Nuclear Theory·nucl-th

Wednesday·June 19, 2019

7 papers—5 primary·2 cross-listed

01
[Submitted on 17 Jun 2019]
Frame dependence of transition form factors in light-front dynamics
Meijian Li🇺🇸 · Yang Li🇺🇸 · Pieter Maris🇺🇸 · James P. Vary🇺🇸
We calculate the transition form factor between vector and pseudoscalar quarkonia in both the timelike and the spacelike region using light-front dynamics. We investigate the frame dependence of the form factors for heavy quarkonia with light-front wavefunctions calculated from the valence Fock sector. This dependence could serve as a measure for the Lorentz symmetry violation arising from the Fock-space truncation. We suggest using frames with minimal longitudinal momentum transfer for calculations in the valence Fock sector, namely the Drell-Yan frame for the space-like region and a specific longitudinal frame for the timelike region; at $q^{2} = 0$ these two frames give the same result. We also use the transition form factor in the timelike region to investigate the electromagnetic Dalitz decay $ψ_{A} \to ψ_{B} l^{+} l^{-}$ ( $l = e, μ$ ) and predict the effective mass spectrum of the lepton pair.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1906.07306 [pdf]
PRD(2019)·17 citations
02
[Submitted on 18 Jun 2019]
Prediction of possible exotic states in the $η K ˉ K^{*}$ system
Xu Zhang🇨🇳 · Ju-Jun Xie🇨🇳
We investigate the $η K ˉ K^{*}$ three body system in order to look for possible $I^{G} (J^{P C}) = 0^{+} (1^{-+})$ exotic states in the framework of the fixed center approximation to the Faddeev equation. We assume the scattering of $η$ on a clusterized system $K ˉ K^{*}$ , which is known to generate the $f_{1} (1285)$ , or a $K ˉ$ on a clusterized system $η K^{*}$ , which is shown to generate the $K_{1} (1270)$ . In the case of the $η$ - $(K ˉ K^{*})_{f_{1} (1285)}$ scattering, we find evidence of a bound state $I^{G} (J^{P C}) = 0^{+} (1^{-+})$ below the $η f_{1} (1285)$ threshold with mass around 1700 MeV and width about 180 MeV. Considering the $K ˉ$ - $(η K^{*})_{K_{1} (1270)}$ scattering, we obtain a bound state $I (J^{P}) = 0 (1^{-})$ just below the $K ˉ K_{1} (1270)$ threshold with a mass around 1680 MeV and a width about 160 MeV.
Comments:
7 pages, 8 figures, published version
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1906.07340 [pdf]
CPC(2020)·16 citations
03
[Submitted on 18 Jun 2019]
Limits on assigning a shape to a nucleus
Alfredo Poves🇪🇸 · Frederic Nowacki🇫🇷 · Yoram Alhassid🇺🇸
The interpretation of nuclear observables in the laboratory frame in terms of the intrinsic deformation parameters beta and gamma is a classical theme in nuclear structure. Here we use the quadrupole invariants (Kumar), calculated within the framework of the configuration-interaction shell model, to clarify the meaning and limitations of nuclear shapes. We introduce a novel method that enables us to calculate accurately higher-order invariants and, therefore, the fluctuations in both beta and gamma. We find that the shape parameter beta often has a non-negligible degree of softness, and that the angle gamma is usually characterized by large fluctuations, rendering its effective value not meaningful. Contrary to common belief, we conclude that doubly magic nuclei are not spherical because the notion of a well-defined shape does not apply to them.
Comments:
Accepted in Physical Review C. Title changed. Added sections on triaxiality and sphericity
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1906.07542 [pdf]
PRC(2020)·55 citations
04
[Submitted on 18 Jun 2019]
Deformed shell effects in $^{48}$ Ca+ $^{249}$ Bk quasifission fragments
K. Godbey · A.S. Umar · C. Simenel
Background: Quasifission is the main reaction channel hindering the formation of superheavy nuclei (SHN). Its understanding will help to optimize entrance channels for SHN studies. Quasifission also provides a probe to understand the influence of shell effects in the formation of the fragments. Purpose: Investigate the role of shell effects in quasifission and their interplay with the orientation of the deformed target in the entrance channel. Methods: $^{48}$ Ca $+^{249}$ Bk collisions are studied with the time-dependent Hartree-Fock approach for a range of angular momenta and orientations. Results: Unlike similar reactions with a $^{238}$ U target, no significant shell effects which could be attributed to $^{208}$ Pb "doubly-magic" nucleus are found. However, the octupole deformed shell gap at $N = 56$ seems to strongly influence quasifission in the most central collisions. Conclusions: Shell effects similar to those observed in fission affect the formation of quasifission fragments. Mass-angle correlations could be used to experimentally isolate the fragments influenced by $N = 56$ octupole shell gaps.
Comments:
12 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1906.07623 [pdf]
PRC(2019)·55 citations
05
[Submitted on 18 Jun 2019]
Sensitivity of one-neutron knockout to the nuclear structure of halo nuclei
Chloë Hebborn · Pierre Capel
Background: Information about the structure of halo nuclei are often inferred from one-neutron knockout reactions. Typically the parallel-momentum distribution of the remaining core is measured after a high-energy collision of the exotic projectile with a light target. Purpose: We study how the structure of halo nuclei affects knockout observables considering an eikonal model of reaction. Method: To evaluate the sensitivity of both the diffractive and stripping parallel-momentum distributions to the structure of halo nuclei, we consider several descriptions of the projectile within a halo effective field theory. We consider the case of 11Be, the archetypical one-neutron halo nucleus, impinging on 12C at 68 MeV/nucleon, which are usual experimental conditions for such measurements. The low-energy constants of the description of 11Be are fitted to experimental data as well as to predictions of an ab initio nuclear-structure model. Results: One-neutron knockout reaction is confirmed to be purely peripheral, the parallel-momentum distribution of the remaining core is only sensitive to the asymptotics of the ground-state wavefunction and not to its norm. The presence of an excited state in the projectile spectrum reduces the amplitude of the breakup cross section; the corresponding probability flux is transferred to the inelastic-scattering channel. Although the presence of a resonance in the core-neutron continuum significantly affects the energy distribution, it has no impact on the parallel-momentum distribution. Conclusions: One-neutron knockout cross section can be used to infer information about the tail of the ground-state wavefunction, viz. its asymptotic normalization coefficient (ANC). The independence of the parallel-momentum distribution on the continuum description makes the extraction of the ANC from this observable very reliable.
Comments:
10 pages, 4 figures, 4 tables. Accepted for publication in Phys. Rev. C. Compared to the first version, two tests in Sec. IIIC are removed and an appendix is added
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1906.07660 [pdf]
PRC(2019)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE

Frame dependence of transition form factors in light-front dynamics

Prediction of possible exotic states in the ηKˉK∗ system

Limits on assigning a shape to a nucleus

Deformed shell effects in 48Ca+249Bk quasifission fragments

Sensitivity of one-neutron knockout to the nuclear structure of halo nuclei

Affiliations

Prediction of possible exotic states in the $η K ˉ K^{*}$ system

Deformed shell effects in $^{48}$ Ca+ $^{249}$ Bk quasifission fragments