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Nuclear Theory·nucl-th

Thursday·August 27, 2020

9 papers—6 primary·3 cross-listed

All9Primary6Cross-lists3
  1. 01

    Curvature-slope correlation of nuclear symmetry energy and its imprints on the crust-core transition, radius and tidal deformability of canonical neutron stars

    Bao-An Li · Macon Magno

    Background: The nuclear symmetry energy encodes information about the energy necessary to make nuclear systems more neutron-rich. While its slope parameter L at the saturation density of nuclear matter has been relatively well constrained by recent astrophysical observations and terrestrial nuclear experiments, its curvature characterizing the around remains largely unconstrained. Over 520 calculations for using various nuclear theories and interactions in the literature have predicted several significantly different correlations. Purpose: If a unique correlation of can be firmly established, it will enable us to progressively better constrain the high-density behavior of using the available constraints on its slope parameter L. We investigate if and by how much the different correlations may affect neutron star observables. Method: A meta-model of nuclear Equation of States (EOSs) with three representative correlation functions is used to generate multiple EOSs for neutron stars. We then examine effects of the correlation on the crust-core transition density and pressure as well as the radius and tidal deformation of canonical neutron stars. Results:The correlation affects significantly both the crust-core transition density and pressure. It also has strong imprints on the radius and tidal deformability of canonical neutron stars especially at small L values. The available data from LIGO/VIRGO and NICER set some useful limits for the slope L but can not distinguish the three representative correlations considered.

    nucl-thastro-ph.HEastro-ph.SRnucl-exPRC(2020)·60 citations
  2. 02

    Statistical treatment of nuclear clusters in the continuum

    S. Mallik🇫🇷 · F. Gulminelli🇫🇷

    The evaluation of the sub-saturation nuclear equation of state at finite temperature requires a proper state counting of the internal partition sum of nuclei which are immersed in the background of their continuum states. This classical statistical problem is addressed within the self-consistent mean-field approximation, which naturally accounts for isospin and effective mass effects in the nuclear density of states. The nuclear free energy is decomposed into bulk and surface terms, allowing a simple analytical prescription for the subtraction of gas states from the nuclear partition sum, that avoids double counting of unbound single particle states. We show that this correction leads to a sizeable effect in the composition of matter at high temperature and low proton fractions, such as it is formed in supernova collapse, early proto-neutron star evolution, as well as laboratory experiments. Specifically, the energy stored in the internal nuclear degrees of freedom is reduced, as well as the mass fraction of heavy clusters in the statistical equilibrium. The gas subtraction prescription is compared to different phenomenological methods proposed in the literature, based on a high energy truncation of the partition sum. We show that none of these methods satisfactorily reproduces the gas subtracted level density, if the temperature overcomes ~4 MeV.

    nucl-thPRC(2021)·11 citations
  3. 03

    Incoherent deeply virtual Compton scattering off He

    Sara Fucini🇮🇹 · Sergio Scopetta🇮🇹 · Michele Viviani🇮🇹

    Very recently, for the first time, the two channels of nuclear deeply virtual Compton scattering (DVCS), the coherent and incoherent ones, have been separated by the CLAS collaboration at JLab, using a He target. The incoherent channel, which can provide a tomographic view of the bound proton and shed light on its elusive parton structure, is thoroughly analyzed here in Impulse Approximation (IA). A convolution formula for the cross sections in terms of those for the bound proton is derived. Novel scattering amplitudes for a bound moving nucleon have been obtained and used. A state-of-the-art nuclear spectral function, based on the AV18 potential, exact in the two-body part, with the recoiling system in its ground state, and modelled in the remaining contribution, with the recoiling system in an excited state, has been used. Different parametrizations of the generalized parton distributions of the struck proton have been tested. A good overall agreement with the data for the beam spin asymmetry (BSA) is obtained. It is found that the predicted conventional nuclear effects are relevant in DVCS and in the competing Bethe-Heitler mechanism, but they cancel each other to a large extent in their ratio, to which the measured asymmetry is proportional. Besides, the calculated ratio of the BSA of the bound proton to that of the free one does not describe that estimated by the experimental collaboration. This points to possible interesting effects beyond the IA analysis presented here. It is therefore clearly demonstrated that the comparison of the results of a conventional realistic approach, as the one presented here, with future precise data, has the potential to expose quark and gluon effects in nuclei. Interesting perspectives for the next measurements at high luminosity facilities, such as JLab at 12 GeV and the future EIC, are addressed.

    nucl-thhep-phPRC(2020)·9 citations
  4. 04

    Status and Scope of MONC Transport Code

    H. Kumawat · P.P.K. Venkata

    nte-carlo ucleon transport ode (MONC) for nucleon transport is being developed for several years. Constructive Solid Geometry concept is applied with the help of solid bodies. Union, subtraction and intersection Boolean operations are used to construct heterogeneous zones. Scaling, rotation, and translation operation of the basic bodies are allowed to construct more complex zones. Module of repetitive structure for lattice, core calculations in reactor and detector simulation is developed. Graphical User Interface along with visualization tools is developed to make input, construction and display of geometry, and analysis of output data. Low energy neutron transport module is developed using continuous linearly interpolable point neutron cross section data below 20MeV neutron energy. The code is benchmarked for simulation of accelerator driven sub-critical system, neutron shielding, heat and neutron flux distribution and keff of the critical assemblies. It is observed that results of keff are in agreement within 3mk with experimental results of critical assemblies as well as the values obtained from MCNP.

    nucl-th0 citations
  5. 05

    Application of artificial intelligence in the determination of impact parameter in heavy-ion collisions at intermediate energies

    Fupeng Li🇨🇳 · Yongjia Wang🇨🇳 · Hongliang Lü · Pengcheng Li🇨🇳 · Qingfeng Li🇨🇳 · Fanxin Liu🇨🇳

    The impact parameter is one of the crucial physical quantities of heavy-ion collisions (HICs), and can affect obviously many observables at the final state, such as the multifragmentation and the collective flow. Usually, it cannot be measured directly in experiments but might be inferred from observables at the final state. Artificial intelligence has had great success in learning complex representations of data, which enables novel modeling and data processing approaches in physical sciences. In this article, we employ two of commonly used algorithms in the field of artificial intelligence, the Convolutional Neural Networks (CNN) and Light Gradient Boosting Machine (LightGBM), to improve the accuracy of determining impact parameter by analyzing the proton spectra in transverse momentum and rapidity on the event-by-event basis. Au+Au collisions with the impact parameter of 010 fm at intermediate energies (=- GeVnucleon) are simulated with the ultrarelativistic quantum molecular dynamics (UrQMD) model to generate the proton spectra data. It is found that the average difference between the true impact parameter and the estimated one can be smaller than 0.1 fm. The LightGBM algorithm shows an improved performance with respect to the CNN on the task in this work. By using the LightGBM's visualization algorithm, one can obtain the important feature map of the distribution of transverse momentum and rapidity, which may be helpful in inferring the impact parameter or centrality in heavy-ion experiments.

    nucl-thnucl-exJ.Phys.G(2020)·44 citations
  6. 06

    Jacobi no-core shell model for -shell hypernuclei

    Hoai Le🇩🇪 · Johann Haidenbauer🇩🇪 · Ulf-G. Meißner🇩🇪 · Andreas Nogga🇩🇪

    We extend the recently developed Jacobi no-core shell model to hypernuclei. Based on the coefficients of fractional parentage for ordinary nuclei, we define a basis where the hyperon is the spectator particle. We then formulate transition coefficients to states that single out a hyperon-nucleon pair which allow us to implement a hypernuclear many-baryon Hamiltonian for -shell hypernuclei. As a first application, we use the basis states and the transition coefficients to calculate the ground states of He, H, He, He, Li, and Li and, additionally, the first excited states of He, H, and Li. In order to obtain converged results, we employ the similarity renormalization group (SRG) to soften the nucleon-nucleon and hyperon-nucleon interactions. Although the dependence on this evolution of the Hamiltonian is significant, we show that a strong correlation of the results can be used to identify preferred SRG parameters. This allows for meaningful predictions of hypernuclear binding and excitation energies. The transition coefficients will be made publicly available as HDF5 data files.

    nucl-thEPJA(2020)·44 citations

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first authorsco-authorsvia INSPIRE