Nuclear Theory·nucl-th

Friday·March 6, 2020

13 papers—7 primary·6 cross-listed

01
Generalized Contact Formalism Analysis of the $^{4}$ He $(e, e^{'} pN)$ Reaction
J.R. Pybus · I. Korover · R. Weiss · A. Schmidt · N. Barnea · D.W. Higinbotham · E. Piasetzky · M. Strikman · L.B. Weinstein · O. Hen
Measurements of short-range correlations in exclusive $^{4}$ He $(e, e^{'} pN)$ reactions are analyzed using the Generalized Contact Formalism (GCF). We consider both instant-form and light-cone formulations with both the AV18 and local N2LO(1.0) nucleon-nucleon ( $N N$ ) potentials. We find that kinematic distributions, such as the reconstructed pair opening angle, recoil neutron momentum distribution, and pair center of mass motion, as well as the measured missing energy, missing mass distributions, are all well reproduced by GCF calculations. The missing momentum dependence of the measured $^{4}$ He $(e, e^{'} pN)$ / $^{4}$ He $(e, e^{'} p)$ cross-section ratios, sensitive to nature of the $N N$ interaction at short-distacnes, are also well reproduced by GCF calculations using either interaction and formulation. This gives credence to the GCF scale-separated factorized description of the short-distance many-body nuclear wave-function.
nucl-thnucl-exPLB(2020)·35 citations
02
Excluded-volume model for quarkyonic Matter: Three-flavor baryon-quark Mixture
Dyana C. Duarte🇺🇸 · Saul Hernandez-Ortiz🇺🇸 · Kie Sang Jeong🇺🇸
The single-flavor excluded-volume model based on the effective size of baryons reproduces the hard-soft density evolution of the equation of state (EoS) required by the recent studies of GW170817. This phenomenological model basically realizes the concept of quarkyonic matter which is introduced from large- $N_{c}$ gauge theory for dense matter. Enhanced nucleon interactions and dynamically generated quark degrees of freedom can reproduce the hard-soft evolution of the EoS. In this paper, we extend the excluded-volume model to a three-flavor system by considering electromagnetic charge and possible weak equilibrium in order to obtain a proper description for the hard-soft behavior of the EoS inferred from the gravitational waves observations.
nucl-thhep-phPRC(2020)·56 citations
03
Neutron-neutron scattering length from $π^{+}$ photoproduction on the deuteron
Satoshi X. Nakamura (Univ. Science and Technology of China)🇨🇳 · Takatsugu Ishikawa (ELPH, Tohoku Univ.)🇯🇵 · Toru Sato (RCNP, Osaka Univ.)🇯🇵
We discuss the possibility of extracting the neutron-neutron scattering length $a_{nn}$ and effective range $r_{nn}$ from cross section data ( $d^{2} σ / d M_{nn} / d Ω_{π}$ ), as a function of the $nn$ invariant mass $M_{nn}$ , for $π^{+}$ photoproduction on the deuteron ( $γ d \to π^{+} nn$ ). The analysis is based on a $γ d \to π^{+} nn$ reaction model in which realistic elementary amplitudes for $γ p \to π^{+} n$ , $N N \to N N$ , and $π N \to π N$ are built in. We show that $M_{nn}$ dependence (lineshape) of a ratio $R_{th}$ , $d^{2} σ / d M_{nn} / d Ω_{π}$ normalized by $d σ / d Ω_{π}$ for $γ p \to π^{+} n$ and the nucleon momentum distribution inside the deuteron, at the kinematics with $θ_{π} = 0^{\circ}$ and $E_{γ} \sim 250$ MeV is particularly useful for extracting $a_{nn}$ and $r_{nn}$ from the corresponding data $R_{exp}$ . It is found that $R_{exp}$ with 2% error, resolved into the $M_{nn}$ bin width of 0.04 MeV (corresponding to the $p_{π}$ bin width of 0.05 MeV $/ c$ ), can determine $a_{nn}$ and $r_{nn}$ with uncertainties of $\pm 0.21$ fm and $\pm 0.06$ fm, respectively, for the case of $a_{nn} = - 18.9$ fm and $r_{nn} = 2.75$ fm. The requirement of such narrow bin widths indicates that the momenta of the incident photon and the emitted $π^{+}$ have to be measured with high resolutions. This can be achieved by utilizing virtual photons of very small $Q^{2}$ from electron scattering at Mainz MAMI facility. The proposed method for determining $a_{nn}$ and $r_{nn}$ from $γ d \to π^{+} nn$ has a great experimental advantage over the previous one utilizing $π^{-} d \to γ nn$ for being free from the formidable task of controlling the neutron detection efficiency and its uncertainty.
nucl-thhep-phnucl-ex5 citations
04
Collision dynamics at medium and relativistic energies
Maria Colonna🇮🇹
Recent results connected to nuclear collision dynamics, from low up to relativistic energies, are reviewed. Heavy ion reactions offer the unique opportunity to probe the complex nuclear many-body dynamics and to explore, in laboratory experiments, transient states of nuclear matter under several conditions of density, temperature and charge asymmetry. From the theoretical point of view, transport models are an essential tool to undertake these investigations and make a connection between the nuclear effective interaction and sensitive observables of experimental interest. In this article, we mainly focus on the description of results of transport models for a selection of reaction mechanisms, also considering comparisons of predictions of different approaches. This analysis can help understanding the impact of the interplay between mean-field and correlation effects, as well as of in-medium effects, on reaction observables, which is an essential point also for extracting information on the nuclear Equation of State. A special emphasis will be given to the review of recent studies aimed at constraining the density behavior of the nuclear symmetry energy. For reactions at medium (Fermi) energies, we will describe light particle and fragment emission mechanisms, together with isospin transport effects. Collective effects characterizing nuclear collision dynamics, such as transverse and elliptic flows, will be discussed for relativistic heavy ion reactions, together with meson production and isotopic ratios.
nucl-thnucl-exPPNP·53 citations
05
On microscopic theory of pygmy- and giant resonances
S. Kamerdzhiev · M. Shitov
The Green function formalism with a consistent account for phonon coupling (PC), based on the self-consistent theory of finite Fermi-systems, is applied for pygmy- and giant multipole resonances in magic nuclei with the aim to consider particle-hole (ph) and complex 1p1h phonon configurations. A new equation for the effective field, which describes nuclear polarizability, is obtained. It contains new PC contributions which are of interest in the energy region under consideration. They are due to: i)the tadpole effect in the standard ph-propagator, ii)two new induced interactions (caused by the exchange of ph-phonon) in the second ph-channel and in the particle-particle channels, and iii) the first and second variations of the effective interaction in the phonon field. The general expressions for energies and probabilities of transitions between the ground and excited states are obtained. The qualitative analysis and discussion of the new terms are performed.
nucl-thnucl-exEPJA(2020)·5 citations
06
Comment on "Enhanced deuterium-tritium fusion cross sections in the presence of strong electromagnetic fields"
Friedemann Queisser · Ralf Schützhold
In their article [Phys.\ Rev.\ C {\bf 100}, 064610 (2019)], Lv, Duan, and Liu study the enhancement of deuterium-tritium fusion reactions by the electromagnetic field of an x-ray free-electron laser (XFEL). While we support the general idea (which was put forward earlier in our rapid communication [Phys.\ Rev.\ C {\bf 100}, 041601(R) (2019)]), we find that the time-averaged potential approximation used by Lv, Duan, and Liu is not justified in this regime and does not take into account important effects. Due to those effects, the enhancement mechanism may actually be more efficient than predicted by Lv, Duan, and Liu.
nucl-th3 citations
07
Understanding fission fragment mass distributions in a modified shape of random neck rupture model
Yogesh Sawant · S. V. Suryanarayana · B. K. Nayak · A. Saxena · R. K. Choudhury
The variances of the fission fragment mass distributions for symmetric fission over a wide range of the fissility of the compound nucleus have been investigated within the frame work of Random Neck Rupture Model (RNRM) proposed by Brosa et. al.,. The shape of the fissioning nucleus is generated using crel=1 in the RNRM model, which results in a smooth and continuous shape of fissioning nucleus. This modified shape of RNRM model has been used to analyse experimental data of mass variances for symmetric mass distributions of 27 systems leading to understanding of scission shape dynamics in a wide region of fissility 0.7-0.95. The neck radius is an important parameter of the RNRM model and this has been varied to fit the experimental mass variances data. The systematics of resulting neck radii are studied of as a function fissility and nuclear potential through {\gamma}o, the surface energy coefficient. Further average total kinetic energies of fission fragments <TKE> are studied of as a function of fissility and {\gamma}o parameter. It is observed that the neck radii that fit the experimentally observed variances of the mass distributions fall into two groups and these groups are related to two groups of experimentally observed <TKE>s. Empirical formulae have been obtained for the neck radii for these two groups of fissioning systems. Use of the empirical formulae for neck radii predict the mass variances reasonably well for these systems and it is shown that these empirical neck radii are better estimates than starting with the Rayleigh criterion.16pages,7 figures
nucl-thnucl-exPramana(2022)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Generalized Contact Formalism Analysis of the 4He(e,e′pN) Reaction

Excluded-volume model for quarkyonic Matter: Three-flavor baryon-quark Mixture

Neutron-neutron scattering length from π+ photoproduction on the deuteron

Collision dynamics at medium and relativistic energies

On microscopic theory of pygmy- and giant resonances

Comment on "Enhanced deuterium-tritium fusion cross sections in the presence of strong electromagnetic fields"

Understanding fission fragment mass distributions in a modified shape of random neck rupture model

Affiliations

Generalized Contact Formalism Analysis of the $^{4}$ He $(e, e^{'} pN)$ Reaction

Neutron-neutron scattering length from $π^{+}$ photoproduction on the deuteron