Nuclear Theory·nucl-th

Tuesday·July 14, 2015

5 papers—3 primary·2 cross-listed

01
[Submitted on 12 Jul 2015]
Symmetry potential of $Δ (1232)$ resonance and its effects on the $π^{-} / π^{+}$ ratio in heavy-ion collisions near the pion production threshold
Bao-An Li
Effects of the completely unknown symmetry (isovector) potential of the \D on the total and differential \rpi in heavy-ion collisions at beam energies from 100 to 1000 MeV/A are explored within an isospin-dependent transport model IBUU. The effects are found to be negligible at beam energies above the pion production threshold due to the very short lifetimes of less than 2 fm/c for $Δ$ resonances with masses around $m_{Δ} = 1232$ MeV, leaving the $π^{-} / π^{+}$ ratios of especially the energetic pions still a reliable probe of the high-density behavior of nuclear symmetry energy $E_{sy m} (ρ)$ . However, as the beam energy becomes deeply sub-threshold for pion production, effects of the $Δ$ symmetry potential becomes appreciable especially on the \rpi of low-energy pions from the decays of low-mass $Δ$ resonances which have lived long enough to be affected by their mean-field potentials, providing a useful tool to study the symmetry potential and spectroscopy of $Δ$ resonances in neutron-rich nuclear matter. Interestingly though, even at the deeply sub-threshold beam energies, the differential \rpi of energetic pions remains sensitive to the \esym at supra saturation densities with little influence from the uncertain symmetry potential of the $Δ$ resonance.
Comments:
Version to appear in PRC (2015)
Subjects:
Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Experiment (nucl-ex)
arXiv:
1507.03279 [pdf]
PRC(2015)·40 citations
02
[Submitted on 13 Jul 2015]
Beyond relativistic mean-field approach for nuclear octupole excitations
J. M. Yao🇯🇵 · E. F. Zhou🇨🇳 · Z. P. Li🇨🇳
We report the first beyond-mean-field study of low-lying parity-doublet states in 224Ra by extending the multireference relativistic energy density functional method to include dynamical correlations related to symmetry restoration and quadrupole-octupole shape fluctuation with a generator coordinate method combined with parity, particle-number, and angular-momentum projections. We clarify full microscopically that the origin of spin-dependent parity splitting in low-spin states is related to the octupole shape stabilization of positive-parity states, the dominated shapes of which drift gradually to that of negative-parity ones.
Comments:
5 pages, 4 figures, to be published as a Rapid Communication in PRC
Subjects:
Nuclear Theory (nucl-th); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1507.03298 [pdf]
PRC(2015)·65 citations
03
[Submitted on 13 Jul 2015]
Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions
G. Chen🇺🇸 · R. J. Fries🇺🇸 · J. I. Kapusta🇺🇸 · Y. Li🇺🇸
Nuclei colliding at very high energy create a strong, quasi-classical gluon field during the initial phase of their interaction. We present an analytic calculation of the initial space-time evolution of this field in the limit of very high energies using a formal recursive solution of the Yang-Mills equations. We provide analytic expressions for the initial chromo-electric and chromo-magnetic fields and for their energy-momentum tensor. In particular, we discuss event-averaged results for energy density and energy flow as well as for longitudinal and transverse pressure of this system. For example, we find that the ratio of longitudinal to transverse pressure very early in the system behaves as $p_{L} / p_{T} = - [1 - \frac{3}{2 a} (Q τ)^{2}] / [1 - \frac{1}{a} (Q τ)^{2}] + O (Q τ)^{4}$ where $τ$ is the longitudinal proper time, $Q$ is related to the saturation scales $Q_{s}$ of the two nuclei, and $a = ln (Q^{2} / m^^{2})$ with $m^$ a scale to be defined later. Our results are generally applicable if $τ ≲ 1/ Q$ . As already discussed in a previous paper, the transverse energy flow $S^{i}$ of the gluon field exhibits hydrodynamic-like contributions that follow transverse gradients of the energy density $\nabla^{i} ε$ . In addition, a rapidity-odd energy flow also emerges from the non-abelian analog of Gauss' Law and generates non-vanishing angular momentum of the field. We will discuss the space-time picture that emerges from our analysis and its implications for observables in heavy ion collisions.
Comments:
26 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1507.03524 [pdf]
PRC(2015)·85 citations
04
[Submitted on 13 Jul 2015] (cross-list from nucl-ex)
Beam-Energy Dependence of Charge Balance Functions from Au+Au Collisions at RHIC
STAR Collaboration
Balance functions have been measured in terms of relative pseudorapidity ( $Δ η$ ) for charged particle pairs at the Relativistic Heavy-Ion Collider (RHIC) from Au+Au collisions at $s_{NN}$ = 7.7 GeV to 200 GeV using the STAR detector. These results are compared with balance functions measured at the Large Hadron Collider (LHC) from Pb+Pb collisions at $s_{NN}$ = 2.76 TeV by the ALICE Collaboration. The width of the balance function decreases as the collisions become more central and as the beam energy is increased. In contrast, the widths of the balance functions calculated using shuffled events show little dependence on centrality or beam energy and are larger than the observed widths. Balance function widths calculated using events generated by UrQMD are wider than the measured widths in central collisions and show little centrality dependence. The measured widths of the balance functions in central collisions are consistent with the delayed hadronization of a deconfined quark gluon plasma (QGP). The narrowing of the balance function in central collisions at $s_{NN}$ = 7.7 GeV implies that a QGP is still being created at this relatively low energy.
Comments:
8 pages, 5 figures, submitted to Physical Review C
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1507.03539 [pdf]
PRC(2016)·31 citations
05
[Submitted on 13 Jul 2015] (cross-list from hep-lat)
Curvature of the chiral pseudo-critical line in QCD: continuum extrapolated results
Claudio Bonati🇮🇹 · Massimo D'Elia🇮🇹 · Marco Mariti🇮🇹 · Michele Mesiti🇮🇹 · Francesco Negro🇮🇹 · Francesco Sanfilippo🇬🇧
We determine the curvature of the pseudo-critical line of strong interactions by means of numerical simulations at imaginary chemical potentials. We consider $N_{f} = 2 + 1$ stout improved staggered fermions with physical quark masses and the tree level Symanzik gauge action, and explore four different sets of lattice spacings, corresponding to $N_{t} = 6, 8, 10, 12$ , in order to extrapolate results to the continuum limit. Our final estimate is $κ = 0.0135 (20)$ .
Comments:
11 pages, 10 figures, 4 tables. Version to appear in Physical Review D
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1507.03571 [pdf]
PRD(2015)·168 citations

Affiliations

first authorsco-authorsvia INSPIRE

Symmetry potential of Δ(1232) resonance and its effects on the π−/π+ ratio in heavy-ion collisions near the pion production threshold

Beyond relativistic mean-field approach for nuclear octupole excitations

Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions

Beam-Energy Dependence of Charge Balance Functions from Au+Au Collisions at RHIC

Curvature of the chiral pseudo-critical line in QCD: continuum extrapolated results

Affiliations

Symmetry potential of $Δ (1232)$ resonance and its effects on the $π^{-} / π^{+}$ ratio in heavy-ion collisions near the pion production threshold