesonic decay width involving $\overline{K}N\ensuremath{\rightarrow}\ensuremath{\pi}Y$ is expected to be in the range 40--70 MeV. Properties of this quasibound ${\mathit{ppK}}^{\ensuremath{-}}$ system (such as density distributions of nucleons and antikaon) are discussed. The $\ensuremath{\Lambda}(1405)$, as an $I=0$ quasibound state of $\overline{K}$ and a nucleon, appears to survive in the ${\mathit{ppK}}^{\ensuremath{-}}$ cluster. Estimates are given for the influence of $p$-wave $\overline{K}N$ interactions and for the width from two-nucleon absorption $(\overline{K}\mathit{NN}\ensuremath{\rightarrow}\mathit{YN})$ processes. With inclusion of these effects and dispersive corrections from absorption, the ${\mathit{ppK}}^{\ensuremath{-}}$ binding energy is expected to be in the range 20--40 MeV, whereas the total decay width can reach 100 MeV but with large theoretical uncertainties.

Systematic comparison of jet energy-loss schemes in a realistic hydrodynamic medium

Abstract: We perform a systematic comparison of three different jet energy-loss approaches. These include the Armesto-Salgado-Wiedemann scheme based on the approach of Baier-Dokshitzer-Mueller-Peigne-Schiff and Zakharov (BDMPS-Z/ASW), the higher twist (HT) approach and a scheme based on the Arnold-Moore-Yaffe (AMY) approach. In this comparison, an identical medium evolution will be utilized for all three approaches: this entails not only the use of the same realistic three-dimensional relativistic fluid dynamics (RFD) simulation, but also the use of identical initial parton-distribution functions and final fragmentation functions. We are, thus, in a unique position to not only isolate fundamental differences between the various approaches but also make rigorous calculations for different experimental measurements using state of the art components. All three approaches are reduced to versions containing only one free tunable parameter, this is then related to the well-known transport parameter $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}$. We find that the parameters of all three calculations can be adjusted to provide a good description of inclusive data on ${R}_{\mathit{AA}}$ vs transverse momentum. However, we do observe slight differences in their predictions for the centrality and azimuthal angular dependence of ${R}_{\mathit{AA}}$ vs ${p}_{T}$. We also note that the values of the transport coefficient $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}$ in the three approaches to describe the data differ significantly.

Microscopic mechanism of charged-particle radioactivity and generalization of the Geiger-Nuttall law

Abstract: A linear relation for charged-particle emissions is presented starting from the microscopic mechanism of the radioactive decay. It relates the logarithms of the decay half-lives with two variables, called ${\ensuremath{\chi}}^{'}$ and ${\ensuremath{\rho}}^{'}$, which depend upon the $Q$ values of the outgoing clusters as well as the masses and charges of the nuclei involved in the decay. This relation explains well all known cluster decays. It is found to be a generalization of the Geiger-Nuttall law in $\ensuremath{\alpha}$ radioactivity, and therefore we call it the universal decay law. Predictions of the most likely emissions of various clusters are presented by applying the law over the whole nuclear chart. It is seen that the decays of heavier clusters with nonequal proton and neutron numbers are mostly located in the trans-lead region. The emissions of clusters with equal protons and neutrons, like $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$, are possible in some neutron-deficient nuclei with $Z\ensuremath{\geqslant}54$.

Importance truncation for large-scale configuration interaction approaches

Abstract: We introduce an iterative importance truncation scheme that aims at reducing the dimension of the model space of configuration interaction approaches by an a priori selection of the physically most relevant basis states. Using an importance measure derived from multiconfigurational perturbation theory in combination with an importance threshold, we construct a model space optimized for the description of individual eigenstates of a given Hamiltonian. We discuss in detail various technical aspects and refinements of the importance truncation, such as perturbative corrections for excluded basis states, threshold extrapolation techniques, and different iterative model-space update schemes. We apply the idea of the importance truncation in the context of the no-core shell model (NCSM) for the ab initio description of nuclear ground states. In a series of benchmark calculations for closed- and open-shell nuclei up to {sup 16}O, we compare the ground-state energies obtained in the importance truncated NCSM to the full NCSM. All calculations show an excellent agreement of importance truncated and full NCSM for all cases where the latter is feasible. The results demonstrate that the importance truncated NCSM, while preserving most of the advantages of the full NCSM, gives access to much larger N{sub max}({Dirac_h}/2{pi}){omega} spaces and heavier nuclei. Inmore » this way we are able to perform importance truncated NCSM calculations for nuclei such as {sup 12}C and {sup 16}O up to N{sub max}=22.« less

Long range correlations and the soft ridge in relativistic nuclear collisions

Abstract: Relativistic Heavy Ion Collider experiments exhibit correlations peaked in relative azimuthal angle and extended in rapidity. Called the ridge, this peak occurs both with and without a jet trigger. We argue that the untriggered ridge arises when particles formed by flux tubes in an early Glasma stage later manifest transverse flow. Combining a blast wave model of flow fixed by single-particle spectra with a simple description of the Glasma, we find excellent agreement with current data.

Quantum Monte Carlo calculation of the equation of state of neutron matter

Abstract: We calculated the equation of state of neutron matter at zero temperature by means of the auxiliary field diffusion Monte Carlo (AFDMC) method combined with a fixed-phase approximation. The calculation of the energy was carried out by simulating up to 114 neutrons in a periodic box. Special attention was given to reducing finite-size effects at the energy evaluation by adding to the interaction the effect due to the truncation of the simulation box, and by performing several simulations using different numbers of neutrons. The finite-size effects due to kinetic energy were also checked by employing the twist-averaged boundary conditions. We considered a realistic nuclear Hamiltonian containing modern two- and three-body interactions of the Argonne and Urbana family. The equation of state can be used to compare and calibrate other many-body calculations and to predict properties of neutron stars.

Experimental energy-dependent nuclear spin distributions

Abstract: A new method is proposed to determine the energy-dependent spin distribution in experimental nuclear-level schemes. This method compares various experimental and calculated moments in the energy-spin plane to obtain the spin-cutoff parameter $\ensuremath{\sigma}$ as a function of mass $A$ and excitation energy using a total of $7202$ levels with spin assignment in $227$ nuclei between F and Cf. A simple formula, ${\ensuremath{\sigma}}^{2}=0.391 {A}^{0.675}(E\ensuremath{-}0.5{\mathit{Pa}}^{'}){}^{0.312}$, is proposed up to about 10 MeV that is in very good agreement with experimental $\ensuremath{\sigma}$ values and is applied to improve the systematics of level-density parameters.

Toward unifying the description of meson and baryon properties

Abstract: We present a Poincar\'e covariant Faddeev equation, which enables the simultaneous prediction of meson and baryon observables using the leading order in a truncation of the Dyson-Schwinger equations that can systematically be improved. The solution describes a nucleon's dressed-quark core. The evolution of the nucleon mass with current-quark mass is discussed. A nucleon-photon current, which can produce nucleon form factors with realistic ${Q}^{2}$ evolution, is described. Axial-vector diquark correlations lead to a neutron Dirac form factor that is negative, with ${r}_{1}^{\mathit{nu}}g{r}_{1}^{\mathit{nd}}$. The proton electric-magnetic form factor ratio falls with increasing ${Q}^{2}$.

Effect of flow fluctuations and nonflow on elliptic flow methods

Abstract: We discuss how the different estimates of elliptic flow are influenced by flow fluctuations and nonflow effects. It is explained why the event-plane method yields estimates between the two-particle correlation methods and the multiparticle correlation methods. It is argued that nonflow effects and fluctuations cannot be disentangled without other assumptions. However, we provide equations where, with reasonable assumptions about fluctuations and nonflow, all measured values of elliptic flow converge to a unique mean v_2,PP elliptic flow in the participant plane and, with a Gaussian assumption on eccentricity fluctuations, can be converted to the mean v_2,RP in the reaction plane. Thus, the 20percent spread in observed elliptic flow measurements from different analysis methods is no longer mysterious.

Quark matter under strong magnetic fields in the su(3) Nambu-Jona-Lasinio Model

Abstract: In the present work we use the mean-field approximation to investigate quark matter described by the su(3) Nambu--Jona-Lasinio (NJL) model subject to a strong magnetic field. We consider two cases: pure quark matter and quark matter in $\ensuremath{\beta}$ equilibrium possibly present in magnetars. The results are compared with the ones obtained with the su(2) version of the model. The energy per baryon of magnetized quark matter becomes more bound than nuclear matter made of iron nuclei, for $B$ around $2\ifmmode\times\else\texttimes\fi{}{10}^{19}$ G. When the su(3) NJL model is applied to stellar matter, the maximum mass configurations are always above $1.45{M}_{\ensuremath{\bigodot}}$ and may be as high as $1.86{M}_{\ensuremath{\bigodot}}$ for a central magnetic field of $5\ifmmode\times\else\texttimes\fi{}{10}^{18}$ G. These numbers are within the masses of observed neutron stars.

Critical points in the linear σ model with quarks

Abstract: We employ a simple effective model to study the chiral dynamics of two flavors of quarks at finite temperature and density. In particular, we determine the phase diagram in the plane of temperature and baryon chemical potential as a function of the pion mass. An interesting phase structure occurs that results in zero, one, or two critical points depending on the value of the vacuum pion mass.