The 50 most-cited articles in Physical Review C, 2020

The ALICE Collaboration reports unique data on particle production in Pb-Pb and inelastic $p$-$p$ collisions at the LHC at 5.02 TeV. The measurements range from very peripheral to the most central collisions, and cover particles with transverse momenta from hundreds of MeV/$c$ to 20 GeV/$c$. The precision and breadth of the data provide tight constraints on our understanding of particle production mechanisms in these collisions.

Superallowed $\ensuremath{\beta}$-decay between nuclear analog states with isospin 1 and spin-parity ${0}^{+}$ offers access to fundamental tests of the properties of the electroweak interaction. With 15 such transitions precisely measured, the data collectively probe the conservation of the weak vector current, set tight limits on the presence of beyond-standard-model scalar currents, and yield the most precise value for the ${V}_{u\phantom{\rule{0}{0ex}}d}$ element of the CKM quark-mixing matrix. ${V}_{u\phantom{\rule{0}{0ex}}d}$ is a critical ingredient required to test the unitarity of that matrix. This work provides an in-depth review of the relevant nuclear physics input and connects these data to the fundamental couplings.

Is the secondary component of GW190814 the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system [Abbott et al. Astrophys. J. 896, L44 (2020)]? This is the central question animating this paper. Covariant density functional theory provides a unique framework to investigate both the properties of finite nuclei and neutron stars, while enforcing causality at all densities. By tuning existing energy density functionals we were able to: (i) account for a $2.6\phantom{\rule{0.16em}{0ex}}{M}_{\ensuremath{\bigodot}}$ neutron star, (ii) satisfy the original constraint on the tidal deformability of a $1.4\phantom{\rule{0.16em}{0ex}}{M}_{\ensuremath{\bigodot}}$ neutron star, and (iii) reproduce ground-state properties of finite nuclei. Yet, for the class of models explored in this work, we find that the stiffening of the equation of state required to support supermassive neutron stars is inconsistent with either constraints obtained from energetic heavy-ion collisions or from the low deformability of medium-mass stars. Thus, we speculate that the…

Background: Recent advances in nuclear structure theory have led to the availability of several complementary ab initio many-body techniques applicable to light and medium-mass nuclei as well as nuclear matter. After successful benchmarks of different approaches, the focus is moving to the development of improved models of nuclear Hamiltonians, currently representing the largest source of uncertainty in ab initio calculations of nuclear systems. In particular, none of the existing two- plus three-body interactions is capable of satisfactorily reproducing all the observables of interest in medium-mass nuclei.Purpose: A novel parametrization of a Hamiltonian based on chiral effective field theory is introduced. Specifically, three-nucleon operators at next-to-next-to-leading order are combined with an existing (and successful) two-body interaction containing terms up to next-to-next-to-next-to-leading order. The resulting potential is labeled $NN+3N\text{(lnl)}$. The objective of the present work is to investigate the performance of this new Hamiltonian across light and medium-mass…

We present calculations of the bulk properties and multiparticle correlations in a large variety of collision systems within a hybrid formalism consisting of impact-parameter-dependent Glasma initial conditions, music viscous relativistic hydrodynamics, and urqmd microscopic hadronic transport. In particular, we study heavy ion collisions at the Large Hadron Collider (LHC), including $\text{Pb}+\text{Pb}$, $\text{Xe}+\text{Xe}$, and $\text{O}+\text{O}$ collisions, and $\text{Au}+\text{Au}$, $\text{U}+\text{U}$, $\text{Ru}+\text{Ru}$, $\text{Zr}+\text{Zr}$, and $\text{O}+\text{O}$ collisions at the Relativistic Heavy Ion Collider (RHIC). We further study asymmetric systems, including $p+\text{Au}$, $d+\text{Au}$, $^{3}\mathrm{He}+\text{Au}$, and $p+\text{Pb}$ collisions at various energies as well as $p+p$ collisions at 0.5 and 13 TeV. We describe experimental observables in all heavy ion systems well with one fixed set of parameters, validating the energy and system dependence of the framework. Many observables in the smaller systems are also well described, although they test the…

We optimize $\mathrm{\ensuremath{\Delta}}$-full nuclear interactions from chiral effective field theory. The low-energy constants of the contact potentials are constrained by two-body scattering phase shifts, and by properties of bound state of $A=2$ to 4 nucleon systems and nuclear matter. The pion-nucleon couplings are taken from a Roy-Steiner analysis. The resulting interactions yield accurate binding energies and radii for a range of nuclei from $A=16$ to $A=132$, and provide accurate equations of state for nuclear matter and realistic symmetry energies. Selected excited states are also in agreement with data.

We construct a family of equations of state for QCD in the temperature range $30\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}\ensuremath{\le}T\ensuremath{\le}800\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ and in the chemical potential range $0\ensuremath{\le}{\ensuremath{\mu}}_{B}\ensuremath{\le}450\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$. These equations of state match available lattice QCD results up to $O({\ensuremath{\mu}}_{B}^{4})$ and in each of them we place a critical point in the three-dimensional (3D) Ising model universality class. The position of this critical point can be chosen in the range of chemical potentials covered by the second Beam Energy Scan at the Relativistic Heavy Ion Collider. We discuss possible choices for the free parameters, which arise from mapping the Ising model onto QCD. Our results for the pressure, entropy density, baryon density, energy density, and speed of sound can be used as inputs in the hydrodynamical simulations of the fireball created in heavy ion collisions. We also show our result for the second cumulant of the baryon number in thermal…

We perform statistically rigorous uncertainty quantification (UQ) for chiral effective field theory ($\ensuremath{\chi}\mathrm{EFT}$) applied to infinite nuclear matter up to twice nuclear saturation density. The equation of state (EOS) is based on high-order many-body perturbation theory calculations with nucleon-nucleon and three-nucleon interactions up to fourth order in the $\ensuremath{\chi}\mathrm{EFT}$ expansion. From these calculations our newly developed Bayesian machine-learning approach extracts the size and smoothness properties of the correlated EFT truncation error. We then propose a novel extension that uses multitask machine learning to reveal correlations between the EOS at different proton fractions. The inferred in-medium $\ensuremath{\chi}\mathrm{EFT}$ breakdown scale in pure neutron matter and symmetric nuclear matter is consistent with that from free-space nucleon-nucleon scattering. These significant advances allow us to provide posterior distributions for the nuclear saturation point and propagate theoretical uncertainties to derived quantities: the pressure…

The global polarization of the $\mathrm{\ensuremath{\Lambda}}$ and $\overline{\mathrm{\ensuremath{\Lambda}}}$ hyperons is measured for Pb-Pb collisions at $\sqrt{{s}_{NN}}=2.76$ and 5.02 TeV recorded with the ALICE at the Large Hadron Collider (LHC). The results are reported differentially as a function of collision centrality and hyperon's transverse momentum (${p}_{T}$) for the range of centrality 5--50%, $0.5<{p}_{T}<5$ GeV/$c$, and rapidity $|y|<0.5$. The hyperon global polarization averaged for Pb-Pb collisions at $\sqrt{{s}_{NN}}=2.76$ and 5.02 TeV is found to be consistent with zero, $\ensuremath{\langle}{P}_{H}\ensuremath{\rangle}(%)\ensuremath{\approx}0.01\ifmmode\pm\else\textpm\fi{}0.06\phantom{\rule{3.33333pt}{0ex}}\text{(stat.)}\ifmmode\pm\else\textpm\fi{}0.03\phantom{\rule{3.33333pt}{0ex}}\text{(syst.)}$ in the collision centrality range 15--50%, where the largest signal is expected. The results are compatible with expectations based on an extrapolation from measurements at lower collision energies at the Relativistic Heavy Ion Collider, hydrodynamical model…

Neutron stars (NSs) contain the densest matter in the universe, and the pressure at densities between 1--3 times nuclear density ($2.8\ifmmode\times\else\texttimes\fi{}{10}^{14}$ g/cm${}^{3}$) determines the relationship between their macroscopic properties, such as mass and radius. The authors compare NS observations from gravitational-wave, X-ray, and radio observations with state-of-the-art theoretical predictions for nuclear forces from chiral effective field theory ($\ensuremath{\chi}$EFT) to determine its validity at high density and when it might break down. The combination of astrophysical observations and $\ensuremath{\chi}$EFT predictions improves the constraints on NS radii and the pressure of dense matter in the NS core. These constraints provide new insights about the phase diagram of dense matter at low temperature and the role of many-body nuclear forces at work within NS cores.

Cluster and hypernuclei production in heavy-ion collisions is presently under active experimental and theoretical investigation. Since clusters are weekly bound objects, their production is very sensitive to the dynamical evolution of the system and its interactions. The theoretical description of cluster formation is related to the $n$-body problem. Here we present the novel $n$-body dynamical transport approach PHQMD (parton-hadron-quantum-molecular dynamics) which is designed to provide a microscopic description of nuclear cluster and hypernucleus formation as well as of general particle production in heavy-ion reactions at relativistic energies. In contrast to the coalescence or statistical models, often used for the cluster formation, in PHQMD clusters are formed dynamically due to the interactions between baryons described on a basis of quantum molecular dynamics (QMD), which allows one to propagate the $n$-body Wigner density and $n$-body correlations in phase space, essential for the cluster formation. The clusters are identified by the MST (minimum spanning tree) procedure…

Strange hadrons are an excellent probe for identifying the phase boundary and onset of deconfinement in the QCD phase diagram. The STAR Collaboration has performed precision measurements of the abundances and transverse-momentum distributions for 8 species of strange mesons and baryons, as functions of centrality during a Au+Au beam-energy scan at RHIC. The results point to a possible change in strange-hadron production dynamics for $\sqrt{{s}_{N\phantom{\rule{0}{0ex}}N}}<20$ GeV. The results significantly improve the experimental knowledge in the energy range where key features of the QCD phase diagram are nowadays being studied.

