17515511
Partonic effects on anisotropic flows at RHIC
We report recent results from a multiphase transport (AMPT) model on the azimuthal anisotropies of particle momentum distributions in heavy ion collisions at the relativistic heavy ion collider. These include higher-order anisotropic flows and their scaling, the rapidity dependence of anisotropic flows and the elliptic flow of charm quarks.
14560383
Charmonium production from hot hadronic matter
Abstract Charmonium production from D D annihilation in the hadron gas formed in ultra-relativistic heavy-ion collisions is studied. With initial conditions taken from the HIJING parton model, we have estimated the number of J / ψ produced from an expanding hadron gas, using the J / ψ absorption and production cross sections obtained from either an effective Lagrangian or the quark-exchange model. We find that J / ψ production is negligible in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) but may be important at the Large Hadron Collider (LHC), where more charm mesons are produced. Similar results are obtained for ψ ′ production from the hadron gas at RHIC and LHC.
118880072
Quark coalescence for charmed mesons in ultrarelativistic heavy-ion collisions
Abstract We investigate effects of charm-quark interactions in a quark–gluon plasma on the production of D and J / ψ mesons in high-energy heavy-ion collisions. Employing a previously constructed coalescence model that successfully reproduces the transverse momentum ( p T ) spectra and elliptic flow ( v 2 ( p T ) ) of light hadrons at RHIC from underlying light-quark distributions at the phase transition temperature  T c , D -meson and J / ψ p T -spectra are evaluated. For the charm-quark distributions, we consider two limiting scenarios: (i) no rescattering, corresponding to perturbative QCD (pQCD) spectra and (ii) complete thermalization including transverse expansion. We find that D -mesons acquire a minimal v 2 inherited from their light-quark content and corresponding semileptonic decay spectra of single electrons practically preserve the v 2 of the parent particles, exhibiting marked differences between the pQCD and thermal scenarios for p T ⩾ 1 GeV . Likewise, the p T -spectra and yields of J / ψ 's differ appreciably in the two scenarios.
39436824
J/psi absorption by nucleons in the meson-exchange model
We reinvestigate the $J/\ensuremath{\psi}$ dissociation processes induced by the reactions with nucleons, $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}{\overline{D}}^{(*)}+{\ensuremath{\Lambda}}_{c}$, in the meson-exchange model. Main constraints used in this work are vector-meson dominance and charm vector-current conservation. We show that the cross section for $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}\overline{D}+{\ensuremath{\Lambda}}_{c}$ can be larger than that for $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}{\overline{D}}^{*}+{\ensuremath{\Lambda}}_{c}$ when these constraints are imposed. The dependence of the cross sections on the coupling constants is analyzed in detail, and the comparison with the recent quark-interchange model predictions is also made.
18998652
Pentaquark Baryon Production in Nuclear Reactions *
Using a hadronic model with empirical coupling constants and form factors, we have evaluated the cross sections for the production of exotic pentaquark Θ + and/or Ξ + 5 and Ξ −− 5 in reactions induced by photons, nucleons, pions, and kaons on nucleon targets. We have also predicted the Θ + yield in relativistic heavy ion collisions using a kinetic model that takes into account both Θ + production from the coalescence of quarks and antiquarks in the quark-gluon plasma and the effects due to subsequent hadronic absorption and regeneration.
119326646
Medium effects on the flow of strange particles in heavy-ion collisions
Strange particles such as the kaon and lambda are useful in probing the properties of dense matter formed in heavy-ion collisions. Here we review the theoretical understanding of their properties in a nuclear medium based on both the effective chiral Lagrangian and the phenomenological hadronic model. We further review the effects due to changes in their in-medium properties on their collective flow in heavy-ion collisions.
16029130
Line and Continuum Emission from the Galactic Center. III. Origin of 6.4 keV Line Emission from Molecular Clouds in the Galactic Center
We analyze the 6.4 keV line and continuum emission from the molecular cloud Sgr B2 and the source HESS J1745-303, which is supposed to be a complex of molecular gas. From the HESS results it follows that Sgr A is a source of high energy protons, which penetrate into molecular clouds producing there a TeV gamma-ray flux. We present arguments that Sgr A may also produce a flux of subrelativistic protons which generate the 6.4 keV line and bremsstrahlung continuum emission from the clouds.
5224194
3D Magneto-hydrodynamic simulations of Parker instability with cosmic rays
This study investigates Parker instability in an interstellar medium (ISM) near the Galactic plane using three-dimensional magneto-hydrodynamic simulations. Parker instability arises from the presence of a magnetic field in a plasma, wherein the magnetic buoyant pressure expels the gas and cause the gas to move along the field lines. The process is thought to induce the formation of giant molecular clouds in the Galaxy. In this study, the effects of cosmic-ray (CR) diffusion are examined. The ISM at equilibrium is assumed to comprise a plasma fluid and a CR fluid at various temperatures, with a uniform magnetic field passing through it in the azimuthal direction of the Galactic disk. After a small perturbation, the unstable gas aggregates at the footpoint of the magnetic fields and forms dense blobs. The growth rate of the instability increases with the strength of the CR diffusion. The formation of dense clouds is enhanced by the effect of cosmic rays (CRs), whereas the shape of the clouds depends sensitively on the initial conditions of perturbation.
118611815
Mass of Galactic Lenses in Modified Newtonian Dynamics
Mu-Chen Chiu, 2 Chung-Ming Ko, 3, 4 Yong Tian, and HongSheng Zhao Institute of Astronomy, National Central University, Jhongli, Taiwan 320, R.O.C. Scottish University Physics Alliance, Institute for Astronomy, the Royal Observatory , University of Edinburgh, Blackford Hill, Edinburgh,EH9 3HJ ,UK Department of Physics, National Central University, Jhongli, Taiwan 320, R.O.C. Center for Complex Systems, National Central University, Jhongli, Taiwan 320, R.O.C. Scottish University Physics Alliance, University of St. Andrews, KY16 9SS,UK (Dated: August 19, 2010)
119432484
Open clusters in a dispersing molecular cloud
Star clusters are formed in molecular clouds which are believed to be the birth places of most stars. From recent observational data, Lada & Lada (2003) estimated that only 4 to 7% of the proto-clusters have survived. A possible reason is the dispersion of molecular clouds by UV radiation, stellar winds or supernova explosions. We study the cloud dispersion in the embedded clusters by N-body simulations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
16205821
Particle propagation in the galactic center and spatial distribution of non-thermal x-rays
We showed that if the non-thermal emission from the galactic center in the range 14–40 keV is due to inverse bremsstrahlung emission of subrelativistic protons, their interactions with hot and cold fractions of the interstellar medium are equally important. Our estimation shows that about 30% of the total non-thermal flux from the GC in the range 14–40 keV is generated in regions of cold gas while the rest is produced by proton interaction with hot plasma. From the spatial distribution of 6.7 keV iron line we concluded the spatial distribution of hot plasma is strongly non-uniform that should be taken into account in analysis of proton propagation in the GC. From the Suzaku data we got independent estimates for the diffusion coefficient of subrelativistic protons in the GC, which was in the range 10 26 –10 27 cm 2 s � 1 .