Nuclear Theory·nucl-th

Wednesday·May 31, 2017

9 papers—5 primary·4 cross-listed

01
Three-nucleon forces and superfluidity in neutron matter
P. Papakonstantinou · J. W. Clark
The existence of superfluidity of the neutron component in the core of a neutron star, associated specifically with triplet $P -$ wave pairing, is currently an open question that is central to interpretation of the observed cooling curves and other neutron-star observables. Ab initio theoretical calculations aimed at resolving this issue face unique challenges in the relevant high-density domain, which reaches beyond the saturation density of symmetrical nuclear matter. These issues include uncertainties in the three-nucleon (3N) interaction and in the effects of strong short-range correlations -- and more generally of in-medium modification of nucleonic self-energies and interactions. A survey of existing solutions to the gap equations in the triplet channel shows that the separate or combined impacts of 3N forces, coupled channels, and mass renormalization range from moderate to strong to devastating, thus motivating a detailed analysis of the competing effects. In the present work we track the effects of the 3N force and in-medium modifications in the representative case of the $^{3} P_{2}$ channel, based on the Argonne V18 two-nucleon (2N) interaction supplemented by 3N interactions of the Urbana IX family. Sensitivity of the results to the input interaction is clearly demonstrated, while consistency issues arise with respect to the simultaneous treatment of 3N forces and in-medium effects. We consider this pilot study as the first step towards a systematic and comprehensive exploration of coupled-channel $^{3} P F_{2}$ pairing using a broad range of 2N and 3N interactions from the current generation of refined semi-phenomenological models and models derived from chiral effective field theory.
nucl-thastro-ph.HEcond-mat.supr-conJ.Low Temp.Phys.(2017)·17 citations
02
The neutron radiation capture process $n + p \to D + γ$ and $^{1} S_{0}$ $n p$ wave function
N.A. Khokhlov
Cross section of the neutron capture reaction $n + p \to d + γ$ at threshold was calculated with different realistic $^{3} S_{1}$ deuteron and $^{1} S_{0}$ $n p$ scattering wave functions stemming from Nijmegen-II, JISP16, Paris, Idaho and Moscow (with forbidden states) potentials. It is found that this reaction with thermal neutrons may be described without a contribution of meson exchange currents.
nucl-th0 citations
03
The potential for $α$ induced nuclear scattering, reaction and decay, and a resonance-pole-decay model with exact explicit analytical solutions
Basudeb Sahu · Swagatika Bhoi
The decay of $α$ particle from a nucleus is viewed as a quantum resonance state of a two-body scattering process of the $α$ +daughter nucleus pair governed by a novel nucleus-nucleus potential in squared Woods-Saxon form. By the application of the rigorous optical model (OM) potential scattering (S-matrix) theory the genuineness of the potential for the system is established by giving good explanation of the elastic scattering and reaction cross sections data of the $α$ +nucleus pair. From the pole position in the complex momentum (k) plane of the S-matrix defined above, the energy and width of the resonance state akin to the decaying state of emission of $α$ particle are extracted and from this width, the result of $α$ -decay half-life is derived to account for the experimental result of half-life in the cases of large number of $α$ -emitters including heavy and super-heavy nuclei. The S-matrix of the full OM calculation above is replaced by an analytical function expressed in terms of exact Schrödinger solutions of a global potential that closely represents the Coulomb-nuclear interaction in the interior and the pure Coulomb wave functions outside, and the resonant poles of this S-matrix in the complex momentum plane are used to give satisfactory results of decay half-lives of $α$ coming out from varieties of nuclei.
nucl-thPRC(2017)·4 citations
04
Generalized Seniority on Deformed Single-Particle Basis
L. Y. Jia
Recently we proposed [62] a fast computing scheme for generalized seniority on spherical single-particle basis. This work redesigns the scheme to make it applicable to deformed single-particle basis. The algorithm is applied to the rare-earth nucleus $_{64}^{158}$ Gd $_{94}$ for intrinsic (body-fixed frame) neutron excitations under the low-momentum {\emph{NN}} interaction $V_{low - k}$ . By allowing as many as four broken pairs, we compute the lowest $300$ intrinsic states of several multipolarity. These states converge well to the exact ones, showing generalized seniority is very effective in truncating the deformed shell model. Under realistic interactions, the picture remains approximately valid that the ground state is a coherent pair condensate, and the pairs gradually break up as excitation energy increases.
nucl-thPRC(2017)·12 citations
05
Initial Angular Momentum and Flow in High Energy Nuclear Collisions
Rainer J. Fries🇺🇸 · Guangyao Chen🇺🇸 · Sidharth Somanathan🇺🇸
We study the transfer of angular momentum in high energy nuclear collisions from the colliding nuclei to the region around midrapidity, using the classical approximation of the Color Glass Condensate (CGC) picture. We find that the angular momentum shortly after the collision (up to times ~ 1/Q_s, where Q_s is the saturation scale) is carried by the "beta-type" flow of the initial classical gluon field, introduced by some of us earlier. beta^i ~ mu_1 nabla^i mu_2 - mu_2 nabla^i mu_1 (i=1,2) describes the rapidity-odd transverse energy flow and emerges from Gauss' Law for gluon fields. Here mu_1 and mu_2 are the averaged color charge fluctuation densities in the two nuclei, respectively. Interestingly, strong coupling calculations using AdS/CFT techniques also find an energy flow term featuring this particular combination of nuclear densities. In classical CGC the order of magnitude of the initial angular momentum per rapidity in the reaction plane, at a time 1/Q_s, is |dL_2/d eta| ~ R_A/Q_s^3 epsilon_0/2 at midrapidity, where R_A is the nuclear radius, and epsilon_0 is the average initial energy density. This result emerges as a cancellation between a vortex of energy flow in the reaction plane aligned with the total angular momentum, and energy shear flow opposed to it. We discuss in detail the process of matching classical Yang-Mills results to fluid dynamics. We will argue that dissipative corrections should not be discarded to ensure that macroscopic conservation laws, e.g. for angular momentum, hold. Viscous fluid dynamics tends to dissipate the shear flow contribution that carries angular momentum in boost-invariant fluid systems. This leads to small residual angular momentum around midrapidity at late times for collisions at high energies.
nucl-thPRC(2018)·15 citations
06
Particle Ratios From Strongly Interacting Hadronic Matter
Waseem Bashir🇮🇳 · Saeed Uddin🇮🇳 · Hamid Nanda🇮🇳
We calculate the particle ratios for a strongly interacting hadronic matter matter using non-linear Walecka model (NLWM) in relativistic mean-field approximation. A comparison with Hadron Resonance Gas Model is made.
↳ hep-phnucl-thAdv.High Energy Phys.(2017)·0 citations
07
Missing-mass spectroscopy of the $^{12} C (p, d)$ reaction near the $η^{'}$ -meson production threshold
Y. K. Tanaka🇯🇵 · K. Itahashi🇯🇵 · H. Fujioka🇯🇵 · Y. Ayyad🇯🇵 · J. Benlliure🇪🇸 · K.-T. Brinkmann🇩🇪 · S. Friedrich🇩🇪 · H. Geissel🇩🇪 · J. Gellanki🇳🇱 · C. Guo🇨🇳 · E. Gutz🇩🇪 · E. Haettner🇩🇪 and 42 other authors
Excitation-energy spectra of $^{11}$ C nuclei near the $η^{'}$ -meson production threshold have been measured by missing-mass spectroscopy using the $^{12}$ C( $p$ , $d$ ) reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce $η^{'}$ meson bound states in $^{11}$ C nuclei. Deuterons emitted at $0^{\circ}$ in the reaction have been momentum-analyzed by the fragment separator (FRS) used as a high-resolution spectrometer. No distinct structure due to the formation of $η^{'}$ -mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of $η^{'}$ -mesic states are determined, and thereby a constraint imposed on the $η^{'}$ -nucleus interaction is discussed.
↳ nucl-exnucl-thPRC(2018)·42 citations
08
Correlated Uncertainties in Monte Carlo Reaction Rate Calculations
Richard Longland
Context. Monte Carlo methods have enabled nuclear reaction rates from uncertain inputs to be presented in a statistically meaningful manner. However, these uncertainties are currently computed assuming no correlations between the physical quantities that enter those calculations. This is not always an appropriate assumption. Astrophysically important reactions are often dominated by resonances, whose properties are usually normalized to a well-known reference resonance. This insight provides a basis from which to develop a flexible framework for including correlations in Monte Carlo reaction rate calculations. Aims. The aim of this work is to develop and test a method for including correlations in Monte Carlo reaction rate calculations when the input has been normalized to a common reference. Methods. A mathematical framework is developed for including correlations between input parameters in Monte Carlo reaction rate calculations. The magnitude of those correlations is calculated from the uncertainties typically reported in experimental papers, where full correlation information is not available. The method is applied to four illustrative examples: a fictional 3-resonance reaction, $^{27}$ Al(p, $γ$ ) $^{28}$ Si, $^{23}$ Na(p, $α$ ) $^{20}$ Ne, and $^{23}$ Na( $α$ ,p) $^{26}$ Al. Results. Reaction rates at low temperatures that are dominated by a few isolated resonances are found to minimally impacted by correlation effects. However, reaction rates determined from many overlapping resonances can be significantly affected. Uncertainties in the $^{23}$ Na( $α$ ,p) $^{26}$ Al reaction, for example, increase by up to a factor of 5. This highlights the need to take correlation effects into account in reaction rate calculations, and provide insight into which cases are expected to be most affected by them. The impact of correlation effects on nucleosynthesis is also investigated.
↳ astro-ph.IMnucl-thAstron.Astrophys.(2017)·7 citations
09
The nuclear configurational entropy impact parameter dependence in the Color-Glass Condensate
Gayane Karapetyan🇧🇷
The impact parameter (b) dependence on the saturation scale, in the framework of the Color Glass Condensate (b-CGC) dipole model, is investigated from the configurational point of view. During the calculations and analysis of the quantum nuclear states, the critical points of stability in the configurational entropy setup are computed, matching the experimental parameters that define the onset of the quantum regime in the b-CGC in the literature with very good accuracy. This new approach is crucial and important for understanding the stability of quantum systems in study of deep inelastic scattering processes.
↳ hep-phnucl-thEPL(2017)·38 citations

Affiliations

first authorsco-authorsvia INSPIRE