Nuclear Theory·nucl-th

Wednesday·October 7, 2015

13 papers—7 primary·6 cross-listed

01
[Submitted on 5 Oct 2015]
Liquid-gas phase transition in strange hadronic matter with relativistic models
James R. Torres🇧🇷 · Francesca Gulminelli🇫🇷 · Débora P. Menezes🇧🇷
Background: The advent of new dedicated experimental programs on hyperon physics is rapidly boosting the field, and the possibility of synthetizing multiple strange hypernuclei requires the addition of the strangeness degree of freedom to the models dedicated to nuclear structure and nuclear matter studies at low energy. Purpose: We want to settle the influence of strangeness on the nuclear liquid-gas phase transition. Because of the large uncertainties concerning the hyperon sector, we do not aim at a quantitative estimation of the phase diagram but rather at a qualitative description of the phenomenology, as model independent as possible. Method: We analyze the phase diagram of low density matter composed of neutrons, protons and $Λ$ hyperons using a Relativistic Mean Field (RMF) model. We largely explore the parameter space to pin down generic features of the phase transition, and compare the results to ab-initio quantum Monte Carlo calculations. Results: We show that the liquid-gas phase transition is only slightly quenched by the addition of hyperons. Strangeness is seen to be an order parameter of the phase transition, meaning that dilute strange matter is expected to be unstable with respect to the formation of hyper-clusters. Conclusions: More quantitative results within the RMF model need improved functionals at low density, possibly fitted to ab-initio calculations of nuclear and $Λ$ matter.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1510.01381 [pdf]
PRC(2016)·16 citations
02
[Submitted on 6 Oct 2015]
Theoretical study of the elastic breakup of weakly bound nuclei at near barrier energies
D. R. Otomar · P. R. S. Gomes · J. Lubian · L. F. Canto · M. S. Hussein
We have performed CDCC calculations for collisions of $^{7}$ Li projectiles on $^{59}$ Co, $^{144}$ Sm and $^{208}$ Pb targets at near-barrier energies, to assess the importance of the Coulomb and the nuclear couplings in the breakup of $^{7}$ Li, as well as the Coulomb-nuclear interference. We have also investigated scaling laws, expressing the dependence of the cross sections on the charge and the mass of the target. This work is complementary to the one previously reported by us on the breakup of $^{6}$ Li. Here we explore the similarities and differences between the results for the two Lithium isotopes. The relevance of the Coulomb dipole strength at low energy for the two-cluster projectile is investigated in details.
Comments:
6 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1510.01408 [pdf]
PRC(2015)·9 citations
03
[Submitted on 6 Oct 2015]
Thermalization of dense hadronic matter in Au + Au collisions at the energies available at FAIR
Somnath De🇮🇳 · Sudipan De🇧🇷 · Subhasis Chattopadhyay🇮🇳
The conditions of local thermodynamic equilibrium of baryons (non-strange, strange) and mesons (strange) are presented for central Au + Au collisions at FAIR energies using the microscopic transport model UrQMD. The net particle density, longitudinal-to-transverse pressure anisotropy and inverse slope parameters of the energy spectra of non-strange and strange hadrons are calculated inside a cell in the central region within rapidity window $∣ y ∣ < 1.0$ at different time steps after the collision. We observed that the strangeness content is dominated by baryons at all energies, however contribution from mesons become significant at higher energies. The time scale obtained from local pressure (momentum) isotropization and thermalization of energy spectra are nearly equal and found to decrease with increase in laboratory energy. The equilibrium thermodynamic properties of the system are obtained with statistical thermal model. The time evolution of the entropy densities at FAIR energies are found very similar with the ideal hydrodynamic behaviour at top RHIC energy.
Comments:
New figures, discussions added. To appear in Physical Review C
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1510.01456 [pdf]
PRC(2016)·8 citations
04
[Submitted on 6 Oct 2015]
Proton-Neutron Pairs in Heavy Deformed Nuclei
Dennis Bonatsos · I.E. Assimakis · Andriana Martinou
The microscopic justification of the emergence of SU(3) symmetry in heavy nuclei remains an interesting problem. In the past, the pseudo-SU(3) approach has been used, with considerable success. Recent results seem to suggest that the key for understanding the emergence of SU(3) symmetry lies in the properties of the proton-neutron interaction, namely in the formation of (S=1, T=0) p-n pairs in heavy nuclei, especially when the numbers of valence protons and valence neutrons are nearly equal. Although this idea has been around for many years, since the introduction of the Federman-Pittel mechanism, it is only recently that information about the p-n interaction could be obtained from nuclear masses, which become available from modern facilities. Based on this information, a new coupling scheme for heavy deformed nuclei has been suggested and is under development.
Comments:
12 pages, 3 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1510.01473 [pdf]
Bulg.J.Phys.(2015)·4 citations
05
[Submitted on 6 Oct 2015]
Hard Probes: After the dust has settled!
Abhijit Majumder🇺🇸
A lot has been learnt in the 15 years since the first data on jet modification at the Relativistic Heavy Ion Collider (RHIC). These proceedings will describe the portion of the theory that is unassailable, and attempt to chart a course for the next period of precision measurements and related calculations. In particular, we will focus on the emerging series of higher order calculations, which may reveal the scale, energy and temperature dependence of jet transport coefficients, as well as develop ingredients for a future NLO calculation of jet modification. Connections with the underlying degrees of freedom in the Quark Gluon Plasma (QGP) will be explored. We will discuss the challenges faced by Monte-Carlo event generators and their comparison with a broad spectrum of jet modification data. First principles calculations of transport coefficients, and the determination of new transport coefficients which encapsulate the transition of energy momentum from the jet scale to the medium scale will also be discussed.
Comments:
6 pages, 2 figures, Plenary talk at Hard Probes 2015 conference
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1510.01581 [pdf]
Nucl.Part.Phys.Proc.(2016)·5 citations
06
[Submitted on 1 Oct 2015]
The effect of tensor interaction in splitting the energy levels of relativistic systems
Mohammad Reza Shojaei · Mohsen Mousavi
In this paper we solve analytically Dirac equation for Eckart plus Hulthen potentials with Coulomb-like and Yukawa-like tensor interaction in the presence of Spin and Pseudo-spin Symmetry for any k number. The Parametric Nikiforov-Uvarov method is used to obtain the energy Eigen-values and wave functions. We also discuss the energy Eigen-values and the Dirac spinors for the Eckart plus Hulthen potentials for the spin and pseudo-spin symmetry with PNU method. To show the accuracy of the present model, some numerical results are shown in both pseudo-spin and spin symmetry limits.
Comments:
19 Pages, 13 Figures,6 Table
Subjects:
Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
1510.01636 [pdf]
Adv.High Energy Phys.(2016)·9 citations
07
[Submitted on 6 Oct 2015]
Microscopic description of fission in neutron-rich Radium isotopes with the Gogny energy density functional
R.R. Rodriguez-Guzman · L.M. Robledo
Mean field calculations, based on the D1S, D1N and D1M parametrizations of the Gogny energy density functional, have been carried out to obtain the potential energy surfaces relevant to fission in several Ra isotopes with the neutron number 144 $\leq$ N $\leq$ 176. Inner and outer barrier heights as well as first and second isomer excitation energies are given. The existence of a well developed third minimum along the fission paths of Ra nuclei, is analyzed in terms of the energetics of the "fragments" defining such elongated configuration. The masses and charges of the fission fragments are studied as functions of the neutron number in the parent Ra isotope. The comparison between fission and $α$ -decay half-lives, reveals that the former becomes faster for increasing neutron numbers. Though there exists a strong variance of the results with respect to the parameters used in the computation of the spontaneous fission rate, a change in tendency is observed at N=164 with a steady increase that makes heavier neutron-rich Ra isotopes stable against fission, diminishing the importance of fission recycling in the r-process.
Comments:
12 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1510.01652 [pdf]
EPJA(2016)·14 citations
08
[Submitted on 16 Jul 2015] (cross-list from quant-ph)
High-precision evaluation of Wigner's d-matrix by exact diagonalization
X. M. Feng · P. Wang🇨🇳 · W. Yang🇨🇳 · G. R. Jin
The precise calculations of the Wigner's d-matrix are important in various research fields. Due to the presence of large numbers, direct calculations of the matrix using the Wigner's formula suffer from loss of precision. We present a simple method to avoid this problem by expanding the d-matrix into a complex Fourier series and calculate the Fourier coefficients by exactly diagonalizing the angular-momentum operator $J_{y}$ in the eigenbasis of $J_{z}$ . This method allows us to compute the d-matrix and its various derivatives for spins up to a few thousand. The precision of the d-matrix from our method is about $1 0^{- 14}$ for spins up to $100$ .
Comments:
4 pages, 3 figures; a Fortran90 code is included; resubmitted to Phys. Rev. E
Subjects:
Quantum Physics (quant-ph); Mathematical Physics (math-ph); math.MP (math.MP); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph); Computational Physics (physics.comp-ph)
arXiv:
1507.04535 [pdf]
PRE(2015)·15 citations
09
[Submitted on 2 Oct 2015] (cross-list from cond-mat.mes-hall)
Fluctuation Phenomena in Chaotic Dirac Quantum Dots: Artificial Atoms on Graphene Flakes
J. G. G. S. Ramos · M. S. Hussein · A. L. R. Barbosa
We develop the stub model for the Dirac Quantum Dot, an electron confining device on a grapheme surface. Analytical results for the average conductance and the correlation functions are obtained and found in agreement with those found previously using semiclassical calculation. Comparison with available data are presented. The results reported here demonstrate the applicability of Random Matrix Theory in the case of Dirac electrons confined in a stadium.
Comments:
9 pages, 4 figures
Subjects:
Mesoscale and Nanoscale Physics (cond-mat.mes-hall); cond-mat.dis-nn (cond-mat.dis-nn); Nuclear Theory (nucl-th)
arXiv:
1510.00750 [pdf]
PRB(2016)·7 citations
10
[Submitted on 5 Oct 2015] (cross-list from hep-ph)
Status of Chiral-Scale Perturbation Theory
R.J. Crewther🇦🇺 · Lewis C. Tunstall🇨🇭
Chiral-scale perturbation theory $χ$ PT $_{σ}$ has been proposed as an alternative to chiral $S U (3)_{L} \times S U (3)_{R}$ perturbation theory which explains the $Δ I = 1/2$ rule for kaon decays. It is based on a low-energy expansion about an infrared fixed point in three-flavor QCD. In $χ$ PT $_{σ}$ , quark condensation $⟨ q ˉ q ⟩_{vac} \neq = 0$ induces nine Nambu-Goldstone bosons: $π, K, η$ and a QCD dilaton $σ$ which we identify with the $f_{0} (500)$ resonance. Partial conservation of the dilatation and chiral currents constrains low-energy constants which enter the effective Lagrangian of $χ$ PT $_{σ}$ . These constraints allow us to obtain new phenomenological bounds on the dilaton decay constant via the coupling of $σ / f_{0}$ to pions, whose value is known precisely from dispersive analyses of $π π$ scattering. Improved predictions for $σ \to γ γ$ and the $σ N N$ coupling are also noted. To test $χ$ PT $_{σ}$ for kaon decays, we revive a 1985 proposal for lattice methods to be applied to $K \to π$ on-shell.
Comments:
10 pages, 1 figure. Presented at the 8th International Workshop on Chiral Dynamics, 29 June 2015 - 03 July 2015, Pisa, Italy. Revision: references and comment added
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1510.01322 [pdf]
PoS(2015)·24 citations
11
[Submitted on 6 Oct 2015] (cross-list from nucl-ex)
Mass measurement of 56Sc reveals a small A=56 odd-even mass staggering, implying a cooler accreted neutron star crust
Z. Meisel🇺🇸 · S. George🇺🇸 · S. Ahn🇺🇸 · D. Bazin🇺🇸 · B.A. Brown🇺🇸 · J. Browne🇺🇸 · J.F. Carpino🇺🇸 · H. Chung🇺🇸 · A.L. Cole🇺🇸 · R.H. Cyburt🇺🇸 · A. Estradé🇬🇧 · M. Famiano🇺🇸 and 20 other authors
We present the mass excesses of 52-57Sc, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of 56Sc and 57Sc were determined for the first time with atomic mass excesses of -24.85(59)(+0 -54) MeV and -21.0(1.3) MeV, respectively, where the asymmetric uncertainty for 56Sc was included due to possible contamination from a long-lived isomer. The 56Sc mass indicates a small odd-even mass staggering in the A = 56 mass-chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of 56Sc, our results strongly reduce uncertainties in model calculations of the heating and cooling at the 56Ti electron-capture layer in the outer crust of accreting neutron stars. We found that, in contrast to previous studies, neither strong neutrino cooling nor strong heating occurs in this layer. We conclude that Urca cooling in the outer crusts of accreting neutron stars that exhibit superbursts or high temperature steady-state burning, which are predicted to be rich in A=56 nuclei, is considerably weaker than predicted. Urca cooling must instead be dominated by electron capture on the small amounts of adjacent odd-A nuclei contained in the superburst and high temperature steady-state burning ashes. This may explain the absence of strong crust Urca cooling inferred from the observed cooling light curve of the transiently accreting x-ray source MAXI J0556-332.
Comments:
Accepted to Physical Review Letters
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1510.01510 [pdf]
PRL(2015)·31 citations
12
[Submitted on 6 Oct 2015] (cross-list from hep-ph)
Diffractive $ρ$ production at small $x$ in future Electron - Ion Colliders
V. P. Goncalves🇸🇪 · F. S. Navarra🇧🇷 · D. Spiering🇧🇷
The future Electron - Ion ( $e A$ ) Collider is expected to probe the high energy regime of the QCD dynamics, with the exclusive vector meson production cross section being one of the most promising observables. In this paper we complement previous studies of exclusive processes presenting a comprehensive analysis of diffractive $ρ$ production at small $x$ . We compute the coherent and incoherent cross sections taking into account non-linear QCD dynamical effects and considering different models for the dipole - proton scattering amplitude and for the vector meson wave function. The dependence of these cross sections with the energy, photon virtuality, nuclear mass number and squared momentum transfer is analysed in detail. Moreover, we compare the non-linear predictions with those obtained in the linear regime. Finally, we also estimate the exclusive photon, $J /Ψ$ and $ϕ$ production and compare with the results obtained for $ρ$ production. Our results demonstrate that the analysis of diffractive $ρ$ production in future electron - ion colliders will be important to understand the non-linear QCD dynamics.
Comments:
12 pages, 8 figures, 1 table. Enlarged and revised version to be published in the Journal of Physics G. arXiv admin note: text overlap with arXiv:1503.00647
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1510.01512 [pdf]
J.Phys.G(2016)·13 citations
13
[Submitted on 6 Oct 2015] (cross-list from nucl-ex)
Strangeness Photoproduction on Quasifree Neutrons
Dominik Werthmüller🇬🇧
Strangeness photoproduction in the elementary reactions $γ N \to K Y$ offers the possibility to study nucleon resonances in the mass region above 1.7 GeV, where the number of states and their properties are still under debate. These reactions could allow the first 'complete' experiment in pseudoscalar meson photoproduction due to the easier access to recoil polarization observables in experiments. In addition to measurements on proton targets, a full isospin decomposition of the $I = 1/2$ electromagnetic amplitudes requires also data obtained from quasifree neutron targets. This contribution shows first preliminary results on feasibility studies for such measurements at the A2 experiment at MAMI.
Comments:
Contribution to the proceedings of the 10th International Workshop on the Physics of Excited Nucleons - NSTAR2015, 25-28 May 2015, Osaka, Japan, to be published in JPS conference proceedings
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1510.01660 [pdf]
JPS Conf.Proc.(2016)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE