Showing papers in "Physical Review C in 2021"

Multisystem Bayesian constraints on the transport coefficients of QCD matter

Abstract: Author(s): Everett, D; Ke, W; Paquet, JF; Vujanovic, G; Bass, SA; Du, L; Gale, C; Heffernan, M; Heinz, U; Liyanage, D; Luzum, M; Majumder, A; McNelis, M; Shen, C; Xu, Y; Angerami, A; Cao, S; Chen, Y; Coleman, J; Cunqueiro, L; Dai, T; Ehlers, R; Elfner, H; Fan, W; Fries, RJ; Garza, F; He, Y; Jacak, BV; Jacobs, PM; Jeon, S; Kim, B; Kordell, M; Kumar, A; Mak, S; Mulligan, J; Nattrass, C; Oliinychenko, D; Park, C; Putschke, JH; Roland, G; Schenke, B; Schwiebert, L; Silva, A; Sirimanna, C; Soltz, RA; Tachibana, Y; Wang, XN; Wolpert, RL | Abstract: We study the properties of the strongly coupled quark-gluon plasma with a multistage model of heavy-ion collisions that combines the TRENTo 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≈ 150-250 MeV, but their constraining power degrades at higher temperatures, T 250 MeV. Furthermore, these viscosity constraints are found to depend significantly on how viscous corrections are handled in the transition from hydrodynamics to the hadronic transport. Several other model parameters, including the free-streaming time, show similar model sensitivity, while the initial condition parameters associated with the TRENTo ansatz are quite robust against variations of the particlization prescription. We also report on the sensitivity of individual observables to the various model parameters. Finally, Bayesian model selection is used to quantitatively compare the agreement with measurements for different sets of model assumptions, including different particlization models and different choices for which parameters are allowed to vary between RHIC and LHC energies.

GW190814 as a massive rapidly rotating neutron star with exotic degrees of freedom

Abstract: 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 to changes in stellar central density, but require a larger amount of baryons than what is allowed in the nonrotating stars. This is not the case for pure quark stars, which can easily reach $2.5\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\mathrm{Sun}}$ and still possess approximately the same amount of baryons as stable nonrotating stars. We also briefly discuss possible origins for fast rotating stars with a large amount of baryons and their stability, showing how the event GW190814 can be associated with a star containing quarks as one of its progenitors.

Limiting masses and radii of neutron stars and their implications

Abstract: 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 $1.4\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ star, ${R}_{1.4}$, by $\ensuremath{\sim}3.5\phantom{\rule{0.16em}{0ex}}\text{km}$. If observations indicate ${R}_{1.4}l11.2\phantom{\rule{0.16em}{0ex}}\text{km}$, then our study implies that either the squared speed of sound ${c}_{s}^{2}g1/2$ for densities above $2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$ or that $\ensuremath{\chi}\mathrm{EFT}$ breaks down below $2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$. We also comment on the nature of the secondary compact object in GW190814 with mass $\ensuremath{\simeq}2.6\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ and discuss the implications of massive neutron stars $g2.1\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}\phantom{\rule{0.16em}{0ex}}(2.6\phantom{\rule{0.16em}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}})$ in future radio and gravitational-wave searches. Some form of strongly interacting matter with ${c}_{s}^{2}g0.35\phantom{\rule{0.16em}{0ex}}(0.55)$ must be realized in the cores of such massive neutron stars. In the absence of phase transitions below $2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$, the small tidal deformability inferred from GW170817 lends support for the relatively small pressure predicted by $\ensuremath{\chi}\mathrm{EFT}$ for the baryon density ${n}_{\mathrm{B}}$ in the range $1\text{--}2\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$. Together they imply that the rapid stiffening required to support a high maximum mass should occur only when ${n}_{\mathrm{B}}\ensuremath{\gtrsim}1.5\text{--}1.8\phantom{\rule{0.16em}{0ex}}{n}_{\mathrm{sat}}$.

