Nuclear Theory·nucl-th

Friday·February 20, 2015

10 papers—9 primary·1 cross-listed

01
Diquark bound states with a completely crossed ladder truncation
Go Mishima🇯🇵 · Ryusuke Jinno🇯🇵 · Teppei Kitahara🇯🇵
The Bethe-Salpeter equation in the diquark channel is investigated by employing the Dyson-Schwinger method together with the Munczek-Nemirovsky model. The novelty of our study is a resummation of completely crossed ladder diagrams in the Bethe-Salpeter kernel. These diagrams are enhanced due to their color factors in the diquark channel, but not in the meson channel. In our analysis, diquark bound-state solutions exist in the Bethe-Salpeter equation.
nucl-thhep-phPRD(2015)·9 citations
02
Multistrangeness in Heavy-Ion Collisions
E.E. Kolomeitsev🇺🇸 · I. Melo🇸🇰 · B. Tomasik🇸🇰 · D.N. Voskresensky🇷🇺
We discuss strangeness production in heavy-ion collisions in the broad energy range --- from SIS energies through AGS-SPS-RHIC and upto LHC energies. On several examples we demonstrate how the strange particle production can reveal information about the collision dynamics and about possible modifications of particle properties in medium. In particular the production of hadrons containing two and more strange quarks, like $Ξ$ and $Ω$ baryons, or a $ϕ$ meson is of interest. We conduct our discussion in the framework of the minimal statistical model, in which the total strangeness yield is fixed by the $K^{+}$ multiplicity. It is emphasized that in collisions with a small number of produced strange particles, the exact strangeness conservation in each collision event must be explicitly preserved.
nucl-thPoS(2015)·1 citation
03
Interaction of antiproton with nuclei
J. Hrtánková · J. Mareš
We performed fully self-consistent calculations of $p ˉ$ -nuclear bound states within the relativistic mean-field (RMF) model. The G-parity motivated $p ˉ$ -meson coupling constants were adjusted to yield potentials consistent with $p ˉ$ -atom data. We confirmed large polarization effects of the nuclear core caused by the presence of the antiproton. The $p ˉ$ absorption in the nucleus was incorporated by means of the imaginary part of a phenomenological optical potential. The phase space reduction for the $p ˉ$ annihilation products was taken into account. The corresponding $p ˉ$ width in the medium significantly decreases, however, it still remains considerable for the $p ˉ$ potential consistent with experimental data.
nucl-thHyperfine Interact.(2015)·0 citations
04
Orbital and spin scissors modes in superfluid nuclei
E. B. Balbutsev🇷🇺 · I. V. Molodtsova🇷🇺 · P. Schuck🇫🇷
Nuclear scissors modes are considered in the frame of Wigner function moments method generalized to take into account spin degrees of freedom and pair correlations simultaneously. 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 in rare earth nuclei.
nucl-thPRC(2015)·20 citations
05
Fission fragment mass yield deduced from density distribution in the pre-scission configuration
M. Warda · A. Zdeb
Static self-consistent methods usually allow to determine the most probable fission fragments mass asymmetry. We have applied random neck rupture mechanism to the nuclei in the configuration at the end of fission paths. Fission fragment mass distributions have been deduced from the pre-scission nuclear density distribution obtained from the self-consistent calculations. Potential energy surfaces as well as nuclear shapes have been calculated in the fully microscopic theory, namely the constrained Hartree-Fock-Bogolubov model with the effective Gogny D1S density-dependent interaction. The method has been applied for analysis of fission of Fm-256,258, Cf-252 and Hg-180 and compared with the experimental data.
nucl-thPhys.Scripta(2015)·10 citations
06
Anisotropic parton escape is the dominant source of azimuthal anisotropy in transport models
Liang He🇺🇸 · Terrence Edmonds🇺🇸 · Zi-Wei Lin🇺🇸 · Feng Liu🇨🇳 · Denes Molnar🇺🇸 · Fuqiang Wang🇺🇸
We trace the development of elliptic anisotropy ( $v_{2}$ ) via parton-parton collision history in two transport models. The parton $v_{2}$ is studied as a function of the number of collisions of each parton in Au+Au and $d$ +Au collisions at $s_{_{NN}} = 200$ GeV. It is found that the majority of $v_{2}$ comes from the anisotropic escape probability of partons, with no fundamental difference at low and high transverse momenta. The contribution to $v_{2}$ from hydrodynamic-type collective flow is found to be small. Only when the parton-parton cross-section is set unrealistically large does this contribution start to take over. Our findings challenge the current paradigm emerged from hydrodynamic comparisons to anisotropy data.
nucl-thnucl-exPLB(2016)·174 citations
07
Enhancement of annihilation cross sections by electric interactions between the antineutron and the field of a large nucleus
A. Bianconi🇮🇹 · E. Lodi Rizzini🇮🇹 · V.Mascagna🇮🇹 · L.Venturelli🇮🇹
Data relative to antineutron and antiproton annihilation on large nuclei in the range 75-200 MeV/c present two unexpected features: (a) antineutron and antiproton cross sections have a similar size, (ii) the rise of the antineutron cross section at decreasing energy is much steeper than predictable for an inelastic process of purely strong nature at that energy. The observed behavior of antineutron-nucleus annihilations is similar to what would be expected for antiproton-nucleus annihilations, where Coulomb attraction focusses antiproton trajectories towards the nucleus, enhancing the inelastic cross section by a factor O(1/p) with respect to antineutrons on the same target. This results in a 1/p^2 behavior at small energies. The presence of a similar enhancement in the antineutron case may only be justified by an interaction with a longer range than strong interactions. Excluding a Coulomb force because of the antineutron neutrality, and taking into account that an intrinsic electric dipole is forbidden for the antineutron, the next choice is an electric dipole that is induced by the nuclear electric field. Recent theoretical works have shown that a non-negligible electric polarization may be induced in a neutron by QED vacuum polarization. Assuming this as a possibility, we have used a simple model to calculate the polarization strengths that are needed to fit the available data in terms of this effect. These are within the magnitude predicted by the vacuum polarization model. We have also discussed alternative scenarios that could induce an electric polarization of the antineutron as a consequence of the interplay between strong and e.m. interactions.
nucl-thhep-phEPJA(2014)·7 citations
08
Statistical Model of the Early Stage of nucleus-nucleus collisions with exact strangeness conservation
R. V. Poberezhnyuk🇺🇦 · M. Gazdzicki🇩🇪 · M. I. Gorenstein🇺🇦
The Statistical Model of the Early Stage, SMES, describes a transition between confined and deconfined phases of strongly interacting matter created in nucleus-nucleus collisions. The model was formulated in the late 1990s for central Pb+Pb collisions at the CERN SPS energies. It predicted several signals of the transition (onset of deconfinement) which were later observed by the NA49 experiment. The grand canonical ensemble was used to calculate entropy and strangeness production. This approximation is valid for reactions with mean multiplicities of particles carrying conserved charges being significantly larger than one. Recent results of NA61/SHINE on hadron production in inelastic p+p interactions suggest that the deconfinement may also take place in these reactions. However, in this case mean multiplicity of particles with non-zero strange charge is smaller than one. Thus for the modeling of p+p interactions the exact strangeness conservation has to be implemented in the SMES. This extension of the SMES is presented in the paper.
nucl-thhep-phActa Phys.Polon.B(2015)·26 citations
09
Pairing in high-density neutron matter including short- and long-range correlations
D. Ding · A. Rios · W. H. Dickhoff · H. Dussan · A. Polls · S. J. Witte
The influence of short-range correlations (SRC) on the spectral distribution of neutrons is incorporated in the solution of the gap equation for the $^{3} P_{2} -^{3} F_{2}$ coupled channel in pure neutron matter at high density. This effect is studied for three different realistic interactions. The gap in this channel is strongly suppressed by these correlations but does not vanish. For a consistent treatment we also include for the first time the effect of long-range correlations (LRC) by incorporating polarization terms in addition to the bare interaction. This allows the neutrons to exchange density and spin fluctuations governed by the strength of Landau parameters with values that are consistent with the available literature. While these LRC have an antiscreening tendency, they only slightly increase the gap in the $^{3} P_{2} -^{3} F_{2}$ coupled channel for all three realistic interactions as long as SRC are included. All three interactions generate maximum gaps around 0.1 to 0.2 MeV at most with a small dependence on the hardness of the interaction. These results are relevant for the cooling scenarios of neutron stars, in particular the young neutron star in Cassiopeia A.
nucl-thastro-ph.SRPhys. Rev. C 94, 025802 (2016)·4 citations

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