Nuclear Theory·nucl-th

Thursday·November 5, 2015

9 papers—4 primary·5 cross-listed

01
[Submitted on 4 Nov 2015]
Fusion and quasi-fission dynamics in nearly-symmetric reactions
Ning Wang · Kai Zhao · Zhuxia Li
Some nearly-symmetric fusion reactions are systematically investigated with the improved quantum molecular dynamics (ImQMD) model. By introducing two-body inelastic scattering in the Fermi constraint procedure, the stability of an individual nucleus and the description of fusion cross sections at energies near the Coulomb barrier can be further improved. Simultaneously, the quasi-fission process in $^{154}$ Sm+ $^{160}$ Gd is also investigated with the microscopic dynamics model for the first time. We find that at energies above the Bass barrier, the fusion probability is smaller than $1 0^{- 5}$ for this reaction, and the nuclear contact-time is generally smaller than $1500$ fm/c. From the central collisions of Sm+Gd, the neutron-rich fragments such as $^{164, 165}$ Gd, $^{192}$ W can be produced in the ImQMD simulations, which implies that the quasi-fission reaction could be an alternative way to synthesize new neutron-rich heavy nuclei.
Comments:
11 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.01194 [pdf]
SCPMA(2015)·13 citations
02
[Submitted on 4 Nov 2015]
Quark and gluon distribution functions in a viscous quark-gluon plasma medium and dilepton production via $q q ˉ$ -- annihilation
Vinod Chandra🇮🇳 · V. Sreekanth🇮🇳
Viscous modifications to the thermal distributions of quark-antiquarks and gluons have been studied in a quasi-particle description of the quark-gluon-plasma medium created in relativistic heavy-ion collision experiments. The model is described in terms of quasi-partons that encode the hot QCD medium effects in their respective effective fugacities. Both shear and bulk viscosities have been taken in to account in the analysis and the modifications to thermal distributions have been obtained by modifying the the energy momentum tensor in view of the non-trivial dispersion relations for the gluons and quarks. The interactions encoded in the equation of state induce significant modifications to the thermal distributions. As an implication, dilepton production rate in the $q q ˉ$ annihilation process has been investigated. The equation of state is found to have significant impact on the dilepton production rate along with the viscosities.
Comments:
11 pages, 5 Figures, two column, version accepted in Phys. Rev. D (arXiv:1403.2245 has been superseded by this version)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.01208 [pdf]
PRD(2015)·16 citations
03
[Submitted on 4 Nov 2015]
Neutron $2 p$ and $1 f$ spin--orbit splittings in $^{40}$ Ca, $^{36}$ S, and $^{34}$ Si $N = 20$ isotones: tensor--induced and pure spin--orbit effects
M. Grasso🇫🇷 · M. Anguiano🇪🇸
Neutron $2 p$ and $1 f$ spin--orbit splittings were recently measured in the isotones $^{37}$ S and $^{35}$ Si by $(d, p)$ transfer reactions. Values were reported by using the major fragments of the states. An important reduction of the $p$ splitting was observed, from $^{37}$ S to $^{35}$ Si, associated to a strong modification of the spin--orbit potential in the central region of the nucleus $^{35}$ Si. We analyze $2 p$ and $1 f$ neutron spin--orbit splittings in the $N = 20$ isotones $^{40}$ Ca, $^{36}$ S, and $^{34}$ Si. We employ several Skyrme and Gogny interactions, to reliably isolate pure spin--orbit and tensor--induced contributions, within the mean--field approximation. We use interactions (i) without the tensor force; (ii) with the tensor force and with tensor parameters adjusted on top of existing parametrizations; (iii) with the tensor force and with tensor and spin--orbit parameters adjusted simultaneously on top of existing parametrizations. We predict in cases (ii) and (iii) a non negligible reduction of both $p$ and $f$ splittings, associated to neutron--proton tensor effects, from $^{40}$ Ca to $^{36}$ S. The two splittings are further decreased for the three types of interactions, going from $^{36}$ S to $^{34}$ Si. This reduction is produced by the spin--orbit force and is not affected by tensor--induced contributions. For both reductions, from $^{40}$ Ca to $^{36}$ S and from $^{36}$ S to $^{34}$ Si, we predict in all cases that the modification is more pronounced for $p$ than for $f$ splittings. The measurement of the centroids for neutron $2 p$ and $1 f$ states in the nuclei $^{36}$ S and $^{34}$ Si would be interesting to validate this prediction experimentally. We show the importance of using interactions of type (iii), because they provide $p$ and $f$ splittings in the nucleus $^{40}$ Ca which are in agreement with the corresponding experimental values.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.01265 [pdf]
