Nuclear Theory·nucl-th

Tuesday·November 29, 2016

15 papers—12 primary·3 cross-listed

01
Isospin splitting of nucleon effective mass and symmetry energy in isotopic nuclear reactions
Ya-Fei Guo · Peng-Hui Chen · Fei Niu · Hong-Fei Zhang · Gen-Ming Jin · Zhao-Qing Feng
Within an isospin and momentum dependent transport model, the dynamics of isospin particles (nucleons and light clusters) in Fermi-energy heavy-ion collisions are investigated for constraining the isospin splitting of nucleon effective mass and the symmetry energy at subsaturation densities. The mass splitting of $m_{n}^{*} > m_{p}^{*}$ and $m_{n}^{*} < m_{p}^{*}$ in nuclear matter and the different stiffness of symmetry energy are used in the model. The single and double neutron to proton ratios of free nucleons and light particles are thoroughly investigated in the isotopic nuclear reactions of $^{112}$ Sn+ $^{112}$ Sn and $^{124}$ Sn+ $^{124}$ Sn at the incident energies of 50 and 120 MeV/nucleon, respectively. It is found that the both effective mass splitting and symmetry energy impact the kinetic energy spectra of the single ratios, in particular at the high energy tail (larger than 20 MeV). Specific constraints are obtained from the double ratio spectra, which are evaluated from the ratios of isospin observables produced in $^{124}$ Sn+ $^{124}$ Sn over $^{112}$ Sn+ $^{112}$ Sn collisions. A mass splitting of $m_{n}^{*} < m_{p}^{*}$ is constrained from the available data at the energy of 120 MeV/nucleon. A soft symmetry energy with the stiffness of $γ_{s} =$ 0.5 is close to the experimental double ratio spectra at both energies.
nucl-thCPC(2017)·9 citations
02
Structure and decay of the pygmy dipole resonance in 26Ne
M.Kimura
The low-lying spectra of $^{24, 25, 26} Ne$ and the structure of the pygmy dipole resonance (PDR) in $^{26} Ne$ have been theoretically studied by the antisymmetrized molecular dynamics (AMD) and its extended version called shifted-basis AMD. The calculated energy and strength of the PDR reasonably agree with the observation, and the analysis of the wave function shows that the PDR is dominated by neutron excitation coupled to the quadrupole excited core nucleus $^{25} Ne$ , which explains the observed unexpected decay of PDR to the excited states of $^{25} Ne$ . The large isoscalar component of PDR is also shown and the enhancement of the core excitation in neutron-rich Ne isotopes is conjectured.
nucl-thPRC(2017)·23 citations
03
Nuclear fragmentation induced by low-energy antiprotons within a microscopic transport approach
Zhao-Qing Feng🇨🇳
Within the framework of the Lanzhou quantum molecular dynamics (LQMD) transport model, the nuclear fragmentation induced by low-energy antiprotons has been investigated thoroughly. A coalescence approach is developed for constructing the primary fragments in phase space. The secondary decay process of the fragments is described by the well-known statistical code. It is found that the localized energy released in antibaryon-baryon annihilation is deposited in a nucleus mainly via pion-nucleon collisions, which leads to the emissions of pre-equilibrium particles, fission, evaporation of nucleons and light fragments etc. The strangeness exchange reactions dominate the hyperon production. The averaged mass loss increases with the mass number of target nucleus. A bump structure in the domain of intermediate mass for heavy targets appears owing to the contribution of fission fragments.
nucl-thPRC(2016)·5 citations
04
Coupled-channels Faddeev AGS calculation of $K^{-} pp n$ and $K^{-} ppp$ quasi-bound states
S. Marri🇮🇷 · S. Z. Kalantari🇮🇷
Using separable $K ˉ N - π Σ$ potentials in the Faddeev equations, we calculated the binding energies and widths of the $K^{-} pp$ , $K^{-} pp n$ and $K^{-} ppp$ quasi-bound states on the basis of three- and four-body Alt-Grassberger-Sandhas equations in the momentum representation. One- and two-pole version of $K ˉ N - π Σ$ interaction are considered and the dependence of the resulting few-body energy on the two-body $K ˉ N - π Σ$ potential was investigated. The $s$ -wave [3+1] and [2+2] sub-amplitudes are obtained by using the Hilbert-Schmidt expansion procedure for the integral kernels. As a result, we found a four-body resonance of the $K^{-} pp n$ and $K^{-} ppp$ quasi-bound states with a binding energy in the range $B_{K^{-} pp n} \sim 55 - 70$ and $B_{K^{-} ppp} \sim 90 - 100$ MeV, respectively. The calculations yielded full width of $Γ_{K^{-} pp n} \sim 16 - 20$ and $Γ_{K^{-} ppp} \sim 7 - 20$ MeV.
nucl-thEPJA(2016)·17 citations
05
Nuclear scissors modes and hidden angular momenta
E.B. Balbutsev🇷🇺 · I.V. Molodtsova🇷🇺 · P. Schuck🇫🇷
The coupled dynamics of low lying modes and various giant resonances are studied with the help of the Wigner Function Moments method generalized to take into account spin degrees of freedom and pair correlations simultaneously. The method is based on Time Dependent Hartree-Fock-Bogoliubov equations. The model of the harmonic oscillator including spin-orbit potential plus quadrupole-quadrupole and spin-spin interactions is considered. New low lying spin dependent modes are analyzed. Special attention is paid to the scissors modes. A new source of nuclear magnetism, connected with counter-rotation of spins up and down around the symmetry axis (hidden angular momenta), is discovered. Its inclusion into the theory allows one to improve substantially the agreement with experimental data in the description of energies and transition probabilities of scissors modes.
nucl-thPhys.Atom.Nucl.(2017)·1 citation
06
Fluctuations of collective coordinates and convexity theorems for energy surfaces
B. G. Giraud🇫🇷 · S. Karataglidis🇿🇦 · T. Sami🇫🇷
Constrained energy minimizations of a many-body Hamiltonian return energy landscapes e(b) where b=<B> representes the average value(s) of one (or several) collective operator(s), B, in an "optimized" trial state Phi_b, and e = <H> is the average value of the Hamiltonian in this state Phi_b. It is natural to consider the uncertainty, Delta e, given that Phi_b usually belongs to a restricted set of trial states. However, we demonstrate that the uncertainty, Delta b, must also be considered, acknowledging corrections to theoretical models. We also find a link between fluctuations of collective coordinates and convexity properties of energy surfaces.
nucl-thmath-phmath.MPquant-phAnnals Phys.(2017)·0 citations
07
Extrapolation of scattering data to the negative-energy region
L. D. Blokhintsev · A. S. Kadyrov · A. M. Mukhamedzhanov · D. A. Savin
Explicit analytic expressions are derived for the effective-range function for the case when the interaction is represented by a sum of the short-range square-well and long-range Coulomb potentials. These expressions are then transformed into forms convenient for extrapolating to the negative-energy region and obtaining the information about bound-state properties. Alternative ways of extrapolation are discussed. Analytic properties of separate terms entering these expressions for the effective-range function and the partial-wave scattering amplitude are investigated.
nucl-thPRC(2017)·19 citations
08
Non-equilibrium dilepton production in hadronic transport approaches
Jan Staudenmaier🇩🇪 · Janus Weil🇩🇪 · Hannah Petersen🇩🇪
In this work the non-equilibrium dilepton production from a hadronic transport approach (SMASH) is presented. The dilepton emission from the hadronic stage is of interest for current HADES results measured at GSI in the beam energy range from 1.25 - 3.5 GeV. Also at high collision energies (RHIC/LHC) the later dilute stages of the reaction are dominated by hadronic dynamics. The newly developed hadronic transport approach called SMASH (=Simulating Many Accelerated Strongly-interacting Hadrons) is introduced first. After explaining the basic interaction mechanisms, a comparison of elementary cross sections for pion production to experimental data is shown. The dilepton production within SMASH is explained in detail. The main contribution to the dilepton spectra in the low energy regime of GSI/FAIR/RHIC-BES originates from resonance decays. Results of the dilepton production with SMASH such as invariant mass spectra are shown.
nucl-thhep-phnucl-exJ.Phys.Conf.Ser.(2017)·6 citations
09
Flow harmonics from self-consistent particlization of a viscous fluid
Zack Wolff🇺🇸 · Denes Molnar🇺🇸
The quantitative extraction of quark-gluon plasma (QGP) properties from heavy-ion data, such as its specific shear viscosity $η / s$ , typically requires comparison to viscous hydrodynamic or "hybrid" hydrodynamics+transport simulations. In either case, one has to convert the fluid to hadrons, yet without additional theory input the conversion is ambiguous for dissipative fluids. Here, shear viscous phase-space corrections calculated using linearized transport theory are applied in Cooper-Frye freezeout to quantify the effects on anisotropic flow coefficients $v_{n} (p_{T})$ at both RHIC and LHC energies. Expanding upon our previous flow harmonics studies [1,2], we calculate pion and proton $v_{2} (p_{T})$ , $v_{4} (p_{T})$ , and $v_{6} (p_{T})$ . Unlike in Ref. [1], we incorporate a hadron gas that is chemically frozen below a temperature of 175 MeV, and use hypersurfaces from realistic viscous hydrodynamic simulations. With additive quark model cross sections and relative phase-space corrections with $p^{3/2}$ momentum dependence, rather than the quadratic Grad form, we find at moderately high transverse momentum noticeably higher $v_{4} (p_{T})$ and $v_{6} (p_{T})$ for protons than for pions. In addition, the value of $η / s$ deduced from elliptic flow data differs by nearly 50\% from the value extracted using the naive "democratic Grad" form of freeze-out distributions. To facilitate the use of the self-consistent viscous corrections calculated here in hydrodynamic and hybrid calculations, we also present convenient parameterizations of the corrections for the various hadron species (cf. Table I).
nucl-thPRC(2017)·10 citations
10
Universality in the neutron $-^{19}$ C scattering using finite range separable interactions
M. A. Shalchi · M. T. Yamashita · M. R. Hadizadeh · T. Frederico · Lauro Tomio
We report a study on the low-energy properties of the elastic $s -$ wave scattering of a neutron ( $n$ ) in the carbon isotope $^{19}$ C near the critical condition for the occurrence of an excited Efimov state in the three-body $n - n -^{18}$ C system. For the separation energy of the two halo neutrons in $^{20}$ C we use the available experimental data. We also investigate to which extent the universal scaling laws, strictly valid in the zero-range limit, will survive when using finite-range interactions. By allowing to vary the $n -^{18}$ C binding energy, a scaling behavior for the real and imaginary parts of the $s -$ wave phase-shift $δ_{0}$ is verified, emerging some universal characteristics given by the pole-position of $k cot (δ_{0}^{R})$ and effective-range parameters.
nucl-thFew Body Syst.(2017)·1 citation
11
Evidence of the mixed phase formation in nucleus-nucleus collisions
V. V. Sagun🇺🇦 · K. A. Bugaev🇺🇦 · A. I. Ivanytskyi🇺🇦 · D. R. Oliinychenko🇺🇦
Searchers for various irregularities in the behavior of thermodynamic quantities at chemical freeze-out (CFO) are rather important in a view of experimental studies of quark-gluon plasma (QGP). Using the multicomponent hadron resonance gas model (HRGM), developed in (Sagun, 2014; Bugaev et al., 2015), we performed a high-quality fit of 111 hadronic ratios measured for 14 values of the center of mass collision energies between 2.7 GeV and 200 GeV with the overall fit quality $χ^{2} / d o f ≃ 0.95$ . In addition to previously reported singularities (Bugaev et al., 2015) at CFO we found that the hadron yield ratios $\frac{Λ}{p}$ , $\frac{K ^{+}}{p}$ , $\frac{K ^{+}}{Λ}$ , $\frac{Ω ^{-}}{p}$ and $\frac{Ξ ^{-}}{p}$ measured in central nuclear collisions demonstrate a significant change of slope in the same range of center of mass collision energy $s_{N N} = 4.3 - 4.9$ GeV (Bugaev et al., 2015). This change of slopes is accompanied by a dramatic increase of resonance decays at CFO. Also at CFO the trace anomaly and baryonic density demonstrate the pronounced peaks at the collision energy $s_{N N} = 4.9$ GeV. We argue that all these and previously found irregularities provide an evidence for the QGP formation in nuclear collisions at about $s_{N N} = 4.9$ GeV.
nucl-thhep-phWDS`16 Proceedings of Contributed Papers …·0 citations
12
Nonlocal energy density functionals for pairing and beyond-mean-field calculations
K. Bennaceur🇫🇷 · A. Idini · J. Dobaczewski🇫🇮 · P. Dobaczewski🇵🇱 · M. Kortelainen🇫🇮 · F. Raimondi🇫🇮
We propose to use two-body regularized finite-range pseudopotential to generate nuclear energy density functional (EDF) in both particle-hole and particle-particle channels, which makes it free from self-interaction and self-pairing, and also free from singularities when used beyond mean field. We derive a sequence of pseudopotentials regularized up to next-to-leading order (NLO) and next-to-next-to-leading order (N2LO), which fairly well describe infinite-nuclear-matter properties and finite open-shell paired and/or deformed nuclei. Since pure two-body pseudopotentials cannot generate sufficiently large effective mass, the obtained solutions constitute a preliminary step towards future implementations, which will include, e.g., EDF terms generated by three-body pseudopotentials.
nucl-thJ.Phys.G(2017)·30 citations
13
Nucleon spin and quark content at the physical point
C. Alexandrou (Univ. of Cyprus and The Cyprus Inst.)🇨🇾 · M. Constantinou🇨🇾 · K. Hadjiyiannakou🇨🇾 · Ch. Kallidonis🇨🇾 · G. Koutsou (The Cyprus Inst.)🇨🇾 · K. Jansen🇩🇪 · Ch. Wiese (DESY-Zeuthen)🇩🇪 · A. Vaquero Avilés-Casco (INFN-Milan)🇮🇹
We present results on the spin and quark content of the nucleon using $N_{f} = 2$ twisted mass clover-improved fermion simulations with a pion mass close to its physical value. We use recently developed methods to obtain accurate results for both connected and disconnected contributions. We provide results for the axial charge, quark and gluon momentum fraction as well as the light, strange and charm $σ$ -terms.
↳ hep-lathep-phnucl-thPoS(2016)·12 citations
14
Phenomenological analysis of associated production of $Z^{0} + b$ in the $b \to J / ψ X$ decay channel at the LHC
Jean-Philippe Lansberg🇫🇷 · Hua-Sheng Shao🇨🇭
The ATLAS collaboration recently reported on the first observation of associated-production of a $Z^{0}$ boson with a $J / ψ$ . We recently claimed that the corresponding yield of the {\it prompt} $J / ψ$ was dominated by double parton scatterings in the ATLAS acceptance with a somewhat small value of $σ_{eff}$ . We also found out that single parton scatterings were only dominant at large transverse momenta. We present here the first phenomenological analysis of another part of the ATLAS data sample, namely of a $Z^{0}$ boson plus a {\it non-prompt} $J / ψ$ . Our study is performed at next-to-leading order in $α_{s}$ and includes parton-shower effects via the {\sc\small MadGraph5_aMC@NLO} framework. We find out that the data, unlike the case of prompt $J / ψ + Z^{0}$ , do not hint at significant DPS contributions. Owing to the current experimental and theoretical uncertainties, there is still a room for these but with a lower limit of $σ_{eff}$ close to 5 mb. We stress the importance of QCD corrections to account for the ATLAS data.
↳ hep-phhep-exnucl-exnucl-thNPB(2017)·30 citations
15
The effect of ionic correlations on radiative properties in the solar interior and terrestrial experiments
Menahem Krief (HUJI) · Yair Kurzweil (NRCN) · Alexander Feigel (HUJI) · Doron Gazit (HUJI)
Intending to solve the decade old problem of solar opacity, we report substantial photoabsorption uncertainty due to the effect of ion-ion correlations. By performing detailed opacity calculations of the solar mixture, we find that taking into account the ionic structure changes the Rosseland opacity near the convection zone by about 10%. We also report about 15% difference in the Rosseland opacity for iron, which was recently measured at the Sandia Z facility, where the temperature reached that prevailing in the convection zone boundary while the density is 2.5 times lower. Finally, we propose a method to measure opacities at solar temperatures and densities that were never reached in the past via laboratory radiation flow experiments, by using plastic foams doped with permilles of dominant photon absorbers in the Sun. The method is advantageous for an experimental study of solar opacities that may lead to a resolution of the solar problem.
↳ astro-ph.SRnucl-thphysics.plasm-phApJ(2018)·5 citations

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