Showing papers in "Physical Review C in 2019"

Multiplicity dependence of light-flavor hadron production in pp collisions at √s = 7 TeV

Abstract: Comprehensive results on the production of unidentified charged particles, π±, K±, KS0, K* (892)0, p, p¯, ϕ(1020), Λ, Λ¯, Ξ−, Ξ¯+, Ω−, and Ω¯+ hadrons in proton-proton (pp) collisions at s=7 TeV at midrapidity (|y|<0.5) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum (pT) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle-to-pion ratios are shown to depend solely on charged- particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in p-Pb and Pb-Pb collisions at Large Hadron Collider energies. The obtained pT distributions and yields are compared to expectations from QCD-based pp event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity pp collisions.

A Search for Neutrinoless Double-Beta Decay in $^{76}$Ge with 26 kg-yr of Exposure from the MAJORANA DEMONSTRATOR

Abstract: Author(s): Cuesta, C; Alvis, SI; Arnquist, IJ; Avignone, FT; Barabash, AS; Barton, CJ; Basu, V; Bertrand, FE; Bos, B; Busch, M; Buuck, M; Caldwell, TS; Chan, YD; Christofferson, CD; Chu, PH; Clark, M; Cuesta, C; Detwiler, JA; Efremenko, Y; Ejiri, H; Elliott, SR; Gilliss, T; Giovanetti, GK; Green, MP; Gruszko, J; Guinn, IS; Guiseppe, VE; Haufe, CR; Hegedus, RJ; Hehn, L; Henning, R; Hervas Aguilar, D; Hoppe, EW; Howe, MA; Kidd, MF; Konovalov, SI; Kouzes, RT; Lopez, AM; Martin, RD; Massarczyk, R; Meijer, SJ; Mertens, S; Myslik, J; Othman, G; Pettus, W; Piliounis, A; Poon, AWP; Radford, DC; Rager, J; Reine, AL; Rielage, K; Ruof, NW; Shanks, B; Shirchenko, M; Tedeschi, D; Varner, RL; Vasilyev, S; White, BR; Wilkerson, JF; Wiseman, C; Xu, W; Yakushev, E; Yu, CH; Yumatov, V; Zhitnikov, I; Zhu, BX | Abstract: The Majorana Collaboration is operating an array of high-purity Ge detectors to search for the neutrinoless double-β decay of Ge76. The Majorana Demonstrator consists of 44.1 kg of Ge detectors (29.7 kg enriched to 88% in Ge76) split between two modules constructed from ultraclean materials. Both modules are contained in a low-background shield at the Sanford Underground Research Facility in Lead, South Dakota. We present updated results on the search for neutrinoless double-β decay in Ge76 with 26.0±0.5 kg yr of enriched exposure. With the Demonstrator's energy resolution of 2.53 keV FWHM at Qββ, which is the best among all neutrinoless double-β decay experiments, we observe one event in the region of interest with 0.65 events expected from the estimated background, resulting in a lower limit on the Ge76 neutrinoless double-β decay half-life of 2.7×1025 yr [90% confidence level (CL)] with a median sensitivity of 4.8×1025 yr (90% CL). Depending on the matrix elements used, a 90% CL upper limit on the effective Majorana neutrino mass in the range of 200-433 meV is obtained. The measured background in the configurations with full shielding and optimized grounding is 11.9±2.0 counts/(FWHM t yr).

Effective kinetic description of event-by-event pre-equilibrium dynamics in high-energy heavy-ion collisions

Abstract: We develop a macroscopic description of the space-time evolution of the energy-momentum tensor during the pre-equilibrium stage of a high-energy heavy-ion collision. Based on a weak coupling effective kinetic description of the microscopic equilibration process (\`a la ``bottom-up''), we calculate the nonequilibrium evolution of the local background energy-momentum tensor as well as the nonequilibrium linear response to transverse energy and momentum perturbations for realistic boost-invariant initial conditions for heavy-ion collisions. We demonstrate how this framework can be used on an event-by-event basis to propagate the energy-momentum tensor from far-from-equilibrium initial-state models to the time ${\ensuremath{\tau}}_{\text{hydro}}$ when the system is well described by relativistic viscous hydrodynamics. The subsequent hydrodynamic evolution becomes essentially independent of the hydrodynamic initialization time ${\ensuremath{\tau}}_{\text{hydro}}$ as long as ${\ensuremath{\tau}}_{\text{hydro}}$ is chosen in an appropriate range where both kinetic and hydrodynamic descriptions overlap. We find that for $\sqrt{{s}_{NN}}=2.76\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\text{TeV}$ central Pb-Pb collisions, the typical timescale when viscous hydrodynamics with shear viscosity over entropy ratio $\ensuremath{\eta}/s=0.16$ becomes applicable is ${\ensuremath{\tau}}_{\text{hydro}}\ensuremath{\sim}1\phantom{\rule{0.16em}{0ex}}\mathrm{fm}/\mathrm{c}$ after the collision.

Toward the determination of heavy-quark transport coefficients in quark-gluon plasma

Abstract: Several transport models have been employed in recent years to analyze heavy-flavor meson spectra in high-energy heavy-ion collisions Heavy-quark transport coefficients extracted from these models with their default parameters vary, however, by up to a factor of 5 at high momenta To investigate the origin of this large theoretical uncertainty, a systematic comparison of heavy-quark transport coefficients is carried out between various transport models Within a common scheme devised for the nuclear modification factor of charm quarks in a brick medium of a quark-gluon plasma, the systematic uncertainty of the extracted drag coefficient among these models is shown to be reduced to a factor of 2, which can be viewed as the smallest intrinsic systematical error band achievable at present time This indicates the importance of a realistic hydrodynamic evolution constrained by bulk hadron spectra and of heavy-quark hadronization for understanding the final heavy-flavor hadron spectra and extracting heavy-quark drag coefficient The transverse transport coefficient is less constrained due to the influence of the underlying mechanism for heavy-quark medium interaction Additional constraints on transport models such as energy loss fluctuation and transverse-momentum broadening can further reduce theoretical uncertainties in the extracted transport coefficients

Thermal vorticity and spin polarization in heavy-ion collisions

Abstract: The hot and dense matter generated in heavy-ion collisions contains intricate vortical structure in which the local fluid vorticity can be very large. Such vorticity can polarize the spin of the produced particles. We study the event-by-event generation of the so-called thermal vorticity in Au+Au collisions at energy region $\sqrt{s}=7.7--200$ GeV and calculate its time evolution, spatial distribution, etc., in a multiphase transport model. We then compute the spin polarization of the $\mathrm{\ensuremath{\Lambda}}$ and $\overline{\mathrm{\ensuremath{\Lambda}}}$ hyperons as a function of $\sqrt{s}$, transverse momentum ${p}_{T}$, rapidity, and azimuthal angle. Furthermore, we study the harmonic flow of the spin, in a manner analogous to the harmonic flow of the particle number. The measurement of the spin harmonic flow may provide a way to probe the vortical structure in heavy-ion collisions. We also discuss the spin polarization of ${\mathrm{\ensuremath{\Xi}}}^{0}$ and ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}$ hyperons, which may provide further information about the spin polarization mechanism of hadrons.

Quantifying Correlated Truncation Errors in Effective Field Theory

Abstract: Effective field theories (EFTs) organize the description of complex systems into an infinite sequence of decreasing importance. Predictions are made with a finite number of terms, which induces a truncation error that is often left unquantified. We formalize the notion of EFT convergence and propose a Bayesian truncation error model for predictions that are correlated across the independent variables, e.g., energy or scattering angle. Central to our approach are Gaussian processes that encode both the naturalness and correlation structure of EFT coefficients. Our use of Gaussian processes permits efficient and accurate assessment of credible intervals, allows EFT fits to easily include correlated theory errors, and provides analytic posteriors for physical EFT-related quantities such as the expansion parameter. We demonstrate that model-checking diagnostics---applied to the case of multiple curves---are powerful tools for EFT validation. As an example, we assess a set of nucleon-nucleon scattering observables in chiral EFT. In an effort to be self-contained, appendices include thorough derivations of our statistical results. Our methods are packaged in Python code, called gsum, that is available for download on GitHub.

