Nuclear Theory·nucl-th

Tuesday·July 13, 2021

14 papers—7 primary·7 cross-listed

01
Coulomb field correction due to virtual $e^{+} e^{-}$ production in heavy ion collisions
Thomas Settlemyre🇺🇸 · Aldo Bonasera🇨🇳 · Hua Zheng🇺🇸
The correction to the Coulomb energy due to virtual production of $e^{+} e^{-}$ pairs, which is on the order of one percent of the Coulomb energy at nuclear scales is discussed. The effects of including a pair-production term in the semi-empirical mass formula and the correction to the Coulomb barrier for a handful of nuclear collisions using the Bass and Coulomb potentials are studied. With an eye toward future work using Constrained Molecular Dynamics (CoMD) model, we also calculate the correction to the Coulomb energy and force between protons after folding with a Gaussian spatial distribution.
nucl-thnucl-exNPA(2021)·4 citations
02
Test of the hyperon-nucleon interaction within leading order covariant chiral effective field theory
Jing Song🇨🇳 · Zhi-Wei Liu🇨🇳 · Kai-Wen Li🇨🇳 · Li-Sheng Geng🇨🇳
Motivated by the recent experimental measurements of differential cross sections of the $Σ^{-} p$ elastic scattering in the momentum range of $470$ to $850$ MeV $/ c$ by the J-PARC E $40$ experiment, we extend our previous studies of $S = - 1$ hyperon-nucleon interactions to relatively higher energies up to $900$ MeV $/ c$ for both the coupled-channel $Λ p \to (Λ p, Σ^{+} n, Σ^{0} p)$ , $Σ^{-} p \to (Λ n, Σ^{0} n, Σ^{-} p)$ and single-channel $Σ^{+} p \to Σ^{+} p$ reactions. We show that although the leading order covariant chiral effective field theory is only constrained by the low energy data, it can describe the high energy data reasonably well, in particular, the J-PARC E40 differential cross sections. The predicted cusp structure close to the $Σ N$ threshold in the $Λ p \to Λ p$ reaction agrees with the latest ALICE observation as well as with the results of the next-to-leading order heavy baryon chiral effective theory. On the other hand, the comparison with the latest CLAS data on the $Λ p$ cross sections between 0.9 and 2.0 GeV $/ c$ clearly indicates the need of higher order chiral potentials for such high momenta. This is also the case for the latest J-PARC data on the $Σ p \to Λ n$ differential cross sections. Nevertheless, even for these cases, the predictions are in qualitative agreement with the data, albeit with large uncertainties, implying that the predicted total and differential cross sections are of relevance for ongoing and planned experiments.
nucl-thhep-exhep-lathep-ph+1PRC(2022)·32 citations
03
Evolution of nuclear charge radii in copper and indium isotopes
Rong An · Xiang Jiang · Li-Gang Cao · Feng-Shou Zhang
Systematic trends in nuclear charge radii are of great interest due to universal shell effects and odd-even staggering (OES). The modified root mean square (rms) charge radius formula, which phenomenologically accounts for the formation of neutron-proton ( $n p$ ) correlations, is here applied for the first time to the study of odd- $Z$ copper and indium isotopes. Theoretical results obtained by the relativistic mean field (RMF) model with NL3, PK1 and NL3 $^{*}$ parameter sets are compared with experimental data. Our results show that both OES and the abrupt changes across $N = 50$ and $82$ shell closures are clearly reproduced in nuclear charge radii. The inverted parabolic-like behaviors of rms charge radii can also be described remarkably well between two neutron magic numbers, namely $N = 28$ to $50$ for copper isotopes and $N = 50$ to $82$ for indium isotopes. This implies that the $n p$ -correlations play an indispensable role in quantitatively determining the fine structures of nuclear charge radii along odd- $Z$ isotopic chains. Also, our conclusions have almost no dependence on the effective forces.
nucl-thnucl-exCPC(2022)·10 citations
04
Quark anomalous magnetic moment and its effects on the $ρ$ meson properties
Zanbin Xing🇨🇳 · Khépani Raya🇨🇳 · Lei Chang🇨🇳
A symmetry-preserving treatment of mesons, within a Dyson-Schwinger and Bethe-Salpeter equations approach, demands an interconnection between the kernels of the quark gap equation and meson Bethe-Salpeter equation. Appealing to those symmetries expressed by the vector and axial-vector Ward-Green-Takahashi identitiges (WGTI), we construct a two-body Bethe-Salpeter kernel and study its implications in the vector channel; particularly, we analyze the structure of the quark-photon vertex, which explicitly develops a vector meson pole in the timelike axis and the quark anomlaous magnetic moment term, as well as a variety of $ρ$ meson properties: mass and decay constants, electromagnetic form factors, and valence-quark distribution amplitudes.
