Nuclear Theory·nucl-th

Thursday·September 17, 2015

9 papers—4 primary·5 cross-listed

01
In-medium and isospin effects on particle production near threshold energies in heavy-ion collisions
Zhao-Qing Feng🇨🇳 · Wen-Jie Xie🇨🇳 · Peng-Hui Chen🇨🇳 · Jie Chen🇨🇳 · Gen-Ming Jin🇨🇳
Dynamics of pseudoscalar mesons ( $π$ , $η$ , $K$ and $K$ ) and hyperons ( $Λ$ and $Σ$ ) produced in heavy-ion collisions near threshold energies has been investigated within the Lanzhou quantum molecular dynamics (LQMD) transport model. The in-medium modifications on particle production in dense nuclear matter are implemented in the model through corrections on the elementary cross sections and by inclusion of the meson (hyperon)-nucleon potentials, in which the isospin effects are considered. It is found that the transportation of particles are influenced with the in-medium corrections. The total number of pions is reduced with an isospin, density and momentum dependent pion-nucleon potential. However, the ratios of charged pions is enhanced with inclusion of the potential. The production of eta in the domain of mid-rapidities and high momenta is sensitive to the $η$ -nucleon potential, but weakly depends on symmetry energy. The attractive antikaon-nucleon potential enhances the subthreshold $K$ production and also influences the structure of phase-space distributions. Dynamics of etas, kaons, antikaons and hyperons is also influenced by the pion potential because of collisions between pions and nucleons (resonances). The impacts of mean-field potentials on particle dynamics are investigated, such as the phase-space distributions from rapidity and transverse momentum spectra, inclusive invariant spectra, collective flows etc.
nucl-thPRC(2015)·35 citations
02
Effects of $N N$ potentials on $p$ nuclides in the A $\sim$ 100-120 region
C. Lahiri · S. K. Biswal · S. K. Patra
Microscopic optical potentials for low energy proton reactions have been obtained by folding density dependent M3Y interaction derived from nuclear matter calculation with densities from mean field approach to study astrophysically important proton rich nuclei in mass 100-120 region. We compare S factors for low-energy $(p, γ)$ reactions with available experimental data and further calculate astrophysical reaction rates for $(p, γ)$ and $(p, n)$ reactions. Again we choose some nonlinear R3Y interactions from RMF calculation and folded them with corresponding RMF densities to reproduce experimental S factor values in this mass region. Finally the effect of nonlinearity on our result is discussed.
nucl-thIJMPE(2016)·24 citations
03
Effect of Delta potential on the pion-/pion+ ratio in heavy-ion collisions at intermediate energies
Wen-Mei Guo🇨🇳 · Gao-Chan Yong🇨🇳 · Wei Zuo🇨🇳
Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck(IBUU) transport model, effects of $Δ$ resonance potential on the free n/p and $π^{-} / π^{+}$ ratios in the central collision of $^{197} A u +^{197} A u$ at beam energies of 200 and 400 MeV/A are studied. It is found that the effect of $Δ$ potential on the ratio of pre-equilibrium free $n / p$ is invisible. The effect of $Δ$ isovector potential on the kinetic energy integrating ratio of $π^{-} / π^{+}$ may be observable only at lower incident beam energies and with stiffer symmetry energy. The strength of the $Δ$ isoscalar potential affects the height of the $π^{-} / π^{+}$ ratio around the Coulomb peak but does not affect the kinetic energy integrating ratio of $π^{-} / π^{+}$ . In heavy-ion collisions at intermediate energies, relating to the question of non-conservation of energy on $Δ$ or $π$ productions, one can replace the $Δ$ potential by nucleon isoscalar potential especially a soft symmetry energy is employed.
nucl-thnucl-exPRC(2015)·17 citations
04
Thermal shape fluctuation model study of the giant dipole resonance in $^{152}$ Gd
A. K. Rhine Kumar · P. Arumugam
We have studied the giant dipole resonance (GDR) in the hot and rotating nucleus $^{152}$ Gd within the framework of thermal shape fluctuation model (TSFM) built on the microscopic-macroscopic calculations of the free energies with a macroscopic approach for the GDR. Our results for GDR cross sections are in good agreement with the experimental values except for a component peaking around 17 MeV where the data has large uncertainties. Such a component is beyond our description which properly takes care of the splitting of GDR components due to the deformation and Coriolis effects. Around this 17 MeV lies the half maximum in experimental cross sections, and hence the extracted GDR widths and deformations (estimated from these widths) turn out to be overestimated and less reliable. Reproducing these widths with empirical formulae could conceal the information contained in the cross sections. Fully microscopic GDR calculations and a more careful look at the data could be useful to understand the GDR component around 17 MeV. We also discuss the occurrence of $γ$ -softness in the free energy surfaces of $^{152}$ Gd and its role on GDR.
nucl-thPRC(2015)·16 citations
05
Quasinormal modes of magnetic and electric black branes versus far from equilibrium anisotropic fluids
Stefan Janiszewski🇨🇦 · Matthias Kaminski🇺🇸
Detailed knowledge about equilibration processes is of interest for various fields of physics, including heavy ion collision experiments and quantum quenched condensed matter systems. We study the approach to equilibrium at late times within two types of strongly coupled thermal systems in 3+1 dimensions: systems in the presence of (i) a non-zero charge density, or (ii) a magnetic field at vanishing charge density. Utilizing the gauge/gravity correspondence, we map the aforementioned problem to the computation of quasinormal frequencies around two particular classes of black branes within the Einstein-Maxwell theory. We compute (i) the tensor and vector quasinormal modes of Reissner-Nordström black branes and (ii) the scalar, as well as tensor quasinormal modes of magnetic black branes. Some of these quasinormal modes correspond to the late-time relaxation of the above systems after starting with initial pressure anisotropy. We provide benchmarks which need to be matched at late-times by all holographic thermalization codes with the appropriate symmetries.
↳ hep-thgr-qcnucl-thPRD(2016)·52 citations
06
The current evaluation of Vud
J.C. Hardy🇺🇸 · I.S. Towner🇨🇦
The Vud element of the Cabibbo-Kobayashi-Maskawa matrix can be determined from several different experimental approaches: either 0+-to-0+ superallowed nuclear beta decays, neutron decay, nuclear mirror decays, or pion beta decay. Currently all give consistent results but, because the nuclear superallowed value has an uncertainty at least a factor of seven less than all other results, it dominates the result. A new survey of world superallowed-decay data establishes the Ft values of 14 separate superallowed transitions to a precision of order 0.1% or better; and all 14 are statistically consistent with one another. This very robust data set yields the result Vud = 0.97417(21), the value we recommend.
↳ nucl-exhep-phnucl-th0 citations
07
$p ˉ p$ annihilation into $D ˉ D$ meson pair within an effective Lagrangian model
R. Shyam🇮🇳 · H. Lenske🇩🇪
We study the charmed meson pair ( $D ˉ^{0} D^{0}$ and $D^{-} D^{+}$ ) production in $p ˉ p$ annihilation within an effective Lagrangian model that has only the baryon-meson degrees of freedom and involves the physical hadron masses. The reaction amplitudes include terms corresponding to the t-channel $Λ_{c}^{+}$ , $Σ_{c}^{+}$ and $Σ_{c}^{++}$ baryon exchanges and the s-channel excitation, propagation and decay of the $Ψ$ (3770) resonance into the charmed mesons. The initial- and final-state distortion effects have been accounted for by using a simple eikonal approximation-based procedure in the same way as was done in our previous study of the $p ˉ p \to Λ ˉ_{c}^{-} Λ_{c}^{+}$ reaction within a similar model. The $D ˉ^{0} D^{0}$ production reaction is dominated by the $Λ_{c}^{+}$ baryon exchange process, and the corresponding total cross sections are predicted to be in the range of 0.18 - 0.7 $μ$ b for antiproton beam momenta varying between threshold and 20 $G e V / c$ . The $Ψ$ (3770) resonance contributions have a large influence on the differential cross sections of the $D^{-} D^{+}$ production reaction.
↳ hep-phhep-exnucl-exnucl-thPRD(2016)·12 citations
08
Nuclear modification of forward $J / ψ$ production in proton-nucleus collisions at the LHC
B. Ducloué🇫🇮 · T. Lappi🇫🇮 · H. Mäntysaari🇫🇮
We re-evaluate the nuclear suppression of forward $J / ψ$ production at high energy in the Color Glass Condensate framework. We use the collinear approximation for the projectile proton probed at large $x$ and an up to date dipole cross section fitted to HERA data to describe the target in proton-proton collisions. We show that using the Glauber approach to generalize the proton dipole cross section to the case of a nucleus target leads to a nuclear modification factor much closer to LHC data than previous estimates using the same framework.
↳ hep-phnucl-thNucl.Part.Phys.Proc.(2016)·2 citations
09
Robust characteristics of nongaussian fluctuations from the NJL model
Jiunn-Wei Chen🇩🇪 · Jian Deng🇨🇳 · Hiroaki Kohyama🇹🇼 · Lance Labun🇺🇸
We evaluate the third- and fourth-order baryon, charge and strangeness susceptibilities near a chiral critical point using the Nambu-Jona-Lasinio model. We identify robust qualitative behaviours of the susceptibilities along hypothetical freeze-out lines that agree with previous model studies. Quantitatively, baryon number fluctuations are the largest in magnitude and thus offer the strongest signal when freeze-out occurs farther away from a critical point. Charge and strangeness susceptibilities also diverge at a critical point, but the area where the divergence dominates is smaller, meaning freeze-out must occur closer to a critical point for a signal to be visible in these observables. In case of strangeness, this is attributable to the relatively large strange quark mass. Plotting the third- and fourth-order susceptibilities against each other along the freeze-out line exhibits clearly their non-montonicity and robust features.
↳ hep-phnucl-exnucl-thPRD(2016)·52 citations

Affiliations

first authorsco-authorsvia INSPIRE