Nuclear Theory·nucl-th

Tuesday·December 16, 2014

13 papers—7 primary·6 cross-listed

01
Decay and structure of the Hoyle state
Souichi Ishikawa
The first $0^{+}$ resonant state of the $^{12}$ C nucleus $^{12}$ C $(0_{2}^{+})$ , so called the Hoyle state, is investigated in a three- $α$ -particle (3- $α$ ) model. A wave function for the photodisintegration reaction of a $^{12}$ C bound state to 3- $α$ final states is defined and calculated by the Faddeev three-body formalism, in which three-body bound- and continuum states are treated consistently. From the wave function at the Hoyle state energy, I calculated distributions of outgoing $α$ -particles and density distributions at interior region of the Hoyle state. Results show that a process through a two- $α$ resonant state is dominant in the decay and contributions of the rest process are very small, less than 1 \%. There appear some peaks in the interior density distribution corresponding to configurations of an equilateral- and an isosceles triangles. It turns out that these results are obtained independently of the choice of $α$ -particle interaction models, when they are made to reproduce the Hoyle state energy.
nucl-thnucl-exPRC(2014)·56 citations
02
Triaxially deformed relativistic point-coupling model for $Λ$ hypernuclei: a quantitative analysis of hyperon impurity effect on nuclear collective properties
W. X. Xue🇨🇳 · J. M. Yao🇨🇳 · K. Hagino🇯🇵 · Z. P. Li🇨🇳 · H. Mei🇨🇳 · Y. Tanimura🇫🇷
The impurity effect of hyperon on atomic nuclei has received a renewed interest in nuclear physics since the first experimental observation of appreciable reduction of $E 2$ transition strength in low-lying states of hypernucleus $_{Λ}^{7}$ Li. Many more data on low-lying states of $Λ$ hypernuclei will be measured soon for $s d$ -shell nuclei, providing good opportunities to study the $Λ$ impurity effect on nuclear low-energy excitations. We carry out a quantitative analysis of $Λ$ hyperon impurity effect on the low-lying states of $s d$ -shell nuclei at the beyond-mean-field level based on a relativistic point-coupling energy density functional (EDF), considering that the $Λ$ hyperon is injected into the lowest positive-parity ( $Λ_{s}$ ) and negative-parity ( $Λ_{p}$ ) states. We adopt a triaxially deformed relativistic mean-field (RMF) approach for hypernuclei and calculate the $Λ$ binding energies of hypernuclei as well as the potential energy surfaces (PESs) in $(β, γ)$ deformation plane. We also calculate the PESs for the $Λ$ hypernuclei with good quantum numbers using a microscopic particle rotor model (PRM) with the same relativistic EDF. The triaxially deformed RMF approach is further applied in order to determine the parameters of a five-dimensional collective Hamiltonian (5DCH) for the collective excitations of triaxially deformed core nuclei. Taking $_{Λ}^{25, 27}$ Mg and $_{Λ}^{31}$ Si as examples, we analyse the impurity effects of $Λ_{s}$ and $Λ_{p}$ on the low-lying states of the core nuclei...
nucl-thnucl-exPRC(2015)·32 citations
03
Hyperons in neutron star matter within relativistic mean-field models
M. Oertel🇫🇷 · C. Providência🇵🇹 · F. Gulminelli🇫🇷 · A. R. Raduta🇷🇴
Since the discovery of neutron stars with masses around 2 solar masses the composition of matter in the central part of these massive stars has been intensively discussed. Within this paper we will (re)investigate the question of the appearance of hyperons. To that end we will perform an extensive parameter study within relativistic mean field models. We will show that it is possible to obtain high mass neutron stars (i) with a substantial amount of hyperons, (ii) radii of 12-13 km for the canonical mass of 1.4 solar masses, and (iii) a spinodal instability at the onset of hyperons. The results depend strongly on the interaction in the hyperon-hyperon channels, on which only very little information is available from terrestrial experiments up to now.
nucl-thJ.Phys.G(2015)·166 citations
04
Hidden dibaryons in one- and two-pion production in NN collisions
M. N. Platonova🇷🇺 · V. I. Kukulin🇷🇺
Processes of one- and two-pion production in $N N$ collisions are considered in connection with excitation of intermediate dibaryon resonances. In particular, relative contributions of the conventional meson-exchange and dibaryon excitation mechanisms in the reaction $pp \to d π^{+}$ are investigated in detail. Inclusion of the intermediate isovector dibaryon resonances is shown to essentially improve the description of experimental data for this reaction, provided the soft meson-baryon form factors consistent with $π N$ elastic scattering are used. Manifestation of the intermediate isoscalar and isovector dibaryons in the two-pion production processes is also studied. The role of the isovector dibaryon resonances in the reaction $pp \to pp π π$ is discussed for the first time. An explanation of the observed strong differences between two-pion production cross sections in $p n$ and $pp$ collisions based in part on the analysis of dibaryon structure is suggested.