nucl-thhep-phPRD(2021)·21 citations
05
Resonances of $A = 4$ $T = 1$ isospin triplet states within the \textit{ab initio} no-core Gamow shell model
J. G. Li · N. Michel · W. Zuo · F. R. Xu
The $A = 4$ nuclei, i.e., $^{4}$ H, $^{4}$ He and $^{4}$ Li, establish an interesting isospin $T = 1$ isobaric system. $^{4}$ H and $^{4}$ Li are unbound broad resonances, whereas $^{4}$ He is deeply bound in its ground state but unbound in all its excited states. The present situation is that experiments so far have not given consistent data on the resonances. Few-body calculations have well studied the scatterings of the $4 N$ systems. In the present work, we provide many-body calculations of the broad resonance structures, in an \textit{ab initio} framework with modern realistic interactions. It occurs that, indeed, $^{4}$ H, $^{4}$ Li and excited $^{4}$ He are broad resonances, which is in accordance with experimental observations. The calculations also show that the first $1^{-}$ excited state almost degenerates with the $2^{-}$ ground state in the pair of mirror isobars of $^{4}$ H and $^{4}$ Li, which may suggest that the experimental data on energy and width are the mixture of the ground state and the first excited state. The $T = 1$ isospin triplet formed with an excited state of $^{4}$ He and ground states of $^{4}$ H and $^{4}$ Li is studied, focusing on the effect of isospin symmetry breaking.
nucl-thnucl-exPRC(2021)·34 citations
06
Non-conformal attractor in boost-invariant plasmas
Chandrodoy Chattopadhyay🇺🇸 · Sunil Jaiswal🇮🇳 · Lipei Du🇺🇸 · Ulrich Heinz🇺🇸 · Subrata Pal🇮🇳
We study the dissipative evolution of (0+1)-dimensionally expanding media with Bjorken symmetry using the Boltzmann equation for massive particles in relaxation-time approximation. Breaking conformal symmetry by a mass induces a non-zero bulk viscous pressure in the medium. It is shown that even a small mass (in units of the local temperature) drastically modifies the well-known attractor for the shear Reynolds number previously observed in massless systems. For generic nonzero particle mass, neither the shear nor the bulk viscous pressure relax quickly to a non-equilibrium attractor; they approach the hydrodynamic limit only late, at small values of the inverse Reynolds numbers. Only the longitudinal pressure, which is a combination of thermal, shear and bulk viscous pressures, continues to show early approach to a far-off-equilibrium attractor, driven by the rapid longitudinal expansion at early times. Second-order dissipative hydrodynamics based on a gradient expansion around locally isotropic thermal equilibrium fails to reproduce this attractor.
nucl-thhep-phphysics.plasm-phPLB(2022)·62 citations
07
A Detailed Examination of Astrophysical Constraints on the Symmetry Energy and the Neutron Skin of $^{208}$ Pb with Minimal Modeling Assumptions
Reed Essick · Philippe Landry · Achim Schwenk · Ingo Tews
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 $0.283 \pm 0.071$ fm for the neutron-skin thickness of $^{208}$ Pb, $R_{skin}^{^{208} Pb}$ , implying a symmetry-energy slope parameter $L$ of $106 \pm 37$ 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 $R_{skin}^{^{208} Pb}$ 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 chiral effective field theory ( $χ$ EFT) and PREX-II constraints yields $S_{0} = 33. 0_{- 1.8}^{+ 2.0}$ MeV, $L = 5 3_{- 15}^{+ 14}$ MeV, and $R_{skin}^{^{208} Pb} = 0.1 7_{- 0.04}^{+ 0.04}$ fm. We also examine the consistency of several individual $χ$ EFT calculations with astrophysical observations and terrestrial experiments. We find that there is only mild tension between $χ$ EFT, astrophysical data, and PREX-II's $R_{skin}^{^{208} Pb}$ measurement ( $p$ -value $= 12.3%$ ) and that there is excellent agreement between $χ$ EFT, astrophysical data, and other nuclear experiments.
nucl-thastro-ph.HEnucl-exPRC(2021)·97 citations
08
A Large- $N$ Expansion for Minimum Bias
Andrew J. Larkoski🇺🇸 · Tom Melia🇯🇵
Despite being the overwhelming majority of events produced in hadron or heavy ion collisions, minimum bias events do not enjoy a robust first-principles theoretical description as their dynamics are dominated by low-energy quantum chromodynamics. In this paper, we present a novel expansion scheme of the cross section for minimum bias events that exploits an ergodic hypothesis for particles in the events and events in an ensemble of data. We identify power counting rules and symmetries of minimum bias from which the form of the squared matrix element can be expanded in symmetric polynomials of the phase space coordinates. This expansion is entirely defined in terms of observable quantities, in contrast to models of heavy ion collisions that rely on unmeasurable quantities like the number of nucleons participating in the collision, or tunes of parton shower parameters to describe the underlying event in proton collisions. The expansion parameter that we identify from our power counting is the number of detected particles $N$ and as $N \to \infty$ the variance of the squared matrix element about its mean, constant value on phase space vanishes. With this expansion, we show that the transverse momentum distribution of particles takes a universal form that only depends on a single parameter, has a fractional dispersion relation, and agrees with data in its realm of validity. We show that the constraint of positivity of the squared matrix element requires that all azimuthal correlations vanish in the $N \to \infty$ limit at fixed center-of-mass energy, as observed in data. The approach we follow allows for a unified treatment of small and large system collective behavior, being equally applicable to describe, e.g., elliptic flow in PbPb collisions and the "ridge" in pp collisions.
↳ hep-phhep-exhep-thnucl-ex+1JHEP(2021)·7 citations
09
Standard Model Physics and the Digital Quantum Revolution: Thoughts about the Interface
Natalie Klco🇺🇸 · Alessandro Roggero🇺🇸 · Martin J. Savage🇺🇸
Advances in isolating, controlling and entangling quantum systems are transforming what was once a curious feature of quantum mechanics into a vehicle for disruptive scientific and technological progress. Pursuing the vision articulated by Feynman, a concerted effort across many areas of research and development is introducing prototypical digital quantum devices into the computing ecosystem available to domain scientists. Through interactions with these early quantum devices, the abstract vision of exploring classically-intractable quantum systems is evolving toward becoming a tangible reality. Beyond catalyzing these technological advances, entanglement is enabling parallel progress as a diagnostic for quantum correlations and as an organizational tool, both guiding improved understanding of quantum many-body systems and quantum field theories defining and emerging from the Standard Model. From the perspective of three domain science theorists, this article compiles thoughts about the interface on entanglement, complexity, and quantum simulation in an effort to contextualize recent NISQ-era progress with the scientific objectives of nuclear and high-energy physics.
↳ quant-phhep-lathep-phnucl-thRept.Prog.Phys.(2022)·233 citations
10
(3+1)-D viscous hydrodynamics CLVisc at finite net baryon density: identified particle spectra, anisotropic flows and flow fluctuations across BES energies
Xiang-Yu Wu🇨🇳 · Guang-You Qin🇨🇳 · Long-Gang Pang🇨🇳 · Xin-Nian Wang🇨🇳
To study the bulk properties of the quark-gluon-plasma (QGP) produced at the beam energy scan (BES) energies at the Relativistic Heavy Ion Collider (RHIC), we extend the (3+1)-dimensional viscous hydrodynamics CLVisc to include net baryon number conservation and Israel-Stewart-like equation for baryon diffusion with the NEOS-BQS equation of state, fluctuating initial conditions from Monte-Carlo Glauber model, and the afterburner SMASH. This integrated framework is shown to provide a good description of identified particle spectra, mean transverse momenta and anisotropic flows for different centralities and over a wide range of collision energies (7.7-62.4 GeV). It is found that the mean momenta of identified particles and anisotropic flows increases mildly with the collision energy due to larger radial flow. We further compute the multiple-particle cumulant ratio $v_{2} {4} / v_{2} {2}$ of elliptic flow across BES energies, and find that the relative fluctuations of elliptic flow are insensitive to the collision energy, consistent with the preliminary STAR data. Our model provides a benchmark for understanding the RHIC-BES data and studying the critical properties and phase structure of hot and dense QCD matter.
↳ hep-phnucl-exnucl-thPRC(2022)·101 citations
11
Projecting the likely importance of weak-interaction-driven bulk viscosity in neutron star mergers
Elias R. Most🇺🇸 · Steven P. Harris🇺🇸 · Christopher Plumberg🇺🇸 · Mark G. Alford🇺🇸 · Jorge Noronha🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸 · Frans Pretorius🇺🇸 · Helvi Witek🇺🇸 · Nicolás Yunes🇺🇸
In this work, we estimate how much bulk viscosity driven by Urca processes is likely to affect the gravitational wave signal of a neutron star coalescence. In the late inspiral, we show that bulk viscosity affects the binding energy at fourth post-Newtonian (PN) order. Even though this effect is enhanced by the square of the gravitational compactness, the coefficient of bulk viscosity is likely too small to lead to observable effects in the waveform during the late inspiral, when only considering the orbital motion itself. In the post-merger, however, the characteristic time-scales and spatial scales are different, potentially leading to the opposite conclusion. We post-process data from a state-of-the-art equal-mass binary neutron star merger simulation to estimate the effects of bulk viscosity (which was not included in the simulation itself). In that scenario, we find that bulk viscosity can reach high values in regions of the merger. We compute several estimates of how much it might directly affect the global dynamics of the considered merger scenario, and find that it could become significant. Even larger effects could arise in different merger scenarios or in simulations that include non-linear effects. This assessment is reinforced by a quantitative comparison with relativistic heavy-ion collisions where such effects have been explored extensively.
↳ astro-ph.HEgr-qcnucl-thMNRAS(2021)·129 citations
12
Bremsstrahlung photons from stopping in heavy-ion collisions
Sohyun Park🇨🇭 · Urs Achim Wiedemann🇨🇭
We examine the spectrum of bremsstrahlung photons that results from the stopping of the initial net charge distributions in ultrarelativistic nucleus-nucleus collisions at the CERN Large Hadron Collier (LHC). This effect has escaped detection so far since it becomes sizable only at very low transverse momentum and at sufficiently forward rapidity. We argue that it may be within reach of the next-generation LHC heavy-ion detector ALICE-3 that is currently under study, and we comment on the physics motivation for measuring it.
↳ hep-phhep-exnucl-thPRC(2021)·5 citations
13
Polarization effects at finite temperature and magnetic field
Pok Man Lo🇵🇱 · Michal Szymanski🇵🇱 · Krzysztof Redlich🇵🇱 · Chihiro Sasaki🇵🇱
We study the screening of four-quark interaction by the ring diagram in an effective chiral quark model. This entails a medium dependent coupling which naturally reduces the chiral transition temperature in a class of models, and is capable of generating an inverse magnetic catalysis at finite temperature. These results are the first coherent description of inverse magnetic catalysis, anchored to a reliable field-theoretical basis.
↳ hep-phhep-latnucl-th3 citations
14
An equation-of-state-meter for CBM using PointNet
Manjunath Omana Kuttan🇩🇪 · Kai Zhou🇩🇪 · Jan Steinheimer🇩🇪 · Andreas Redelbach🇩🇪 · Horst Stoecker🇩🇪
A novel method for identifying the nature of QCD transitions in heavy-ion collision experiments is introduced. PointNet based Deep Learning (DL) models are developed to classify the equation of state (EoS) that drives the hydrodynamic evolution of the system created in Au-Au collisions at 10 AGeV. The DL models were trained and evaluated in different hypothetical experimental situations. A decreased performance is observed when more realistic experimental effects (acceptance cuts and decreased resolutions) are taken into account. It is shown that the performance can be improved by combining multiple events to make predictions. The PointNet based models trained on the reconstructed tracks of charged particles from the CBM detector simulation discriminate a crossover transition from a first order phase transition with an accuracy of up to 99.8%. The models were subjected to several tests to evaluate the dependence of its performance on the centrality of the collisions and physical parameters of fluid dynamic simulations. The models are shown to work in a broad range of centralities (b=0-7 fm). However, the performance is found to improve for central collisions (b=0-3 fm). There is a drop in the performance when the model parameters lead to reduced duration of the fluid dynamic evolution or when less fraction of the medium undergoes the transition. These effects are due to the limitations of the underlying physics and the DL models are shown to be superior in its discrimination performance in comparison to conventional mean observables.
↳ hep-phnucl-exnucl-thJHEP(2021)·32 citations

Affiliations

first authorsco-authorsvia INSPIRE