The 50 most-cited articles in Physical Review C, 2021

We study the properties of the strongly coupled quark-gluon plasma with a multistage model of heavy-ion collisions that combines the ${\mathrm{T}}_{\mathrm{R}}\mathrm{ENTo}$ initial condition ansatz, free-streaming, viscous relativistic hydrodynamics, and a relativistic hadronic transport. A model-to-data comparison with Bayesian inference is performed, revisiting assumptions made in previous studies. The role of parameter priors is studied in light of their importance for the interpretation of results. We emphasize the use of closure tests to perform extensive validation of the analysis workflow before comparison with observations. Our study combines measurements from the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC), achieving a good simultaneous description of a wide range of hadronic observables from both colliders. The selected experimental data provide reasonable constraints on the shear and the bulk viscosities of the quark-gluon plasma at $T\ensuremath{\approx}$ 150--250 MeV, but their constraining power degrades at higher temperatures,…

We introduce a model for heavy ion collisions named trajectum, which includes an expanded initial stage with a variable free streaming velocity ${v}_{\mathrm{fs}}$ and a hydrodynamic stage with three varying second order transport coefficients. We describe how to obtain a Gaussian emulator for this 20-parameter model and show results for key observables. This emulator can be used to obtain Bayesian posterior estimates on the parameters, which we test by an elaborate closure test as well as a convergence study. Lastly, we employ the optimal values of the parameters found in Nijs et al. [G. Nijs, W. van der Schee, U. G\"ursoy, and R. Snellings, Phys. Rev. Lett. 126, 202301 (2021)] to perform a detailed comparison to experimental data from PbPb and $p\mathrm{Pb}$ collisions. This includes both observables that have been used to obtain these values as well as wider transverse momentum ranges and new observables such as correlations of event-plane angles.

We report a systematic measurement of cumulants, ${C}_{n}$, for net-proton, proton, and antiproton multiplicity distributions, and correlation functions, ${\ensuremath{\kappa}}_{n}$, for proton and antiproton multiplicity distributions up to the fourth order in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, 39, 54.4, 62.4, and 200 GeV. The ${C}_{n}$ and ${\ensuremath{\kappa}}_{n}$ are presented as a function of collision energy, centrality and kinematic acceptance in rapidity, $y$, and transverse momentum, ${p}_{T}$. The data were taken during the first phase of the Beam Energy Scan (BES) program (2010--2017) at the BNL Relativistic Heavy Ion Collider (RHIC) facility. The measurements are carried out at midrapidity ($|y|<$ 0.5) and transverse momentum $0.4<{p}_{T}<2.0\phantom{\rule{4pt}{0ex}}\mathrm{GeV}/c$, using the STAR detector at RHIC. We observe a nonmonotonic energy dependence ($\sqrt{{s}_{NN}}$ = 7.7--62.4 GeV) of the net-proton ${C}_{4}/{C}_{2}$ with the significance of $3.1\ensuremath{\sigma}$ for the 0--5% central…

We combine the equation of state of dense matter up to twice nuclear saturation density ${n}_{\mathrm{sat}}$ obtained using chiral effective field theory $(\ensuremath{\chi}\mathrm{EFT})$ and recent observations of neutron stars to gain insights about the high-density matter encountered in their cores. A key element in our study is the recent Bayesian analysis of correlated EFT truncation errors based on order-by-order calculations up to next-to-next-to-next-to-leading order in the $\ensuremath{\chi}\mathrm{EFT}$ expansion. We refine the bounds on the maximum mass imposed by causality at high densities and provide stringent limits on the maximum and minimum radii of $\ensuremath{\sim}1.4\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ and $\ensuremath{\sim}2.0\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ stars. Including $\ensuremath{\chi}\mathrm{EFT}$ predictions from ${n}_{\mathrm{sat}}$ to $2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$ reduces the permitted ranges of the radius of a…

In the context of the massive secondary object recently observed in the compact-star merger GW190814, we investigate the possibility of producing massive neutron stars from a few different equation of state models that contain exotic degrees of freedom, such as hyperons and quarks. Our work shows that state-of-the-art relativistic mean-field models can generate massive stars reaching $\ensuremath{\gtrsim}2.05\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\mathrm{Sun}}$, while being in good agreement with gravitational-wave events and x-ray pulsar observations, when quark vector interactions and nonstandard self-vector interactions are introduced. In particular, we present a new version of the Chiral Mean Field (CMF) model in which a different quark-deconfinement potential allows for stable stars with a pure quark core. When rapid rotation is considered, our models generate stellar masses that approach, and in some cases surpass $2.5\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\mathrm{Sun}}$. We find that in such cases fast rotation does not necessarily suppress exotic degrees of freedom due…

We report a new determination of $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}$, the jet transport coefficient of the quark-gluon plasma. We use the JETSCAPE framework, which incorporates a novel multistage theoretical approach to in-medium jet evolution and Bayesian inference for parameter extraction. The calculations, based on the Matter and Lbt jet quenching models, are compared to experimental measurements of inclusive hadron suppression in $\mathrm{Au}+\mathrm{Au}$ collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and $\mathrm{Pb}+\mathrm{Pb}$ collisions at the CERN Large Hadron Collider (LHC). The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. The functional dependence of $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{q}$ on jet energy or virtuality and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of Matter and Lbt. In the multistage approach, the switch between Matter and Lbt is governed by a virtuality scale ${Q}_{0}$.…

