Nuclear Theory·nucl-th

Tuesday·February 1, 2022

21 papers—12 primary·9 cross-listed

01
Statistical Nuclear Spectroscopy with $q$ -normal and bivariate $q$ -normal distributions and $q$ -Hermite polynomials
V.K.B. Kota · Manan Vyas
Statistical nuclear spectroscopy (also called spectral distribution method), introduced by J.B. French in late 60's and developed in detail in the later years by his group and many other groups, is based on the Gaussian forms for the state (eigenvalue) and transition strength densities in shell model spaces with their extension to partial densities defined over shell model subspaces. The Gaussian forms have their basis in embedded random matrix ensembles with nuclear Hamiltonians consisting of a mean-field one-body part and a residual two-body part. However, following the recent random matrix results for the so called Sachdev-Ye-Kitaev model due to Verbaaarschot et al, embedded random matrix ensembles with $k$ -body interactions are re-examined and it is shown that the density of states, transition strength densities and strength functions (partial densities) in fact follow more closely the $q$ -normal distribution (the parameter $q$ is related to the fourth moment of these distributions with $q = 1$ giving Gaussian and $q = 0$ giving semi-circle form). The $q$ -normal has the important property that it is bounded for $0 \leq q < 1$ . The $q$ -normal (also its bivariate and general multi-variate extensions) and the associated $q$ -Hermite polynomials are studied for their properties by Bryc, Szabowski and others [P.J. Szabowski, Electronic Journal of Probability {\bf 15}, 1296 (2010)]. Following these, in the present article developed is statistical nuclear spectroscopy based on $q$ -normal (univariate and bivariate) distributions and the associated $q$ -Hermite polynomials. In particular, formulation is presented for nuclear level densities, shell model orbit occupancies, transition strengths (for electromagnetic and $β$ and double $β$ -decay type operators) and strength sums.
nucl-thnlin.CDAnnals Phys.(2022)·7 citations
02
Relativistic description of dense matter equation of state and compatibility with neutron star observables: a Bayesian approach
Tuhin Malik · Márcio Ferreira · B. K. Agrawal · Constança Providência
The general behavior of the nuclear equation of state (EOS), relevant for the description of neutron stars (NS), is studied within a Bayesian approach applied to a set of models based on a density dependent relativistic mean field description of nuclear matter. The EOS is subjected to a minimal number of constraints based on nuclear saturation properties and the low density pure neutron matter EOS obtained from a precise next-to-next-to-next-to-leading order (N $^{3}$ LO) calculation in chiral effective field theory ( $χ$ EFT). The posterior distributions of the model parameters obtained under these minimal constraints are employed to construct the distributions of various nuclear matter properties and NS properties such as radii, tidal deformabilites, central energy densities and speeds of sound etc. We found that 90% confidence interval (CI) for allowed NS mass - radius relationship and tidal deformabilites are compatible with GW170817 and recent NICER observations, without invoking the exotic degrees of freedom. A central speed-of-sound of the order of $2/3$ $c$ is obtained. The maximum neutron star mass allowed by the model is 2.5 $M_{⊙}$ .
nucl-thastro-ph.HEApJ(2022)·105 citations
03
Bayesian reconstruction of impact parameter distributions from two observables for intermediate energy heavy ion collisions
Xiang Chen🇨🇳 · Li Li🇨🇳 · Ying Cui🇨🇳 · Junping Yang🇨🇳 · Zhuxia Li🇨🇳 · Yingxun Zhang🇨🇳
To reconstruct the impact parameter distributions from the selected events sample or centrality, which is defined by two-observables, at intermediate energy heavy ion collisions, we extend the approach proposed by Das \textit{et al.} [Phys. Rev. C 97, 014905 (2018)], Rogly \textit{et al.} [Phys. Rev. C 98, 024902 (2018)], and Frankland \textit{et al.} [Phys. Rev. C 104, 034609 (2021)]. Based on deep investigations of the fluctuation mechanism, we found that the intrinsic fluctuations are mainly generated in the microscopic stochasticity of initialization and nucleon-nucleon collisions in the nonequilibrium process of heavy ion collisions, and this leads the observables to fluctuate with respect to impact parameter in a Gaussian form. In this work, the multiplicity of the charged particles and the total transverse momentum of the light charged particles are used simultaneously to model-independently reconstruct the impact parameter distributions for selected events or centrality based on the Bayesian method. For sorting the centrality with two observables, we propose to use the $K$ -means clustering method (an unsupervised machine learning algorithm), which can automatically sort events when the class number is given. Furthermore, the reconstructed impact parameter distributions from data of the two observables can be used to learn the correlation between multiplicity and transverse momentum at different centralities, which may be useful for understanding the fragmentation mechanism.
nucl-thnucl-exPRC(2023)·12 citations
04
The Interplay of Femtoscopic and Charge-Balance Correlations
Scott Pratt🇺🇸 · Karina Martirosova🇺🇸
Correlations driven by the constraints of local charge conservation have been shown to provide insight into the chemical evolution and diffusivity of the high-temperature matter created in ultra-relativistic heavy ion collisions. Two-particle correlations driven by final-state interactions have allowed the extraction of critical femtoscopic space-time information about the expansion and dissolution of the same collisions. Whereas correlations from final-state interactions mainly appear at small relative momenta, a few tens of MeV/ $c$ , charge-balance correlations extend over a range of hundreds of MeV/ $c$ . In nearly all previous analyses, this separation of scales is used to focus solely on one class or the other. The purpose of this study is to quantitatively understand the degree to which correlations from final-state interactions distort the interpretation of charge-balance correlations and vice versa.
nucl-thPRC(2022)·4 citations
05
Coulomb-nuclear dynamics in the weakly-bound 8Li breakup
Bahati Mukeru · Jesus Lubian · Lauro Tomio
A detailed study of total, Coulomb and nuclear breakup cross sections dependence on the projectile ground-state binding energy $ε_{b}$ is presented, by considering the $^{8}$ Li+ $^{12}$ C and $^{8}$ Li+ $^{208}$ Pb breakup reactions. To this end, apart from the experimental one-neutron separation energy of $^{8}$ Li nucleus ( $ε_{b} = 2.03$ ~MeV), lower values of $ε_{b}$ down to $ε_{b} = 0.01$ ~MeV, are also being considered. It is shown that all breakup processes become peripheral as $ε_{b} \to 0.01$ MeV, which is understood as due to the well-known large spacial extension of ground-state wave functions associated to weakly-bound projectiles. The Coulomb breakup cross section is found to be more strongly dependent on $ε_{b}$ than the nuclear breakup cross section, such that the Coulomb breakup becomes more significant as $ε_{b}$ decreases, even in a naturally nuclear-dominated reaction. This is mainly due to the long-range nature of the Coulomb forces, leading to a direct dependence of the Coulomb breakup on the electromagnetic transition matrix. It is also highlighted the fact that the nuclear absorption plays a minor role for small binding when the breakup becomes more peripheral.
nucl-thPRC(2022)·4 citations
06
Global calculation of two-neutrino double- $β$ decay within the finite amplitude method in nuclear density functional theory
Nobuo Hinohara🇯🇵 · Jonathan Engel🇺🇸
Two-neutrino double-beta ( $2 ν β β$ ) decay has been used to constrain the neutron-proton part of effective interactions, which in turn is used to compute the nuclear matrix elements for neutrinoless double-beta decay, the observation of which would have important consequences for fundamental physics. We carefully examine $2 ν β β$ matrix elements within the proton-neutron quasiparticle random-phase approximation with nuclear energy density functionals. We work with functionals that are fit globally to single-beta-decay half-lives and charge-exchange giant-resonance energies, but not to $2 ν β β$ half-lives themselves, to evaluate the $2 ν β β$ nuclear matrix elements for all important nuclei, including those whose half-lives have not yet been measured. Such a comprehensive evaluation in large model spaces without configuration truncation requires an efficient computational scheme; we employ a double contour integration within the finite amplitude method. The results generally reproduce the nuclear matrix element extracted from half-lives well, without the use of any of those half-lives in the fitting procedure. We present predictions of the matrix elements in a total of 27 nuclei with half-lives that are still unmeasured.
nucl-thPRC(2022)·23 citations
07
Predictions of {\alpha}-decay half-lives for neutron-deficient nuclei with the aid of artificial neural network
A. A. Saeed · W. A. Yahya · O. K. Azeez
In recent years, artificial neural network (ANN) has been successfully applied in nuclear physics and some other areas of physics. This study begins with the calculations of {\alpha}-decay half-lives for some neutron-deficient nuclei using Coulomb and proximity potential model (CPPM), temperature dependent Coulomb and proximity potential model (CPPMT), Royer empirical formula, new Ren B (NRB) formula, and a trained artificial neural network model (TANN ). By comparison with experimental values, the ANN model is found to give very good descriptions of the half-lives of the neutron-deficient nuclei. Moreover CPPMT is found to perform better than CPPM, indicating the importance of employing temperature-dependent nuclear potential. Furthermore, to predict the {\alpha}-decay half-lives of unmeasured neutron-deficient nuclei, another ANN algorithm is trained to predict the Q {\alpha} values. The results of the Q {\alpha} predictions are compared with the Weizsäcker-Skyrme-4+RBF (WS4+RBF) formula. The half-lives of unmeasured neutron-deficient nuclei are then predicted using CPPM, CPPMT, Royer, NRB, and TANN , with Q{\alpha} values predicted by ANN as inputs. This study concludes that half-lives of {\alpha}-decay from neutron-deficient nuclei can successfully be predicted using ANN, and this can contribute to the determination of nuclei at the driplines.
nucl-thActa Phys.Polon.B(2022)·0 citations
08
Probing neutron-star matter in the lab: similarities and differences between binary mergers and heavy-ion collisions
Elias R. Most🇺🇸 · Anton Motornenko🇩🇪 · Jan Steinheimer🇩🇪 · Veronica Dexheimer🇺🇸 · Matthias Hanauske🇩🇪 · Luciano Rezzolla🇩🇪 · Horst Stoecker🇩🇪
Binary neutron-star mergers and heavy-ion collisions are related through the properties of the hot and dense nuclear matter formed during these extreme events. In particular, low-energy heavy-ion collisions offer exciting prospects to recreate such {extreme} conditions in the laboratory. However, it remains unexplored to what degree those collisions can actually reproduce hot and dense matter formed in binary neutron star mergers. As a way to understand similarities and differences between these systems, we {discuss their geometry and }perform a direct numerical comparison of the thermodynamic conditions probed in both collisions. To enable a direct comparison, we employ a finite-temperature equation of state able to describe the entire high-energy phase diagram of Quantum Chromodynamics. Putting side by side the evolution of both systems, we find that laboratory heavy-ion collisions at the energy range of $E_{lab} = 0.4 - 0.6 A$ MeV probe (thermodynamic) states of matter that are very similar to those created in binary neutron-star mergers. These results can inform future low-energy heavy-ion collisions probing this regime.
nucl-thastro-ph.HEgr-qcPRD(2023)·76 citations
09
The Sturdiness of the Shell Model: Informal Review
Castaly Fan · Larry Zamick
With shell model codes being able to encompassing larger and larger spaces we find that the percentage occupancy of the leading spaces becomes smaller and smaller. How can the shell model survive in such circumstances? We will not solve this puzzle here but rather will show examples where, with some explanations, the shell model holds fast. We will use nuclear moments as an example.
nucl-thnucl-ex0 citations
10
Early time behavior of spatial and momentum anisotropies in kinetic theory across different Knudsen numbers
Nicolas Borghini🇩🇪 · Marc Borrell🇩🇪 · Hendrik Roch🇩🇪
We investigate the early time development of the anisotropic transverse flow and spatial eccentricities of a fireball with various particle-based transport approaches using a fixed initial condition. In numerical simulations ranging from the quasi-collisionless case to the hydrodynamic regime, we find that the onset of $v_{n}$ and of related measures of anisotropic flow can be described with a simple power-law ansatz, with an exponent that depends on the amount of rescatterings in the system. In the few-rescatterings regime we perform semi-analytical calculations, based on a systematic expansion in powers of time and the cross section, which can reproduce the numerical findings.
nucl-thhep-phphysics.flu-dynEPJC(2022)·9 citations
11
Deuteron Production in Ultra-Relativistic Heavy-Ion Collisions: A Comparison of the Coalescence and the Minimum Spanning Tree Procedure
Viktar Kireyeu🇷🇺 · Jan Steinheimer🇩🇪 · Jörg Aichelin🇩🇪 · Marcus Bleicher🇩🇪 · Elena Bratkovskaya🇩🇪
The formation of deuterons in heavy-ion collisions at relativistic energies is investigated by employing two recently advanced models -- the Minimum Spanning Tree (MST) method and the coalescence model by embedding them in the PHQMD and the UrQMD transport approaches. While the coalescence mechanism combines nucleons into deuterons at the kinetic freeze-out hypersurface, the MST identifies the clusters during the different stages of time evolution. We find that both clustering procedures give very similar results for the deuteron observables in the UrQMD as well as in the PHQMD environment. Moreover, the results agree well with the experimental data on deuteron production in Pb+Pb collisions at $s_{N N} = 8.8$ GeV (selected for the comparison of the methods and models in this study). A detailed investigation shows that the coordinate space distribution of the produced deuterons differs from that of the free nucleons and other hadrons. Thus, deuterons are not destroyed by additional rescattering.
nucl-thhep-phPRC(2022)·34 citations
12
Modern approaches to optical potentials
J. W. Holt · T. R. Whitehead
This chapter presents an overview of the optical model description of nucleon-nucleus scattering and reactions based on fundamental nuclear two-body and many-body forces. The chapter begins with a historical review followed by a discussion of several commonly used theoretical techniques for deriving nucleon-nucleus optical model potentials that account for antisymmetry, Pauli blocking, and multiple scattering. This is followed by a summary of current efforts to derive microscopic nuclear forces consistent with the fundamental theory of strong interactions, quantum chromodynamics, and the use of such interactions in the construction of microscopic optical potentials. The chapter will also outline the dispersive optical potential approach, which despite being primarily phenomenological, has its origins in formal Green's function theory. Finally, the results from modern optical potentials will be benchmarked to experimental data.
nucl-th6 citations

Affiliations

first authorsco-authorsvia INSPIRE