Renormalized approach to neutrinoless double- β decay

Abstract: The process at the heart of neutrinoless double-$\ensuremath{\beta}$ decay, $nn\ensuremath{\rightarrow}pp\phantom{\rule{0.16em}{0ex}}{e}^{\ensuremath{-}}{e}^{\ensuremath{-}}$ induced by a light Majorana neutrino, is investigated in pionless and chiral effective field theory. We show in various regularization schemes the need to introduce a short-range lepton-number-violating operator at leading order, confirming earlier findings. We demonstrate that such a short-range operator is only needed in spin-singlet $S$-wave transitions, while leading-order transitions involving higher partial waves depend solely on long-range currents. Calculations are extended to include next-to-leading-order corrections in perturbation theory, where to this order no additional undetermined parameters appear. We establish a connection based on chiral symmetry between neutrinoless double-$\ensuremath{\beta}$ decay and nuclear charge-independence breaking induced by electromagnetism. Data on the latter confirm the need for a leading-order short-range operator but do not allow for a full determination of the corresponding lepton-number-violating coupling. Using a crude estimate of this coupling, we perform ab initio calculations of the matrix elements for neutrinoless double-$\ensuremath{\beta}$ decay for $^{6}\mathrm{He}$ and $^{12}\mathrm{Be}$. We speculate on the phenomenological impact of the leading short-range operator on the basis of these results.

Microscopic study of deuteron production in PbPb collisions at s = 2.76 TeV via hydrodynamics and a hadronic afterburner

Abstract: Author(s): Oliinychenko, D; Pang, LG; Elfner, H; Koch, V | Abstract: The deuteron yield in Pb+Pb collisions at sNN=2.76TeV is consistent with thermal production at a freeze out temperature of T=155MeV. The existence of deuterons with binding energy of 2.2 MeV at this temperature was described as "snowballs in hell" [P. Braun-Munzinger, B. Donigus, and N. Loher, CERN Courier, August 2015]. We provide a microscopic explanation of this phenomenon, utilizing relativistic hydrodynamics and switching to a hadronic afterburner at the above-mentioned temperature of T=155MeV. The measured deuteron pT spectra and coalescence parameter B2(pT) are reproduced without free parameters, only by implementing experimentally known cross sections of deuteron reactions with hadrons, most importantly πd↔πnp.

Equation of state at finite densities for QCD matter in nuclear collisions

Abstract: We construct the QCD equation of state at finite chemical potentials including net baryon, electric charge, and strangeness, based on the conserved charge susceptibilities determined from lattice QCD simulations and the equation of state of the hadron resonance gas model. For the application to relativistic heavy-ion collisions we consider the situation of strangeness neutrality and matter with a fixed electric charge-to-baryon ratio, resembling that of heavy nuclei. The importance of finite electric charge and strangeness chemical potentials for particle production in heavy-ion collisions is demonstrated using hydrodynamic simulations.

Few- and many-nucleon systems with semilocal coordinate-space regularized chiral two- and three-body forces

Abstract: We present calculations of nucleon-deuteron scattering as well as ground and low-lying excited states of light nuclei in the mass range $A=3--16$ up through next-to-next-to-leading order in chiral effective field theory using semilocal coordinate-space regularized two- and three-nucleon forces. It is shown that both of the low-energy constants entering the three-nucleon force at this order can be determined from the triton binding energy and the differential cross section minimum in elastic nucleon-deuteron scattering. From all considered nucleon-deuteron scattering observables, the strongest constraint on these low-energy constants emerges from the precisely measured cross section minimum at ${E}_{N}=70$ MeV. The inclusion of the three-nucleon force is found to improve the agreement with the data for most of the considered observables.

Fission dynamics of Pu 240 from saddle to scission and beyond

Abstract: Calculations are presented for the time evolution of $^{240}\mathrm{Pu}$ from the proximity of the outer saddle point until the fission fragments are well separated, using the time-dependent density functional theory extended to superfluid systems. We have tested three families of nuclear energy density functionals and found that all functionals exhibit a similar dynamics: The collective motion is highly dissipative and with little trace of inertial dynamics, due to the one-body dissipation mechanism alone. This finding justifies the validity of using the overdamped collective motion approach and to some extent the main assumptions in statistical models of fission. This conclusion is robust with respect to the nuclear energy density functional used. The configurations and interactions left out of the present theory framework only increase the role of the dissipative couplings. An unexpected finding is varying the pairing strength within a quite large range has only minor effects on the dynamics. We find notable differences in the excitation energy sharing between the fission fragments in the cases of spontaneous and induced fission. With increasing initial excitation energy of the fissioning nucleus, more excitation energy is deposited in the heavy fragment, in agreement with experimental data on average neutron multiplicities.

Defining the proton radius: A unified treatment

Abstract: An analysis of the proton radius puzzle helps to define what the proton radius really means.

Consistent relativistic mean field models constrained by GW170817

Abstract: We have obtained the Love number and corresponding tidal deformabilities $(\mathrm{\ensuremath{\Lambda}})$ associated with the relativistic mean-field parametrizations shown to be consistent (CRMF) with the nuclear matter, pure neutron matter, symmetry energy, and its derivatives [Dutra et al., Phys. Rev. C 90, 055203 (2014)]. Our results show that CRMF models present very good agreement with the recent data from binary neutron star merger event GW170817. They also confirm the strong correlation between ${\mathrm{\ensuremath{\Lambda}}}_{1.4}$ and the radius of canonical stars $({R}_{1.4})$. When a recent GW170817 constraint on ${\mathrm{\ensuremath{\Lambda}}}_{1.4}$ and the corresponding radius ${R}_{1.4}$ is used, the majority of the models tested are shown to satisfy it.

Deuteron production from phase-space coalescence in the UrQMD approach

Abstract: Ultrarelativistic quantum molecular dynamics phase-space coalescence calculations for the production of deuterons are compared with available data for various reactions from the Facility for Antiproton and Ion Research energy regime energy regime over the CERN Super Proton Synchrotron--Relativistic Heavy Ion Collider Beam Energy Scan region up to CERN Large Hadron Collider energies. It is found that the production process of deuterons, as reflected in their rapidity and transverse-momentum distributions in $p+p$, $p+A$, and $A+A$ collisions in the mentioned energy regime, are in good agreement with experimental data. We further explore the energy and centrality dependence of the $d$/$p$ and $\overline{d}/\overline{p}$ ratios and compare with thermal model results. Finally, we discuss antideuteron production for selected systems. Overall, a good description of the experimental data is observed. Most importantly this good description is based only on a single set of coalescence parameters that is independent of energy and system size and can also be applied for antideuterons.

Feed-down effect on Λ spin polarization

Abstract: We develop a theoretical framework to study the feed-down effect of higher-lying strange baryons on the spin polarization of the Λ hyperon. In this framework, we consider two-body decays through strong, electromagnetic, and weak processes and derive general formulas for the angular distribution and spin polarization of the daughter particle by adopting the helicity formalism. Using the realistic experimental data as input, we explore the feed-down contribution to the global and the local Λ polarizations and find that such a contribution suppresses the primordial Λ polarization, which is not strong enough to resolve the discrepancy between the current theoretical and the experimental results on the azimuthal-angle dependence of Λ polarization. Our paper may also be useful for the measurement of spin polarization of baryons heavier than Λ (e.g., Ξ−) in future experiments.

Exact solutions and attractors of higher-order viscous fluid dynamics for Bjorken flow

Abstract: We consider causal higher order theories of relativistic viscous hydrodynamics in the limit of one-dimensional boost-invariant expansion and study the associated dynamical attractor. We obtain evolution equations for the inverse Reynolds number as a function of Knudsen number. The solutions of these equations exhibit attractor behavior which we analyze in terms of Lyapunov exponents using several different techniques. We compare the attractors of the second-order M\"uller-Israel-Stewart (MIS), transient Denicol-Niemi-Molnar-Rischke (DNMR), and third-order theories with the exact solution of the Boltzmann equation in the relaxation-time approximation. It is shown that for Bjorken flow the third-order theory provides a better approximation to the exact kinetic theory attractor than both MIS and DNMR theories. For three different choices of the time dependence of the shear relaxation rate we find analytical solutions for the energy density and shear stress and use these to study the attractors analytically. By studying these analytical solutions at both small and large Knudsen numbers we characterize and uniquely determine the attractors and Lyapunov exponents. While for small Knudsen numbers the approach to the attractor is exponential, strong power-law decay of deviations from the attractor and rapid loss of initial state memory are found even for large Knudsen numbers. Implications for the applicability of hydrodynamics in far-off-equilibrium situations are discussed.

First-forbidden transitions in the reactor anomaly

Abstract: We describe here microscopic calculations performed on the dominant forbidden transitions in reactor antineutrino spectra above 4 MeV using the nuclear shell model. By taking into account Coulomb corrections in the most complete way, we calculate the shape factor with the highest fidelity and show strong deviations from allowed approximations and previously published results. Despite small differences in the ab initio electron cumulative spectra, large differences on the order of several percent are found in the antineutrino spectra. Based on the behavior of the numerically calculated shape factors we propose a parametrization of forbidden spectra. Using Monte Carlo techniques we derive an estimated spectral correction and uncertainty due to forbidden transitions. We establish the dominance and importance of forbidden transitions in both the reactor anomaly and spectral shoulder analysis with their respective uncertainties. Based on these results, we conclude that a correct treatment of forbidden transitions is indispensable in both the normalization anomaly and spectral shoulder.

p−p, p−Λ, and Λ−Λ correlations studied via femtoscopy in pp reactions at √s=7 TeV

Abstract: We report on the first femtoscopic measurement of baryon pairs, such as p-p, p-Λ, and Λ-Λ, measured by ALICE at the Large Hadron Collider (LHC) in proton-proton collisions at s=7TeV. This study demonstrates the feasibility of such measurements in pp collisions at ultrarelativistic energies. The femtoscopy method is employed to constrain the hyperon-nucleon and hyperon-hyperon interactions, which are still rather poorly understood. A new method to evaluate the influence of residual correlations induced by the decays of resonances and experimental impurities is hereby presented. The p-p, p-Λ, and Λ-Λ correlation functions were fitted simultaneously with the help of a new tool developed specifically for the femtoscopy analysis in small colliding systems: Correlation Analysis Tool using the Schrodinger equation (CATS). Within the assumption that in pp collisions the three particle pairs originate from a common source, its radius is found to be equal to r0=1.125±0.018(stat)−0.035+0.058(syst) fm. The sensitivity of the measured p-Λ correlation is tested against different scattering parameters, which are defined by the interaction among the two particles, but the statistics is not sufficient yet to discriminate among different models. The measurement of the Λ-Λ correlation function constrains the phase space spanned by the effective range and scattering length of the strong interaction. Discrepancies between the measured scattering parameters and the resulting correlation functions at LHC and RHIC energies are discussed in the context of various models.

Predictions of nuclear β -decay half-lives with machine learning and their impact on r -process nucleosynthesis

Abstract: Nuclear $\ensuremath{\beta}$ decay is a key process to understand the origin of heavy elements in the universe, while the accuracy is far from satisfactory for the predictions of $\ensuremath{\beta}$-decay half-lives by nuclear models to date. In this work, we pave a novel way to accurately predict $\ensuremath{\beta}$-decay half-lives with the machine learning based on the Bayesian neural network, in which the known physics has been explicitly embedded, including the ones described by the Fermi theory of $\ensuremath{\beta}$ decay, and the dependence of half-lives on pairing correlations and decay energies. The other potential physics, which is not clear or even missing in nuclear models nowadays, will be learned by the Bayesian neural network. The results well reproduce the experimental data with a very high accuracy and further provide reasonable uncertainty evaluations in half-life predictions. These accurate predictions for half-lives with uncertainties are essential for the $r$-process simulations.

Equation of state effects in the core collapse of a 20 -M ☉ star

Abstract: Uncertainties in our knowledge of the properties of dense matter near and above nuclear saturation density are among the main sources of variations in multimessenger signatures predicted for core-c ...

Longitudinal spin polarization in a thermal model

Abstract: We use a thermal model with single freeze-out to determine longitudinal polarization of $\mathrm{\ensuremath{\Lambda}}$ hyperons emitted from a hot and rotating hadronic medium. We consider the top RHIC energies and use the model parameters determined in the previous analyses of particle spectra and elliptic flow. Using a direct connection between the spin polarization tensor and thermal vorticity, we reproduce earlier results which indicate a quadrupole structure of the longitudinal component of the polarization three-vector with an opposite sign compared to that found in the experiment. We further use only the spatial components of the thermal vorticity in the laboratory system to define polarization and show that this leads to the correct sign and magnitude of the quadrupole structure. This procedure resembles a non-relativistic connection between the polarization three-vector and vorticity employed in other works. In general, our results bring further evidence that the spin polarization dynamics in heavy-ion collisions may be not directly related to the thermal vorticity. The additional material explains the construction of the hydrodynamically consistent gradients of fluid velocity and temperature in thermal models with the help of the perfect-fluid equations of motion.

Centrality and transverse momentum dependence of D0 -meson production at mid-rapidity in Au + Au collisions at s NN =200 GeV

Abstract: Author(s): Adam, J; Adamczyk, L; Adams, JR; Adkins, JK; Agakishiev, G; Aggarwal, MM; Ahammed, Z; Alekseev, I; Anderson, DM; Aoyama, R; Aparin, A; Arkhipkin, D; Aschenauer, EC; Ashraf, MU; Atetalla, F; Attri, A; Averichev, GS; Bairathi, V; Barish, K; Bassill, AJ; Behera, A; Bellwied, R; Bhasin, A; Bhati, AK; Bielcik, J; Bielcikova, J; Bland, LC; Bordyuzhin, IG; Brandenburg, JD; Brandin, AV; Brown, D; Bryslawskyj, J; Bunzarov, I; Butterworth, J; 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, JH; Chen, X; Cheng, J; Cherney, M; Christie, W; Contin, G; Crawford, HJ; Csanad, M; Das, S; Dedovich, TG; Deppner, IM; Derevschikov, AA; Didenko, L; Dilks, C; Dong, X; Drachenberg, JL; Dunlop, JC; Edmonds, T; Efimov, LG; Elsey, N; Engelage, J; Eppley, G; Esha, R; Esumi, S; Evdokimov, O; Ewigleben, J; Eyser, O; Fatemi, R; Fazio, S; Federic, P; Fedorisin, J; Filip, P; Finch, E; Fisyak, Y; Flores, CE; Fulek, L; Gagliardi, CA; Galatyuk, T; Geurts, F; Gibson, A | Abstract: We report a new measurement of D0-meson production at mid-rapidity (|y|l1) in Au + Au collisions at sNN=200GeV utilizing the heavy flavor tracker, a high resolution silicon detector at the STAR experiment. Invariant yields of D0 mesons with transverse momentum pT9GeV/c are reported in various centrality bins (0-10%, 10-20%, 20-40%, 40-60%, and 60-80%). Blast-wave thermal models are used to fit the D0-meson pT spectra to study D0 hadron kinetic freeze-out properties. The average radial flow velocity extracted from the fit is considerably smaller than that of light hadrons (π,K, and p), but comparable to that of hadrons containing multiple strange quarks (φ,Ξ-), indicating that D0 mesons kinetically decouple from the system earlier than light hadrons. The calculated D0 nuclear modification factors reaffirm that charm quarks suffer a large amount of energy loss in the medium, similar to those of light quarks for pTg4GeV/c in central 0-10% Au + Au collisions. At low pT, the nuclear modification factors show a characteristic structure qualitatively consistent with the expectation from model predictions that charm quarks gain sizable collective motion during the medium evolution. The improved measurements are expected to offer new constraints to model calculations and help gain further insights into the hot and dense medium created in these collisions.

Beam energy dependence of (anti-)deuteron production in Au + Au collisions at the BNL Relativistic Heavy Ion Collider

Abstract: Author(s): Adam, J; Adamczyk, L; Adams, JR; Adkins, JK; Agakishiev, G; Aggarwal, MM; Ahammed, Z; Alekseev, I; Anderson, DM; Aoyama, R; Aparin, A; Arkhipkin, D; Aschenauer, EC; Ashraf, MU; Atetalla, F; Attri, A; Averichev, GS; Bairathi, V; Barish, K; Bassill, AJ; Behera, A; Bellwied, R; Bhasin, A; Bhati, AK; Bielcik, J; Bielcikova, J; Bland, LC; Bordyuzhin, IG; Brandenburg, JD; Brandin, AV; Bryslawskyj, J; Bunzarov, I; Butterworth, J; 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, JH; Chen, X; Cheng, J; Cherney, M; Christie, W; Crawford, HJ; Csanad, M; Das, S; Dedovich, TG; Deppner, IM; Derevschikov, AA; Didenko, L; Dilks, C; Dong, X; Drachenberg, JL; Dunlop, JC; Edmonds, T; Elsey, N; Engelage, J; Eppley, G; Esha, R; Esumi, S; Evdokimov, O; Ewigleben, J; Eyser, O; Fatemi, R; Fazio, S; Federic, P; Fedorisin, J; Feng, Y; Filip, P; Finch, E; Fisyak, Y; Fulek, L; Gagliardi, CA; Galatyuk, T; Geurts, F; Gibson, A; Grosnick, D; Gupta, A; Guryn, W | Abstract: We report the energy dependence of mid-rapidity (anti-)deuteron production in Au+Au collisions at sNN=7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV, measured by the STAR experiment at the BNL Relativistic Heavy Ion Collider. The yield of deuterons is found to be well described by the thermal model. The collision energy, centrality, and transverse momentum dependence of the coalescence parameter B2 are discussed. We find that the values of B2 for antideuterons are systematically lower than those for deuterons, indicating that the correlation volume of antibaryons is larger than that of baryons at sNN from 19.6 to 39 GeV. In addition, values of B2 are found to vary with collision energy and show a broad minimum around sNN=20-40 GeV, which might imply a change of the equation of state of the medium in these collisions.

Λ and Λ ¯ spin interaction with meson fields generated by the baryon current in high energy nuclear collisions

Abstract: We propose a dynamical mechanism which provides an interaction between the spins of hyperons and antihyperons and the vorticity of the baryon current in noncentral high energy nuclear collisions. The interaction is mediated by massive vector and scalar bosons, which is well known to describe the nuclear spin-orbit force. It follows from the Foldy-Wouthuysen transformation and leads to a strong-interaction Zeeman effect. The interaction may explain the difference in polarizations of $\mathrm{\ensuremath{\Lambda}}$ and $\overline{\mathrm{\ensuremath{\Lambda}}}$ hyperons as measured by the STAR Collaboration at the BNL Relativistic Heavy Ion Collider. The signs and magnitudes of the meson-baryon couplings are closely connected to the binding energies of hypernuclei and to the abundance of hyperons in neutron stars.

Extended-soft-core baryon-baryon model ESC16. II. Hyperon-nucleon interactions

Abstract: This hyperon-nucleon paper is part of a simultaneous treatment of all baryon-baryon systems: $N\phantom{\rule{0}{0ex}}N$, $Y\phantom{\rule{0}{0ex}}N$, and $Y\phantom{\rule{0}{0ex}}Y$. Utilizing a meson-exchange potential approach, all $8\ifmmode\times\else\texttimes\fi{}8$ baryon-baryon channels are described in a model with SU(3)-symmetric couplings consistent with the constituent quark model. A high-quality fit is achieved for the $N\phantom{\rule{0}{0ex}}N$ data (${T}_{\text{Lab}}l350$ MeV) and the available $p$-$\mathrm{\ensuremath{\Lambda}}$ and $p$-$\mathrm{\ensuremath{\Sigma}}$ data.

Impact of the neutron star crust on the tidal polarizability

Abstract: Background: The first direct detection of a binary neutron star merger by the LIGO Scientific Collaboration and the Virgo Collaboration (LIGO-Virgo) [Phys. Rev. Lett. 119, 161101 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.161101] has opened the brand new era of multimessenger astronomy. This historic detection has been instrumental in providing initial constraints on the tidal polarizability (or deformability) of neutron stars. In turn, the tidal polarizability—an observable highly sensitive to stellar compactness—has been used to impose limits on stellar radii and ultimately on the underlying equation of state (EOS). Purpose: Besides its strong dependence on the stellar compactness, the tidal polarizability is also sensitive to the second tidal Love number k2. It is the main purpose of this paper to perform a detailed study of k2 which, for a given compactness parameter, encodes the entire sensitivity of the tidal polarizability to the underlying equation of state. In particular, we examine the important role that the crustal component of the EOS plays in the determination of k2. Methods: A set of realistic models of the equation of state that yield an accurate description of the properties of finite nuclei support neutron stars of two solar masses and provide a Lorentz covariant extrapolation to dense matter are used to solve both the Tolman-Oppenheimer-Volkoff and the differential equations for the induced quadrupole gravitational field from which k2 is extracted. Results: Given that the tidal polarizability scales as the fifth power of the compactness parameter, a universal relation exists among the tidal polarizability and the compactness parameter that is highly insensitive to the underlying equation of state. Thus, besides an extraction of the tidal polarizabilities, a measurement of the individual stellar masses is also required to impact the mass-radius relation. However, we observe a strong sensitivity of the second Love number to the underlying equation of state—particularly to the contribution from the inner crust. Conclusions: Although by itself the tidal polarizability cannot contribute to the determination of the mass-radius relation, future detections of binary neutron star mergers by the LIGO-Virgo Collaborations during the third observing run and beyond are poised to provide significant constraints on both the tidal polarizabilities and the masses of the individual stars, and thus ultimately on the mass-radius relation. Yet, subleading corrections to the tidal polarizability are encoded in the second Love number k2, which displays a large sensitivity to the entire—crust-plus-core—equation of state.

Azimuthal angle dependence of the longitudinal spin polarization in relativistic heavy ion collisions

Abstract: The longitudinal quark spin polarization along the beam direction in noncentral relativistic heavy ion collisions is studied in the chiral kinetic approach. Its azimuthal angle dependence in the transverse plane of the collision is found to have a quadrupole structure as in studies from hydrodynamic and transport models based on the relativistic spin-vorticity coupling in a thermodynamically equilibrated hadronic matter at kinetic freeze-out. The direction of the quark longitudinal spin polarization is, however, opposite to that from these models, and this is due to the axial charge current induced by the transverse component of the vorticity field in the chiral kinetic approach. Our finding is consistent with the azimuthal angle dependence of the longitudinal spin polarization of $\mathrm{\ensuremath{\Lambda}}$ hyperons, which is mainly determined by that of the strange quark, recently measured in the experiments by the STAR Collaboration at the BNL Relativistic Heavy Ion Collider.

Hybrid equation of state with pasta phases, and third family of compact stars

Abstract: The effect of pasta phases on the quark-hadron phase transition is investigated for a set of relativistic mean-field equations of state for both hadron and quark matter. The results of the full numerical solution with pasta phases are compared with those of an interpolating construction used in previous works, for which we demonstrate an adequate description of the numerical results. A one-to-one mapping of the free parameter of the construction to the physical surface tension of the quark-hadron interface is obtained for which a fit formula is given. For each pair of quark and hadron matter models the critical value of the surface tension is determined, above which the phase transition becomes close to the Maxwell construction. This result agrees well with earlier theoretical estimates. The study is extended to neutron star matter in beta equilibrium with electrons and muons and is applied to investigate the effect of pasta phases on the structure of hybrid compact stars and the robustness of a possible third family solution.

Comparison of heavy-ion transport simulations: Collision integral with pions and Δ resonances in a box

Abstract: Author(s): Ono, A; Xu, J; Colonna, M; Danielewicz, P; Ko, CM; Tsang, MB; Wang, YJ; Wolter, H; Zhang, YX; Chen, LW; Cozma, D; Elfner, H; Feng, ZQ; Ikeno, N; Li, BA; Mallik, S; Nara, Y; Ogawa, T; Ohnishi, A; Oliinychenko, D; Su, J; Song, T; Zhang, FS; Zhang, Z | Abstract: Background: Simulations by transport codes are indispensable for extracting valuable physical information from heavy-ion collisions. Pion observables such as the π-/π+ yield ratio are expected to be sensitive to the symmetry energy at high densities. Purpose: To evaluate, understand, and reduce the uncertainties in transport-code results originating from different approximations in handling the production of Δ resonances and pions. Methods: We compare ten transport codes under controlled conditions for a system confined in a box, with periodic boundary conditions, and initialized with nucleons at saturation density and at a temperature of 60 MeV. The reactions NN↔NΔ and Δ↔Nπ are implemented, but the Pauli blocking and the mean-field potential are deactivated in the present comparison. Thus, these are cascade calculations including pions and Δ resonances. Results are compared to those from the two reference cases of a chemically equilibrated ideal gas mixture and of the rate equation. Results: For the numbers of Δ and π, deviations from the reference values are observed in many codes, and they depend significantly on the size of the time step. These deviations are tied to different ways in ordering the sequence of reactions, such as collisions and decays, that take place in the same time step. Better agreements with the reference values are seen in the reaction rates and the number ratios among the isospin species of Δ and π. Both the reaction rates and the number ratios are, however, affected by the correlations between particle positions, which are absent in the Boltzmann equation, but are induced by the way particle scatterings are treated in many of the transport calculations. The uncertainty in the transport-code predictions of the π-/π+ ratio, after letting the existing Δ resonances decay, is found to be within a few percent for the system initialized at n/p=1.5. Conclusions: The uncertainty in the final π-/π+ ratio in this simplified case of particles in a box is sufficiently small so that it does not strongly impact constraining the high-density symmetry energy from heavy-ion collisions. Most of the sources of uncertainties have been understood, and individual codes may be further improved in future applications. This investigation will be extended in the future to heavy-ion collisions to ensure the problems identified here remain under control.

Microscopic description for polarization in particle scattering

Abstract: We propose a microscopic description for the polarization from the first principle through the spin-orbit coupling in particle collisions. It is based on scatterings of particles as wave packets, an effective method to deal with particle scatterings at specified impact parameters. The polarization is then the consequence of particle collisions in a nonequilibrium state of spins. The spin-vorticity coupling naturally emerges from the spin orbit one encoded in polarized scattering amplitudes of collisional integrals when one assumes local equilibrium in momentum but not in spin.