Nuclear Theory·nucl-th

Tuesday·November 24, 2015

10 papers—7 primary·3 cross-listed

01
Stochastic Estimation of Nuclear Level Density in the Nuclear Shell Model: An Application to Parity-Dependent Level Density in $^{58}$ Ni
Noritaka Shimizu🇯🇵 · Yutaka Utsuno🇯🇵 · Yasunori Futamura🇯🇵 · Tetsuya Sakurai🇯🇵 · Takahiro Mizusaki🇯🇵 · Takaharu Otsuka🇯🇵
We introduce a novel method to obtain level densities in large-scale shell-model calculations. Our method is a stochastic estimation of eigenvalue count based on a shifted Krylov-subspace method, which enables us to obtain level densities of huge Hamiltonian matrices. This framework leads to a successful description of both low-lying spectroscopy and the experimentally observed equilibration of $J^{π} = 2^{+}$ and $2^{-}$ states in $^{58}$ Ni in a unified manner.
nucl-thPLB(2016)·33 citations
02
The $K^{* 0} Λ$ photoproduction off a neutron
Xiao-Yun Wang🇨🇳 · Jun He🇨🇳
Inspired by the preliminary experimental data by the CLAS Collaboration, the $K^{* 0} Λ$ photoproduction off a neutron is studied within an effective Lagrangian approach. The contributions from the Born terms including $s$ , $u$ , and $t$ channels are considered to calculate the amplitude, with which the cross sections are calculated and compared with preliminary CLAS data. The theoretical results indicate that the contribution from the $K$ -exchange $t$ channel plays a dominant role for the $K^{* 0} Λ$ photoproduction. The contribution from the $κ$ exchange is found one order of magnitude smaller than that from the $K$ exchange. Both the Regge model and the Feynman model are applied to treat the $t$ -channel contribution. The discrepancy between two models is found small in the energy range of CLAS data and predicted to become obvious at energies higher than 3 GeV. More precise experimental data especially at backward angles will be helpful to further understand the interaction mechanism of the $K^{* 0} Λ$ photoproduction.
nucl-thhep-phnucl-exPRC(2016)·17 citations
03
Symmetry energy and neutron star properties in the saturated Nambu-Jona-Lasinio model
Si-Na Wei🇨🇳 · Wei-Zhou Jiang🇨🇳 · Rong-Yao Yang🇨🇳 · Dong-Rui Zhang🇨🇳
In this work, we adopt the Nambu-Jona-Lasinio (NJL) model that ensures the nuclear matter saturation properties to study the density dependence of the symmetry energy. With the interactions constrained by the chiral symmetry, the symmetry energy shows novel characters different from those in conventional mean-field models. First, the negative symmetry energy at high densities that is absent in relativistic mean-field (RMF) models can be obtained in the RMF approximation by introducing a chiral isovector-vector interaction, although it would be ruled out by the neutron star (NS) stability. Second, with the inclusion of the isovector-scalar interaction the symmetry energy exhibits a general softening at high densities even for the large slope parameter of the symmetry energy. The NS properties obtained in the present NJL model can be in accord with the observations. The NS maximum mass obtained with various isovector-scalar couplings and momentum cutoffs is well above the $2 M_{⊙}$ , and the NS radius obtained well meets the limits extracted from recent measurements. In particular, the significant reduction of the canonical NS radius occurs with the moderate decrease of the slope of the symmetry energy.
nucl-thPLB(2016)·17 citations
04
Effect of correlations on cumulants in heavy-ion collisions
D. K. Mishra🇮🇳 · P. Garg🇮🇳 · P. K. Netrakanti🇮🇳
We study the effects of correlations on cumulants and their ratios of net-proton multiplicity distributions which have been measured for central (0\%-5\%) Au + Au collisions at the Relativistic Heavy Ion Collider (RHIC). This effect has been studied assuming individual proton and anti-proton distributions as a Poisson or Negative Binomial Distribution (NBD). In-spite of significantly correlated production due to baryon number, electric charge conservation and kinematical correlations of protons and anti-protons, the measured cumulants of the net-proton distribution follow the independent production model. In the present work we demonstrate how the introduction of the correlations will affect the cumulants and their ratios for the difference distributions. We have also demonstrated this study using the proton and anti-proton distributions obtained from the HIJING event generator.
nucl-thnucl-exPRC(2016)·5 citations
05
Cooperative internal conversion process
Péter Kálmán · Tamás Keszthelyi
A new phenomenon, called cooperative internal conversion process, in which the coupling of bound-free electron and neutron transitions due to the dipole term of their Coulomb interaction permits cooperation of two nuclei leading to neutron exchange if it is allowed by energy conservation, is discussed theoretically. General expression of the cross section of the process is reported in one particle nuclear and spherical shell models as well in the case of free atoms (e.g. noble gases). A half-life characteristic of the process is also determined. The case of $N e$ is investigated numerically. The process may have significance in fields of nuclear waste disposal and nuclear energy production.
nucl-th1 citation
06
Hydrodynamical noise and Gubser flow
Li Yan🇫🇷 · Hanna Grönqvist🇫🇷