nucl-thNPA(2016)·45 citations
05
Precision nucleon-nucleon potential at fifth order in the chiral expansion
E. Epelbaum🇩🇪 · H. Krebs🇩🇪 · U.-G. Meißner🇩🇪
We present a nucleon-nucleon potential at fifth order in chiral effective field theory. We find a substantial improvement in the description of nucleon-nucleon phase shifts as compared to the fourth-order results of Ref. [E. Epelbaum, H. Krebs, U.-G. Meißner, arXiv:1412.0142 [nucl-th]]. This provides clear evidence of the corresponding two-pion exchange contributions with all low-energy constants being determined from pion-nucleon scattering. The fifth-order corrections to nucleon-nucleon observables appear to be of a natural size which confirms the good convergence of the chiral expansion for nuclear forces. Furthermore, the obtained results provide strong support for the novel way of quantifying the theoretical uncertainty due to the truncation of the chiral expansion proposed in Ref. [E. Epelbaum, H. Krebs, U.-G. Meißner, arXiv:1412.0142 [nucl-th]]. Our work opens up new perspectives for precision ab initio calculations in few- and many-nucleon systems and is especially relevant for ongoing efforts towards a quantitative understanding the structure of the three-nucleon force in the framework of chiral effective field theory.
nucl-thhep-phnucl-exPRL(2015)·444 citations
06
Low-energy excitations and quasielastic contribution to electron-nucleus and neutrino-nucleus scattering in the continuum random phase approximation
V. Pandey🇧🇪 · N. Jachowicz🇧🇪 · T. Van Cuyck🇧🇪 · J. Ryckebusch🇧🇪 · M. Martini🇧🇪
We present a detailed study of a continuum random phase approximation approach to quasielastic electron-nucleus and neutrino-nucleus scattering. The formalism is validated by confronting ( $e, e^{'}$ ) cross-section predictions with electron scattering data for the nuclear targets $^{12}$ C, $^{16}$ O, and $^{40}$ Ca, in the kinematic region where quasielastic scattering is expected to dominate. We examine the longitudinal and transverse contributions to $^{12}$ C( $e, e^{'}$ ) and compare them with the available data. Further, we study the $^{12}$ C( $ν_{μ}, μ^{-}$ ) cross sections relevant for accelerator-based neutrino-oscillation experiments. We pay special attention to low-energy excitations which can account for non-negligible contributions in measurements, and require a beyond-Fermi-gas formalism.
nucl-thPRC(2015)·122 citations
07
Alternative ansatz to wounded nucleon and binary collision scaling in high-energy nuclear collisions
J. Scott Moreland🇺🇸 · Jonah E. Bernhard🇺🇸 · Steffen A. Bass🇺🇸
We introduce TRENTO, a new parametric initial condition model for high-energy nuclear collisions based on eikonal entropy deposition via a "reduced thickness" function. The model simultaneously describes experimental proton-proton, proton-nucleus, and nucleus-nucleus multiplicity distributions, and generates nucleus-nucleus eccentricity harmonics consistent with experimental flow constraints. In addition, the model is compatible with ultra-central uranium-uranium data unlike existing models that include binary collision terms.
nucl-thhep-phnucl-exPRC(2015)·602 citations
08
Symmetry energy dependence of long timescale isospin transport
K. Stiefel · Z. Kohley · R. T. deSouza · S. Hudan · K. Hammerton
Isospin transport occurring within dinuclear projectile-like fragments (PLFs) produced in heavy- ion collisions is explored as a probe of the nuclear symmetry energy. Within the framework of the Constrained Molecular Dynamics model (CoMD), the existence of the long-lived dinuclear PLFs, for up to 800 fm/c, is observed. It is demonstrated that changes in the <N/Z> of the two fragments resulting from the breakup of the dinuclear PLF is due to isospin transport. The rate of the transport between the two fragments is shown to be dependent on the slope of the symmetry energy at saturation density. Comparison of the CoMD calculations with experimental data establish that the evolution of <N/Z> could be used to constrain the density dependence of the symmetry energy.
↳ nucl-exnucl-thPRC(2014)·17 citations
09
Probing Dynamics of Phase Transitions occurring inside a Pulsar
Partha Bagchi🇮🇳 · Arpan Das🇮🇳 · Biswanath Layek🇮🇳 · Ajit M. Srivastava🇮🇳
During the evolution of a pulsar, various phase transitions may occur in its dense interior, such as superfluid transition, as well as transition to various exotic phases of quantum chromodynamics (QCD). We propose a technique which allows to probe these phases and associated transitions by detecting changes in rotation of the star arising from density changes and fluctuations during the transition affecting star's moment of inertia. Our results suggest that these changes may be observable, and may possibly account for glitches and (recently observed) anti-glitches. Accurate measurements of pulsar timing and intensity modulations (arising from wobbling of star due to development of the off-diagonal components of moment of inertia) may be used to pin down the particular phase transition occurring inside the pulsar core. We also discuss the possibility of observing gravitational waves from the changes in the quadrupole moment arising from these rapidly evolving density fluctuations.
↳ astro-ph.HEgr-qcnucl-thSpringer Proc.Phys.(2016)·2 citations
10
Recent Advances and Open Questions in Neutrino-induced Quasi-elastic Scattering and Single Photon Production
G. T. Garvey🇺🇸 · D. A. Harris🇺🇸 · H. A. Tanaka🇨🇦 · R. Tayloe🇺🇸 · G. P. Zeller🇺🇸
The study of neutrino-nucleus interactions has recently seen rapid development with a new generation of accelerator-based neutrino experiments employing medium and heavy nuclear targets for the study of neutrino oscillations. A few unexpected results in the study of quasi-elastic scattering and single photon production have spurred a revisiting of the underlying nuclear physics and connections to electron-nucleus scattering. A thorough understanding and resolution of these issues is essential for future progress in the study of neutrino oscillations. A recent workshop hosted by the Institute of Nuclear Theory at the University of Washington (INT-13-54W) examined experimental and theoretical developments in neutrino-nucleus interactions and related measurements from electron and pion scattering. We summarize the discussions at the workshop pertaining to the aforementioned issues in quasi-elastic scattering and single photon production, particularly where there was consensus on the highest priority issues to be resolved and the path towards resolving them.
↳ hep-exnucl-exnucl-thPhys.Rept.(2015)·40 citations
11
Use of the Husimi distribution for nucleon tomography
Yoshikazu Hagiwara🇯🇵 · Yoshitaka Hatta🇯🇵
In the context of nucleon structure, the Wigner distribution has been commonly used to visualize the phase-space distribution of quarks and gluons inside the nucleon. However, the Wigner distribution does not allow for a probabilistic interpretation because it takes negative values. In pursuit of a positive phase-space distribution in QCD, we introduce the Husimi distribution and demonstrate its advantages via a simple one-loop example. We also comment on a possible connection to the semiclassical approach to saturation physics at small- $x$ .
↳ hep-phnucl-thNPA(2015)·27 citations
12
Hadron Structure from Lattice QCD
Jeremy Green🇩🇪
Recent progress in lattice QCD calculations of nucleon structure will be presented. Calculations of nucleon matrix elements and form factors have long been difficult to reconcile with experiment, but with advances in both methodology and computing resources, this situation is improving. Some calculations have produced agreement with experiment for key observables such as the axial charge and electromagnetic form factors, and the improved understanding of systematic errors will help to increase confidence in predictions of unmeasured quantities. The long-omitted disconnected contributions are now seeing considerable attention and some recent calculations of them will be discussed.
↳ hep-lathep-phnucl-thAIP Conf.Proc.(2016)·13 citations
13
Limitation of multi-particle correlations for studying the event-by-event distribution of harmonic flow in heavy-ion collisions
Jiangyong Jia🇺🇸 · Sooraj Krishnann🇺🇸
The sensitivity of flow harmonics from cumulants on the event-by-event flow distribution $p (v_{n})$ is investigated using a simple central moment expansion approach. For narrow distribution whose width is much smaller than the mean $σ_{n} ≪< v_{n} >$ , the difference between the first three higher-order cumulant estimates $v_{n} {4}$ , $v_{n} {6}$ and $v_{n} {8}$ are not very sensitive to the shape of $p (v_{n})$ . For broad distribution $σ_{n} ≳ < v_{n} >$ , the higher-order cumulant estimates differ from each other but may change sign and become ill-defined. This sign change arises from the choice of $p (v_{n})$ , without the need to invoke non-flow effects. Direct extraction of $p (v_{n})$ via a data-driven unfolding method is a more preferred approach for flow distribution measurement.
↳ nucl-exnucl-thPRC(2015)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE