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Nuclear Theory·nucl-th

Monday·March 4, 2024

12 papers—4 primary·8 cross-listed

All12Primary4Cross-lists8
  1. 01

    Five-dimensional collective Hamiltonian with improved inertial functions

    Kouhei Washiyama · Nobuo Hinohara · Takashi Nakatsukasa

    Background: To describe shape fluctuations associated with large-amplitude collective motion in the quadrupole degrees of freedom, the five-dimensional collective Hamiltonian (5DCH) has been widely used. The inertial functions in the 5DCH are microscopically calculated with the energy density functional (EDF) theory employing the cranking formula. However, since the cranking formula ignores dynamical residual effects, it is known to fail to reproduce the correct inertial functions, for instance, the total mass for the translational motion. Purpose: We aim to resolve problems of the insufficient description of the inertial functions in the 5DCH. We provide a practical method to include the dynamical residual effects in the inertial functions that depend on the quadrupole deformation parameters and . Methods: We use the local quasiparticle random-phase approximation (LQRPA) based on the constrained Hartree-Fock-Bogoliubov states in the -- plane with the Skyrme EDF. The finite-amplitude method is used for efficient computations of the LQRPA. Results: The inertial functions evaluated with the LQRPA significantly increase from the ones with the cranking formula due to the dynamical residual effects. This increase also shows a strong -- dependence. We show an application of the present method to a transitional nucleus Pd. The low-lying positive-parity spectra are well reproduced with the LQRPA inertial functions. Conclusions: We clarify the importance of the dynamical residual effects in the inertial functions of the 5DCH for the description of the low-lying spectra. The 5DCH with the improved inertial functions provides a reliable and efficient description of low-lying spectra in nuclei associated with the quadrupole shape fluctuation.

    nucl-thnucl-exPRC(2024)·6 citations
  2. 02

    Novel Pauli blocking method in quantum molecular dynamics type models

    Xiang Chen · Junping Yang · Ying Cui · Kai Zhao · Zhuxia Li · Yingxun Zhang

    In this work, we propose a novel method for calculating the occupation probability in the Pauli blocking of the quantum molecular dynamics type models. This method refines the description of the Pauli blocking ratio in the nuclear matter and that in the finite nucleus. The influence of the new Pauli blocking method on the heavy ion collisions observables, such as the charge distribution, the free neutron to proton yield ratios, and the extracted physical quantities, such as the in-medium nucleon-nucleon cross sections, are investigated. For the extracted in-medium nucleon-nucleon cross sections, our results show that it will be enhanced 1.12.5 times than that with the conventional Pauli blocking method at the beam energy less than 150 MeV/u, which highlights the importance of a refined Pauli blocking method for developing an advanced transport model to describe complex heavy ion collisions.

    nucl-thPRC(2024)·1 citation
  3. 03

    Production of Resonances in Partial Chemical Equilibrium

    Boris Tomasik🇸🇰 · Sandor Lokos🇸🇰

    Within the model of partial chemical equilibrium (PCE) we calculate the multiplicity ratios of selected unstable resonances to given stable species. We focus on those ratios that have been measured either in Pb+Pb collisions at the LHC or in Au+Au collisions at the top RHIC energy. The model provides an interpretation how in an expanding hadronic fireball with decreasing temperature the final numbers of stable hadrons after decays of all resonances remain unchanged. Each stable species acquires its own chemical potential and the resonances are kept in equilibrium with them. Multiplicities of unstable resonances provide a test of this scenario. We observe that the ratios of and fit reasonably well into the picture of single kinetic freeze-out of the single-particle spectra, but the -meson and hyperon resonances are not reproduced by this model.

    nucl-thNuovo Cim.C(2025)·0 citations
  4. 04

    The role of the likelihood for elastic scattering uncertainty quantification

    C. D. Pruitt · A. E. Lovell · C. Hebborn · F. M. Nunes

    Background: Analyses of elastic scattering with the optical model (OMP) are widely used in nuclear reactions. Purpose: Previous work compared a traditional frequentist approach and a Bayesian approach to quantify uncertainties in the OMP. In this study, we revisit this comparison and consider the role of the likelihood used in the analysis. Method: We compare the Levenberg-Marquardt algorithm for minimization with Markov Chain Monte Carlo sampling to obtain parameter posteriors. Following previous work, we consider how results are affected when /N is used for the likelihood function, N being the number of data points, to account for possible correlations in the model and underestimation of the error in the data. Results: We analyze a simple linear model and then move to OMP analysis of elastic angular distributions using a) a 5-parameter model and b) a 6-parameter model. In the linear model, the frequentist and Bayesian approaches yield consistent optima and uncertainty estimates. The same is qualitatively true for the 5-parameter OMP analysis. For the 6-parameter OMP analysis, the parameter posterior is no longer well-approximated by a Gaussian and a covariance-based frequentist prediction becomes unreliable. In all cases, when the Bayesian approach uses /N in the likelihood, uncertainties increase by . Conclusions: When the parameter posterior is near-Gaussian and the same likelihood is used, the frequentist and Bayesian approaches recover consistent parameter uncertainty estimates. If the parameter posterior has significant higher moments, the covariance-only frequentist approach becomes unreliable and the Bayesian approach should be used. Empirical coverage can serve as an important internal check for uncertainty estimation, providing red flags for uncertainty analyses.

    nucl-thPRC(2024)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE