Nuclear Theory·nucl-th

Monday·July 15, 2019

12 papers—8 primary·4 cross-listed

01
[Submitted on 11 Jul 2019]
Correlations between azimuthal anisotropy Fourier harmonics in PbPb collisions at $s_{_{NN}} = 2.76$ TeV in the HYDJET++ and AMPT models
M. Dordevic🇷🇸 · J. Milosevic🇷🇸 · L. Nadderd🇷🇸 · M. Stojanovic🇷🇸 · F. Wang🇺🇸 · X. Zhu🇨🇳
Correlations between azimuthal anisotropy Fourier harmonics $v_{n}$ ( $n = 2, 3, 4$ ) are studied using the events from PbPb collisions at $s_{_{NN}} = 2.76$ TeV generated by the HYDJET++ and AMPT models, and compared to the corresponding experimental results obtained by the ATLAS Collaboration. The Fourier harmonics $v_{n}$ are measured over a wide centrality range using the two-particle azimuthal correlation method. The slopes of the $v_{2}$ -- $v_{3}$ correlation from both models are in a good agreement with the ATLAS data. The HYDJET++ model predicts a stronger slope for the $v_{2}$ -- $v_{4}$ and $v_{3}$ -- $v_{4}$ correlations than the ones experimentally measured, while the results from the AMPT model are in a rather good agreement with the experimental results. In contrast to the HYDJET++ predictions, the AMPT model predicts a boomerang-like shape in the structure of the correlations as found in the experimental data.
Comments:
10 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1907.05450 [pdf]
PRC(2020)·7 citations
02
[Submitted on 11 Jul 2019]
On the Cottingham formula and the electromagnetic contribution to the proton-neutron mass splitting
Andre Walker-Loud🇺🇸
The excess mass of the neutron over the proton arises from two sources within the Standard Model, electromagnetism and the splitting of the down and up quark masses. The Cottingham Formula provides a means of determining the QED corrections from the forward Compton Amplitude, but this is challenged by the need for a subtraction function and the mixing of the QED and QCD (electro-weak) effects. I review the present understanding of the Cottingham Formula, including a discussion on the development of the formula, its renormalization which induces the mixing of QED and QCD effects, and the necessary modeling of the subtraction function that must be done to arrive a numerical prediction. I summarize the Regge Model originally proposed by Gasser and Leutwyler and I also review the proposed model by Walker-Loud, Carlson and Miller, which is an interpolation function between the low and high $Q^{2}$ regimes, both of which are anchored by rigorous theoretical underpinnings, for which I argue a more reliable theoretical uncertainty estimate can be obtained.
Comments:
The 9th International workshop on Chiral Dynamics
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1907.05459 [pdf]
PoS(2019)·10 citations
03
[Submitted on 11 Jul 2019]
Variational approximations to exact solutions in shell-model valence spaces: calcium isotopes in the pf-shell
B. Bally · A. Sánchez-Fernández · T. R. Rodríguez
We study the performance of self-consistent mean-field and beyond-mean-field approximations in shell-model valence spaces. In particular, Hartree-Fock-Bogolyubov, particle-number variation after projection and projected generator coordinate methods are applied to obtain ground-state and excitation energies for even-even and odd-even Calcium isotopes in the pf-shell. The standard (and non-trivial) KB3G nuclear effective interaction has been used. The comparison with the exact solutions -- provided by the full diagonalization of the Hamiltonian -- shows an outstanding agreement when particle-number and angular-momentum restorations are performed and both quadrupole and neutron-neutron pairing degrees of freedom are explicitly explored as collective coordinates.
Comments:
14 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.05493 [pdf]
PRC(2019)·37 citations
04
[Submitted on 12 Jul 2019]
Decoherence of collective motion in warm nuclei
S. Frauendorf🇺🇸 · C. M. Petrache🇫🇷 · R. Schwengner🇩🇪 · K.Wimmer🇯🇵
Collective states in cold nuclei are represented by a wave function that assigns coherent phases to the participating nucleons. The degree of coherence decreases with excitation energy above the yrast line because of coupling to the increasingly dense background of quasiparticle excitations. The consequences of decoherence are discussed, starting with the well studied case of rotational damping. In addition to superdeformed bands, a highly excited oblate band is presented as a new example of screening from rotational damping. Suppression of pair correlation leads to incoherent thermal M1 radiation, which appears as an exponential spike (LEMAR) at zero energy in the $γ$ strength function of spherical nuclei. In deformed nuclei a Scissors Resonance appears and LEMAR changes to damped magnetic rotation, which is interpreted as partial restoration of coherence.
Comments:
Proceedings of the conference on Nuclear structure and dynamics 2019
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.05569 [pdf]
EPJ Web Conf.(2019)·1 citation
05
[Submitted on 12 Jul 2019]
Post-formation in alpha emission from nuclei
Junki Tanaka · Carlos Bertulani · Stefan Typel
We propose a novel mechanism to explain nuclear decay by emission of an alpha particle. We show that the famous Geiger-Nuttall law can be explained by post-forming an alpha particle outside the range of the nuclear interaction with the daughter nucleus. This contrasts with the commonly accepted mechanism of first alpha particle pre-formation followed by emission through barrier penetration. We predict that the post-formation mechanism is more likely to occur for alpha-particles with higher energy.
Comments:
12 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.05574 [pdf]
EPJ Web Conf.(2020)·1 citation
06
[Submitted on 12 Jul 2019]
Origin of energy shift in kaonic atom and kaon-nucleus interaction
Yutaro Iizawa🇯🇵 · Daisuke Jido🇯🇵 · Natsumi Ikeno🇯🇵 · Junko Yamagata-Sekihara🇯🇵 · Satoru Hirenzaki🇯🇵
The $K^{-}$ -nucleus optical potential is revisited to investigate its global feature phenomenologically. It is a puzzle that the energy shift is found to be repulsive in all of the observed kaonic atom, although the $K^{-} N$ interaction is known to be so attractive as to form the $Λ (1405)$ resonance. To solve this puzzle, we examine the $K^{-}$ optical potential in the linear density approximation and determine the potential parameters of each kaonic atom so as to reproduce the observed energy shift and absorption width. We find two types of the potentials. One potential has a so large real part as to provide nuclear states with the same quantum number to the atomic state in the last orbit. The level repulsion between the atomic state and the nuclear states takes place due to their mixing, and it makes the atomic state shifted repulsively. The other type of the potential has a large imaginary part and the imaginary part works repulsively for atomic states. We find that only the latter solution reproduce a wide of the observed data, and thus is realized as a $K^{-}$ -nucleus potential for kaonic atom. In the linear nuclear density optical potential, the picture that the repulsive shifts in the atomic states stem from the existence of the nuclear states does not globally stand up. This implies that the $K^{-}$ -nucleus optical potential should have a large imaginary part. We examine some nonlinear density effects and find that the conclusion does not change. We also confirm that the conventionally known optical potentials are categorized into the latter type of the potential.
Comments:
12 pages, 16 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.05626 [pdf]
0 citations
07
[Submitted on 12 Jul 2019]
Deuteron wave function for Reid93 potential and polarization observables in elastic lepton-deuteron scattering
V.I. Zhaba🇺🇦
Elastic lepton-deuteron scattering was considered within the limit of zero lepton mass. The deuteron wave function in the coordinate representation for the Reid93 potential was applied to numerical calculations. The angular-momentum dependence of values spin correlation coefficients $C_{x z}^{(0)}$ , $C_{z z}^{(0)}$ and tensor asymmetries $A_{xx}^{(0)}$ , $A_{x z}^{(0)}$ , $A_{z z}^{(0)}$ have been evaluated in 3D format for Reid93 potential. These polarization observables are analyzed for different energies and scattering angles. Application of the obtained values allows better explanation and illustration of the laws of elastic lepton-deuteron scattering.
Comments:
14 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.05726 [pdf]
IJMPE(2019)·4 citations
08
[Submitted on 12 Jul 2019]
Symmetric nuclear matter from the strong interaction
M. Leonhardt🇩🇪 · M. Pospiech🇩🇪 · B. Schallmo🇩🇪 · J. Braun🇩🇪 · C. Drischler🇺🇸 · K. Hebeler🇩🇪 · A. Schwenk🇩🇪
We study the equation of state of symmetric nuclear matter at zero temperature over a wide range of densities using two complementary theoretical approaches. At low densities up to twice nuclear saturation density, we compute the energy per particle based on modern nucleon-nucleon and three-nucleon interactions derived within chiral effective field theory. For higher densities we derive for the first time constraints in a Fierz-complete setting directly based on quantum chromodynamics using functional renormalization group techniques. We find remarkable consistency of the results obtained from both approaches as they come together in density and the natural emergence of a maximum in the speed of sound $c_{S}$ at supranuclear densities with a value beyond the asymptotic $c_{S}^{2} = 1/3$ . The presence of a maximum appears tightly connected to the formation of a diquark gap.
Comments:
7 pages, 2 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.05814 [pdf]
PRL(2020)·135 citations
09
[Submitted on 11 Jul 2019] (cross-list from nucl-ex)
Experimental investigation of $α$ -condensation in light nuclei
Jack Bishop🇬🇧 · Tzany Kokalova🇬🇧 · Martin Freer🇬🇧 · L Acosta🇮🇹 · M Assie🇫🇷 · S Bailey🇬🇧 · G Cardella🇮🇹 · N Curtis🇬🇧 · E De Filippo🇮🇹 · D Dell'Aquila🇮🇹 · S De Luca🇮🇹 · L Francalanza🇮🇹 and 20 other authors
Method: To examine signatures of this alpha-condensation, a compound nucleus reaction using 160, 280, and 400 MeV 16O beams impinging on a carbon target was used to investigate the 12C(16O,7a) reaction. This permits a search for near-threshold states in the alpha-conjugate nuclei up to 24Mg. Results: Events up to an alpha-particle multiplicity of 7 were measured and the results were compared to both an Extended Hauser-Feshbach calculation and the Fermi break-up model. The measured multiplicity distribution exceeded that predicted from a sequential decay mechanism and had a better agreement with the multi-particle Fermi break-up model. Examination of how these 7 alpha final states could be reconstructed to form 8Be and 12C(0_2+) showed a quantitative difference in which decay modes were dominant compared to the Fermi break-up model. No new states were observed in 16O, 20Ne, and 24Mg due to the effect of the N-alpha penetrability suppressing the total alpha-particle dissociation decay mode. Conclusion: The reaction mechanism for a high energy compound nucleus reaction can only be described by a hybrid of sequential decay and multi-particle breakup. Highly alpha-clustered states were seen which did not originate from simple binary reaction processes. Direct investigations of near-threshold states in N-alpha systems are inherently impeded by the Coulomb barrier prohibiting the observation of states in the N-alpha decay channel. No evidence of a highly clustered 15.1 MeV state in 16O was observed from (28Si*,12C(0_2+))16O(0_6+) when reconstructing the Hoyle state from 3 alpha-particles. Therefore, no experimental signatures for alpha-condensation were observed.
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1907.05471 [pdf]
PRC(2019)·31 citations
10
[Submitted on 12 Jul 2019] (cross-list from hep-ph)
Predictions of $Υ (4 S) \to h_{b} (1 P, 2 P) π^{+} π^{-}$ transitions
Yun-Hua Chen🇨🇳
In this work, we study the contributions of the intermediate bottomoniumlike $Z_{b}$ states and the bottom meson loops in the heavy quark spin flip transitions $Υ (4 S) \to h_{b} (1 P, 2 P) π^{+} π^{-}$ . Depending on the constructive or destructive interferences between the $Z_{b}$ -exchange and the bottom meson loops mechanisms, we predict two possible branching ratios for each process: BR $_{Υ (4 S) \to h_{b} (1 P) π^{+} π^{-}} ≃ (1. 2_{- 0.4}^{+ 0.8} \times 1 0^{- 6})$ or $(0. 5_{- 0.2}^{+ 0.5} \times 1 0^{- 6})$ , and BR $_{Υ (4 S) \to h_{b} (2 P) π^{+} π^{-}} ≃ (7. 1_{- 1.1}^{+ 1.7} \times 1 0^{- 10})$ or $(2. 4_{- 0.1}^{+ 0.2} \times 1 0^{- 10})$ . The bottom meson loops contribution is found to be much larger than the $Z_{b}$ -exchange contribution in the $Υ (4 S) \to h_{b} (1 P) π π$ transitions, while it can not produce decay rates comparable to the heavy quark spin conserved $Υ (4 S) \to Υ (1 S, 2 S) π π$ processes. We also predict the branch fractions of $ψ (3 S, 4 S) \to h_{c} (1 P) π^{+} π^{-}$ contributed from the charm meson loops.
Comments:
17 pages, 4 figures; the direct gluon hadronization mechanism contribution within QCD multipole expansion discussed, the distributions of the $π π$ and $h_{b} π$ invariant mass spectra, and the angular distribution presented, the branch fractions of $ψ (3 S, 4 S) \to h_{c} (1 P) π^{+} π^{-}$ estimated, more discussions added; version to appear in CPC
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1907.05547 [pdf]
CPC(2020)·7 citations
11
[Submitted on 11 Jul 2019] (cross-list from hep-ph)
Particle Ratios within EPOS, UrQMD and Thermal Models at AGS, SPS and RHIC Energies
Mahmoud Hanafy (Benha U. and WLCAPP, Cairo)🇪🇬 · Abdel Nasser Tawfik (Nile U., ECTP and Johann Wolfgang Goethe-Universitat)🇪🇬 · Muhammad Maher (Helwan U. and WLCAPP, Cairo)🇪🇬 · Werner Scheinast (LHEP JINR, Dubna)🇷🇺
The particle ratios $k^{+} / π^{+}$ , $π^{-} / K^{-}$ , $p ˉ / π^{-}$ , $Λ/ π^{-}$ , $Ω/ π^{-}$ , $p / π^{+}$ , $π^{-} / π^{+}$ , $K^{-} / K^{+}$ , $p ˉ / p$ , $Λ ˉ /Λ$ , $Σ ˉ /Σ$ , $Ω ˉ /Ω$ measured at AGS, SPS and RHIC energies are compared with large statistical ensembles of $100, 000$ events deduced from the CRMC EPOS $1.99$ and the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) hybrid model. In the UrQMD hybrid model two types of phase transitions are taken into account. All these are then confronted to the Hadron Resonance Gas Model. The two types of phase transitions are apparently indistinguishable. Apart from $k^{+} / π^{+}$ , $k^{-} / π^{-}$ , $Ω/ π^{-}$ , $p ˉ / π^{+}$ , and $Ω ˉ /Ω$ , the UrQMD hybrid model agrees well with the CRMC EPOS $1.99$ . Also, we conclude that the CRMC EPOS $1.99$ seems to largely underestimate $k^{+} / π^{+}$ , $k^{-} / π^{-}$ , $Ω/ π^{-}$ , and $p ˉ / π^{+}$ .
Comments:
8 pages, 2 figures, submitted to JETP
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1907.05729 [pdf]
IJMPE(2021)·1 citation
12
[Submitted on 12 Jul 2019] (cross-list from hep-ph)
Compact star properties from an extended linear sigma model
János Takátsy🇭🇺 · Péter Kovács🇭🇺 · Zsolt Szép🇭🇺 · György Wolf🇭🇺
The equation of state provided by effective models of strongly interacting matter should comply with the restrictions imposed by current astrophysical observations of compact stars. Using the equation of state given by the (axial-)vector meson extended linear sigma model, we determine the mass-radius relation and study whether these restrictions are satisfied under the assumption that most of the star is filled with quark matter. We also compare the mass-radius sequence with those given by the equations of state of somewhat simpler models.
Comments:
11 pages, 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1907.05841 [pdf]
Universe(2019)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE