Nuclear Theory·nucl-th

Monday·December 14, 2020

6 papers—3 primary·3 cross-listed

01
[Submitted on 11 Dec 2020]
Fire streaks, electromagnetic effects, directed flow and lifetime of the plasma at SPS energies
Vitalii Ozvenchuk🇵🇱 · Antoni Szczurek🇵🇱 · Andrzej Rybicki🇵🇱
We present our calculation of electromagnetic effects, induced by the spectator charge on Feynman- $x_{F}$ distributions of charged pions in peripheral $P b + P b$ collisions at CERN SPS energies, including realistic initial space-time-momentum conditions for pion emission. The calculation is performed in the framework of a specific implementation of the fire-streak model, adopted to the production of both $π^{-}$ and $π^{+}$ mesons. Isospin effects are included to take into account the asymmetry in production of $π^{+}$ and $π^{-}$ at high rapidity. A comparison to a simplified model from the literature is made. We obtain a good description of the NA49 data on the $x_{F}$ - and $p_{T}$ -dependence of the ratio of cross sections $π^{+} / π^{-}$ . The experimental data favors short times ( $0.5 < τ < 2$ ~fm/ $c$ ) for fast pion creation in the local fire-streak rest frame. The possibility of the expansion of the spectators is considered in our calculation, and its influence on the electromagnetic effect observed for the $π^{+} / π^{-}$ ratio is discussed. The influence of directed and elliptic flow, and vorticity on the observed effect is also estimated. We conclude that the fire-streak model, which properly describes the centrality dependence of $π^{-}$ rapidity spectra at CERN SPS energies, also provides realistic initial conditions for pion production. Consequently, it provides a quantitative description of the electromagnetic effect on the $π^{+} / π^{-}$ ratio as a function of $x_{F}$ .
Comments:
6 pages, 4 figures. arXiv admin note: substantial text overlap with arXiv:1910.04544
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2012.06243 [pdf]
PoS(2021)·1 citation
02
[Submitted on 11 Dec 2020]
Vector meson mass in the chiral symmetry restored vacuum
Jisu Kim🇰🇷 · Su Houng Lee🇰🇷
We calculate the mass of the vector meson in the chiral symmetry restored vacuum. This is accomplished by separating the four quark operators appearing in the vector and axial vector meson sum rules into chiral symmetric and symmetry breaking parts depending on the contribution of the fermion zero modes. We then identify each part from the fit to the vector and axial vector meson masses. By taking the chiral symmetry breaking part to be zero while keeping the symmetric operator to the vacuum value, we find that the chiral symmetric part of the vector and axial vector meson mass to be between 550 and 600 MeV. This demonstrates that chiral symmetry breaking, while responsible for the mass difference between chiral partner, accounts only for a small fraction of the symmetric part of the mass.
Comments:
5 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2012.06463 [pdf]
PRD(2021)·19 citations
03
[Submitted on 11 Dec 2020]
Microscopic origin of reflection-asymmetric nuclear shapes
Mengzhi Chen · Tong Li · Jacek Dobaczewski · Witold Nazarewicz
Background: The presence of nuclear ground states with stable reflection-asymmetric shapes is supported by rich experimental evidence. Theoretical surveys of odd-multipolarity deformations predict the existence of pear-shaped isotopes in several fairly localized regions of the nuclear landscape in the vicinity of near-lying single-particle shells with $Δ ℓ = Δ j = 3$ . Purpose: We analyze the role of isoscalar, isovector, neutron-proton, neutron-neutron, and proton-proton multipole interaction energies in inducing the onset of reflection-asymmetric ground-state deformations. Methods: The calculations are performed in the framework of axial reflection-asymmetric Hartree-Fock-Bogoliubov theory using two Skyrme energy density functionals and density-dependent pairing force. Results: We show that reflection-asymmetric ground-state shapes of atomic nuclei are driven by the odd-multipolarity neutron-proton (or isoscalar) part of the nuclear interaction energy. This result is consistent with the particle-vibration picture, in which the main driver of octupole instability is the isoscalar octupole-octupole interaction giving rise to large $E 3$ polarizability.
Comments:
11 pages, 12 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2012.06500 [pdf]
PRC(2021)·24 citations

Affiliations

first authorsco-authorsvia INSPIRE

Fire streaks, electromagnetic effects, directed flow and lifetime of the plasma at SPS energies

Vector meson mass in the chiral symmetry restored vacuum

Microscopic origin of reflection-asymmetric nuclear shapes

Affiliations