Global hyperon polarization, ${\overline{P}}_{\mathrm{H}}$, in $\mathrm{Au}+\mathrm{Au}$ collisions over a large range of collision energy, $\sqrt{{s}_{\mathrm{NN}}}$, was recently measured and successfully reproduced by hydrodynamic and transport models with intense fluid vorticity of the quark-gluon plasma. While na\"{\i}ve extrapolation of data trends suggests a large ${\overline{P}}_{\mathrm{H}}$ as the collision energy is reduced, the behavior of ${\overline{P}}_{\mathrm{H}}$ at small $\sqrt{{s}_{\mathrm{NN}}}<7.7$ GeV is unknown. Operating the STAR experiment in fixed-target mode, we measured the polarization of $\mathrm{\ensuremath{\Lambda}}$ hyperons along the direction of global angular momentum in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=3$ GeV. The observation of substantial polarization of $4.91\ifmmode\pm\else\textpm\fi{}0.81(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}0.15(\mathrm{syst}.)%$ in these collisions may require a reexamination of the viscosity of any fluid created in the collision, of the thermalization timescale of rotational modes,…

In this paper, we start with chiral kinetic theory and construct the spin hydrodynamic framework for a chiral spinor system. Using the 14-moment expansion formalism, we obtain the equations of motion of second-order dissipative relativistic fluid dynamics with nontrivial spin-polarization density. In a chiral spinor system, the spin-alignment effect could be treated in the same framework as the chiral vortical effect (CVE). However, the quantum corrections due to fluid vorticity induce not only CVE terms in the vector/axial charge currents, but also corrections to the stress tensor. In this framework, viscous corrections to the hadron spin polarization are self-consistently obtained, which will be important for precise prediction of the polarization rate for the observed hadrons, e.g., $\mathrm{\ensuremath{\Lambda}}$ hyperon.

We study local spin polarization in the relativistic hydrodynamic model. Generalizing the Wigner functions previously obtained from chiral kinetic theory by Y. Hidaka et al. [Phys. Rev. D 97, 016004 (2018)] to the massive case, we present the possible contributions up to the order of $\ensuremath{\hbar}$ from thermal vorticity, shear viscous tensor, other terms associated with the temperature and chemical-potential gradients, and electromagnetic fields to the local spin polarization. We then implement the $(3+1)$--dimensional viscous hydrodynamic model to study the spin polarizations from these sources with a small chemical potential and ignorance of electromagnetic fields by adopting an equation of state different from those in other recent studies. Although the shear correction alone upon the local polarization results in a sign and azimuthal-angle dependence more consistent with experimental observations, as also discovered in other recent studies, it is mostly suppressed by the contributions from thermal vorticity and other terms that yield an opposite trend. It is found that…

Background: Entanglement plays a central role in a diverse array of increasingly important research areas, including quantum computation, simulation, measurement, sensing, and communication. Extensive suites of investigations have been performed to better understand entanglement in atomic and molecular quantum many-body systems, while the exploration of entanglement in the structure of nuclei and their reactions is presently in its infancy.Purpose: The goal of this work is to begin investigating the entanglement properties of nuclei from first-principles nuclear many-body calculations. We attempt to identify common features and emergent structures of entanglement that could ultimately lead to new and natural many-body schemes. With an eye toward quantum accelerators in future hybrid-supercomputers, criteria for partitioning nuclear many-body calculations into quantum and classical components may provide advantages in future large-scale computations. Along the way we look for explanations of the relative success of phenomenological models such as the nuclear shell model, and for…

This Low Energy Nuclear Physics International Collaboration (LENPIC) paper provides an example of $a\phantom{\rule{0}{0ex}}b$-$i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ nuclear structure calculations worth noting. Using chiral effective field theory starting from two-body and three-body nuclear data, the authors work up through $p$-shell nuclei, with careful attention paid to quantifying the theoretical uncertainties. The remaining discrepancies with experiment, particularly overbinding in the upper $p$ shell, point to next steps to be taken. As a caveat, known excited states that cannot be well described within current computational limitations are missing.

We perform a systematic study of the spin polarization of hyperons in heavy ion collisions using the music hydrodynamic model with a multiphase transport preequilibrium dynamics. Our model calculations nicely describe the measured collision energy, centrality, rapidity, and ${p}_{T}$ dependence of the $\mathrm{\ensuremath{\Lambda}}$ polarization. We also study and predict the global spin polarization of ${\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}$ and ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}$ as a function of collision energy, which provides a baseline for the studies of the magnetic moment, spin, and mass dependence of the spin polarization. For the local spin polarization, we calculate the radial and azimuthal components of the transverse $\mathrm{\ensuremath{\Lambda}}$ polarization and find specific modulating behavior which could reflect the circular vortical structure. However, our model fails to describe the azimuthal-angle dependence of the longitudinal and transverse $\mathrm{\ensuremath{\Lambda}}$ polarizations, which indicates that the hydrodynamic framework with…

We calculate the electric dipole moment of the nucleon induced by the quantum chromodynamics $\ensuremath{\theta}$ term. We use the gradient flow to define the topological charge and use ${N}_{f}=2+1$ flavors of dynamical quarks corresponding to pion masses of 700, 570, and $410\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$, and perform an extrapolation to the physical point based on chiral perturbation theory. We perform calculations at three different lattice spacings in the range of $0.07\phantom{\rule{0.16em}{0ex}}\mathrm{fm}<a<0.11\phantom{\rule{0.16em}{0ex}}\mathrm{fm}$ at a single value of the pion mass, to enable control on discretization effects. We also investigate finite-size effects using two different volumes. A novel technique is applied to improve the signal-to-noise ratio in the form factor calculations. The very mild discretization effects observed suggest a continuumlike behavior of the nucleon electric dipole moment toward the chiral limit. Under this assumption our results read…

Angular correlation spectra of ${e}^{+}{e}^{\ensuremath{-}}$ pairs produced in the $^{3}\mathrm{H}(p,{e}^{+}{e}^{\ensuremath{-}})^{4}\mathrm{He}$ nuclear reaction have been studied at ${E}_{p}=510$, 610, and 900 keV proton energies. The main features of the spectra can be understood by taking into account the internal and external pair creations following the proton capture by $^{3}\mathrm{H}$. However, these processes cannot account for an observed peak around ${115}^{\ensuremath{\circ}}$ in the angular correlation spectra. This anomalous excess of ${e}^{+}{e}^{\ensuremath{-}}$ pairs can be described by the creation and subsequent decay of a light particle during the direct capture process. The derived mass of the particle is ${m}_{\mathrm{X}}{c}^{2}=16.94\ifmmode\pm\else\textpm\fi{}0.12(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.21(\mathrm{syst})$ MeV. According to the mass this is likely the same X17 particle, which we recently suggested [Phys. Rev. Lett. 116, 042501 (2016)] for describing the anomaly observed in the decay of $^{8}\mathrm{Be}$.

We present new equations of state for applications in core-collapse supernova and neutron star merger simulations. We start by introducing an effective mass parametrization that is fit to recent microscopic calculations up to twice saturation density. This is important to capture the predicted thermal effects, which have been shown to determine the proto--neutron star contraction in supernova simulations. The parameter range of the energy-density functional underlying the equation of state is constrained by chiral effective field theory results at nuclear densities as well as by functional renormalization group computations at high densities based on QCD. We further implement observational constraints from measurements of heavy neutron stars, the gravitational wave signal of GW170817, and from the recent NICER results. Finally, we study the resulting allowed ranges for the equation of state and for properties of neutron stars, including the predicted ranges for the neutron star radius and maximum mass.

The symmetry energy and its density dependence are pivotal for many nuclear physics and astrophysics applications, as they determine properties ranging from the neutron-skin thickness of nuclei to the crust thickness and the radius of neutron stars. Recently, PREX-II reported a value of $0.283\ifmmode\pm\else\textpm\fi{}0.071$ fm for the neutron-skin thickness of $^{208}\mathrm{Pb}$, ${R}_{\mathrm{skin}}^{^{208}\mathrm{Pb}}$, implying a symmetry-energy slope parameter $L$ of $106\ifmmode\pm\else\textpm\fi{}37$ MeV, larger than most ranges obtained from microscopic calculations and other nuclear experiments. We use a nonparametric equation of state representation based on Gaussian processes to constrain the symmetry energy ${S}_{0}$, $L$, and ${R}_{\mathrm{skin}}^{^{208}\mathrm{Pb}}$ directly from observations of neutron stars with minimal modeling assumptions. The resulting astrophysical constraints from heavy pulsar masses, LIGO/Virgo, and NICER favor smaller values of the neutron skin and $L$, as well as negative symmetry incompressibilities. Combining astrophysical data with…

The transport properties of the strongly coupled quark-gluon plasma created in ultrarelativistic heavy-ion collisions are extracted by Bayesian parameter estimate methods with the latest collision beam energy data from the CERN Large Hadron Collider. This Bayesian analysis includes sophisticated flow harmonic observables for the first time. We found that the temperature dependence of specific shear viscosity appears weaker than in the previous studies. The results prefer a lower value of specific bulk viscosity and a higher switching temperature to reproduce additional observables. However, the improved statistical uncertainties both on the experimental data and hydrodynamic calculations with additional observables do not help to reduce the final credibility ranges much, indicating a need for improving the dynamical collision model before the hydrodynamic takes place. In addition, the sensitivities of experimental observables to the parameters in hydrodynamic model calculations are quantified. It is found that the analysis benefits most from the symmetric cumulants and nonlinear…

We explore the constraints on the three-nucleon force (3NF) of chiral effective field theory $(\ensuremath{\chi}\mathrm{EFT})$ that are provided by bound-state observables in the $A=3$ and $A=4$ sectors. Our statistically rigorous analysis incorporates experimental error, computational method uncertainty, and the uncertainty due to truncation of the $\ensuremath{\chi}\mathrm{EFT}$ expansion at next-to-next-to-leading order. A consistent solution for the $^{3}\mathrm{H}$ binding energy, the $^{4}\mathrm{He}$ binding energy and radius, and the $^{3}\mathrm{H}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay rate can only be obtained if $\ensuremath{\chi}\mathrm{EFT}$ truncation errors are included in the analysis. The $\ensuremath{\beta}$-decay rate is the only one of these that yields a nondegenerate constraint on the 3NF low-energy constants, which makes it crucial for the parameter estimation. We use eigenvector continuation for fast and accurate emulation of no-core shell model calculations of the few-nucleon observables. This facilitates sampling of the posterior probability…

We systematically study the hyperon global polarization's sensitivity to a collision system's initial longitudinal flow velocity in hydrodynamic simulations. By explicitly imposing local energy-momentum conservation when mapping the initial collision geometry to macroscopic hydrodynamic fields, we study the evolution of the system's orbital angular momentum (OAM) and fluid vorticity. We find that a simultaneous description of the $\mathrm{\ensuremath{\Lambda}}$ hyperon's global polarization and the slope of the pion's directed flow can strongly constrain the size of longitudinal flow at the beginning of hydrodynamic evolution. We extract the size of the initial longitudinal flow and the fraction of orbital angular momentum in the produced quark-gluon plasma fluid as a function of collision energy with the STAR measurements in the Beam Energy Scan program at the BNL Relativistic Heavy-Ion Collider. We find that there is about 100--200 $\ensuremath{\hbar}$ OAM that remains in the mid-rapidity fluid at the beginning of hydrodynamic evolution. We further examine the effects of different…

Within the transport model evaluation project (TMEP) of simulations for heavy-ion collisions, the mean-field response is examined here. Specifically, zero-sound propagation is considered for neutron-proton symmetric matter enclosed in a periodic box, at zero temperature and around normal density. The results of several transport codes belonging to two families (BUU-like and QMD-like) are compared among each other and to exact calculations. For BUU-like codes, employing the test particle method, the results depend on the combination of the number of test particles and the spread of the profile functions that weight integration over space. These parameters can be properly adapted to give a good reproduction of the analytical zero-sound features. QMD-like codes, using molecular dynamics methods, are characterized by large damping effects, attributable to the fluctuations inherent in their phase-space representation. Moreover, for a given nuclear effective interaction, they generally lead to slower density oscillations, as compared to BUU-like codes. The latter problem is mitigated in…

The body of experimental measurements of intermediate-energy reactions that remove a single nucleon from a secondary beam of neutron- or proton-rich nuclei continues to grow. These data have been analyzed consistently using an approximate, eikonal-model treatment of the reaction dynamics combined with appropriate shell-model descriptions of the projectile initial state, the bound final states spectrum of the reaction residue, and single-particle removal strengths computed from their wave-function overlaps. The systematics of the ratio ${R}_{s}$ of the measured inclusive cross section to all bound final states and the calculated cross section to bound shell-model states---in different regions of the nuclear chart and involving both very weakly bound and strongly bound valence nucleons---is important in relating the empirically deduced orbital occupancies to those from the best available shell-model predictions. Importantly, several new higher-energy measurements, for which the sudden-approximation aspect of the dynamical description is placed on an even stronger footing, now…

Background: Precise measurements of atomic transitions affected by electron-nucleus hyperfine interactions offer sensitivity to explore basic properties of the atomic nucleus and study fundamental symmetries, including the search for new physics beyond the standard model of particle physics. In particular, such measurements, augmented by atomic and nuclear calculations, will enable extraction of the higher-order radial moments of the charge-density distribution in spherical and deformed nuclei. The new data impose higher precision requirements on a theoretical description.Purpose: The nuclear charge density is composed of the proton point distribution folded with the nucleonic charge distributions. The latter induce subtle relativistic corrections due to the coupling of nucleon magnetic moments with the nuclear spin-orbit density. Additional corrections come from the effect of center-of-mass projection. We assess the precision of nuclear charge density calculations by studying the behavior of relativistic and center-of-mass motion corrections to the second and fourth charge radial…

The predictive power of the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) for nuclear mass is examined in the superheavy region, $102\ensuremath{\le}Z\ensuremath{\le}120$. The accuracy of predicting the 10 (56) measured (measured and empirical) masses is 0.635 (0.642) MeV, in comparison with 0.515 (1.360) MeV by WS4 and 0.910 (2.831) MeV by FRDM. Possible stability against multineutron emission beyond the two-neutron drip line is explored by the DRHBc theory, which takes into account simultaneously the deformation effects, the pairing correlations, and the continuum effects. Nuclei stable against two- and multineutron emissions beyond the two-neutron drip line are predicted in $_{106}\mathrm{Sg}, _{108}\mathrm{Hs}, _{110}\mathrm{Ds}$, and $_{112}\mathrm{Cn}$ isotopic chains, forming a peninsula of stability adjacent to the nuclear mainland. This stability is mainly due to the deformation which significantly affects the shell structure around the Fermi surface. The pairing correlations and continuum influence the stability peninsula in a self-consistent way.

Over the past decade the in-medium similarity renormalization group (IMSRG) approach has proven to be a powerful and versatile ab initio many-body method for studying medium-mass nuclei. So far, the IMSRG was limited to the approximation in which only up to two-body operators are incorporated in the renormalization group flow, referred to as the IMSRG(2). In this work, we extend the IMSRG(2) approach to fully include three-body operators yielding the IMSRG(3) approximation. We use a perturbative scaling analysis to estimate the importance of individual terms in this approximation and introduce truncations that aim to approximate the IMSRG(3) at a lower computational cost. The IMSRG(3) is systematically benchmarked for different nuclear Hamiltonians for $^{4}\mathrm{He}$ and $^{16}\mathrm{O}$ in small model spaces. The IMSRG(3) systematically improves over the IMSRG(2) relative to exact results. Approximate IMSRG(3) truncations constructed based on computational cost are able to reproduce much of the systematic improvement offered by the full IMSRG(3). We also find that the…

The nuclear landscape is investigated within the triaxial relativistic Hartree-Bogoliubov theory with the PC-PK1 density functional, and the beyond-mean-field dynamical correlation energies are taken into account by a microscopically mapped five-dimensional collective Hamiltonian without additional free parameters. The effects of triaxial deformation and dynamical correlations on the nuclear landscape are analyzed. The present results provide a better description of the experimental binding energies of even-even nuclei, in particular for medium and heavy mass regions, in comparison with previous global calculations with the state-of-the-art covariant density functionals DD-PC1 and TMA. The inclusion of the dynamical correlation energies plays an important role in the PC-PK1 results. It is emphasized that the nuclear landscape is considerably extended by the PC-PK1 functional in comparison with the previous results obtained with the covariant density functionals DD-PC1 and TMA, which may be due to the different isovector properties in the density functionals.

The authors provide a systematic global study of differential charge radii of nuclei within covariant density functional theory. They present results for chains of isotopes as they cross major closed neutron shell numbers, where there is usually a change of slope (kink) in the charge radii. The odd-even staggering of charge radii is also investigated, and particle-vibration coupling in odd-mass nuclei is suggested to play a significant role in addition to pairing. This detailed study lays a solid foundation to assess how various forms of interactions within the nuclear many-body system affect fundamental nuclear properties such as nuclear radii and how they evolve with nucleon number.

We report on the first application of the stochastic Laplacian Heaviside method for computing multiparticle interactions with lattice QCD to the two-nucleon system. Like the Laplacian Heaviside method, this method allows for the construction of interpolating operators which can be used to construct a set of positive-definite two-nucleon correlation functions, unlike nearly all other applications of lattice QCD to two nucleons in the literature. It also allows for a variational analysis in which optimal linear combinations of the interpolating operators are formed that couple predominantly to the eigenstates of the system. Utilizing such methods has become of paramount importance to help resolve the discrepancy in the literature on whether two nucleons in either isospin channel form a bound state at pion masses heavier than physical, with the discrepancy persisting even in the SU(3)-flavor-symmetric point with all quark masses near the physical strange quark mass. This is the first in a series of papers aimed at resolving this discrepancy. In the present work, we employ the…

Medium induced parton energy loss is not conclusively established either in very peripheral heavy-ion collisions or in proton-ion collisions. However, the standard interpretation of azimuthal momentum anisotropies in these systems implies some partonic rescattering. The upcoming light-ion runs at the Large Hadron Collider (LHC) provide a unique opportunity to search for parton energy loss in different systems of similar size. Here, we make predictions for the expected parton energy loss signal in the charged hadron spectra in a system size scan at LHC. We test a large set of model assumptions against the transverse momentum and centrality dependence of the charged hadron nuclear modification factor in lead-lead and xenon-xenon collisions at the LHC. We then attempt to make a model agnostic prediction for the charged hadron nuclear modification factor in oxygen-oxygen collisions.

Two-particle long-range azimuthal correlations are measured in photonuclear collisions using $1.7\phantom{\rule{4pt}{0ex}}{\mathrm{nb}}^{\ensuremath{-}1}$ of 5.02 TeV $\mathrm{Pb}+\mathrm{Pb}$ collision data collected by the ATLAS experiment at the CERN Large Hadron Collider. Candidate events are selected using a dedicated high-multiplicity photonuclear event trigger, a combination of information from the zero-degree calorimeters and forward calorimeters, and from pseudorapidity gaps constructed using calorimeter energy clusters and charged-particle tracks. Distributions of event properties are compared between data and Monte Carlo simulations of photonuclear processes. Two-particle correlation functions are formed using charged-particle tracks in the selected events, and a template-fitting method is employed to subtract the nonflow contribution to the correlation. Significant nonzero values of the second- and third-order flow coefficients are observed and presented as a function of charged-particle multiplicity and transverse momentum. The results are compared with flow…

Atomic nuclei are important laboratories for exploring and testing new insights into the universe, such as experiments to directly detect dark matter or explore properties of neutrinos. The targets of interest are often heavy, complex nuclei that challenge our ability to reliably model them (as well as quantify the uncertainty of those models) with classical computers. Hence there is great interest in applying quantum computation to nuclear structure for these applications. As an early step in this direction, especially with regards to the uncertainties in the relevant quantum calculations, we develop circuits to implement variational quantum eigensolver (VQE) algorithms for the Lipkin-Meshkov-Glick model, which is often used in the nuclear physics community as a testbed for many-body methods. We present quantum circuits for VQE for two and three particles and discuss the construction of circuits for more particles. Implementing the VQE for a two-particle system on the IBM Quantum Experience, we identify initialization and two-qubit gates as the largest sources of error. We find…

We conjecture and verify a set of relations between global parameters of hot and fast-rotating compact stars which do not depend on the equation of state, including a relation connecting the masses of the mass-shedding (Kepler) and static configurations. We apply these relations to the GW170817 event by adopting the scenario in which a hypermassive compact star remnant formed in a merger evolves into a supramassive compact star that collapses into a black hole once the stability line for such stars is crossed. We deduce an upper limit on the maximum mass of static, cold neutron stars $2.{15}_{\ensuremath{-}0.17}^{+0.18}\ensuremath{\le}{M}_{\mathrm{TOV}}^{★}/{M}_{\ensuremath{\bigodot}}\ensuremath{\le}2.{24}_{\ensuremath{-}0.44}^{+0.45}$ for the typical range of entropy per baryon, $2\ensuremath{\le}S/A\ensuremath{\le}3$, and electron fraction ${Y}_{e}=0.1$ characterizing the hot hypermassive star. Our result implies that accounting for the finite temperature of the merger remnant relaxes previously derived constraints on the value of the maximum mass of a cold, static compact star.

We construct an equation of state (EOS) for neutron stars by interpolating hadronic EOS at low density and quark EOS at high density. A hadronic model based on the parity doublet structure is used for hadronic matter and a quark model of Nambu--Jona-Lasinio type is for quark matter. We assume crossover between hadronic matter and quark matter in the color-flavor locked phase. The nucleon mass of the parity doublet model has a mass associated with the chiral symmetry breaking, and a chiral invariant mass ${m}_{0}$ which is insensitive to the chiral condensate. The value of ${m}_{0}$ affects the nuclear EOSs at low density, and has strong correlations with the radii of neutron stars. Using the constraint to the radius obtained by LIGO-Virgo and NICER, we find that ${m}_{0}$ is restricted as $600\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}\ensuremath{\lesssim}{m}_{0}\ensuremath{\lesssim}900\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$.

The nuclear symmetry energy is a key quantity in nuclear (astro)physics. It describes the isospin dependence of the nuclear equation of state, which is commonly assumed to be almost quadratic. In this work, we confront this standard quadratic expansion of the equation of state with explicit asymmetric nuclear-matter calculations based on a set of commonly used Hamiltonians including two- and three-nucleon forces derived from chiral effective-field theory. We study, in particular, the importance of nonquadratic contributions to the symmetry energy, including the nonanalytic logarithmic term introduced by Kaiser [Phys. Rev. C 91, 065201 (2015)]. Our results suggest that the nonquadratic contribution to the symmetry energy can be systematically determined from the various Hamiltonians employed, and we obtain $0.{74}_{\ensuremath{-}0.08}^{+0.11}$ MeV (or $\ensuremath{-}1.{02}_{\ensuremath{-}0.08}^{+0.11}$ MeV for the potential term with the effective-mass contribution) at nuclear saturation density, while the logarithmic contribution to the symmetry energy is relatively small and…

The beam energy scan (BES) program at the BNL Relativistic Heavy Ion Collider (RHIC) was extended to energies below $\sqrt{{s}_{NN}}=7.7$ GeV in 2015 by successful implementation of the fixed-target mode of operation in the STAR (Solenoidal Tracker At RHIC) experiment. In this mode, ions circulate in one ring of the collider and interact with a stationary target at the entrance of the STAR time projection chamber. The first results for $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=4.5$ GeV are presented, demonstrating good performance of all the relevant detector subsystems in fixed-target mode. Results presented here include directed and elliptic flow of identified hadrons, and radii from pion femtoscopy. The latter, together with recent HADES results, reveal a long-sought peak structure that may be caused by the system evolving through a first-order phase transition from quark-gluon plasma to the hadronic phase. Directed and elliptic flow for pions are presented for the first time at this beam energy. Pion and proton elliptic flow show behavior which hints at…

Background: The remarkable progress in recent multimessenger observations of both isolated neutron stars (NSs) and their mergers has provided some of the much needed data to improve our understanding about the equation of state (EOS) of dense neutron-rich matter. Various EOSs with or without some kinds of phase transitions from hadronic to quark matter (QM) have been widely used in many forward modelings of NS properties. Direct comparisons of these predictions with observational data sometimes also using ${\ensuremath{\chi}}^{2}$ minimizations have provided very useful constraints on the model EOSs. However, it is normally difficult to perform uncertain quantifications and analyze correlations of the EOS model parameters involved in forward modelings especially when the available data are still very limited.Purpose: We infer the posterior probability distribution functions (PDFs) and correlations of nine parameters characterizing the EOS of dense neutron-rich matter encapsulating a first-order hadron-quark phase transition from the radius data of canonical NSs reported by…

Background: Recently, novel statistical methods such as neural networks and Bayesian learning methods are implemented to describe the nuclear masses.Purpose: Based on previous studies, an improved naive Bayesian probability (iNBP) classifier is proposed to study the nuclear masses by refining the results of sophisticated nuclear models.Method: In the iNBP method, the prediction for nuclear masses is treated as a classification problem. The residuals are classified into several groups to generate prior and conditional probabilities, and the posterior probabilities are further determined by the Bayesian formula. We choose the expectation with maximum probability as the final prediction. Reliability of the iNBP method is assessed by analyzing the global optimizations and the extrapolating capabilities.Results: The iNBP method exhibits impressive improvements on global descriptions for different mass models. Moreover, the method shows robust extrapolating capabilities. Results demonstrate the iNBP method can be applied to predict the nuclear masses of unknown regions.Conclusions:…

Ground state properties of $^{19}\mathrm{B}$ are studied by using the deformed relativistic Hartree-Bogoliubov theory in continuum. The calculations with the density functional PK1 show that $^{19}\mathrm{B}$ is a deformed two-neutron ($2n$) halo nucleus. By examining the evolution of single neutron levels, it is found that the valence levels, which are weakly bound or embedded in the continuum due to pairing, contain considerable $s$-wave components with the probability amplitude of 0.359 and lead to the formation of the halo. Strong quadrupole correlations mix $sd$ orbitals and drive $^{19}\mathrm{B}$ to be prolate. The calculated density of the neutron core presents a prolate shape while the neutron halo is oblate, meaning $^{19}\mathrm{B}$ is a $2n$ halo candidate with shape decoupling effects.

The authors provide a state-of-the-art overview of projection techniques employed in beyond-mean-field many-body methods. They focus on two symmetries that are of critical importance for the description of nuclear spectroscopy, particle number, and angular momentum. The presentation covers formal aspects of symmetry restoration (group theory) and practical aspects related to numerical implementation. A number of illustrative examples are given, including cranked states in odd-$A$ nuclei.

Background: The competing $^{22}\mathrm{Ne}(\ensuremath{\alpha},\ensuremath{\gamma})^{26}\mathrm{Mg}$ and $^{22}\mathrm{Ne}(\ensuremath{\alpha},n)^{25}\mathrm{Mg}$ reactions control the production of neutrons for the weak $s$ process in massive and asymptotic giant branch (AGB) stars. In both systems, the ratio between the corresponding reaction rates strongly impacts the total neutron budget and strongly influences the final nucleosynthesis. A number of experimental studies have been performed over recent years which necessitate the reevaluation of the $^{22}\mathrm{Ne}(\ensuremath{\alpha},\ensuremath{\gamma})^{26}\mathrm{Mg}$ and $^{22}\mathrm{Ne}(\ensuremath{\alpha},n)^{25}\mathrm{Mg}$ reaction rates. Evaluations of the reaction rates following the collection of new nuclear data presently show differences of up to a factor of 500, resulting in considerable uncertainty in the resulting nucleosynthesis.Purpose: To reevaluate the $^{22}\mathrm{Ne}(\ensuremath{\alpha},\ensuremath{\gamma})^{26}\mathrm{Mg}$ and $^{22}\mathrm{Ne}(\ensuremath{\alpha},n)^{25}\mathrm{Mg}$ reaction rates…

An enhanced comprehension of the fission process is essential to our understanding of nuclear dynamics as well as other phenomena such as stellar nucleosynthesis and nuclear reactor spectra that probe fundamental physics. In this paper the authors take an important step toward understanding the role of angular momentum in nuclear fission.

As the densities in the interior of neutron stars exceed those of terrestrial nuclear experiments, they provide a scope for studying the nature of dense matter under extreme conditions. The composition of the inner core of neutron stars is highly uncertain, and it is speculated that exotic forms of matter such as hyperons may appear there. Gravitational waves emitted by unstable oscillation modes in neutron stars contain information about their interior composition and therefore allow us to probe the interior directly. Recently, a systematic investigation of $f$-mode oscillations in neutron stars revealed the role of the uncertainty in nuclear saturation parameters, particularly the effective nucleon mass, on its frequency. In this work, we study the influence of the appearance of hyperons on $f$-mode oscillation frequencies and therefore on the emission of gravitational waves. We also speculate whether a future detection of $f$-mode frequencies could provide a possibility of probing the presence of hyperons in the neutron star core.

The puzzling observation that deuterons, having a binding energy of only 2.2 MeV, survive final-state temperatures of more than 100 MeV in high-energy heavy-ion collisions, has been explained as a delicate balance between creation and destruction at similar rates. However, because the process involves collisions between more than two particles, one had to use workarounds for a satisfactory description. The authors treat deuteron catalysis from nucleons and pions with stochastic multiparticle reactions, making previous workarounds for collisions between more than two particles obsolete.

Exclusive dimuon production in ultraperipheral collisions (UPC), resulting from photon-photon interactions in the strong electromagnetic fields of colliding high-energy lead nuclei, $\mathrm{PbPb}(\ensuremath{\gamma}\ensuremath{\gamma})\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}({\mathrm{Pb}}^{(★)}{\mathrm{Pb}}^{(★)})$, is studied using ${\mathcal{L}}_{\mathrm{int}}=0.48\phantom{\rule{4pt}{0ex}}{\mathrm{nb}}^{\ensuremath{-}1}$ of $\sqrt{{s}_{NN}}=5.02\phantom{\rule{4pt}{0ex}}\text{TeV}$ lead-lead collision data at the LHC with the ATLAS detector. Dimuon pairs are measured in the fiducial region ${p}_{\mathrm{T},\ensuremath{\mu}}>4$ $\text{GeV}$, $|{\ensuremath{\eta}}_{\ensuremath{\mu}}|<2.4$, invariant mass ${m}_{\ensuremath{\mu}\ensuremath{\mu}}>10$ $\text{GeV}$, and ${p}_{\mathrm{T},\ensuremath{\mu}\ensuremath{\mu}}<2$ $\text{GeV}$. The primary background from single-dissociative processes is extracted from the data using a template fitting technique. Differential cross sections are presented as a function of…

We present a comprehensive analysis of the deuteron charge and quadrupole form factors based on the latest two-nucleon potentials and charge-density operators derived in chiral effective field theory. The single- and two-nucleon contributions to the charge density are expressed in terms of the proton and neutron form factors, for which the most up to date empirical parametrizations are employed. By adjusting the fifth-order short-range terms in the two-nucleon charge-density operator to reproduce the world data on the momentum-transfer dependence of the deuteron charge and quadrupole form factors, we predict the values of the structure radius and the quadrupole moment of the deuteron: ${r}_{\mathrm{str}}=1.{9729}_{\ensuremath{-}0.0012}^{+0.0015}\phantom{\rule{4pt}{0ex}}\mathrm{fm},\phantom{\rule{4pt}{0ex}}{Q}_{d}=0.{2854}_{\ensuremath{-}0.0017}^{+0.0038}\phantom{\rule{4pt}{0ex}}{\mathrm{fm}}^{2}.$ A comprehensive and systematic analysis of various sources of uncertainty in our predictions is performed. Following the strategy advocated in our recent publication [Filin, Baru,…

Background: Observation of asymmetric fission of $^{180}\mathrm{Hg}$ has led to intensive theoretical and experimental studies of fission of neutron-deficient nuclei in the lead region.Purpose: The study of asymmetric and symmetric fission modes of $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ nuclei.Methods: Mass-energy distributions of fission fragments of $^{180,190}\mathrm{Hg}$ and $^{184}\mathrm{Pb}$ formed in the $^{36}\mathrm{Ar}+^{144,154}\mathrm{Sm}$ and $^{40}\mathrm{Ca}+^{144}\mathrm{Sm}$ reactions, respectively, at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET and compared with previously measured $^{192,202}\mathrm{Pb}$ isotopes produced in the $^{48}\mathrm{Ca}+^{144,154}\mathrm{Sm}$ reactions. The mass distributions for $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ together with old data for $^{187}\mathrm{Ir}, ^{195}\mathrm{Au}, ^{198}\mathrm{Hg}, ^{201}\mathrm{Tl}, ^{205,207}\mathrm{Bi}, ^{210}\mathrm{Po}$, and $^{213}\mathrm{At}$ [J. Nucl. Phys. 53, 1225 (1991)] have been decomposed…

The nuclear symmetry energy plays a key role in understanding physics of neutron-rich matter from the valley of stability up to neutron-star masses. Analysis of two of the best symmetry energy constraints---the neutron-skin thickness of ${}^{208}$Pb recently extracted from parity-violating electron scattering and the electric dipole polarizability measured in photoabsorption experiments---lead to different conclusions, which highlights a long-standing question in nuclear physics.

We study the in-medium effects in strangeness production in heavy-ion collisions at (sub)threshold energies of (1--2)$A$ GeV based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach. The in-medium modifications of the antikaon $(\overline{K}={K}^{\ensuremath{-}},{\overline{K}}^{0})$ properties are described via the self-consistent coupled-channel unitarized scheme based on a SU(3) chiral Lagrangian which incorporates explicitly the $s$ and $p$ waves of the kaon-nucleon interaction. This scheme provides the antikaon potential, spectral functions, and reaction cross sections as well as their dependence on baryon density, temperature, and antikaon momentum in the nuclear medium, which are incorporated in the off-shell dynamics of the PHSD. The in-medium modification of kaons $(K={K}^{+},{K}^{0})$ are accounted via the kaon-nuclear potential, which is assumed to be proportional to the local baryon density. The manifestation of the medium effects in observables is investigated for the $K$ and $\overline{K}$ rapidity distributions, ${p}_{T}$ spectra, the polar and…

The impact of anisotropic pressure models in neutron stars (NSs) is increasing their compactness. Therefore, for the relatively soft NS equation of state (EOS), we can still obtain a relatively large maximum mass of NSs and a relatively short canonical NS radius. We systematically study the anisotropic NS properties using a refined EOS. We compare the results with the recent NS multimessenger constraints. We use a relativistic mean-field (RMF) model with the G3 parameter set to calculate the NS core EOSs. The standard SU(3) prescription and hyperon potential depths determine the hyperon coupling constants. We use the inner and outer crusts EOSs from Miyatsu et al. [Astrophys. J. 777, 4 (2013)]. We consider two kinds of EOSs at high densities: one with the maximum speed of sound in NS matter obeying the conformal bound, i.e., ${v}_{s}^{\mathrm{max}}=\frac{1}{\sqrt{3}}$ (WHSS) and one without considering this bound (WH). We have found for the WH EOS with $\mathrm{\ensuremath{\Delta}}=\ensuremath{-}1.8$ that NS properties predicted for an anisotropic NS based on the Horvat et al. model…

The production cross section of prompt ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$ charm baryons was measured with the ALICE detector at the LHC at midrapidity in proton-proton ($pp$) and proton-lead ($p\text{--Pb}$) collisions at a center-of-mass energy per nucleon pair of $\sqrt{{s}_{\mathrm{NN}}}=5.02\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$. The ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$ and $\overline{\mathrm{\ensuremath{\Lambda}}}{}_{c}^{\ensuremath{-}}$ baryons were reconstructed in the hadronic decay channels ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}p{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ and ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}p{K}_{S}^{0}$ and respective charge conjugates. The measured differential cross sections as a function of transverse momentum (${p}_{T}$) and the ${p}_{T}$-integrated ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$ production cross section in $pp$ and in $p\text{--Pb}$ collisions are presented. The ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}$ nuclear modification factor (${R}_{p\mathrm{Pb}}$), calculated…

We develop a flexible, relativistically covariant parametrization of the dense nuclear matter equation of state suited for inclusion in computationally demanding hadronic transport simulations. Within an implementation in the hadronic transport code smash, we show that effects due to bulk thermodynamic behavior are reproduced in dynamic hadronic systems, demonstrating that hadronic transport can be used to study critical behavior in dense nuclear matter, both at and away from equilibrium. We also show that two-particle correlations calculated from hadronic transport simulation data follow theoretical expectations based on the second-order cumulant ratio, and constitute a clear signature of the crossover region above the critical point.