We posit a unified hydrodynamic and microscopic description of the quark-gluon plasma (QGP) produced in ultrarelativistic $p\text{\ensuremath{-}}\mathrm{Pb}$ and Pb-Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02\phantom{\rule{0.28em}{0ex}}\mathrm{TeV}$ and evaluate our assertion using Bayesian inference. Specifically, we model the dynamics of both collision systems using initial conditions with parametric nucleon substructure, a preequilibrium free streaming stage, event-by-event viscous hydrodynamics, and a microscopic hadronic afterburner. Free parameters of the model, which describe the initial state and QGP medium are then simultaneously calibrated to fit charged-particle yields, mean ${p}_{T}$, and flow cumulants. We argue that the global agreement of the calibrated model with the experimental data strongly supports the existence of hydrodynamic flow in small collision systems at ultrarelativistic energies, and that the flow produced develops at length scales smaller than a single proton. Posterior estimates for the model's input parameters are obtained, and new insights into…

The Royer formulas are often used to calculate the $\ensuremath{\alpha}$-decay half-lives [G. Royer, J. Phys. G 26, 1149 (2000); Nucl. Phys. A 848, 279 (2010)]. In recent years, the amount of experimental data on $\ensuremath{\alpha}$ decay has increased and these formulas have been examined again. They describe precisely the favored $\ensuremath{\alpha}$ decays. For unfavored decays, they are less accurate and important deviations may occur between the calculations and experimental data. The underlying physics of this phenomenon has been revealed and an improved formula with only eight parameters is proposed. This formula takes into account both the blocking effect of unpaired nucleons and the contribution of centrifugal potential. Compared with the original formulas and other improvements, our new formula is more simple to use and more accurate. Encouraged by this, the $\ensuremath{\alpha}$-decay half-lives of even-even nuclei and odd-$A$ nuclei with $Z=117$, 118, 119, and 120 are predicted using our improved formula and the universal decay law [C. Qi et al., Phys. Rev. Lett. 103,…

We present a simple way to construct three-dimensional initial conditions for relativistic heavy-ion collisions based on the Glauber collision geometry. Local energy and momentum conservation conditions are imposed to set non-trivial constraints on our parametrizations of longitudinal profiles for the system's initial energy density and flow velocity. After calibrating parameters with charged hadron rapidity distributions in central $\mathrm{Au}+\mathrm{Au}$ collisions, we test model predictions for particle rapidity distributions in $d+\text{Au}$ and peripheral $\mathrm{Au}+\mathrm{Au}$ collisions in the Beam Energy Scan program at the Relativistic Heavy-Ion Collider. Simulations and comparisons with measurements are also made for $\mathrm{Pb}+\mathrm{Pb}$ collisions at Super Proton Synchrotron energies. We demonstrate that elliptic flow measurements in heavy-ion collisions at $\sqrt{s}\ensuremath{\sim}10$ GeV can set strong constraints on the dependence of quark-gluon plasma shear viscosity on temperature and net baryon chemical potential.

Background: The study of exotic nuclei far from the $\ensuremath{\beta}$ stability line is stimulated by the development of radioactive ion beam facilities worldwide and brings opportunities and challenges to existing nuclear theories. Including self-consistently the nuclear superfluidity, deformation, and continuum effects, the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) has turned out to be successful in describing both stable and exotic nuclei. Due to several challenges, however, the DRHBc theory has only been applied to study light nuclei so far.Purpose: The aim of this work is to develop the DRHBc theory based on the point-coupling density functional and examine its possible application for all even-even nuclei in the nuclear chart by taking Nd isotopes as examples.Method: The nuclear superfluidity is taken into account via Bogoliubov transformation. Densities and potentials are expanded in terms of Legendre polynomials to include the axial deformation degrees of freedom. Sophisticated relativistic Hartree-Bogoliubov equations in coordinate space are…

A search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the $^{50}\mathrm{Ti}+^{249}\mathrm{Bk}$ and $^{50}\mathrm{Ti}+^{249}\mathrm{Cf}$ fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the $^{249}\mathrm{Bk}$ target partially decayed into $^{249}\mathrm{Cf}$, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the $^{50}\mathrm{Ti}+^{249}\mathrm{Bk}$ and $^{50}\mathrm{Ti}+^{249}\mathrm{Cf}$ reactions, respectively, at a midtarget beam energy of ${E}_{\mathrm{lab}}=281.5$ MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical predictions on the fission-barrier heights of superheavy nuclei in the region of the island of stability.

Accurate modeling of $r$-process nucleosynthesis requires reliable calculations for $\ensuremath{\beta}$ decay of nuclei far from stability. The quasiparticle random-phase approximation (QRPA) has been widely used, but deformation and odd numbers of protons and/or neutrons introduce challenges. The authors explain and apply novel advances in the QRPA that address these challenges, providing an enhanced tool for describing astrophysically important decays.

One of the strongest challenges to the shell-model concept of nuclei are the islands of inversion, where empirical evidence shows the ground states being dominated by intruder configurations, i.e., states that would be excitations in the normal shell-model picture. Whereas phenomenological calculations have previously supported this concept, the work of Miyagi $e\phantom{\rule{0}{0ex}}t$ $a\phantom{\rule{0}{0ex}}l$. demonstrates how one can arrive at these non-intuitive results from an $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ perspective.

Background: The chart of the nuclides is limited by particle drip lines beyond which nuclear stability to proton or neutron emission is lost. Predicting the range of particle-bound isotopes poses an appreciable challenge for nuclear theory as it involves extreme extrapolations of nuclear masses well beyond the regions where experimental information is available. Still, quantified extrapolations are crucial for a wide variety of applications, including the modeling of stellar nucleosynthesis.Purpose: We use microscopic nuclear global mass models, current mass data, and Bayesian methodology to provide quantified predictions of proton and neutron separation energies as well as Bayesian probabilities of existence throughout the nuclear landscape all the way to the particle drip lines.Methods: We apply nuclear density-functional theory with several energy density functionals. We also consider two global mass models often used in astrophysical nucleosynthesis simulations. To account for uncertainties, Bayesian Gaussian processes are trained on the separation-energy residuals for each…

The phase-space structure of zero-temperature quarkyonic matter is a Fermi sphere of quark matter surrounded by a shell of nucleonic matter. We construct a quasiparticle model of quarkyonic matter based on the constituent quark model, where the quark and nucleon masses are related by ${m}_{Q}={m}_{N}/{N}_{c}$, and ${N}_{c}$ is the number of quark colors. The region of occupied states is for quarks ${k}_{Q}<{k}_{F}/{N}_{c}$ and for nucleons ${k}_{F}<{k}_{N}<{k}_{F}+\mathrm{\ensuremath{\Delta}}$. We first consider the general problem of quarkyonic matter with hard-core nucleon interactions. We then specialize to a quasiparticle model where the hard-core nucleon interactions are accounted for by an excluded volume. In this model, we show that the nucleonic shell forms past some critical density related to the hard-core size and for large densities becomes a thin shell. We explore the basic features of such a model and argue this model has the semiquantitative behavior needed to describe neutron stars.

The thermodynamic properties of high temperature and high density QCD matter are explored within the chiral SU(3)-flavor parity-doublet Polyakov-loop quark-hadron mean-field model, CMF. The quark sector of the CMF model is tuned to describe the ${\ensuremath{\mu}}_{B}=0$ thermodynamics data of lattice QCD. The resulting lines of constant physical variables as well as the baryon number susceptibilities are studied in some detail in the temperature--chemical-potential plane. The CMF model predicts three consecutive transitions: the nuclear first-order liquid-vapor phase transition, chiral symmetry restoration, and the crossover transition to a quark matter phase. All three phenomena are crossovers, for most of the $T\text{\ensuremath{-}}{\ensuremath{\mu}}_{B}$ plane. The deviations from the free ideal hadron gas baseline at ${\ensuremath{\mu}}_{B}=0$ and $T\ensuremath{\approx}100\text{--}200$ MeV can be attributed to remnants of the liquid-vapor first-order phase transition in nuclear matter. The chiral crossing transition determines the baryon fluctuations at much higher…

We compute the charge radii and ground-state energies of even-mass neon and magnesium isotopes from neutron number $N=8$ to the dripline. Our calculations are based on nucleon-nucleon and three-nucleon potentials from chiral effective field theory that include $\mathrm{\ensuremath{\Delta}}$ isobars. These potentials yield an accurate saturation point and symmetry energy of nuclear matter. We use the coupled-cluster method and start from an axially symmetric reference state. Binding energies and two-neutron separation energies largely agree with data, and the dripline in neon is accurate. The computed charge radii are accurate for many isotopes where data exist. Finer details, such as isotope shifts, however, are not accurately reproduced. These chiral potentials indicate a subshell closure at $N=14$ for the radii (but not for two-neutron separation energies) and a decrease in charge radii at $N=8$ (observed in neon and predicted for magnesium). They yield a continued increase of charge radii as neutrons are added beyond $N=14$ yet underestimate the large increase at $N=20$ in…

The QCD critical endpoint (CEP) is a very distinct feature of the phase diagram of nuclear matter, but it can presently not be located from first-principle calculations; experimental observations are needed to constrain its position. The HADES Collaboration at GSI measured cumulants and correlators for net-proton number fluctuations, the most important observable so far to search for the CEP. This extends experimental results below the lowest beam energies available at RHIC and will be useful to discern the possibility of a critical point in the QCD phase diagram.

This article reports measurements of the ${p}_{\mathrm{T}}$-differential inclusive jet cross section in $pp$ collisions at $\sqrt{s}=5.02\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$ and the ${p}_{\mathrm{T}}$-differential inclusive jet yield in $\text{Pb-Pb}$ 0--10% central collisions at $\sqrt{{s}_{NN}}=5.02\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$. Jets were reconstructed at midrapidity with the ALICE tracking detectors and electromagnetic calorimeter using the anti-${k}_{\mathrm{T}}$ algorithm. For $pp$ collisions, we report jet cross sections for jet resolution parameters $R=0.1--0.6$ over the range $20<{p}_{\mathrm{T},\mathrm{jet}}<140$ $\mathrm{GeV}/c$, as well as the jet cross-section ratios of different $R$ and comparisons to two next-to-leading-order (NLO)--based theoretical predictions. For $\text{Pb-Pb}$ collisions, we report the $R=0.2$ and $R=0.4$ jet spectra for $40<{p}_{\mathrm{T},\mathrm{jet}}<140$ $\mathrm{GeV}/c$ and $60<{p}_{\mathrm{T},\mathrm{jet}}<140$ $\mathrm{GeV}/c$, respectively. The scaled ratio of jet yields observed in $\text{Pb-Pb}$ to $pp$ collisions,…

We approach the calculation of the nuclear matrix element of the neutrinoless double-$\ensuremath{\beta}$ decay process, considering the light-neutrino-exchange channel, by way of the realistic shell model. To this end, we start from a realistic nucleon-nucleon potential and then derive the effective shell-model Hamiltonian and $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay operator within the many-body perturbation theory. We focus on investigating the perturbative properties of the effective shell-model operator of such a decay process, aiming to establish the degree of reliability of our predictions. The contributions of the so-called short-range correlations and of the correction of Pauli-principle violations to the effective shell-model operator, the latter introduced in many-valence nucleon systems, are also taken into account. The subjects of our study are a few candidates to the $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay detection, in a mass interval ranging from $A=48$ up to $A=136$, whose spin- and spin-isospin-dependent decay properties…

In high-energy nuclear collisions, the spatial distribution of the initial energy density fluctuates between individual collision events. These fluctuations (and their gradients) drive the collective flow of the system, and thus leave a measurable imprint. The authors propose observables that quantify the relative fluctuations in the total transverse momentum at fixed multiplicity. The observables can be used to diagnose the quark gluon plasma in different regimes, for instance to gain insight into the entropy initially produced at a given system size, or to provide new constraints on the temperature dependence of energy loss.

Background: The phenomenon of reflection-asymmetric nuclear shapes is relevant to nuclear stability, nuclear spectroscopy, nuclear decays and fission, and the search for new physics beyond the standard model. Global surveys of ground-state octupole deformation, performed with a limited number of models, suggest that the number of pear-shaped isotopes is fairly limited across the nuclear landscape.Purpose: We carry out a global analysis of ground-state octupole deformations for particle-bound even-even nuclei with $Z\ensuremath{\le}110$ and $N\ensuremath{\le}210$ using nuclear density functional theory (DFT) with several nonrelativistic and covariant energy density functionals. In this way, we can identify the best candidates for reflection-asymmetric shapes.Methods: The calculations are performed in the frameworks of axial reflection-asymmetric Hartree-Fock-Bogoliubov theory and relativistic Hartree-Bogoliubov theory using DFT solvers employing harmonic oscillator basis expansion. We consider five Skyrme and four covariant energy density functionals.Results: We predict several…

Background: The nuclear charge radii provide direct information for the nuclear structures. In recent years, many pioneering researches have been devoted to the nuclear charge radii based on the Bayesian neural networks (BNN) method.Purpose: The neural networks always have complex structure. To analyze the data relationships clearly, a statistical method is introduced to study the nuclear properties by combining the sophisticated nuclear models with the naive Bayesian probability (NBP) classifier.Method: In the framework of the NBP method, the predicted charge radii are interpreted as the most reasonable expectations. The prior probabilities and the condition probabilities are computed by the experimental data and the raw results of nuclear models. The posterior probabilities of expectations are updated by the Bayesian formula. The predicted charge radii are regarded as the expectations with maximum probability. Moreover, the abilities of global optimizations and extrapolations of the NBP method are analyzed to demonstrate the availability of the NBP method.Results: For the HFB…

A feed-forward neural network model is trained to calculate the nuclear charge radii. The model is trained with the input data set of proton and neutron number $Z,N$, the electric quadrupole transition strength $B(E2)$ from the first excited ${2}^{+}$ state to the ground state, together with the symmetry energy. The model reproduces well not only the isotope dependence of charge radii, but also the kinks of charge radii at the neutron magic numbers $N=82$ for Sn and Sm isotopes, and also $N=126$ for Pb isotopes. The important role of the $B(E2)$ value is pointed out to reproduce the kink of the isotope dependence of charge radii in these nuclei. Moreover, with the inclusion of the symmetry energy term in the inputs, the charge radii of Ca isotopes are well reproduced. This result suggests a new correlation between the symmetry energy and charge radii of Ca isotopes. The Skyrme Hartree-Fock-Bogoliubov calculation is performed to confirm the existence of this correlation in a microscopic model.

We study the kinematic and thermal vorticities in low-energy heavy-ion collisions by using the ultrarelativistic quantum molecular dynamics model. We explore their time evolution and spatial distribution. We find that the initial vorticities have a nonmonotonic dependence on the collision energy $\sqrt{{s}_{\mathrm{NN}}}$: as $\sqrt{{s}_{\mathrm{NN}}}$ grows the vorticities first increase steeply and then decrease with a turning point around $\sqrt{{s}_{\mathrm{NN}}}\ensuremath{\approx}3--5$ GeV depending on the centrality.

Quantum Monte Carlo calculations of electroweak transitions are performed for $A\ensuremath{\le}10$ nuclei based upon two- and three-nucleon chiral interactions and the associated one- and two-body axial currents. Except for $\ensuremath{\beta}$ decay of ${}^{8}$He, ${}^{8}$Li, and ${}^{8}$B, two-body currents contribute less than 3%. The exceptional nuclei exhibit matrix elements suppressed in impulse approximation based on the leading order (GT) transition operator. For a given interaction, the two-body transition densities exhibit a universal behavior at short distance for all systems under study.

We study the role of pions in hot dense matter encountered in astrophysics. We find that strong interactions enhance the number density of negatively charged pions and that this enhancement can be calculated reliably for a relevant range of density and temperature by using the virial expansion. We assess the influence of pions and muons on the equation of state (EOS) and weak-interaction rates in hot dense matter. We find that thermal pions increase the proton fraction and soften the EOS. We also find that charged current weak reactions involving pions and muons ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}+{\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\pi}$ and ${\ensuremath{\nu}}_{\ensuremath{\mu}}+{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}$ make an important contribution to the opacity of muon neutrinos. This could influence the dynamics of core-collapse supernovae and neutron-star mergers. Finally, we note that pion-nucleon reactions can alter the evolution of the proton fraction when weak…

The symmetry energy obtained with the effective Skyrme energy density functional is related to the values of isoscalar effective mass and isovector effective mass, which is also indirectly related to the incompressibility of symmetric nuclear matter. In this work, we analyze the values of symmetry energy and its related nuclear matter parameters in five-dimensional parameter space by describing the heavy ion collision data, such as isospin diffusion data at 35 MeV/u and 50 MeV/u, neutron skin of $^{208}\mathrm{Pb}$, and tidal deformability and maximum mass of neutron star. We obtain the parameter sets which can describe the isospin diffusion, neutron skin, tidal deformability, and maximum mass of neutron star, and give the incompressibility ${K}_{0}=250.23\ifmmode\pm\else\textpm\fi{}20.16$ MeV, symmetry energy coefficient ${S}_{0}=31.35\ifmmode\pm\else\textpm\fi{}2.08$ MeV, the slope of symmetry energy $L=59.57\ifmmode\pm\else\textpm\fi{}10.06$ MeV, isoscalar effective mass ${m}_{s}^{*}/m=0.75\ifmmode\pm\else\textpm\fi{}0.05$, and quantity related to effective mass splitting…

The kernel ridge regression (KRR) approach is employed to improve the nuclear mass predictions for the first time, and more importantly, a careful study of the expected predictive power in the neutron-rich region of the nuclear chart is presented, which is crucial for astrophysical simulations of nucleosynthesis processes. The ridge penalty influences the optimized kernel function significantly and plays an essential role in reducing the risk of overfitting and improving the accuracy of the predictions. By taking the WS4 mass model as an example, the mass for each nucleus in the nuclear chart is predicted with the KRR network, which is trained with the mass model residuals, i.e., deviations between experimental and calculated masses, of other nuclei with known masses. The resultant root-mean-square mass deviation from the available experimental data for the 2353 nuclei with $Z\ensuremath{\ge}8$ and $N\ensuremath{\ge}8$ can be reduced to 199 keV. This is at the same level with other machine-learning-rooted approaches, such as the radial basis function and Bayesian neural network…

With the advent of nuclear interactions based on chiral effective field theory, it is becoming possible to accurately describe atomic nuclei and infinite nuclear matter as found in neutron stars. A key challenge is the simultaneous quantification of uncertainties associated to the nuclear interaction and many-body approaches. By performing benchmark calculations of pure neutron matter with realistic interactions and several many-body approaches, this manuscript presents a first step in this direction.

We have calculated a complete set of primary fission fragment mass yields, $Y(A)$, for heavy nuclei across the chart of nuclides, including those of particular relevance to the rapid neutron capture process ($r$ process) of nucleosynthesis. We assume that the nuclear shape dynamics are strongly damped, which allows for a description of the fission process via Brownian shape motion across nuclear potential-energy surfaces. The macroscopic energy of the potential was obtained with the Finite-Range Liquid-Drop Model (FRLDM), while the microscopic terms were extracted from the single-particle level spectra in the fissioning system by the Strutinsky procedure for the shell energies and the BCS treatment for the pairing energies. For each nucleus considered, the fission fragment mass yield, $Y(A)$, is obtained from 50 000 to 500 000 random walks on the appropriate potential-energy surface. The full mass and charge yield, $Y(Z,A)$, is then calculated by invoking the Wahl systematics. With this method, we have calculated a comprehensive set of fission-fragment yields from over 3800 nuclides…

The authors investigate correlations between protons and $\mathrm{\ensuremath{\Omega}}$ baryons, and between two $\mathrm{\ensuremath{\Omega}}$ baryons, in heavy-ion collisions at RHIC and LHC. Given sufficient statistics in upcoming experiments, such measurements could provide valuable information on the existence of strange dibaryons and on the equation of state relevant to neutron stars.

The generalized liquid drop model (GLDM) is first extended to study the two-proton $(2p)$ radioactivity half-lives of the ground state of nuclei. According to the comparison between the calculated half-lives and the experimental data, it is shown that the GLDM describes the $2p$ radioactivity half-lives well. In addition, by comparing its accuracy with other models, it is found that the GLDM has a comparable accuracy with them. Finally, the $2p$ radioactivity half-lives of some of the most probable candidates are predicted with the GLDM by inputting the ${Q}_{2p}$ values (the released energy of the $2p$ radioactivity) from the updated 2016 Atomic Mass Evaluation mass table, which may be useful for future experiments.

We investigate the impact of charged-current--neutrino processes on the formation and evolution of neutrino spectra during the deleptonization of proto-neutron stars. To this end we develop the full kinematics of these reaction rates consistent with the nuclear equation of state, including weak magnetism contributions. This allows us to systematically study the impact of inelastic contributions and weak magnetism on the ${\ensuremath{\nu}}_{e}$ and ${\overline{\ensuremath{\nu}}}_{e}$ luminosities and average energies. Furthermore, we explore the role of the inverse neutron decay, also known as the direct Urca process, on the emitted spectra of ${\overline{\ensuremath{\nu}}}_{e}$. This process is commonly considered in the cooling scenario of cold neutron stars but has so far been neglected in the evolution of hot proto-neutron stars. We find that the inverse neutron decay becomes the dominating opacity source for low-energy ${\overline{\ensuremath{\nu}}}_{e}$. Accurate three-flavor Boltzmann neutrino transport enables us to relate the magnitude of neutrino fluxes and spectra to…

The event generator based on the higher-twist energy loss formalism---Modular All Twist Transverse-scattering Elastic-drag and Radiation (Matter)---is further developed and coupled to a hydrodynamic model for studying jet modification in relativistic nuclear collisions. The probability of parton splitting is calculated using the Sudakov form factor that is constructed by a combination of vacuum and medium-induced splitting functions; and the full parton showers are simulated, including both energy-momentum and space-time evolutions of all jet partons. With the assumption that partons below a virtual scale of 1 GeV is absorbed by the medium, this framework is able to provide a reasonable description of the nuclear modification of both leading hadrons and jets at high transverse momentum at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider.

Background: The limits of the nuclear landscape are determined by nuclear binding energies. Beyond the proton drip lines, where the separation energy becomes negative, there is not enough binding energy to prevent protons from escaping the nucleus. Predicting properties of unstable nuclear states in the vast territory of proton emitters poses an appreciable challenge for nuclear theory as it often involves far extrapolations. In addition, significant discrepancies between nuclear models in the proton-rich territory call for quantified predictions.Purpose: With the help of Bayesian methodology, we mix a family of nuclear mass models corrected with statistical emulators trained on the experimental mass measurements. We study the impact of such model mixing in the proton-rich region of the nuclear chart.Methods: Separation energies were computed within nuclear density functional theory using several Skyrme and Gogny energy density functionals. We also considered mass predictions based on two models used in astrophysical studies. Quantified predictions were obtained for each model using…

Preliminary data by the STAR collaboration at the BNL Relativistic Heavy Ion Collider shows that the elliptic flow, ${v}_{2}$, and the average transverse momentum, $\ensuremath{\langle}{p}_{t}\ensuremath{\rangle}$, of final-state hadrons produced in high-multiplicity $^{238}\mathrm{U}+^{238}\mathrm{U}$ collisions are negatively correlated. This observation brings experimental evidence of a significant prolate deformation, $\ensuremath{\beta}\ensuremath{\approx}0.3$, in the colliding $^{238}\mathrm{U}$ nuclei. I show that a quantitative description of this new phenomenon can be achieved within the hydrodynamic framework of heavy-ion collisions, and that thus such kind of data in the context of high-energy nuclear experiments can help constrain the quadrupole deformation of the colliding species.

This paper describes the measurements of flow harmonics ${v}_{2}$--${v}_{6}$ in $3\ensuremath{\mu}{\mathrm{b}}^{\ensuremath{-}1}$ of $\mathrm{Xe}+\mathrm{Xe}$ collisions at $\sqrt{{s}_{NN}}=5.44$ TeV performed using the ATLAS detector at the Large Hadron Collider (LHC). Measurements of the centrality, multiplicity, and ${p}_{\mathrm{T}}$ dependence of the ${v}_{n}$ obtained using two-particle correlations and the scalar product technique are presented. The measurements are also performed using a template-fit procedure, which was developed to remove nonflow correlations in small collision systems. This nonflow removal is shown to have a significant influence on the measured ${v}_{n}$ at high ${p}_{\mathrm{T}}$, especially in peripheral events. Comparisons of the measured ${v}_{n}$ with measurements in $\mathrm{Pb}+\mathrm{Pb}$ collisions and $p+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=5.02$ TeV are also presented. The ${v}_{n}$ values in $\mathrm{Xe}+\mathrm{Xe}$ collisions are observed to be larger than those in $\mathrm{Pb}+\mathrm{Pb}$ collisions for $n=2$, 3, and 4 in the most…

Two new USD-type Hamiltonians, USDC and USDI, have been developed that directly incorporate Coulomb and other isospin-breaking interactions. Starting from ab initio interactions, linear combinations of two-body matrix elements were constrained by experimental energy levels in sd-shell nuclei. With this method, binding energies and excitation energies of proton-rich nuclei in the shell can be added to the data set used in the fit. USDC is based on the same renormalized $G$ matrix used in the derivation of previous USD-type Hamiltonians, while USDI is derived from in-medium similarity renormalization group (IMSRG) interactions. Both contain an analytic Coulomb interaction with Miller-Spencer short-range correlations and an effective isotensor interaction. Also presented are modifications to these interactions, USDCm and USDIm, that have had the Coulomb interaction constrained to better reproduce the experimental $b$ coefficients of the isobaric mass multiplet equation. These Hamiltonians are used to provide new predictions for the proton-dripline and to examine isospin-level mixing…

The interpretation of nuclear observables in the laboratory frame in terms of the intrinsic deformation parameters $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ is a classical theme in nuclear structure. Here we use the quadrupole invariants, calculated within the framework of the configuration-interaction shell model, to clarify the meaning and limitations of nuclear shapes. We introduce a novel method that enables us to calculate accurately higher-order invariants and, therefore, the fluctuations in both $\ensuremath{\beta}$ and $\ensuremath{\gamma}$. We find that the shape parameter $\ensuremath{\beta}$ often has a non-negligible degree of softness and that the angle $\ensuremath{\gamma}$ is usually characterized by large fluctuations, rendering its effective value not meaningful. Contrary to common belief, we conclude that doubly magic nuclei are not spherical, because the notion of a well-defined shape does not apply to them.

We have studied the compound nucleus probability, the survival probability, and the evaporation residue cross sections for 6645 projectile-target combinations to synthesize the superheavy nuclei with atomic numbers $Z=110$--126 in the light of the entrance channel effects such as mass asymmetry, charge asymmetry, isospin asymmetry, non-compound nuclear fission probability, and Businaro-Gallone mass asymmetry. The role of quasifission in every reaction has also been considered. Decay chains of various superheavy nuclei produced from the reactions are portrayed as well. The most striking results are that the measured evaporation residue cross sections are of the order of picobarns, whereas the proposed reactions can yield up to microbarn cross sections for the superheavy nuclei with $110\ensuremath{\le}Z\ensuremath{\le}126$. We suggest future experiments may utilize these hot fusion reactions to synthesize new elements ($Z>118$) or to study the properties of the known superheavy nuclei in greater detail. In particular, a proposed reaction containing both projectiles and targets that…

To describe dynamics of bulk and fluctuations near the QCD critical point we develop general relativistic fluctuation formalism for a fluid carrying baryon charge. Feedback of fluctuations modifies hydrodynamic coefficients including bulk viscosity and conductivity and introduces nonlocal and noninstantaneous terms in constitutive equations. We perform necessary ultraviolet (short-distance) renormalization to obtain cutoff-independent deterministic equations suitable for numerical implementation. We use the equations to calculate the universal nonanalytic small-frequency dependence of transport coefficients due to fluctuations (long-time tails). Focusing on the critical mode we show how this general formalism matches existing $\text{Hydro+}$ description of fluctuations near the QCD critical point and nontrivially extends it inside and outside of the critical region.

A relativistic quantum molecular dynamics model, including momentum-dependent mean fields, is used to study directed and elliptic flow of protons in relativistic heavy ion collisions. The model agrees well with experimental data up to a center-of-momentum energy of about 10 GeV. However, above that energy the measured directed flow collapses to near zero, suggesting a transition to a different state of matter with a softened equation of state.

The historic first detection of the binary neutron star merger GW170817 by the LIGO-Virgo collaboration has set a limit on the gravitational deformability of neutron stars. In contrast, radio observations of PSR $\mathrm{J}0740+6620$ find a very massive neutron star. Tension between the small deformability and the large maximum mass may suggest that the pressure rises rapidly with density and thus the speed of sound in dense matter is likely a large fraction of the speed of light. We use these observations and simple constant sound-speed model equations of state to set a lower bound on the maximum speed of sound in neutron stars. If the tidal deformability of a $1.4\phantom{\rule{0.16em}{0ex}}{M}_{\ensuremath{\bigodot}}$ neutron star is less than 600, as is suggested by subsequent analyses of GW170817, then we find that the sound speed in the cores of neutron stars is likely larger than the conformal limit of $c/\sqrt{3}$. Implications of this for our understanding of both hadronic and quark-gluon descriptions of dense matter are discussed.