Hydrodynamical noise is introduced on top of Gubser's analytical solution to viscous hydrodynamics. With respect to the ultra-central collision events of Pb-Pb, p-Pb and p-p at the LHC energies, we solve the evolution of noisy fluid systems and calculate the radial flow velocity correlations. We show that the absolute amplitude of the hydrodynamical noise is determined by the multiplicity of the collision event. The evolution of azimuthal anisotropies, which is related to the generation of harmonic flow, receives finite enhancements from hydrodynamical noise. Although it is strongest in the p-p systems, the effect of hydrodynamical noise on flow harmonics is found to be negligible, especially in the ultra-central Pb-Pb collisions. For the short-range correlations, hydrodynamical noise contributes to the formation of a near-side peak on top of the correlation structure originated from initial state fluctuations. The shape of the peak is affected by the strength of hydrodynamical noise, whose height and width grow from the Pb-Pb system to the p-Pb and p-p systems.
nucl-thhep-phnucl-exJHEP(2016)·31 citations
07
Tensor-optimized antisymmetrized molecular dynamics in nuclear physics
Takayuki Myo · Hiroshi Toki · Kiyomi Ikeda · Hisashi Horiuchi · Tadahiro Suhara
We develop a new formalism to treat nuclear many-body systems using bare nucleon-nucleon interaction. It has become evident that the tensor interaction plays important role in nuclear many-body systems due to the role of the pion in strongly interacting system. We take the antisymmetrized molecular dynamics (AMD) as a basic framework and add a tensor correlation operator acting on the AMD wave function using the concept of the tensor-optimized shell model (TOSM). We demonstrate a systematical and straightforward formulation utilizing the Gaussian integration and differentiation method and the antisymmetrization technique to calculate all the matrix elements of the many-body Hamiltonian. We can include the three-body interaction naturally and calculate the matrix elements systematically in the progressive order of the tensor correlation operator. We call the new formalism "tensor-optimized antisymmetrized molecular dynamics".
nucl-thPTEP(2015)·36 citations
08
Searching for minimum in dependence of squared speed-of-sound on collision energy
Fu-Hu Liu🇨🇳 · Li-Na Gao🇨🇳 · Roy A. Lacey🇺🇸
Experimental results of the rapidity distributions of negatively charged pions produced in proton-proton ( $p$ - $p$ ) and beryllium-beryllium (Be-Be) collisions at different beam momentums, measured by the NA61/SHINE Collaboration at the super proton synchrotron (SPS), are described by a revised (three-source) Landau hydrodynamic model. The squared speed-of-sound parameter $c_{s}^{2}$ is then extracted from the width of rapidity distribution. There is a local minimum (knee point) which indicates a softest point in the equation of state (EoS) appearing at about 40 $A$ GeV/ $c$ (or 8.8 GeV) in $c_{s}^{2}$ excitation function [the dependence of $c_{s}^{2}$ on incident beam momentum (or center-of-mass energy)]. This knee point should be related to the searching for the onset of quark deconfinement and the critical point of quark-gluon plasma (QGP) phase transition.
↳ hep-phhep-exnucl-exnucl-thAdv.High Energy Phys.(2016)·5 citations
09
Vector Meson Masses from Hidden Local Symmetry in Constant Magnetic Field
Mamiya Kawaguchi🇯🇵 · Shinya Matsuzaki🇯🇵
We discuss the magnetic responses of vector meson masses based on the hidden local symmetry (HLS) model in constant magnetic field, described by the lightest two-flavor system including the pion, rho and omega mesons in the spectrum. The effective masses influenced under the magnetic field are evaluated in a way of the derivative/chiral expansion established in the HLS model. At the leading order O(p^2) the g-factor of the charged rho meson is fixed to be 2, implying that the rho meson at this order is treated just like a point-like spin-1 particle. Beyond the leading order, one finds anomalous magnetic interactions of the charged rho meson, involving the anomalous magnetic moment, which give corrections to the effective mass. It is then suggested that up to O(p^4) the charged rho meson tends to become massless. Of interest is that nontrivial magnetic-dependence of neutral mesons emerges to give rise to the significant mixing among neutral mesons. Consequently, it leads to the dramatic enhancement of the omega meson mass, which is testable in future lattice simulations. Corrections from terms beyond O(p^4) are also addressed.
↳ hep-phhep-latnucl-thPRD(2016)·39 citations
10
Excited Baryon Structure Using Exclusive Reactions with CLAS12
Daniel S. Carman (for the CLAS Collaboration)🇺🇸
Studying excited nucleon structure through exclusive electroproduction reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. Electrocouplings for $N^{*}$ states in the mass range below 1.8~GeV have been determined from analyses of CLAS $π N$ , $η N$ , and $π π N$ data. This work made it clear that consistency of independent analyses of exclusive channels with different couplings and non-resonant backgrounds but the same $N^{*}$ electro-excitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic coupling, many high-lying $N^{*}$ states preferentially decay through the $π π N$ channel instead of $π N$ . Data from the $K Y$ channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying $N^{*}$ states against those determined from the $π N$ and $π π N$ channels. A program to study excited $N^{*}$ decays to non-strange and strange exclusive final states using CLAS12 will measure differential cross sections to be used as input to extract the $γ_{v} N N^{*}$ transition form factors for the most prominent $N^{*}$ states in the range of invariant energy $W$ up 3~GeV in the virtually unexplored domain of momentum transfers $Q^{2}$ up to 12~GeV $^{2}$ .
↳ nucl-exnucl-thAIP Conf.Proc.(2016)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE