Nuclear Theory·nucl-th

Tuesday·December 15, 2020

16 papers—11 primary·5 cross-listed

01
Extrapolating from neural network models: a cautionary tale
A. Pastore · M. Carnini
We present three different methods to estimate error bars on the predictions made using a neural network. All of them represent lower bounds for the extrapolation errors. For example, we did not include an analysis on robustness against small perturbations of the input data. At first, we illustrate the methods through a simple toy model, then, we apply them to some realistic cases related to nuclear masses. By using theoretical data simulated either with a liquid-drop model or a Skyrme energy density functional, we benchmark the extrapolation performance of the neural network in regions of the Segrè chart far away from the ones used for the training and validation. Finally, we discuss how error bars can help identifying when the extrapolation becomes too uncertain and thus unreliable
nucl-thJ.Phys.G(2021)·11 citations
02
Statistical tools for a better optical model
M. Catacora-Rios · G. B. King · A. E. Lovell · F. M. Nunes
Background: Modern statistical tools provide the ability to compare the information content of observables and provide a path to explore which experiments would be most useful to give insight into and constrain theoretical models. Purpose: In this work we study three such tools in the context of nuclear reactions with the goal of constraining the optical potential. Method: The three statistical tools examined are: i) the principal component analysis; ii) the sensitivity analysis based on derivatives; and iii) the Bayesian evidence. We first apply these tools to a toy-model case, comparing the form of the imaginary part of the optical potential. Then we consider two different reaction observables, elastic angular distributions and polarization data for reactions on 48Ca at two different beam energies. Results: For the toy-model case, we find significant discrimination power in the sensitivities and the Bayesian evidence, showing clearly that the volume imaginary term is more useful to describe scattering at higher energies. When comparing between elastic cross sections and polarization data using realistic optical models, sensitivity studies indicate that both observables are roughly equally sensitive but the variability of the optical model parameters is strongly angle dependent. The Bayesian evidence shows some variability between the two observables, but the Bayes factor obtained is not sufficient to discriminate between angular distributions and polarization. Conclusions: From the cases considered, we conclude that in general elastic scattering angular distributions have similar impact in constraining the optical potential parameters compared to the polarization data. The angular ranges for the optimum experimental constraints can vary significantly with the observable considered.
nucl-thPRC(2021)·22 citations
03
Comparison of semiclassical transfer to continuum model with Ichimura-Austern-Vincent model in medium energy knockout reactions
Jin Lei🇮🇹 · Angela Bonaccorso🇮🇹
The full quantum mechanical (QM) model of inclusive breakup of Ichimura-Austern-Vincent (IAV) is implemented in this paper to calculate breakup from heavy radioactive nuclei on a $^{9}$ Be target at intermediate energies. So far it had been implemented and applied only to low energy reactions with light projectiles. The IAV model is successful in predicting absolute cross sections among other observables. In order to get insight on the content of the model in the case of the complicated heavy-ion reactions, results are compared with those of the semiclassical transfer to the continuum (TC) model. Because the TC is based on analytical formulae the dynamics of the breakup as it is contained in the rather involved IAV formalism will become more transparent. Heavy-ion reactions at high energies ( $>$ 50A.MeV) are demanding from the computational point of view because of the high number of partial waves involved, typically around 100. The TC constitutes a useful alternative to the full QM calculations whenever predictions and/or estimates are necessary. It allows also for a systematic, fast evaluation of breakup observables. In the applications of both methods we use state-of-the art optical potentials and structure information. Excellent agreement is found between the calculated results of both methods and with available experimental data which shows that the qualitative and quantitative understanding of most aspects of one nucleon breakup is well under control.
nucl-thPLB(2021)·13 citations
04
Taming nucleon density distributions with deep neural network method
Zu-Xing Yang · Wei Zuo · Peng Yin · Xiao-Hua Fan
We investigate the density distributions of finite nuclei employing a well-designed deep neural network method. We calculate the target nucleon density distributions with Skyrme density functional theories, which are used to train the networks. We find that the training with only about $10%$ nuclei ( $300 - 400$ ) is sufficient to describe the nucleon density distributions of all the nuclear chart within 2\% relative error. The relative error comes to 5\% when about 200 proton(neutron) density distributions are used for training. We obtained very similar results for different Skyrme density functional theories. Therefore the ability to train networks is weakly dependent on the theoretical model. Moreover, in the process of machine learning, there is a turning point showing the transition from the Fermi-like distribution to the realistic Skyrme distribution, which provides significant properties of convergence process.
nucl-thPLB(2021)·16 citations
05
Multifarious roles of hidden chiral-scale symmetry:"Quenching" $g_{A}$ in nuclei
Mannque Rho🇫🇷
I discuss how the axial current coupling constant $g_{A}$ renormalized in scale symmetric chiral EFT defined at a chiral matching scale impacts on the axial current matrix elements on beta decays in nuclei with and without neutrinos. The "quenched" $g_{A}$ observed in nuclear superallowed Gamow-Teller transitions, a long-standing puzzle in nuclear physics, is shown to encode the emergence of chiral-scale symmetry hidden in QCD in the vacuum. This enables one to explore how trace-anomaly-induced scale symmetry breaking enters in the renormalized $g_{A}$ in nuclei applicable to certain non-unique forbidden processes involved in neutrinoless double beta decays. A parallel is made between the roles of chiral-scale symmetry in quenching $g_{A}$ in highly dense medium and in hadron-quark continuity in the EoS of dense matter in massive compact stars. A systematic chiral-scale EFT, presently lacking in nuclear theory and potentially crucial for the future progress, is suggested as a challenge in the field.
nucl-thhep-phSymmetry(2021)·7 citations
06
Nucleon-Nucleus Optical Potential computed with the Gogny interaction
Juan Lopez-Moraña · Xavier Viñas
The ability of the Gogny forces of the D1 family to describe the nucleon-nucleus scattering is studied. To this end, we use an optical model potential built up using a semi-microscopic nuclear matter approach. The real and imaginary parts of the optical model are provided by the first and second-order terms, respectively, of the Taylor expansion of the mass operator calculated within the Brueckner-Hartree-Fock method using the reaction G-matrix built up with the effective Gogny force instead of a microscopic interaction. The optical potential in finite nuclei is obtained through the Local Density Approximation using the neutron and proton densities provided by a quasi-local Hartree-Fock calculation with the same Gogny force for the sake of consistency. A reasonable good agreement is found between the theoretical differential cross-sections and the analyzing powers of the elastic neutron and proton scattering along the periodic table from Ca to Pb calculated with the Gogny forces and the corresponding values predicted by the global phenomenological potential of Koning and Delaroche. To investigate the limits of the approximations used in this work, comparisons with the results of nucleon-nucleus elastic scattering in $^{40}$ Ca and $^{48}$ Ca obtained using the Nuclear Structure Model are also performed.
nucl-thJ.Phys.G(2021)·6 citations
07
Role of baryon resonances in the $π^{-} p \to n e^{+} e^{-}$ reaction within an effective-Lagrangian model
Miklós Zétényi🇭🇺 · Deniz Nitt🇩🇪 · Michael Buballa🇩🇪 · Tetyana Galatyuk🇩🇪
We present a study of the reaction $π^{-} p \to n e^{+} e^{-}$ for $s = 1.49 GeV$ , including non-resonant Born terms and contributions of the $N (1440)$ , $N (1520)$ , $N (1535)$ resonances ( $R$ ), using an effective-Lagrangian model, which we extended by a phenomenological phase factor at the $R N ρ$ vertex function. We give predictions for both the differential cross section $d σ / d m$ and the spin density matrix elements of the virtual photon that decays into the lepton pair. In the studied energy range, the cross section is dominated by the Born and $N (1520)$ contributions.
nucl-thhep-phPRC(2021)·9 citations
08
Global $Λ$ polarization in moderately relativistic nuclear collisions
Yu. B. Ivanov🇷🇺
Predictions for the global polarization of $Λ$ hyperons in Au+Au collisions at moderately relativistic collision energies, 2.4 $\leq s_{N N} \leq$ 11 GeV, are made. 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 $s_{N N} \approx$ 3 GeV. It is found that the global polarization increases with increasing width of the rapidity window around the midrapidity.
nucl-thhep-phnucl-exPRC(2021)·54 citations
09
Dynamical instabilities for model with point-coupling interactions: Vlasov formalism method
Yanjun Chen · Juan Zou · Zipeng Cheng · Binguang He
We explore the effects of the density dependence of symmetry energy on the dynamical instabilities and crust-core phase transition in the cold and warm neutron stars in the RMF theory with point-coupling interactions using the Vlasov approach. The role of the temperature and neutrino trapping has also been considered. The distillation effect, crust-core transition density and pressure, the cluster size and growth rates have been discussed. The present work shows that the slope of symmetry energy, temperature, and neutrino trapping have obvious effects.
nucl-th0 citations
10
Coupling dynamical and statistical mechanisms for baryonic cluster production in nucleus collisions of intermediate and high energies
A.S. Botvina🇩🇪 · N. Buyukcizmeci🇹🇷 · M. Bleicher🇩🇪
Central nucleus-nucleus collisions produce many new baryons and the nuclear clusters can be formed from these species. The phenomenological coalescence models were sufficiently good for description of light nuclei yields in a very broad range of collision energies. We demonstrate that in reality the coalescence process can be considered as 1) the formation of primary diluted excited baryon clusters and 2) their following statistical decay leading to the final cold fragment production. We argue that the formation of such excited systems from the interacting baryons is a natural consequence of the nuclear interaction at subnuclear densities resulting in the nuclear liquid-gas type phase transition in finite systems. In this way one can provide a consistent interpretation of the experimental fragment yields (FOPI data) including the important collision energy dependence in relativistic ion reactions. We investigate the regularities of this new kind of fragment production, for example, their yield, isospin, and kinetic energy characteristics. A generalization of such a clusterization mechanism for hypernuclear matter is suggested. The isotope yields and particle correlations should be adequate for studying these phenomena.
nucl-thnucl-exPRC(2021)·21 citations
11
Get on the BAND Wagon: A Bayesian Framework for Quantifying Model Uncertainties in Nuclear Dynamics
D.R. Phillips🇺🇸 · R.J. Furnstahl🇺🇸 · U. Heinz🇺🇸 · T. Maiti🇺🇸 · W. Nazarewicz🇺🇸 · F.M. Nunes🇺🇸 · M. Plumlee🇺🇸 · M.T. Pratola🇺🇸 · S. Pratt🇺🇸 · F.G. Viens🇺🇸 · S.M. Wild🇺🇸
We describe the Bayesian Analysis of Nuclear Dynamics (BAND) framework, a cyberinfrastructure that we are developing which will unify the treatment of nuclear models, experimental data, and associated uncertainties. We overview the statistical principles and nuclear-physics contexts underlying the BAND toolset, with an emphasis on Bayesian methodology's ability to leverage insight from multiple models. In order to facilitate understanding of these tools we provide a simple and accessible example of the BAND framework's application. Four case studies are presented to highlight how elements of the framework will enable progress on complex, far-ranging problems in nuclear physics. By collecting notation and terminology, providing illustrative examples, and giving an overview of the associated techniques, this paper aims to open paths through which the nuclear physics and statistics communities can contribute to and build upon the BAND framework.
nucl-thnucl-exphysics.data-anJ.Phys.G(2021)·102 citations
12
Explainable machine learning of the underlying physics of high-energy particle collisions
Yue Shi Lai🇺🇸 · Duff Neill🇺🇸 · Mateusz Płoskoń🇺🇸 · Felix Ringer🇺🇸
We present an implementation of an explainable and physics-aware machine learning model capable of inferring the underlying physics of high-energy particle collisions using the information encoded in the energy-momentum four-vectors of the final state particles. We demonstrate the proof-of-concept of our White Box AI approach using a Generative Adversarial Network (GAN) which learns from a DGLAP-based parton shower Monte Carlo event generator. We show, for the first time, that our approach leads to a network that is able to learn not only the final distribution of particles, but also the underlying parton branching mechanism, i.e. the Altarelli-Parisi splitting function, the ordering variable of the shower, and the scaling behavior. While the current work is focused on perturbative physics of the parton shower, we foresee a broad range of applications of our framework to areas that are currently difficult to address from first principles in QCD. Examples include nonperturbative and collective effects, factorization breaking and the modification of the parton shower in heavy-ion, and electron-nucleus collisions.
↳ hep-phnucl-exnucl-thPLB(2022)·36 citations
13
Symmetry energy investigation with pion production from Sn+Sn systems
G. Jhang · J. Estee · J. Barney · G. Cerizza · M. Kaneko · J. W. Lee · W. G. Lynch · T. Isobe · M. Kurata-Nishimura · T. Murakami · C. Y .Tsang · M. B. Tsang and 68 other authors
In the past two decades, pions created in the high density regions of heavy ion collisions have been predicted to be sensitive at high densities to the symmetry energy term in the nuclear equation of state, a property that is key to our understanding of neutron stars. In a new experiment designed to study the symmetry energy, the multiplicities of negatively and positively charged pions have been measured with high accuracy for central $^{132}$ Sn+ $^{124}$ Sn, $^{112}$ Sn+ $^{124}$ Sn, and $^{108}$ Sn+ $^{112}$ Sn collisions at $E / A = 270 MeV$ with the S $π$ RIT Time Projection Chamber. While the uncertainties of individual pion multiplicities are measured to 4\%, those of the charged pion multiplicity ratios are measured to 2\%. We compare these data to predictions from seven major transport models. The calculations reproduce qualitatively the dependence of the multiplicities and their ratios on the total neutron to proton number in the colliding systems. However, the predictions of the transport models from different codes differ too much to allow extraction of reliable constraints on the symmetry energy from the data. This finding may explain previous contradictory conclusions on symmetry energy constraints obtained from pion data in Au+Au system. These new results call for better understanding of the differences among transport codes, and new observables that are more sensitive to the density dependence of the symmetry energy.
↳ nucl-exnucl-thPLB(2021)·69 citations
14
The strongly intensive observable in pp collisions at LHC energies in the string fusion model
V.V. Vechernin🇷🇺 · S.N. Belokurova🇷🇺
The properties of the strongly intensive variable characterizing correlations between the number of particles in two separated rapidity interval in pp interactions at LHC energies are studied in the framework of the string fusion model. We perform the MC simulations of string distributions in the impact parameter plane to take into account the experimental conditions of pp collisions. We account the string fusion processes, leading to the formation of string clusters, embedding a finite lattice (a grid) in the impact parameter plane. As a result, we found the dependence of this variable both on the distance between the centers of the observation windows and their width for the minbias pp collisions at several initial energies. Analyzing these dependencies we can extract the important information on the properties of string clusters. We show that in pp collisions at LHC energies the string fusion effects have a significant impact on the behavior of this strongly intensive variable. The role of these effects is increasing with the initial energy and centrality of collisions. In particular, we found that the increase of this variable with initial energy takes place due to the growth of the portion of the fused string clusters in string configurations arising in pp interactions.
↳ hep-phnucl-thJ.Phys.Conf.Ser.(2020)·11 citations
15
Octet and decuplet baryon self-energies in relativistic SU(3) chiral effective theory
P. M. Copeland🇺🇸 · Chueng-Ryong Ji🇺🇸 · W. Melnitchouk🇺🇸
The self-energies of the full set of flavor SU(3) octet and decuplet baryons are computed within a relativistic chiral effective theory framework. The leading nonanalytic chiral behavior is derived for the octet and decuplet masses, and a finite-range regularization consistent with Lorentz and gauge invariance is applied to account for the finite size of the baryons. Using a four-dimensional dipole form factor, the relative importance of various meson-baryon loop contributions to the self-energies is studied numerically as a function of the dipole range parameter and meson mass, and comparison is made between the relativistic results and earlier approximations within the heavy baryon limit.
↳ hep-phnucl-thPRD(2021)·5 citations
16
Chemical potential on the lattice: Universal or Unique?
Rajiv V. Gavai🇩🇪
Lattice techniques are the most reliable ones to investigate non-perturbative aspects of quantum chromodynamics (QCD) such as its phase diagram in the temperature-baryon density plane. They are, however, well-known to be beset with a variety of problems as one increases the density. We address here the old question of placing the baryonic (quark) chemical potential on the lattice. We point out that it may have important consequences for the current and future experimental searches of QCD critical point.
↳ hep-lathep-phnucl-th1 citation

Affiliations

first authorsco-authorsvia INSPIRE