Nuclear Theory·nucl-th

Wednesday·June 24, 2015

9 papers—5 primary·4 cross-listed

01
[Submitted on 22 Jun 2015]
Event shape sorting
Renata Kopecna🇨🇿 · Boris Tomasik🇨🇿
We propose a novel method for sorting events of multiparticle production according to the azimuthal anisotropy of their momentum distribution. Although the method is quite general, we advocate its use in analysis of ultra-relativistic heavy-ion collisions where large number of hadrons is produced. The advantage of our method is that it can automatically sort out samples of events with histograms that indicate similar distributions of hadrons. It takes into account the whole measured histograms with all orders of anisotropy instead of a specific observable (e.g. $v_{2}$ , $v_{3}$ , $q_{2}$ ). It can be used for more exclusive experimental studies of flow anisotropies which are then more easily compared to theoretical calculations. It may also be useful in the construction of mixed-events background for correlation studies as it allows to select events with similar momentum distribution.
Comments:
11 pages, 7 figures, to appear in European Physical Journal A, section added in v2 with analysis of AMPT-generated events
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Data Analysis, Statistics and Probability (physics.data-an)
arXiv:
1506.06776 [pdf]
EPJA(2016)·10 citations
02
[Submitted on 23 Jun 2015]
Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions
Jun Xu🇨🇳 · Bao-An Li🇺🇸 · Wen-Qing Shen🇨🇳 · Yin Xia🇨🇳
It is well known that non-central nuclear forces, such as the spin-orbital coupling and the tensor force, play important roles in understanding many interesting features of nuclear structures. However, their dynamical effects in nuclear reactions are poorly known since only the spin-averaged observables are normally studied both experimentally and theoretically. Realizing that spin-sensitive observables in nuclear reactions may carry useful information about the in-medium properties of non-central nuclear interactions, besides earlier studies using the time-dependent Hartree-Fock approach to understand effects of spin-orbital coupling on the threshold energy and spin polarization in fusion reactions, some efforts have been made recently to explore dynamical effects of non-central nuclear forces in intermediate-energy heavy-ion collisions using transport models. The focuses of these studies have been on investigating signatures of the density and isospin dependence of the form factor in the spin-dependent single-nucleon potential. Interestingly, some useful probes were identified in the model studies while so far there is still no data to compare with. In this brief review, we summarize the main physics motivations as well as the recent progress in understanding the spin dynamics and identifying spin-sensitive observables in heavy-ion reactions at intermediate energies. We hope the interesting, important, and new physics potentials identified in the spin dynamics of heavy-ion collisions will stimulate more experimental work in this direction.
Comments:
invited review, 13 pages, 16 figures, minor modifications and references added, to appear in Frontiers of Physics
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1506.06860 [pdf]
Front.Phys.(Beijing)(2015)·7 citations
03
[Submitted on 23 Jun 2015]
Shape evolution and collective dynamics of quasifission in TDHF
A.S. Umar · V.E. Oberacker · C. Simenel
Background: At energies near the Coulomb barrier, capture reactions in heavy-ion collisions result either in fusion or in quasifission. The former produces a compound nucleus in statistical equilibrium, while the second leads to a reseparation of the fragments after partial mass equilibration without formation of a compound nucleus. Extracting the compound nucleus formation probability is crucial to predict superheavy-element formation cross-sections. It requires a good knowledge of the fragment angular distribution which itself depends on quantities such as moments of inertia and excitation energies which have so far been somewhat arbitrary for the quasifission contribution. Methods: We investigate the evolution of the nuclear density in time-dependent Hartree-Fock (TDHF) calculations leading to quasifission. Our main goal is to extract ingredients of the formula used in the analysis of experimental angular distributions. These include the moment-of-inertia and temperature. We study the dependence of these quantities on various initial conditions of the reaction process. Results: The evolution of the moment of inertia is clearly non-trivial and depends strongly on the characteristics of the collision. The temperature rises quickly when the kinetic energy is transformed into internal excitation. Then, it rises slowly during mass transfer. Conclusions: Fully microscopic theories are useful to predict the complex evolution of quantities required in macroscopic models of quasifission.
Comments:
10 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.06880 [pdf]
PRC(2015)·80 citations
04
[Submitted on 23 Jun 2015]
Antinucleon-nucleus interaction near threshold from the Paris $N ˉ N$ potential
E. Friedman🇮🇱 · A. Gal🇮🇱 · B. Loiseau🇫🇷 · S. Wycech🇵🇱
A general algorithm for handling the energy dependence of hadron-nucleon amplitudes in the nuclear medium, consistently with their density dependence, has been recently applied to antikaons, eta mesons and pions interacting with nuclei. Here we apply this approach to antiprotons below threshold, analyzing experimental results for antiprotonic atoms across the periodic table. It is also applied to antiproton and antineutron interaction with nuclei up to 400 MeV/c, comparing with elastic scattering and annihilation cross sections. The underlying $p ˉ N$ scattering amplitudes are derived from the Paris $N ˉ N$ potential, including modifications in the medium. Emphasis is placed on the role of the $P$ -wave amplitudes with respect to the repulsive $S$ -wave amplitudes.
Comments:
24 pages, 2 tables, 10 figures submitted for publication. V2 matches submitted version. V3 accepted by NPA
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1506.06965 [pdf]
NPA(2015)·14 citations
05
[Submitted on 23 Jun 2015]
The concept of nuclear cluster forbiddenness
Huitzilin H. Yepez-Martinez · Peter Otto Hess
In nuclear cluster systems, a rigorous structural forbiddenness of virtual nuclear division into unexcited fragments is obtained. We re-analyze the concept of forbiddenness, introduced in Ref. 1 for the understanding of structural effects in nuclear cluster physics. We show that the concept is more involved than the one presented previously, where some errors were committed. Due to its importance, it is reanalyzed here. In the present contribution a simple way for the determination of forbiddenness is given, which may easily be extended to any number of clusters, though in this contribution we discuss only two-cluster systems, for illustrative reasons. A simple rule is obtained for the minimization of the forbiddenness, namely to start from a cluster system with a large SU(3) irrep (lambda,mu), but minimizing (lambda-mu), i.e. the system has to be oblate. The rule can be easily implemented in structural studies, done up to now with an oversimplified definition of forbiddenness. The new method is applied to various systems of light clusters and to some decay channels of 236U and 252Cf.
Comments:
15 pages, 2 figures, 4 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.06991 [pdf]
J.Phys.G(2015)·4 citations
06
[Submitted on 22 Jun 2015] (cross-list from hep-ph)
Cottingham formula and nucleon polarizabilities
J. Gasser🇨🇭 · M. Hoferichter🇨🇭 · H. Leutwyler🇨🇭 · A. Rusetsky🇩🇪
The difference between the electromagnetic self-energies of proton and neutron can be calculated with the Cottingham formula, which expresses the self-energies as an integral over the electroproduction cross sections---provided the nucleon matrix elements of the current commutator do not contain a fixed pole. We show that, under the same proviso, the subtraction function occurring in the dispersive representation of the virtual Compton forward scattering amplitude is determined by the cross sections. The representation in particular leads to a parameter-free sum rule for the nucleon polarizabilities. We evaluate the sum rule for the difference between the electric polarizabilities of proton and neutron by means of the available parameterizations of the data and compare the result with experiment.
Comments:
30 pages, 7 figures; The typos in Eqs. (10), (27), (56), (57), (63) and (B.46) are corrected. None of the results of the paper is affected
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1506.06747 [pdf]
EPJC(2015)·75 citations
07
[Submitted on 23 Jun 2015] (cross-list from hep-ph)
Effects of a $N^{*}$ resonance with hidden charm in the $π^{-} p \to D^{-} Σ_{c}^{+}$ reaction near threshold
E. J. Garzon🇨🇳 · Ju-Jun Xie🇨🇳
We study the effect of a hidden charm nuclear excited state $N_{c c ˉ}^{*}$ in the $π^{-} p \to D^{-} Σ_{c}^{+}$ reaction near threshold using an effective Lagrangian approach. We calculate the background contribution of the $t$ and $u$ channels by the $D^{* 0}$ vector meson exchange and $Σ_{c}^{++}$ intermediate state, respectively. We show that the consideration of a $N_{c c ˉ}^{*}$ resonance provides an enhancement of the total cross section close to the reaction threshold. We also evaluate the differential cross section for different energies and we study the angle dependence. It is expected that our model calculations will be tested in future experiments.
Comments:
Published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1506.06834 [pdf]
PRC(2015)·44 citations
08
[Submitted on 23 Jun 2015] (cross-list from cond-mat.quant-gas)
Quantum fluctuations in the BCS-BEC crossover of two-dimensional Fermi gases
Lianyi He🇺🇸 · Haifeng Lv🇨🇳 · Gaoqing Cao🇨🇳 · Hui Hu🇦🇺 · Xia-Ji Liu🇦🇺
We present a theoretical study of the ground state of the BCS-BEC crossover in dilute two-dimensional Fermi gases. While the mean-field theory provides a simple and analytical equation of state, the pressure is equal to that of a noninteracting Fermi gas in the entire BCS-BEC crossover, which is not consistent with the features of a weakly interacting Bose condensate in the BEC limit and a weakly interacting Fermi liquid in the BCS limit. The inadequacy of the 2D mean-field theory indicates that the quantum fluctuations are much more pronounced than those in 3D. In this work, we show that the inclusion of the Gaussian quantum fluctuations naturally recovers the above features in both the BEC and the BCS limits. In the BEC limit, the missing logarithmic dependence on the boson chemical potential is recovered by the quantum fluctuations. Near the quantum phase transition from the vacuum to the BEC phase, we compare our equation of state with the known grand canonical equation of state of 2D Bose gases and determine the ratio of the composite boson scattering length $a_{B}$ to the fermion scattering length $a_{2D}$ . We find $a_{B} ≃ 0.56 a_{2D}$ , in good agreement with the exact four-body calculation. We compare our equation of state in the BCS-BEC crossover with recent results from the quantum Monte Carlo simulations and the experimental measurements and find good agreements.
Comments:
Published version
Subjects:
Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con); Nuclear Theory (nucl-th)
arXiv:
1506.07156 [pdf]
PRA(2015)·29 citations
09
[Submitted on 23 Jun 2015] (cross-list from hep-ph)
Anisotropic matching principle for the hydrodynamics expansion
Leonardo Tinti🇵🇱
Following the recent success of anisotropic hydrodynamics we propose a new, general prescription for the hydrodynamics expansion around an anisotropic background. The anisotropic distribution is fixing exactly the complete energy-momentum tensor, just like the effective temperature is fixing the proper energy density in the ordinary expansion around local equilibrium. This means that momen- tum anisotropies are already included at the leading order, allowing for large pressure anisotropies without the need of a next to leading order treatment. The first moment of the Boltzmann equation (local four-momentum conservation) provides the time evolution of the proper energy density and the four velocity. Differently from previous prescriptions, the dynamic equations for the pressure corrections are not derived from the zeroth or second moment of the Boltzmann equation, but they are taken directly from the exact evolution given by the Boltzmann equation. We check the effec- tiveness of this new approach by matching with the exact solution of the Boltzmann equation in the Bjorken limit with the collisional kernel treated in relaxation time approximation, finding an unprecedented agreement.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1506.07164 [pdf]
PRC(2016)·65 citations

Affiliations

first authorsco-authorsvia INSPIRE