Nuclear Theory·nucl-th

Tuesday·August 16, 2016

14 papers—4 primary·10 cross-listed

01
[Submitted on 14 Aug 2016]
Extracting temperature and transverse flow by fitting transverse mass spectra and HBT radii together
Ronghua He🇨🇳 · Jing Qian🇨🇳 · Jianyi Chen🇨🇳 · Qingxin Wu🇨🇳 · Lei Huo🇨🇳
Single particle transverse mass spectra and HBT radii of identical pion and identical kaon are analyzed with a blast-wave parametrization under the assumptions local thermal equilibrium and transverse expansion. Under the assumptions, temperature parameter $T$ and transverse expansion rapidity $ρ$ are sensitive to the shapes of transverse mass $m_{T}$ spectrum and HBT radius $R_{s} (K_{T})$ . Negative and positive correlations between $T$ and $ρ$ are observed by fitting $m_{T}$ spectrum and HBT radius $R_{s} (K_{T})$ , respectively. For a Monte Carlo simulation using the blast-wave function, $T$ and $ρ$ are extracted by fitting $m_{T}$ spectra and HBT radii together utilizing a combined optimization function $χ^{2}$ . With this method, $T$ and $ρ$ of the Monte Carlo sources can be extracted. Using this method for A Multi-Phase Transport model (AMPT) at RHIC energy, the differences of $T$ and $ρ$ between pion and kaon are observed obviously, and the tendencies of $T$ and $ρ$ vs collision energy $s_{NN}$ are similar with the results extracted directly from the AMPT model.
Comments:
14 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1608.04068 [pdf]
Mod.Phys.Lett.A(2017)·0 citations
02
[Submitted on 15 Aug 2016]
Role of ( $α$ ,n) reactions under $r$ -process conditions in neutrino-driven winds revisited
Peter Mohr
Background: The astrophysical $r$ -process occurs in an explosive astrophysical event under extremely neutron-rich conditions, leading to (n, $γ$ )-( $γ$ ,n) equilibrium along isotopic chains which peaks around neutron separation energies of a few MeV. Nuclei with larger $Z$ are usually produced by $β^{-}$ -decay, but under certain conditions also $α$ -induced reactions may become relevant for the production of nuclei with $Z + 2$ . Purpose: The uncertainties of the reaction rates of these $α$ -induced reactions are discussed within the statistical model. As an example, $α$ -induced ( $α$ ,n) and $(α$ , $x$ n) reaction cross sections for the neutron-rich $^{86}$ Se nucleus are studied in detail. Method: In a first step, the relevance of ( $α$ ,n) and $(α$ , $x$ n) reactions is analyzed. Next the uncertainties are determined from a variation of the $α$ -nucleus potential which is the all-dominant parameter for the astrophysical $Z \to Z + 2$ reaction rate. Results: It is found that the $r$ -process flow towards nuclei with larger $Z$ is essentially influenced only by the $α$ -nucleus potential whereas the other ingredients of the statistical model play a very minor role. This finding is based on the fact that the flow towards larger $Z$ depends on the sum over all ( $α$ , $x$ n) cross sections which is practically identical to the total $α$ -induced reaction cross section. Conclusions: $α$ -nucleus potentials play an important role under certain $r$ -process conditions because the flow towards larger $Z$ depends sensitively on the total $α$ -induced reaction cross section. The uncertainty of the reaction rate is about a factor of two to three at higher temperatures and exceeds one order of magnitude at very low temperatures.
Comments:
7 pages, 3 figures, Phys. Rev. C, accepted for publication
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1608.04277 [pdf]
PRC(2016)·28 citations
03
[Submitted on 15 Aug 2016]
Hydrodynamic modeling of a pure-glue initial scenario in high-energy hadron and heavy-ion collisions
V. Vovchenko🇩🇪 · Long-Gang Pang🇩🇪 · H. Niemi🇩🇪 · Iu. A. Karpenko🇺🇦 · M. I. Gorenstein🇺🇦 · L. M. Satarov🇩🇪 · I. N. Mishustin🇩🇪 · B. Kämpfer🇩🇪 · H. Stoecker🇩🇪
Partonic matter produced in the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, and quarks and antiquarks are produced at later times. The comparable hydrodynamic simulations of heavy-ion collisions for (2+1)-flavor and Yang-Mills equations of state performed by using three different hydrodynamic codes are presented. Assuming slow chemical equilibration of quarks, the spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy of $s_{_{NN}} = 2.76$ TeV. It is shown that a suppression of quarks at early times leads to a significant reduction of the yield of the thermal dileptons, but only to a rather modest suppression of the $p_{T}$ -distribution of direct photons. It is demonstrated that an enhancement of photon and dilepton elliptic flows might serve as a promising signature of the pure-glue initial state. Calculations based on Bjorken hydrodynamics suggest that collisions of small systems at intermediate energies available at RHIC or future FAIR facilities may show stronger effects associated with initial pure gluodynamic evolution.
Comments:
14 pages, 12 figures. Proceedings for 54th International Winter Meeting on Nuclear Physics, 25-29 January 2016, Bormio, Italy
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1608.04318 [pdf]
PoS(2016)·8 citations
04
[Submitted on 15 Aug 2016]
From pQCD to neutron stars: matching equations of state to constrain global star properties
Tyler Gorda🇺🇸
The equation of state (EoS) of quantum chromodynamics (QCD) at zero temperature can be calculated in two different perturbative regimes: for small values of the baryon chemical potential $μ$ , one may use chiral perturbation theory (ChEFT); and for large values of $μ$ , one may use perturbative QCD (pQCD). There is, however, a gap for $μ \in (0.97 GeV, 2.6 GeV)$ , where these theories becomes non-perturbative, and where there is currently no known microscopic description of QCD matter. Unfortunately, this interval obscures the values of $μ$ found within the cores of neutron stars (NSs). In this thesis, we argue that thermodynamic matching of the ChEFT and pQCD EoSs is a legitimate way to obtain quantitative constraints on the non-pertubative QCD EoS. Moreover, we argue that this method is effective, verifiable, and systematically improvable. First, we carry out a simplified matching procedure in QCD-like theories that can be simulated on the lattice without a sign problem. Our calculated pressure band serves as a prediction for lattice-QCD practitioners and will allow them to verify or refute the simplified procedure. Second, we apply the state-of-the-art matched EoS of Kurkela et al. (2014) to rotating NSs. This allows us to obtain bounds on observable NS properties, as well as point towards future observations that would more tightly constrain the current state-of-the-art EoS band. Finally, as evidence of the ability to improve the procedure, we carry out calculations in pQCD to improve the zero-temperature pressure. We calculate the full $O (g^{6} ln^{2} g)$ contribution to the pQCD pressure for $n_{f}$ massless quarks, as well as a significant portion of the $O (g^{6} ln g)$ piece and even some of the $O (g^{6})$ piece.
Comments:
Ph.D. Thesis, 108 pages, 13 figures, 1 appendix
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1608.04358 [pdf]
0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Extracting temperature and transverse flow by fitting transverse mass spectra and HBT radii together

Role of (α,n) reactions under r-process conditions in neutrino-driven winds revisited

Hydrodynamic modeling of a pure-glue initial scenario in high-energy hadron and heavy-ion collisions

From pQCD to neutron stars: matching equations of state to constrain global star properties

Affiliations

Role of ( $α$ ,n) reactions under $r$ -process conditions in neutrino-driven winds revisited