PRC(2015)·11 citations
04
[Submitted on 4 Nov 2015]
On microscopic theory of radiative nuclear reaction characteristics
Sergei Kamerdzhiev · Oleg Achakovskiy · Alexander Avdeenkov · Stephane Goriely
A survey of some results in the modern microscopic theory of properties of nuclear reactions with gamma-rays is given. First of all, we discuss the impact of phonon coupling (PC) on the photon strength function (PSF) because it represents the most natural physical source of additional strength found for Sn isotopes in recent experiments that could not be explained within the stan- dard HFB+QRPA approach. The self-consistent version of the Extended Theory of Finite Fermi Systems in the Quasiparticle Time Blocking Approximation, or simply QTBA, is applied. It uses the HFB mean field and includes both the QRPA and PC effects on the basis of the SLy4 Skyrme force. With our microscopic E1 PSFs, the following properties have been calculated for many stable and unstable even-even semi-magic Sn and Ni isotopes as well as for double-magic 132Sn and 208Pb using the reaction codes EMPIRE and TALYS with several nuclear level density (NLD) models: 1) the neutron capture cross sections, 2) the corresponding neutron capture gamma spectra, 3) the av- erage radiative widths of neutron resonances. In all the properties considered, the PC contribution turned out to be significant, as compared with the standard QRPA one, and necessary to explain the available experimental data. The results with the phenomenological so-called generalized super- fluid NLD model turned out to be worse, on the whole, than those obtained with the microscopic HFB+combinatorial NLD model. Finally, we also discuss the modern microscopic NLD models based on the self-consistent HFB method and show their relevance to explain experimental data as compared with the phenomeno- logical models. The use of these self-consistent microscopic approaches is of particular relevance for nuclear astrophysics, but also for the study of double-magic nuclei.
Comments:
13 pages, 14 figures, a survey given as a plenary talk to the Intern. Conference "NUCLEUS 2015" (June 29 - July 3, 2015, Saint-Petersburg, Russia). To be published in Phys. Atom. Nucl
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1511.01301 [pdf]
Phys.Atom.Nucl.(2016)·2 citations
05
[Submitted on 4 Nov 2015] (cross-list from hep-ph)
Neutrino-induced meson productions
Satoshi X. Nakamura (Osaka University)🇯🇵
We develop a dynamical coupled-channels (DCC) model for neutrino-nucleon reactions in the resonance region, by extending the DCC model that we have previously developed through an analysis of $π N, γ N \to π N, η N, K Λ, K Σ$ reaction data for $W \leq 2.1$ GeV. We analyze electron-induced reaction data for both proton and neutron targets to determine the vector current form factors up to $Q^{2} \leq$ 3.0 (GeV/ $c$ ) $^{2}$ . Axial-current matrix elements are derived in accordance with the Partially Conserved Axial Current (PCAC) relation to the $π N$ interactions of the DCC model. As a result, we can uniquely determine the interference pattern between resonant and non-resonant amplitudes. Our calculated cross sections for neutrino-induced single-pion productions are compared with available data, and are found to be in reasonable agreement with the data. We also calculate the double-pion production cross sections in the resonance region, for the first time, with relevant resonance contributions and channel couplings. The result is compared with the double-pion production data. For a future development of a neutrino-nucleus reaction model and/or a neutrino event generator for analyses of neutrino experiments, the DCC model presented here can give a useful input.
Comments:
8 pages, 12 figures, Contribution to the proceedings of 10th International Workshop on the Physics of Excited Nucleons (NSTAR2015), May 25-28 2015, Osaka, Japan
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1511.01187 [pdf]
JPS Conf.Proc.(2016)·1 citation
06
[Submitted on 4 Nov 2015] (cross-list from hep-ph)
Compositeness of baryonic resonances: Applications to the Delta(1232), N(1535), and N(1650) resonances
Takayasu Sekihara (Osaka U., Res. Ctr. Nucl. Phys.)🇯🇵 · Takashi Arai (KEK, Tsukuba)🇯🇵 · Junko Yamagata-Sekihara (Nat. Inst. Tech., Oshima Coll.)🇯🇵 · Shigehiro Yasui (Tokyo Inst. Tech.)🇯🇵
We present a formulation of the compositeness for baryonic resonances in order to discuss the meson-baryon molecular structure inside the resonances. For this purpose, we derive a relation between the residue of the scattering amplitude at the resonance pole position and the two-body wave function of the resonance in a sophisticated way, and we define the compositeness as the norm of the two-body wave functions. As applications, we investigate the compositeness of the $Δ (1232)$ , $N (1535)$ , and $N (1650)$ resonances from precise $π N$ scattering amplitudes in a unitarized chiral framework with the interaction up to the next-to-leading order in chiral perturbation theory. The $π N$ compositeness for the $Δ (1232)$ resonance is evaluated in the $π N$ single-channel scattering, and we find that the $π N$ component inside $Δ (1232)$ in the present framework is nonnegligible, which supports the previous work. On the other hand, the compositeness for the $N (1535)$ and $N (1650)$ resonances is evaluated in a coupled-channels approach, resulting that the $π N$ , $η N$ , $K Λ$ and $K Σ$ components are negligible for these resonances.
Comments:
23 pages, 7 eps figures, version accepted for publication in PRC, discussions improved
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1511.01200 [pdf]
PRC(2016)·46 citations
07
[Submitted on 4 Nov 2015] (cross-list from physics.atom-ph)
Level-resolved quantum statistical theory of electron capture into many-electron compound resonances in highly charged ions
J. C. Berengut · C. Harabati · V. A. Dzuba · V. V. Flambaum · G. F. Gribakin
The strong mixing of many-electron basis states in excited atoms and ions with open $f$ shells results in very large numbers of complex, chaotic eigenstates that cannot be computed to any degree of accuracy. Describing the processes which involve such states requires the use of a statistical theory. Electron capture into these 'compound resonances' leads to electron-ion recombination rates that are orders of magnitude greater than those of direct, radiative recombination, and cannot be described by standard theories of dielectronic recombination. Previous statistical theories considered this as a two-electron capture process which populates a pair of single-particle orbitals, followed by 'spreading' of the two-electron states into chaotically mixed eigenstates. This method is similar to a configuration-average approach, as it neglects potentially important effects of spectator electrons and conservation of total angular momentum. In this work we develop a statistical theory which considers electron capture into 'doorway' states with definite angular momentum obtained by the configuration interaction method. We apply this approach to electron recombination with W $^{20 +}$ , considering 2 million doorway states. Despite strong effects from the spectator electrons, we find that the results of the earlier theories largely hold. Finally, we extract the fluorescence yield (the probability of photoemission and hence recombination) by comparison with experiment.
Comments:
11 pages, 5 figures
Subjects:
Atomic Physics (physics.atom-ph); Nuclear Theory (nucl-th)
arXiv:
1511.01221 [pdf]
PRA(2015)·2 citations
08
[Submitted on 4 Nov 2015] (cross-list from nucl-ex)
First measurement of several $β$ -delayed neutron emitting isotopes beyond N=126
R. Caballero-Folch · C. Domingo-Pardo · J. Agramunt · A. Algora · F. Ameil · A. Arcones · Y. Ayyad · J. Benlliure · I.N. Borzov · M. Bowry · F. Calvino · D. Cano-Ott and 53 other authors
The $β$ -delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with $β$ -decay half-lives for 20 isotopes of Au, Hg, Tl, Pb and Bi in the mass region N $≳$ 126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the $β$ -decay strength distribution. In doing so, it provides important constraints to global theoretical models currently used in $r$ -process nucleosynthesis.
Comments:
Submitted to Phys. Rev. Lett
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1511.01296 [pdf]
PRL(2016)·60 citations
09
[Submitted on 4 Nov 2015] (cross-list from hep-ph)
Glueball decay patterns in top-down holographic QCD
Frederic Brünner🇦🇹 · Denis Parganlija🇦🇹 · Anton Rebhan🇦🇹
We discuss our results on scalar glueball decay in the top-down holographic Witten-Sakai-Sugimoto model for low-energy QCD and compare with available experimental data, which appear to disfavor the glueball candidate $f_{0} (1500)$ but seem to be perfectly consistent with interpreting $f_{0} (1710)$ as a nearly unmixed glueball. The holographic model moreover makes definite predictions for future experiments.
Comments:
6 pages. To appear in the Proceedings of the EPS-HEP Conference 22-29 July 2015, Vienna, Austria
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1511.01391 [pdf]
PoS(2015)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE