The 50 most-cited articles in Physical Review C, 2016

We quantitatively estimate properties of the quark-gluon plasma created in ultrarelativistic heavy-ion collisions utilizing Bayesian statistics and a multiparameter model-to-data comparison. The study is performed using a recently developed parametric initial condition model, ${\mathrm{T}}_{\mathrm{R}}\text{ENTo}$, which interpolates among a general class of particle production schemes, and a modern hybrid model which couples viscous hydrodynamics to a hadronic cascade. We calibrate the model to multiplicity, transverse momentum, and flow data and report constraints on the parametrized initial conditions and the temperature-dependent transport coefficients of the quark-gluon plasma. We show that initial entropy deposition is consistent with a saturation-based picture, extract a relation between the minimum value and slope of the temperature-dependent specific shear viscosity, and find a clear signal for a nonzero bulk viscosity.

The microscopic description of heavy-ion reactions at low beam energies is achieved within hadronic transport approaches. In this article a new approach called ``Simulating Many Accelerated Strongly interacting Hadrons'' (SMASH) is introduced and applied to study the production of nonstrange particles in heavy-ion reactions at ${E}_{\mathrm{kin}}=0.4A--2A$ GeV. First, the model is described including details about the collision criterion, the initial conditions and the resonance formation and decays. To validate the approach, equilibrium properties such as detailed balance are presented and the results are compared to experimental data for elementary cross sections. Finally results for pion and proton production in $\text{C}+\text{C}$ and $\text{Au}+\text{Au}$ collisions is confronted with data from the high-acceptance dielectron spectrometer (HADES) and FOPI. Predictions for particle production in $\ensuremath{\pi}+A$ collisions are made.

In this work it is shown that the use of a hydrodynamical model of heavy-ion collisions which incorporates recent developments, together with updated photon emission rates, greatly improves agreement with both ALICE and PHENIX measurements of direct photons, supporting the idea that thermal photons are the dominant source of direct photon momentum anisotropy. The event-by-event hydrodynamical model uses the impact parameter dependent Glasma model (IP-Glasma) initial states and includes, for the first time, both shear and bulk viscosities, along with second-order couplings between the two viscosities. The effect of both shear and bulk viscosities on the photon rates is studied, and those transport coefficients are shown to have measurable consequences on the photon momentum anisotropy.

The uncertainties in neutron star radii and crust properties due to our limited knowledge of the equation of state are quantitatively analyzed. We first demonstrate the importance of a unified microscopic description for the different baryonic densities of the star. If the pressure functional is obtained matching a crust and a core equation of state based on models with different properties at nuclear matter saturation, the uncertainties can be as large as $\ensuremath{\sim}30$ % for the crust thickness and 4% for the radius. Necessary conditions for causal and thermodynamically consistent matchings between the core and the crust are formulated and their consequences examined. A large set of unified equations of state for purely nucleonic matter is obtained based on twenty-four Skyrme interactions and nine relativistic mean-field nuclear parametrizations. In addition, for relativistic models fifteen equations of state including a transition to hyperonic matter at high density are presented. All these equations of state have in common the property of describing a…

This paper introduces an event-by-event perturbative QCD plus saturation framework for the initial state of high-energy heavy-ion collisions and evolves the matter using dissipative fluid dynamics. The results favor a ratio of shear viscosity-to-entropy density that has a minimum near a temperature of 150 MeV, in line with theoretical expectations.

Background: $r$-process nucleosynthesis models rely, by necessity, on nuclear structure models for input. Particularly important are $\ensuremath{\beta}$-decay half-lives of neutron-rich nuclei. At present only a single systematic calculation exists that provides values for all relevant nuclei making it difficult to test the sensitivity of nucleosynthesis models to this input. Additionally, even though there are indications that their contribution may be significant, the impact of first-forbidden transitions on decay rates has not been systematically studied within a consistent model.Purpose: Our goal is to provide a table of $\ensuremath{\beta}$-decay half-lives and $\ensuremath{\beta}$-delayed neutron emission probabilities, including first-forbidden transitions, calculated within a fully self-consistent microscopic theoretical framework. The results are used in an $r$-process nucleosynthesis calculation to asses the sensitivity of heavy element nucleosynthesis to weak interaction reaction rates.Method: We use a fully self-consistent covariant density functional theory (CDFT)…

A linearized Boltzmann transport (LBT) model coupled with hydrodynamical background is established to describe the evolution of jet shower partons and medium excitations in high energy heavy-ion collisions. We extend the LBT model to include both elastic and inelastic processes for light and heavy partons in the quark-gluon plasma. A hybrid model of fragmentation and coalescence is developed for the hadronization of heavy quarks. Within this framework, we investigate how heavy flavor observables depend on various ingredients, such as different energy loss and hadronization mechanisms, the momentum and temperature dependences of the transport coefficients, and the radial flow of the expanding fireball. Our model calculations show good descriptions of the $D$ meson suppression and elliptic flow observed at the Larege Hadron Collider and the Relativistic Heavy-Ion Collider. The prediction for the Pb-Pb collisions at $\sqrt{{s}_{NN}}=5.02$ TeV is provided.

We study the rotational collective motion of the quark-gluon plasma in relativistic heavy-ion collisions using the widely adopted a multiphase transport (AMPT) model. The global angular momentum, the average vorticity carried by the quark-gluon plasma, and the locally defined vorticity fields are computed for $\mathrm{Au}+\mathrm{Au}$ collisions, with detailed information of their time evolution, spatial distribution, as well as the dependence on beam energy and collision centrality.

Directed and elliptic flows of neutrons and light-charged particles were measured for the reaction $^{197}\mathrm{Au}+^{197}\mathrm{Au}$ at 400 MeV/nucleon incident energy within the ASY-EOS experimental campaign at the GSI laboratory. The detection system consisted of the Large Area Neutron Detector (LAND), combined with parts of the CHIMERA multidetector, the ALADIN Time-of-flight Wall, and the Washington University Microball detector. The latter three arrays were used for the event characterization and reaction-plane reconstruction. In addition, an array of triple telescopes, KRATTA was used for complementary measurements of the isotopic composition and flows of light-charged particles. From the comparison of the elliptic-flow ratio of neutrons with respect to charged particles with UrQMD predictions, a value $\ensuremath{\gamma}=0.72\ifmmode\pm\else\textpm\fi{}0.19$ is obtained for the power-law coefficient describing the density dependence of the potential part in the parametrization of the symmetry energy. It represents a new and more stringent constraint for the regime of…

The production of (anti-)deuteron and (anti-)$^{3}\text{He}$ nuclei in Pb-Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=2.76$ TeV has been studied using the ALICE detector at the LHC. The spectra exhibit a significant hardening with increasing centrality. Combined blast-wave fits of several particles support the interpretation that this behavior is caused by an increase of radial flow. The integrated particle yields are discussed in the context of coalescence and thermal-statistical model expectations. The particle ratios, $^{3}\text{He}/d$ and $^{3}\text{He}/p$, in Pb-Pb collisions are found to be in agreement with a common chemical freeze-out temperature of ${T}_{\mathrm{chem}}\ensuremath{\approx}156$ MeV. These ratios do not vary with centrality which is in agreement with the thermal-statistical model. In a coalescence approach, it excludes models in which nucleus production is proportional to the particle multiplicity and favors those in which it is proportional to the particle density instead. In addition, the observation of 31 anti-tritons in Pb-Pb collisions is reported. For…

Nuclear mass models provide essential input for astrophysical applications such as $r$-process nucleosynthesis and neutron-star structure. By using a Bayesian neural network formalism, the authors obtain a significant improvement of about 40% in the mass predictions, complemented with statistical errors, of existing models. From an average of these predictions a mass model is obtained that is used to predict the composition of the outer crust of a neutron star.

We study the event-by-event generation of flow vorticity in the BNL Relativistic Heavy Ion Collider $\mathrm{Au}+\mathrm{Au}$ collisions and CERN Large Hadron Collider $\mathrm{Pb}+\mathrm{Pb}$ collisions by using the hijing model. Different definitions of the vorticity field and velocity field are considered. A variety of properties of the vorticity are explored, including the impact parameter dependence, the collision energy dependence, the spatial distribution, the event-by-event fluctuation of the magnitude and azimuthal direction, and the time evolution. In addition, the spatial distribution of the flow helicity is also studied.

Fermions become polarized in a vortical fluid due to spin-vorticity coupling. Such a polarization can be calculated from the Wigner function in a quantum kinetic approach. By extending previous results for chiral fermions, we derive the Wigner function for massive fermions up to next-to-leading order in spatial gradient expansion. The polarization density of fermions can be calculated from the axial vector component of the Wigner function and is found to be proportional to the local vorticity $\mathbf{\ensuremath{\omega}}$. The polarizations per particle for fermions and antifermions decrease with the chemical potential and increase with energy (mass). Both quantities approach the asymptotic value $\ensuremath{\hbar}\mathbf{\ensuremath{\omega}}/4$ in the large energy (mass) limit. The polarization per particle for fermions is always smaller than that for antifermions, whose ratio of fermions to antifermions also decreases with the chemical potential. The polarization per particle on the Cooper-Frye freeze-out hypersurface can also be formulated and is consistent with the previous…

Extending our earlier work, a new family of three Hartree-Fock-Bogoliubov (HFB) mass models, labeled HFB-30, HFB-31, and HFB-32, is presented, along with their underlying interactions, BSk30, BSk31, and BSk32, respectively. The principle new feature is a purely phenomenological pairing term that depends on the density gradient. This enables us to have a bulk pairing term that is fitted to realistic nuclear-matter calculations in which for the first time the self-energy corrections are included, while the behavior of the nucleon effective masses in asymmetric homogeneous nuclear matter is significantly improved. Furthermore, in the particle-hole channel all the highly realistic constraints of our earlier work are retained. In particular, the unconventional Skyrme forces containing ${t}_{4}$ and ${t}_{5}$ terms are still constrained to fit realistic equations of state of neutron matter stiff enough to support the massive neutron stars PSR J1614--2230 and PSR J0348+0432. All unphysical long-wavelength spin and spin-isospin instabilities of nuclear matter, including the unphysical…

We calculate the properties of isospin-asymmetric nuclear matter based on chiral nucleon-nucleon (NN) and three-nucleon (3N) interactions. To this end, we develop an improved normal-ordering framework that allows us to include general 3N interactions starting from a plane-wave partial-wave-decomposed form. We present results for the energy per particle for general isospin asymmetries based on a set of different Hamiltonians, study their saturation properties, the incompressibility, symmetry energy, and also provide an analytic parametrization for the energy per particle as a function of density and isospin asymmetry.

Chiral effective field theory (EFT) enables a systematic description of low-energy hadronic interactions with controlled theoretical uncertainties. For strongly interacting systems, quantum Monte Carlo (QMC) methods provide some of the most accurate solutions, but they require as input local potentials. We have recently constructed local chiral nucleon-nucleon (NN) interactions up to next-to-next-to-leading order (${\mathrm{N}}^{2}\mathrm{LO}$). Chiral EFT naturally predicts consistent many-body forces. In this paper, we consider the leading chiral three-nucleon (3N) interactions in local form. These are included in auxiliary field diffusion Monte Carlo (AFDMC) simulations. We present results for the equation of state of neutron matter and for the energies and radii of neutron drops. In particular, we study the regulator dependence at the Hartree-Fock level and in AFDMC and find that present local regulators lead to less repulsion from 3N forces compared to the usual nonlocal regulators.

We present fully local versions of the minimally nonlocal nucleon-nucleon potentials constructed in a previous paper [Piarulli et al., Phys. Rev. C 91, 024003 (2015)], and use them in hypersperical harmonics and quantum Monte Carlo calculations of ground and excited states of $^{3}\mathrm{H}$, $^{3}\mathrm{He}$, $^{4}\mathrm{He}$, $^{6}\mathrm{He}$, and $^{6}\mathrm{Li}$ nuclei. The long-range part of these local potentials includes one- and two-pion exchange contributions without and with $\mathrm{\ensuremath{\Delta}}$ isobars in the intermediate states up to order ${Q}^{3}$ ($Q$ denotes generically the low momentum scale) in the chiral expansion, while the short-range part consists of contact interactions up to order ${Q}^{4}$. The low-energy constants multiplying these contact interactions are fitted to the 2013 Granada database in two different ranges of laboratory energies, either 0--125 MeV or 0--200 MeV, and to the deuteron binding energy and $nn$ singlet scattering length. Fits to these data are performed for three models characterized by long- and short-range cutoffs,…

We study charm production in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=2.76$ TeV in the parton-hadron-string-dynamics (PHSD) transport approach and the charm dynamics in the partonic and hadronic medium. The charm quarks are produced through initial binary nucleon-nucleon collisions by using the pythia event generator, taking into account the (anti-)shadowing incorporated in the eps09 package. The produced charm quarks interact with off-shell massive partons in the quark-gluon plasma and are hadronized into $D$ mesons through coalescence or fragmentation close to the critical energy density, and then interact with hadrons in the final hadronic stage with scattering cross sections calculated in an effective Lagrangian approach with heavy-quark spin symmetry. The PHSD results show a reasonable ${R}_{\mathrm{AA}}$ and elliptic flow of $D$ mesons in comparison to the experimental data for $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=2.76$ TeV from the ALICE Collaboration. We also study the effect of temperature-dependent off-shell charm quarks in relativistic…

Neutron matter is an ideal laboratory for nuclear interactions derived from chiral effective field theory since all contributions are predicted up to next-to-next-to-next-to-leading order (${\mathrm{N}}^{3}\mathrm{LO}$) in the chiral expansion. By making use of recent advances in the partial-wave decomposition of three-nucleon ($3N$) forces, we include for the first time ${\mathrm{N}}^{3}\mathrm{LO} 3N$ interactions in many-body perturbation theory (MBPT) up to third order and in self-consistent Green's function theory (SCGF). Using these two complementary many-body frameworks we provide improved predictions for the equation of state of neutron matter at zero temperature and also analyze systematically the many-body convergence for different chiral EFT interactions. Furthermore, we present an extension of the normal-ordering framework to finite temperatures. These developments open the way to improved calculations of neutron-rich matter including estimates of theoretical uncertainties for astrophysical applications.

Transport simulations are very valuable for extracting physics information from heavy-ion-collision experiments. With the emergence of many different transport codes in recent years, it becomes important to estimate their robustness in extracting physics information from experiments. We report on the results of a transport-code-comparison project. Eighteen commonly used transport codes were included in this comparison: nine Boltzmann-Uehling-Uhlenbeck-type codes and nine quantum-molecular-dynamics-type codes. These codes have been asked to simulate $\mathrm{Au}+\mathrm{Au}$ collisions using the same physics input for mean fields and for in-medium nucleon-nucleon cross sections, as well as the same impact parameter, the similar initialization setup, and other calculational parameters at $100A$ and $400A$ MeV incident energy. Among the codes we compare one-body observables such as rapidity and transverse flow distributions. We also monitor nonobservables such as the initialization of the internal states of colliding nuclei and their stability, the collision rates, and the Pauli…

We apply improved nucleon-nucleon potentials up to fifth order in chiral effective field theory, along with a new analysis of the theoretical truncation errors to study nucleon-deuteron $(\mathrm{N}d)$ scattering and selected low-energy observables in $^{3}\mathrm{H},^{4}\mathrm{He}$, and $^{6}\mathrm{Li}$. Calculations beyond second order differ from experiment well outside the range of quantified uncertainties, providing truly unambiguous evidence for missing three-nucleon forces within the employed framework. The sizes of the required three-nucleon-force contributions agree well with expectations based on Weinberg's power counting. We identify the energy range in elastic $\mathrm{N}d$ scattering best suited to study three-nucleon-force effects and estimate the achievable accuracy of theoretical predictions for various observables.

Background: Accurate knowledge of fission fragment yields is an essential ingredient of numerous applications ranging from the formation of elements in the $r$ process to fuel cycle optimization for nuclear energy. The need for a predictive theory applicable where no data are available, together with the variety of potential applications, is an incentive to develop a fully microscopic approach to fission dynamics.Purpose: In this work, we calculate the pre-neutron emission charge and mass distributions of the fission fragments formed in the neutron-induced fission of $^{239}\mathrm{Pu}$ using a microscopic method based on nuclear density functional theory (DFT).Methods: Our theoretical framework is the nuclear energy density functional (EDF) method, where large-amplitude collective motion is treated adiabatically by using the time-dependent generator coordinate method (TDGCM) under the Gaussian overlap approximation (GOA). In practice, the TDGCM is implemented in two steps. First, a series of constrained EDF calculations map the configuration and potential-energy landscape of the…

A systematic investigation of octupole-deformed nuclei is presented for even-even systems with $Z\ensuremath{\le}106$ located between the two-proton and two-neutron driplines. For this study we use five most-up-to-date covariant energy density functionals of different types, with a nonlinear meson coupling, with density-dependent meson couplings, and with density-dependent zero-range interactions. Pairing correlations are treated within relativistic Hartree-Bogoliubov theory based on an effective separable particle-particle interaction of finite range. This allows us to assess theoretical uncertainties within the present covariant models for the prediction of physical observables relevant for octupole-deformed nuclei. In addition, a detailed comparison with the predictions of nonrelativistic models is performed. A new region of octupole deformation, centered around $Z\ensuremath{\sim}98,N\ensuremath{\sim}196$ is predicted for the first time. In terms of its size in the $(Z,N)$ plane and the impact of octupole deformation on binding energies this region is similar to the best known…

Transverse momentum $({p}_{\mathrm{T}})$ spectra of pions, kaons, and protons up to ${p}_{\mathrm{T}}=20\phantom{\rule{0.28em}{0ex}}\text{GeV}/c$ have been measured in Pb-Pb collisions at $\sqrt{{s}_{\mathit{NN}}}=2.76\phantom{\rule{0.28em}{0ex}}\text{TeV}$ using the ALICE detector for six different centrality classes covering 0%--80%. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at ${p}_{\mathrm{T}}\ensuremath{\approx}3\phantom{\rule{0.28em}{0ex}}\text{GeV}/c$ in central Pb-Pb collisions that decreases for more peripheral collisions. For ${p}_{\mathrm{T}}>10\phantom{\rule{0.28em}{0ex}}\text{GeV}/c$, the nuclear modification factor is found to be the same for all three particle species in each centrality interval within systematic uncertainties of 10%--20%. This suggests there is no direct interplay between the energy loss in the medium and the particle species composition in the hard core of the quenched jet. For ${p}_{\mathrm{T}}<10\phantom{\rule{0.28em}{0ex}}\text{GeV}/c$, the data provide important constraints for models aimed at describing the…

The authors performed extensive simulations for the ${}^{64}$Ni + ${}^{238}$U reaction, which is a promising candidate for synthesizing the superheavy element 120. They place special emphasis on the effects of nuclear deformation and shell structure on quasifission dynamics, which prevents the fusion of the colliding nuclei. The authors suggest an interesting possibility, that element 120 may be synthesized with high probability when ${}^{64}$Ni collides with ${}^{238}$U side-on and at higher incident energies than in past experiments.

Neutrinoless double-$\ensuremath{\beta}$ ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decay is a promising beyond standard model process. Two-neutrino double-$\ensuremath{\beta}$ ($2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decay is an associated process that is allowed by the standard model, and it was observed in about 10 isotopes, including decays to the excited states of the daughter. $^{124}\mathrm{Sn}$ was the first isotope whose double-$\ensuremath{\beta}$ decay modes were investigated experimentally, and despite few other recent efforts, no signal has been seen so far. Shell model calculations were able to make reliable predictions for $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay half-lives. Here we use shell model calculations to predict the $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay half-life of $^{124}\mathrm{Sn}$. Our results are quite different from the existing quasiparticle random-phase approximation results, and we envision that they will be useful for guiding future experiments. We also present shell…

We present ab initio predictions for ground and excited states of doubly open-shell fluorine and neon isotopes based on chiral two- and three-nucleon interactions. We use the in-medium similarity renormalization group to derive mass-dependent $sd$ valence-space Hamiltonians. The experimental ground-state energies are reproduced through neutron number $N=14$, beyond which a new targeted normal-ordering procedure improves agreement with data and large-space multireference calculations. For spectroscopy, we focus on neutron-rich $^{23\ensuremath{-}26}\mathrm{F}$ and $^{24\ensuremath{-}26}\mathrm{Ne}$ isotopes near $N=14,16$ magic numbers. In all cases we find agreement with experiment and established phenomenology. Moreover, yrast states are well described in $^{20}\mathrm{Ne}$ and $^{24}\mathrm{Mg}$, providing a path toward an ab initio description of deformation in the medium-mass region.

Glauber models based on nucleon-nucleon interactions are commonly used to characterize the initial state in high-energy nuclear collisions and the dependence of its properties on impact parameter or number of participating nucleons. In this paper, an extension to the Glauber model is presented, which accounts for an arbitrary number of effective subnucleon degrees of freedom, or active constituents, in the nucleons. Properties of the initial state, such as the number of constituent participants and collisions, as well as eccentricity and triangularity, are calculated and systematically compared for different assumptions of how to distribute the subnuclear degrees of freedom and for various collision systems. It is demonstrated that at high collision energy the number of produced particles scales with an average number of subnucleon degrees of freedom of between 3 and 5. The source codes for the constituent Monte Carlo Glauber extension, as well as for the calculation of the overlap area and participant density in a standard Glauber model, are made publicly available.

We study the relation between elliptic flow, ${v}_{2}$, and the initial eccentricity, ${\ensuremath{\varepsilon}}_{2}$, in heavy-ion collisions, using hydrodynamic simulations. Significant deviations from linear eccentricity scaling are seen in more peripheral collisions. We identify the mechanism responsible for these deviations as a cubic response, which we argue is a generic property of the hydrodynamic response to the initial density profile. The cubic response increases elliptic flow fluctuations, thereby improving agreement of initial condition models with experimental data.

We study ground- and excited-state properties of all $sd$-shell nuclei with neutron and proton numbers $8\ensuremath{\le}N,Z\ensuremath{\le}20$, based on a set of low-resolution two- and three-nucleon interactions that predict realistic saturation properties of nuclear matter. We focus on estimating the theoretical uncertainties due to variation of the resolution scale, the low-energy couplings, as well as from the many-body method. The experimental two-neutron and two-proton separation energies are reasonably well reproduced, with an uncertainty range of $\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\text{MeV}$. The first excited ${2}^{+}$ energies also show overall agreement, with a more narrow uncertainty range of $\ensuremath{\sim}500\phantom{\rule{0.16em}{0ex}}\text{keV}$. In most cases, this range is dominated by the uncertainties in the Hamiltonian.

We study the production of hadronic resonances and their interaction in the partonic and hadronic medium using the EPOS3 model, which employs the UrQMD model for the description of the hadronic phase. We investigate the centrality dependence of the yields and momentum distributions for various resonances [$\ensuremath{\rho}{(770)}^{0}$, ${K}^{*}{(892)}^{0}$, $\ensuremath{\phi}(1020)$, $\mathrm{\ensuremath{\Delta}}{(1232)}^{++}$, $\mathrm{\ensuremath{\Sigma}}{(1385)}^{\ifmmode\pm\else\textpm\fi{}}$, $\mathrm{\ensuremath{\Lambda}}(1520)$, $\mathrm{\ensuremath{\Xi}}{(1530)}^{0}$ and their antiparticles] in Pb-Pb collisions at $\sqrt{{s}_{NN}}=\phantom{\rule{4.pt}{0ex}}2.76$ TeV. The predictions for ${K}^{*}{(892)}^{0}$ and $\ensuremath{\phi}(1020)$ will be compared with the experimental data from the ALICE collaboration. The observed signal suppression of the ${K}^{*}{(892)}^{0}$ with increasing centrality will be discussed with respect to the resonance interaction in the hadronic medium. The mean transverse momentum and other particle ratios such as $\ensuremath{\phi}(1020)/p$ and…

Background: Octupole-deformed nuclei, such as that of $^{225}\mathrm{Ra}$, are expected to amplify observable atomic electric dipole moments (EDMs) that arise from time-reversal and parity-violating interactions in the nuclear medium. In 2015 we reported the first ``proof-of-principle'' measurement of the $^{225}\mathrm{Ra}$ atomic EDM.Purpose: This work reports on the first of several experimental upgrades to improve the statistical sensitivity of our $^{225}\mathrm{Ra}$ EDM measurements by orders of magnitude and evaluates systematic effects that contribute to current and future levels of experimental sensitivity.Method: Laser-cooled and trapped $^{225}\mathrm{Ra}$ atoms are held between two high-voltage electrodes in an ultrahigh-vacuum chamber at the center of a magnetically-shielded environment. We observe Larmor precession in a uniform magnetic field using nuclear-spin-dependent laser light scattering and look for a phase shift proportional to the applied electric field, which indicates the existence of an EDM. The main improvement to our measurement technique is an…

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider has measured second- and third-order Fourier coefficients of the azimuthal distributions of direct photons emitted at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{{}_{NN}}}=200$ GeV for various collision centralities. Combining two different analysis techniques, results were obtained in the transverse momentum range of $0.4<{p}_{T}<4.0 \text{GeV}/c$. At low ${p}_{T}$ the second-order coefficients, ${v}_{2}$, are similar to the ones observed in hadrons. Third-order coefficients, ${v}_{3}$, are nonzero and almost independent of centrality. These new results on ${v}_{2}$ and ${v}_{3}$, combined with previously published results on yields, are compared to model calculations that provide yields and asymmetries in the same framework. Those models are challenged to explain simultaneously the observed large yield and large azimuthal anisotropies.

Background: Synthesis of superheavy elements (SHEs) with fusion-evaporation reactions is strongly hindered by the quasifission (QF) mechanism which prevents the formation of an equilibrated compound nucleus and which depends on the structure of the reactants. New SHEs have been recently produced with doubly-magic $^{48}\mathrm{Ca}$ beams. However, SHE synthesis experiments with single-magic $^{50}\mathrm{Ti}$ beams have so far been unsuccessful.Purpose: In connection with experimental searches for $Z=117,119$ superheavy elements, we perform a theoretical study of fusion and quasifission mechanisms in $^{48}\mathrm{Ca},^{50}\mathrm{Ti}+^{249}\mathrm{Bk}$ reactions in order to investigate possible differences in reaction mechanisms induced by these two projectiles.Methods: The collision dynamics and the outcome of the reactions are studied using unrestricted time-dependent Hartree-Fock (TDHF) calculations as well as the density-constrained TDHF method to extract the nucleus-nucleus potentials and the excitation energy in each fragment.Results: Nucleus-nucleus potentials, nuclear…

Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we present large-scale calculations of the $E1\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-ray strength function obtained in the framework of the axially symmetric deformed quasiparticle random-phase approximation based on the finite-range Gogny force. This approach is applied to even-even nuclei, the strength function for odd nuclei being derived by interpolation. The convergence with respect to the adopted number of harmonic oscillator shells and the cutoff energy introduced in the 2-quasiparticle $(2\ensuremath{-}qp)$ excitation space is analyzed. The calculations performed with two different Gogny interactions, namely D1S and D1M, are compared. A systematic energy shift of the $E1$ strength is found for D1M relative to D1S, leading to a lower energy centroid and a smaller energy-weighted sum rule for D1M. When comparing with experimental photoabsorption data, the Gogny-QRPA predictions are…

Measurements of midrapidity charged-particle multiplicity distributions, $d{N}_{\mathrm{ch}}/d\ensuremath{\eta}$, and midrapidity transverse-energy distributions, $d{E}_{T}/d\ensuremath{\eta}$, are presented for a variety of collision systems and energies. Included are distributions for $\mathrm{Au}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Au}$ collisions at $\sqrt{{s}_{{}_{NN}}}=200$, 130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, $\mathrm{Cu}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Cu}$ collisions at $\sqrt{{s}_{{}_{NN}}}=200$ and 62.4 GeV, $\mathrm{Cu}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Au}$ collisions at $\sqrt{{s}_{{}_{NN}}}=200$ GeV, $\mathrm{U}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{U}$ collisions at $\sqrt{{s}_{{}_{NN}}}=193$ GeV, $d+\mathrm{Au}$ collisions at $\sqrt{{s}_{{}_{NN}}}=200$ GeV, $^{3}\mathrm{He}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}\mathrm{Au}$ collisions at $\sqrt{{s}_{{}_{NN}}}=200$ GeV, and $p+p$ collisions at $\sqrt{{s}_{{}_{NN}}}=200$ GeV.…

$\ensuremath{\beta}$-decay rates are an important ingredient in simulations of the astrophysical $r$ process, but parts of the $r$-process path are still not accessible to experiment. The authors develop a computationally efficient method that provides Skyrme-QRPA $\ensuremath{\beta}$-transition strengths for essentially all even-even nuclei, both spherical and deformed, between the valley of stability and the neutron drip line. The results will be important for global nucleosynthesis calculations.

We present a phenomenological study of nuclear effects in neutrino charged-current interactions, using transverse kinematic imbalances in exclusive measurements. Novel observables with minimal dependence on neutrino energy are proposed to study quasielastic scattering and especially resonance production. They should be able to provide direct constraints on nuclear effects in neutrino- and antineutrino-nucleus interactions.

The quark-gluon matter produced in relativistic heavy-ion collisions may contain local domains in which parity ($\mathcal{P}$) and combined charge conjugation and parity ($\mathcal{C}\mathcal{P}$) symmetries are not preserved. When coupled with an external magnetic field, such $\mathcal{P}$- and $\mathcal{C}\mathcal{P}$-odd domains will generate electric currents along the magnetic field---a phenomenon called the chiral magnetic effect (CME). Recently, the STAR Collaboration at the BNL Relativistic Heavy Ion Collider (RHIC) and the ALICE Collaboration at the CERN Large Hadron Collider (LHC) released data of charge-dependent azimuthal-angle correlators with features consistent with the CME expectation. However, the experimental observable is contaminated with significant background contributions from elliptic-flow-driven effects, which makes the interpretation of the data ambiguous. We show that the collisions of isobaric nuclei, $_{44}^{96}\mathrm{Ru}+_{44}^{96}\mathrm{Ru}$ and $_{40}^{96}\mathrm{Zr}+_{40}^{96}\mathrm{Zr}$, provide an ideal tool to disentangle the CME signal from…

The structure of even-even neutron-rich Ru, Mo, Zr, and Sr nuclei in the $A\ensuremath{\approx}100$ mass region is studied within the interacting boson model (IBM) with microscopic input from the self-consistent mean-field approximation based on the Gogny-D1M energy density functional. The deformation-energy surface in the quadrupole deformation space $(\ensuremath{\beta},\ensuremath{\gamma})$, computed within the constrained Hartree--Fock--Bogoliubov framework, is mapped onto the expectation value of the appropriately chosen IBM Hamiltonian with configuration mixing in the boson condensate state. The mapped IBM Hamiltonian is used to study the spectroscopic properties of $^{98--114}\mathrm{Ru}, ^{96--112}\mathrm{Mo}, ^{94--110}\mathrm{Zr}$, and $^{92--108}\mathrm{Sr}$. Several cases of $\ensuremath{\gamma}$-soft behavior are predicted in Ru and Mo nuclei while a pronounced coexistence between strongly prolate and weakly oblate deformed shapes is found for Zr and Sr nuclei. The method describes well the evolution of experimental yrast and nonyrast states as well as selected $B(E2)$…

We argue that a crucial determinant of the acceptance dependence of fluctuation measures in heavy-ion collisions is the range of correlations in the momentum space, e.g., in rapidity, $\mathrm{\ensuremath{\Delta}}{y}_{\mathrm{corr}}$. The value of $\mathrm{\ensuremath{\Delta}}{y}_{\mathrm{corr}}\ensuremath{\sim}1$ for critical thermal fluctuations is determined by the thermal rapidity spread of the particles at freeze-out, and has little to do with position space correlations, even near the critical point where the spatial correlation length $\ensuremath{\xi}$ becomes as large as 2--3 fm (this is in contrast to the magnitudes of the cumulants, which are sensitive to $\ensuremath{\xi}$). When the acceptance window is large, $\mathrm{\ensuremath{\Delta}}y\ensuremath{\gg}\mathrm{\ensuremath{\Delta}}{y}_{\mathrm{corr}}$, the cumulants of a given particle multiplicity, ${\ensuremath{\kappa}}_{k}$, scale linearly with $\mathrm{\ensuremath{\Delta}}y$, or mean multiplicity in acceptance, $\ensuremath{\langle}N\ensuremath{\rangle}$, and cumulant ratios are acceptance independent. In the…

A microscopic calculation of $\ensuremath{\alpha}$-cluster preformation probability and $\ensuremath{\alpha}$-decay width in the typical $\ensuremath{\alpha}$ emitter $^{212}\mathrm{Po}$ is presented. Results are obtained by improving a recent approach to describe $\ensuremath{\alpha}$ preformation in $^{212}\mathrm{Po}$ [Phys. Rev. C 90, 034304 (2014)] implementing four-nucleon correlations (quartetting). Using the actually measured density distribution of the $^{208}\mathrm{Pb}$ core, the calculated $\ensuremath{\alpha}$-decay width of $^{212}\mathrm{Po}$ agrees fairly well with the measured one.

We calculate the rate of production of hypothetical light vector bosons (LVBs) from nucleon-nucleon bremsstrahlung reactions in hot and dense matter. We use the soft-radiation approximation and express the rates directly in terms of the measured nucleon-nucleon elastic differential cross sections. These results are combined with the observation of neutrinos from supernova SN1987a to deduce constraints on the couplings of vector bosons with masses $\ensuremath{\lesssim}200$ MeV to either electric charge (dark photons) or to baryon number. We establish for the first time strong constraints on LVB that couple only to baryon number and revise earlier constraints on the dark photon. For the latter, we find that the excluded region of parameter space is diminished by about a factor of 10.

New results of the NA61/SHINE Collaboration at the CERN SPS on mean hadron multiplicities in proton-proton (p+p) interactions are analyzed within the transport models and the hadron resonance gas (HRG) statistical model. The chemical freeze-out parameters in p+p interactions and central Pb+Pb (or Au+Au) collisions are found and compared with each other in the range of the center-of-mass energy of the nucleon pair $\sqrt{{s}_{NN}}=3.2--17.3$ GeV. The canonical ensemble formulation of the HRG model is used to describe mean hadron multiplicities in p+p interactions and the grand canonical ensemble in central Pb+Pb and Au+Au collisions. The chemical freeze-out temperatures in p+p interactions are found to be larger than the corresponding temperatures in central nucleus-nucleus collisions.

Assuming that the recently observed hidden-charm pentaquark state, ${P}_{c}(4450)$, is of molecular nature as predicted in the unitary approach, we propose to study the decay of ${\mathrm{\ensuremath{\Xi}}}_{b}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{\ensuremath{-}}\mathrm{\ensuremath{\Lambda}}$ to search for the strangeness counterpart of the ${P}_{c}(4450)$. There are three ingredients in the decay mechanism: the weak decay mechanism, the hadronization mechanism, and the final state interactions in the meson-baryon system of strangeness $S=\ensuremath{-}2$ and isospin $I=1/2$ and of the $J/\ensuremath{\psi}\mathrm{\ensuremath{\Lambda}}$. All these have been tested extensively. As a result, we provide a genuine prediction of the invariant mass distributions where a strangeness hidden-charm pentaquark state, the counterpart of the ${P}_{c}(4450)$, can be clearly seen. The decay rate is estimated to be of similar magnitude as the ${\mathrm{\ensuremath{\Lambda}}}_{b}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{\ensuremath{-}}p$ measured by the LHCb…

For the first time the ALICE Collaboration has measured $D$-meson production down to zero transverse momentum at midrapidity in proton-proton collisions at the CERN Large Hadron Collider. This provides an important constraint on perturbative QCD calculations and the low-$x$ parton distribution functions. It will have implications for cosmic-ray and neutrino astrophysics as well as for modeling high-energy heavy-ion collisions.

The transition helicity amplitudes from the proton ground state to the $N(1440)1/{2}^{+}, N(1520)3/{2}^{\ensuremath{-}}$, and $\mathrm{\ensuremath{\Delta}}(1620)1/{2}^{\ensuremath{-}}$ resonances (${\ensuremath{\gamma}}_{v}p{N}^{*}$ electrocouplings) were determined from the analysis of nine independent onefold differential ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}p$ electroproduction cross sections off a proton target, taken with CLAS at photon virtualities $0.5\phantom{\rule{4.pt}{0ex}}{\text{GeV}}^{2}<{Q}^{2}<1.5$ ${\mathrm{GeV}}^{2}$. The phenomenological reaction model employed for separation of the resonant and nonresonant contributions to this exclusive channel was further developed. The $N(1440)1/{2}^{+}, N(1520)3/{2}^{\ensuremath{-}}$, and $\mathrm{\ensuremath{\Delta}}(1620)1/{2}^{\ensuremath{-}}$ electrocouplings were obtained from the resonant amplitudes of charged double-pion electroproduction off the proton in the aforementioned area of photon virtualities for the first time. Consistent results on ${\ensuremath{\gamma}}_{v}p{N}^{*}$ electrocouplings…

We propose a methodology to calculate microscopically the mass and charge distributions of spontaneous fission yields. We combine the multidimensional minimization of collective action for fission with stochastic Langevin dynamics to track the relevant fission paths from the ground-state configuration up to scission. The nuclear potential energy and collective inertia governing the tunneling motion are obtained with nuclear density functional theory in the collective space of shape deformations and pairing. We obtain a quantitative agreement with experimental data and find that both the charge and mass distributions in the spontaneous fission of $^{240}\mathrm{Pu}$ are sensitive both to the dissipation in collective motion and to adiabatic fission characteristics.

When the quark-gluon plasma emerges in the wake of a heavy-ion collision, a magnetic field created by the valence charges has already permeated the entire interaction region. Evolution of this ``initial'' field in the plasma is governed by the Maxwell equations in an electrically conducting medium. As the plasma expands, external valence charges induce a magnetic field that also contributes to the total magnetic field in the plasma. I solve the initial value problem describing these processes and argue that the initial magnetic field often dominates over the one induced by the valence charges. In particular, it grows approximately proportional to the collision energy, unlike the induced component, which is energy independent. As a result, the magnetic field has a significant phenomenological influence on the quark-gluon plasma at CERN Large Hadron Collider energies over its entire lifetime.

We examine the correlations of neutron star radii with the nuclear matter incompressibility, symmetry energy, and their slopes, which are the key parameters of the equation of state (EoS) of asymmetric nuclear matter. The neutron star radii and the EoS parameters are evaluated using a representative set of 24 Skyrme-type effective forces and 18 relativistic mean field models, and two microscopic calculations, all describing $2{M}_{\ensuremath{\bigodot}}$ neutron stars. Unified EoSs for the inner-crust--core region have been built for all the phenomenological models, both relativistic and nonrelativistic. Our investigation shows the existence of a strong correlation of the neutron star radii with the linear combination of the slopes of the nuclear matter incompressibility and the symmetry energy coefficients at the saturation density. Such correlations are found to be almost independent of the neutron star mass in the range $0.6\text{--}1.8\phantom{\rule{0.16em}{0ex}}{M}_{\ensuremath{\bigodot}}$. This correlation can be linked to the empirical relation existing between the star…