Confirming the Existence of the strong CP Problem in Lattice QCD with the Gradient Flow

Abstract: 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 $0.07\phantom{\rule{0.16em}{0ex}}\mathrm{fm}lal0.11\phantom{\rule{0.16em}{0ex}}\mathrm{fm}$ 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 ${d}_{n}=\ensuremath{-}0.00152(71)\phantom{\rule{4pt}{0ex}}\overline{\ensuremath{\theta}}\phantom{\rule{4pt}{0ex}}e\phantom{\rule{0.16em}{0ex}}\text{fm}$ and ${d}_{p}=0.0011(10)\phantom{\rule{4pt}{0ex}}\overline{\ensuremath{\theta}}\phantom{\rule{4pt}{0ex}}e\phantom{\rule{0.16em}{0ex}}\text{fm}$. Assuming the $\ensuremath{\theta}$ term is the only source of CP violation, the experimental bound on the neutron electric dipole moment limits $\left|\overline{\ensuremath{\theta}}\right|l1.98\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ ($90%$ CL). A first attempt at calculating the nucleon Schiff moment in the continuum resulted in ${S}_{p}=0.50(59)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\phantom{\rule{4pt}{0ex}}\overline{\ensuremath{\theta}}\phantom{\rule{4pt}{0ex}}e\phantom{\rule{0.16em}{0ex}}{\text{fm}}^{3}$ and ${S}_{n}=\ensuremath{-}0.10(43)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\phantom{\rule{4pt}{0ex}}\overline{\ensuremath{\theta}}\phantom{\rule{4pt}{0ex}}e\phantom{\rule{0.16em}{0ex}}{\text{fm}}^{3}$.

From chiral kinetic theory to relativistic viscous spin hydrodynamics

Abstract: 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.

Bayesian analysis of heavy ion collisions with the heavy ion computational framework Trajectum

Abstract: 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.

Cumulants and correlation functions of net-proton, proton, and antiproton multiplicity distributions in Au+Au collisions at energies available at the BNL Relativistic Heavy Ion Collider

Abstract: Author(s): Abdallah, MS; Adam, J; Adamczyk, L; Adams, JR; Adkins, JK; Agakishiev, G; Aggarwal, I; Aggarwal, MM; Ahammed, Z; Alekseev, I; Anderson, DM; Aparin, A; Aschenauer, EC; Ashraf, MU; Atetalla, FG; Attri, A; Averichev, GS; Bairathi, V; Baker, W; Ball Cap, JG; Barish, K; Behera, A; Bellwied, R; Bhagat, P; Bhasin, A; Bielcik, J; Bielcikova, J; Bordyuzhin, IG; Brandenburg, JD; Brandin, AV; Bunzarov, I; Butterworth, J; Cai, XZ; Caines, H; Calderon De La Barca Sanchez, M; Cebra, D; Chakaberia, I; Chaloupka, P; Chan, BK; Chang, FH; Chang, Z; Chankova-Bunzarova, N; Chatterjee, A; Chattopadhyay, S; Chen, D; Chen, J; Chen, JH; Chen, X; Chen, Z; Cheng, J; Chevalier, M; Choudhury, S; Christie, W; Chu, X; Crawford, HJ; Csanad, M; Daugherity, M; Dedovich, TG; Deppner, IM; Derevschikov, AA; Dhamija, A; Di Carlo, L; Didenko, L; Dong, X; Drachenberg, JL; Dunlop, JC; Elsey, N; Engelage, J; Eppley, G; Esumi, S; Evdokimov, O; Ewigleben, A; Eyser, O; Fatemi, R; Fawzi, FM; Fazio, S; Federic, P; Fedorisin, J; Feng, CJ; Feng, Y; Filip, P; Finch, E; Fisyak, Y; Francisco, A; Fu, C | Abstract: We report a systematic measurement of cumulants, Cn, for net-proton, proton, and antiproton multiplicity distributions, and correlation functions, κn, for proton and antiproton multiplicity distributions up to the fourth order in Au+Au collisions at sNN=7.7, 11.5, 14.5, 19.6, 27, 39, 54.4, 62.4, and 200 GeV. The Cn and κn are presented as a function of collision energy, centrality and kinematic acceptance in rapidity, y, and transverse momentum, pT. 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|l 0.5) and transverse momentum 0.4

Hydrodynamic study of hyperon spin polarization in relativistic heavy ion collisions

Abstract: 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 the spin Cooper-Frye formula under the assumption of thermal equilibrium of the spin degree of freedom needs to be improved.

Light nuclei with semilocal momentum-space regularized chiral interactions up to third order

Abstract: We present a systematic investigation of few-nucleon systems and light nuclei using the current LENPIC interactions comprising semilocal momentum-space regularized two- and three-nucleon forces up to third chiral order (N$^2$LO). Following our earlier study utilizing the coordinate-space regularized interactions, the two low-energy constants entering the three-body force are determined from the triton binding energy and the differential cross section minimum in elastic nucleon-deuteron scattering. Predictions are made for selected observables in elastic nucleon-deuteron scattering and in the deuteron breakup reactions, for properties of the $A=3$ and $A=4$ nuclei, and for spectra of $p$-shell nuclei up to $A = 16$. A comprehensive error analysis is performed including an estimation of correlated truncation uncertainties for nuclear spectra. The obtained predictions are generally found to agree with experimental data within errors. Similar to the coordinate-space regularized chiral interactions at the same order, a systematic overbinding of heavier nuclei is observed, which sets in for $A \sim 10$ and increases with $A$.

Projection on particle number and angular momentum: Example of triaxial Bogoliubov quasiparticle states

Abstract: Background: Many quantal many-body methods that aim at the description of self-bound nuclear or mesoscopic electronic systems make use of auxiliary wave functions that break one or several of the symmetries of the Hamiltonian in order to include correlations associated with the geometrical arrangement of the system's constituents. Such reference states have been used already for a long time within self-consistent methods that are either based on effective valence-space Hamiltonians or energy density functionals, and they are presently also gaining popularity in the design of novel ab initio methods. A fully quantal treatment of a self-bound many-body system, however, requires the restoration of the broken symmetries through the projection of the many-body wave functions of interest onto good quantum numbers. Purpose: The goal of this work is threefold. First, we want to give a general presentation of the formalism of the projection method starting from the underlying principles of group representation theory. Second, we want to investigate formal and practical aspects of the numerical implementation of particle-number and angular-momentum projection of Bogoliubov quasiparticle vacua, in particular with regard of obtaining accurate results at minimal computational cost. Third, we want to analyze the numerical, computational, and physical consequences of intrinsic symmetries of the symmetry-breaking states when projecting them. Methods: Using the algebra of group representation theory, we introduce the projection method for the general symmetry group of a given Hamiltonian. For realistic examples built with either a pseudopotential-based energy density functional or a valence-space shell-model interaction, we then study the convergence and accuracy of the quadrature rules for the multidimensional integrals that have to be evaluated numerically and analyze the consequences of conserved subgroups of the broken symmetry groups. Results: The main results of this work are also threefold. First, we give a concise, but general, presentation of the projection method that applies to the most important potentially broken symmetries whose restoration is relevant for nuclear spectroscopy. Second, we demonstrate how to achieve high accuracy of the discretizations used to evaluate the multidimensional integrals appearing in the calculation of particle-number and angular-momentum projected matrix elements while limiting the order of the employed quadrature rules. Third, for the example of a point-group symmetry that is often imposed on calculations that describe collective phenomena emerging in triaxially deformed nuclei, we provide the group-theoretical derivation of relations between the intermediate matrix elements that are integrated, which permits a further significant reduction of the computational cost of the method. These simplifications are valid regardless of the number parity of the quasiparticle states and therefore can be used in the description of even-even, odd-mass, and odd-odd nuclei. Conclusions: The quantum-number projection technique is a versatile and efficient method that permits to restore the symmetry of any arbitrary many-body wave function. Its numerical implementation is relatively simple and accurate. In addition, it is possible to use the conserved symmetries of the reference states to reduce the computational burden of the method. More generally, the ever-growing computational resources and the development of nuclear ab-initio methods opens new possibilities of applications of the method.

Entanglement rearrangement in self-consistent nuclear structure calculations

Abstract: 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 better ways to match to low-energy nuclear effective field theories and lattice QCD calculations to nuclear many-body techniques that are based upon entanglement.Method: We explore the entanglement between single-particle states in $^{4}\mathrm{He}$ and $^{6}\mathrm{He}$. The patterns of entanglement emerging from different single-particle bases are compared, and possible links with the convergence of observables are explored, in particular, ground-state energies. The nuclear wave functions are obtained by performing active-space no-core configuration-interaction calculations using a two-body nucleon-nucleon interaction derived from chiral effective field theory. Entanglement measures within single-particle bases exhibiting different degrees of complexity are determined, in particular, harmonic oscillator (HO), Hartree-Fock (HF), natural (NAT) and variational natural (VNAT) bases. Specifically, single-orbital entanglement entropy, two-orbital mutual information, and negativity are studied.Results: The entanglement structures in $^{4}\mathrm{He}$ and $^{6}\mathrm{He}$ are found to be more localized within NAT and VNAT bases than within a HO basis for the optimal HO parameters we have worked with. In particular a core-valence structure clearly emerges from the full no-core calculation of $^{6}\mathrm{He}$. The two-nucleon mutual information shows that the VNAT basis, which typically exhibits good convergence properties, effectively decouples the active and inactive spaces.Conclusions: Measures of one- and two-nucleon entanglement are found to be useful in analyzing the structure of nuclear wave functions, in particular the efficacy of basis states, and may provide useful metrics toward developing more efficient schemes for ab initio computations of the structure and reactions of nuclei, and quantum many-body systems more generally.

Two-nucleon S -wave interactions at the SU(3) flavor-symmetric point with m u d ≈m s phys : A first lattice QCD calculation with the stochastic Laplacian Heaviside method

Abstract: Author(s): Horz, B; Howarth, D; Rinaldi, E; Hanlon, A; Chang, CC; Korber, C; Berkowitz, E; Bulava, J; Clark, MA; Lee, WT; Morningstar, C; Nicholson, A; Vranas, P; Walker-Loud, A | Abstract: 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 stochastic Laplacian Heaviside method without a hexaquark operator in the basis at a lattice spacing of a≈0.086 fm, lattice volume of L=48a≈4.1 fm and pion mass mπ≈714 MeV. With this setup, the observed spectrum of two-nucleon energy levels strongly disfavors the presence of a bound state in either the deuteron or dineutron channel.

Determining the jet transport coefficient q ̂ from inclusive hadron suppression measurements using Bayesian parameter estimation

Abstract: Author(s): Cao, S; Chen, Y; Coleman, J; Mulligan, J; Jacobs, PM; Soltz, RA; Angerami, A; Arora, R; Bass, SA; Cunqueiro, L; Dai, T; Du, L; Ehlers, R; Elfner, H; Everett, D; Fan, W; Fries, RJ; Gale, C; Garza, F; He, Y; Heffernan, M; Heinz, U; Jacak, BV; Jeon, S; Ke, W; Kim, B; Kordell, I; Kumar, A; Majumder, A; Mak, S; McNelis, M; Nattrass, C; Oliinychenko, D; Park, C; Paquet, JF; Putschke, JH; Roland, G; Silva, A; Schenke, B; Schwiebert, L; Shen, C; Sirimanna, C; Tachibana, Y; Vujanovic, G; Wang, XN; Wolpert, RL; Xu, Y | Abstract: We report a new determination of 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 Au+Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and Pb+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 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 Q0. Comparison of the posterior model predictions to the RHIC and LHC hadron suppression data shows reasonable agreement, with moderate tension in limited regions of phase space. The distribution of q/T3 extracted from the posterior distributions exhibits weak dependence on jet momentum and medium temperature T, with 90% credible region (CR) depending on the specific choice of model configuration. The choice of Matter+Lbt, with switching at virtuality Q0, has 90% CR of 240 GeV/c. The value of Q0, determined here for the first time, is in the range 2.0-2.7 GeV.

In-medium similarity renormalization group with three-body operators

Abstract: 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 approximate IMSRG(3) truncations behave consistently with expectations from our perturbative analysis, indicating that this strategy may also be used to systematically approximate the IMSRG(3).

Flow and interferometry results from Au+Au collisions at sNN =4.5 GeV

Abstract: The beam energy scan (BES) program at the BNL Relativistic Heavy Ion Collider (RHIC) was extended to energies below sNN=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 Au+Au collisions at sNN=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 constituent quark scaling, and demonstrate that a definitive conclusion will be achievable using the full statistics of the ongoing second phase of BES (BES-II). In particular, BES-II to date has recorded fixed-target data sets with two orders of magnitude more events at each of nine energies between sNN=3.0 and 7.7 GeV.

Nuclear symmetry energy from neutron skins and pure neutron matter in a Bayesian framework

Abstract: We present an inference of the nuclear symmetry energy magnitude $J$, the slope $L$, and the curvature ${K}_{\mathrm{sym}}$ from combining neutron skin data on calcium, lead and tin isotopes, and our best theoretical information about pure neutron matter. A Bayesian framework is used to consistently incorporate prior knowledge of the pure neutron matter equation of state from chiral effective field theory calculations. Neutron skins are modeled in a fully quantum Skyrme-Hartree-Fock approach using an extended Skyrme energy-density functional which allows for independent variation of $J$, $L$, and ${K}_{\mathrm{sym}}$ without affecting the symmetric nuclear matter equation of state. The effect of using neutron skin data obtained with different physical probes is quantified. We argue that, given the existing data, combining the errors in quadrature is the more appropriate way to obtain unified errors for each nuclide, and in doing so we obtain 95% credible values of $J=31.3\begin{array}{c}+4.2\\ \ensuremath{-}5.9\end{array}\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$, $L=40\begin{array}{c}+34\\ \ensuremath{-}26\end{array}\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$, and ${K}_{\ensuremath{\tau}}=L\ensuremath{-}6{K}_{\mathrm{sym}}=\ensuremath{-}444\begin{array}{c}+100\\ \ensuremath{-}84\end{array}\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ using uninformative priors in $J$, $L$, and ${K}_{\mathrm{sym}}$, and $J=31.9\begin{array}{c}+1.3\\ \ensuremath{-}1.3\end{array}\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$, $L=37\begin{array}{c}+9\\ \ensuremath{-}8\end{array}\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$, and ${K}_{\ensuremath{\tau}}=\ensuremath{-}480\begin{array}{c}+25\\ \ensuremath{-}26\end{array}\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ using pure neutron matter (PNM) priors. We also show that the nonpositive correlation between $J$ and $L$ induced by neutron skin data is consistent with the nuclear droplet model. Neutron skin data alone are shown to place limits on the symmetry energy parameters as stringent as those obtained from chiral effective field theory alone, and when combined the 95% credible intervals are reduced by a factor of 4--5. It is also shown that the majority of nuclear interactions used in the literature have subsaturation density dependencies that are inconsistent with the combination of PNM priors and neutron skin data. We show measurements of lead and calcium neutron skins from upcoming parity-violating electron scattering experiments at Jefferson Lab and Mainz Superconducting Accelerator should obtain total error ranges $\mathrm{\ensuremath{\Delta}}L\ensuremath{\approx}50\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and $\mathrm{\ensuremath{\Delta}}{K}_{\ensuremath{\tau}}\ensuremath{\approx}240\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ for uninformative priors and $\mathrm{\ensuremath{\Delta}}L\ensuremath{\approx}30\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and $\mathrm{\ensuremath{\Delta}}{K}_{\ensuremath{\tau}}\ensuremath{\approx}100\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ for PNM priors at 67% credible bounds. Ahead of those experiments, we make predictions based on existing data on neutron skins of tin alone for the neutron skins of calcium and lead of $0.166\ifmmode\pm\else\textpm\fi{}0.008$ fm and $0.169\ifmmode\pm\else\textpm\fi{}0.014$ fm, respectively, using uninformative priors and $0.167\ifmmode\pm\else\textpm\fi{}0.008$ fm and $0.172\ifmmode\pm\else\textpm\fi{}0.015$ fm, respectively, using PNM priors.

Quartic cumulant of baryon number in the presence of a QCD critical point

Abstract: In the context of the ongoing search for the QCD critical point at the Relativistic Heavy-Ion Collider, we study the equation of state near the critical point in the temperature and baryon chemical potential plane. We use the parametric representation introduced in earlier literature, which maps the universal three-dimensional Ising equation of state onto the QCD phase diagram using several non-universal parameters. We focus on the quartic cumulant of the baryon number, or baryon number susceptibility ${\ensuremath{\chi}}_{4}^{B}$, which can be accessed experimentally via net-proton fluctuation kurtosis measurements. It was originally predicted, through universality arguments based on the leading singular contribution, that ${\ensuremath{\chi}}_{4}^{B}$ and net-proton kurtosis should show a specific nonmonotonic behavior due to the critical point. In particular, when following the freeze-out curve on the phase diagram by decreasing beam energy, the kurtosis is expected to dip, and then peak, when the beam energy scan passes close to the critical point. We study the effects of the nonuniversal and thus far unknown parameters of the Ising-to-QCD mapping on the behavior of ${\ensuremath{\chi}}_{4}^{B}$. We find that, while the peak remains a solid feature, the presence of the critical point does not necessarily cause a dip in ${\ensuremath{\chi}}_{4}^{B}$ on the freeze-out line below the transition temperature. The critical point contribution to the dip appears only for a narrow set of mapping parameters, when subleading singular terms are sufficiently suppressed.

Deuteron production in AuAu collisions at s N N = 7 – 200 GeV via pion catalysis

Abstract: We study deuteron production using no-coalescence hydrodynamic $+$ transport simulations of central AuAu collisions at $\sqrt{{s}_{NN}}=7--200$ GeV. Deuterons are sampled thermally at the transition from hydrodynamics to transport and interact in transport dominantly via $\ensuremath{\pi}pn\ensuremath{\leftrightarrow}\ensuremath{\pi}d$ reactions. The measured proton, lambda, and deuteron transverse momentum spectra and yields are reproduced well for all collision energies considered. We further provide a possible explanation for the measured minimum in the energy dependence of the coalescence parameter ${B}_{2}(\sqrt{{s}_{NN}})$ as well as for the difference between ${B}_{2}(d)$ for deuterons and that for antideuterons, ${B}_{2}(\overline{d})$.

Multiplicity dependence of (multi)strange baryons in the canonical ensemble with phase shift corrections

Abstract: The increase in strangeness production with charged particle multiplicity, as seen by the ALICE collaboration at CERN in $p\text{\ensuremath{-}}p$, $p$-Pb, and Pb-Pb collisions, is investigated in the hadron resonance gas model taking into account interactions among hadrons using $S$-matrix corrections based on known phase shift analyses. Strangeness conservation is taken into account in the framework of the canonical strangeness ensemble. A very good description is obtained for the variation of the strangeness content in the final state as a function of the number of charged hadrons in the midrapidity region using the same fixed temperature value as obtained in the most central Pb-Pb collisions and with a fixed strangeness suppression factor ${\ensuremath{\gamma}}_{s}=1$. It is shown that the number of charged hadrons is linearly proportional to the volume of the system. For small multiplicities the canonical ensemble with local strangeness conservation restricted to midrapidity leads to a stronger suppression of (multi)strange baryons than seen in the data. This is compensated by introducing a global conservation of strangeness in the whole phase-space which is parametrized by the canonical correlation volume larger than the fireball volume at the midrapidity. The results on comparing the hadron resonance gas model with and without S-matrix corrections, are presented in detail. It is shown that the interactions introduced by the phase shift analysis via the $S$-matrix formalism are essential for a better description of the yields data.

Natural orbitals for many-body expansion methods

Abstract: The nuclear many-body problem for medium-mass systems is commonly addressed using wave-function expansion methods that build upon a second-quantized representation of many-body operators with respect to a chosen computational basis. While various options for the computational basis are available, perturbatively constructed natural orbitals recently have been shown to lead to significant improvement in many-body applications yielding faster model-space convergence and lower sensitivity to basis set parameters in large-scale no-core shell model diagonalizations. This work provides a detailed comparison of single-particle basis sets and a systematic benchmark of natural orbitals in nonperturbative many-body calculations using the in-medium similarity renormalization group approach. As a key outcome we find that the construction of natural orbitals in a large single-particle basis enables for performing the many-body calculation in a reduced space of much lower dimension, thus offering significant computational savings in practice that help extend the reach of ab initio methods towards heavier masses and higher accuracy.

Bayesian inference of the dense-matter equation of state encapsulating a first-order hadron-quark phase transition from observables of canonical neutron stars

Abstract: 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 LIGO/VIRGO, NICER, and Chandra Collaborations. We also infer the QM mass fraction and its radius in a $1.4\phantom{\rule{4pt}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ NS and predict their values in more massive NSs.Method: Metamodelings are used to generate both hadronic and QM EOSs in the Markov-Chain Monte Carlo sampling process within the Bayesian statistical framework. An explicitly isospin-dependent parametric EOS for the $npe\ensuremath{\mu}$ matter in NSs at $\ensuremath{\beta}$ equilibrium is connected through the Maxwell construction to the QM EOS described by the constant speed of sound (CSS) model of Alford, Han, and Prakash with and without using the Seidov stability condition for first-order phase transitions.Results: In the default calculation with the Seidov stability condition, we find that (i) The most probable values of the hadron-quark transition density ${\ensuremath{\rho}}_{t}/{\ensuremath{\rho}}_{0}$ and the relative energy density jump there $\mathrm{\ensuremath{\Delta}}\ensuremath{\varepsilon}/{\ensuremath{\varepsilon}}_{t}$ are ${\ensuremath{\rho}}_{t}/{\ensuremath{\rho}}_{0}=1.{6}_{\ensuremath{-}0.4}^{+1.2}$ and $\mathrm{\ensuremath{\Delta}}\ensuremath{\varepsilon}/{\ensuremath{\varepsilon}}_{t}=0.{4}_{\ensuremath{-}0.15}^{+0.20}$ at 68% confidence level, respectively. The corresponding probability distribution of QM fraction in a $1.4\phantom{\rule{4pt}{0ex}}{\mathrm{M}}_{\ensuremath{\bigodot}}$ NS peaks around 0.9 in a 10 km sphere. Strongly correlated to the PDFs of ${\ensuremath{\rho}}_{t}$ and $\mathrm{\ensuremath{\Delta}}\ensuremath{\varepsilon}/{\ensuremath{\varepsilon}}_{t}$, the PDF of the QM speed of sound squared ${c}_{\mathrm{QM}}^{2}/{c}^{2}$ peaks at $0.{95}_{\ensuremath{-}0.35}^{+0.05}$, and the total probability of being less than 1/3 is very small. (ii) The correlations between PDFs of hadronic and QM EOS parameters are very weak. While the most probable values of parameters describing the EOS of symmetric nuclear matter remain almost unchanged, the high-density symmetry energy parameters of neutron-rich matter are significantly different with or without considering the hadron-quark phase transition. Removing the Seidov condition, while there are appreciable and interesting changes in the PDFs of quark matter EOS parameters, the qualitative conclusions remain the same.Conclusions: The available astrophysical data considered together with all known EOS constraints from theories and terrestrial nuclear experiments prefer the formation of a large volume of QM even in canonical NSs.

Predicting parton energy loss in small collision systems

Abstract: 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.

Maximum mass of compact stars from gravitational wave events with finite-temperature equations of state

Abstract: 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.

Global Λ polarization in moderately relativistic nuclear collisions

Abstract: Predictions are made for the global polarization of $\mathrm{\ensuremath{\Lambda}}$ hyperons in $\mathrm{Au}+\mathrm{Au}$ collisions at moderately relativistic collision energies, 2.4 $\ensuremath{\le}\sqrt{{s}_{NN}}\ensuremath{\le}$ 11 GeV. These are based on the thermodynamic approach to the global polarization incorporated into the model of the three-fluid dynamics. Centrality dependence of the polarization is studied. It is predicted that the polarization reaches a maximum or a plateau (depending on the equation of state and centrality) at $\sqrt{{s}_{NN}}\ensuremath{\approx}$ 3 GeV. It is found that the global polarization increases with increasing width of the rapidity window around the midrapidity.

High-accuracy calculation of the deuteron charge and quadrupole form factors in chiral effective field theory

Abstract: 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, Epelbaum, Krebs, M\"oller, and Reinert, Phys. Rev. Lett. 124, 082501 (2020)], we employ the extracted structure radius together with the accurate atomic data for the deuteron-proton mean-square charge radii difference to update the determination of the neutron charge radius, for which we find ${r}_{n}^{2}=\ensuremath{-}0.{105}_{\ensuremath{-}0.006}^{+0.005}\phantom{\rule{0.16em}{0ex}}{\text{fm}}^{2}$. Given the observed rapid convergence of the deuteron form factors in the momentum-transfer range of $Q\ensuremath{\simeq}1--2.5\phantom{\rule{4pt}{0ex}}{\mathrm{fm}}^{\ensuremath{-}1}$, we argue that this intermediate energy domain is particularly sensitive to the details of the nucleon form factors and can be used to test different parametrizations.

New equations of state constrained by nuclear physics, observations, and QCD calculations of high-density nuclear matter

Abstract: 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.

Comparison of heavy-ion transport simulations: Mean-field dynamics in a box

Abstract: 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 more recent lattice formulation of some of the QMD codes. The significance of these results for the description of real heavy-ion collisions is discussed.

Implications of PREX-2 on the electric dipole polarizability of neutron-rich nuclei

Abstract: 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.

Neutron matter at finite temperature based on chiral effective field theory interactions

Abstract: We study the equation of state of neutron matter at finite temperature based on two- and three-nucleon interactions derived within chiral effective field theory to next-to-next-to-next-to-leading order. The free energy, pressure, entropy, and internal energy are calculated using many-body perturbation theory including terms up to third order around the self-consistent Hartree-Fock solution. We include contributions from three-nucleon interactions without employing the normal-ordering approximation and provide theoretical uncertainty estimates based on an order-by-order analysis in the chiral expansion. Our results demonstrate that thermal effects can be captured remarkably well via a thermal index and a density-dependent effective mass. The presented framework provides the basis for studying the dense matter equation of state at general temperatures and proton fractions relevant for core-collapse supernovae and neutron star mergers.