14 research outputs found
Gamma Ray Emissions from Binary Pulsar Systems
A method is developed for estimating the gamma ray flux impinging upon the earth from production in binary pulsar systems. We calculate production of the 6.13 MeV gamma ray line characteristic of 16O. These are produced by protons emitted by the pulsar interacting with 16O atoms at the surface of the companion. We examine different types of companion stars and estimate the gamma ray flux at the earth as a function of proton emission from the pulsar and distance from the earth. Prospects for detection from earth are discussed
Directed flow of neutral strange particles at AGS
Directed flow of neutral strange particles in heavy ion collisions at AGS is
studied in the ART transport model. Using a lambda mean-field potential which
is 2/3 of that for a nucleon as predicted by the constituent quark model,
lambdas are found to flow with protons but with a smaller flow parameter as
observed in experiments. For kaons, their repulsive potential, which is
calculated from the impulse approximation using the measured kaon-nucleon
scattering length, leads to a smaller anti-flow than that shown in the
preliminary E895 data. Implications of this discrepancy are discussed.Comment: 6 pages, 2 figure
Probing Mechanical and Chemical Instabilities in Neutron-Rich Matter
The isospin-dependence of mechanical and chemical instabilities is
investigated within a thermal and nuclear transport model using a Skyrme-type
phenomenological equation of state for neutron-rich matter. Respective roles of
the nuclear mean field and the 2-body stochastic scattering on the evolution of
density and isospin fluctuations in either mechanically or chemically unstable
regions of neutron-rich matter are investigated. It is found that the mean
field dominates overwhelmingly the fast growth of both fluctuations, while the
2-body scattering influences significantly the later growth of the isospin
fluctuation only. The magnitude of both fluctuations decreases with the
increasing isospin asymmetry because of the larger reduction of the attractive
isoscalar mean field by the stronger repuslive neutron symmetry potential in
the more neutron-rich matter. Moreover, it is shown that the isospin
fractionation happens later, but grows faster in the more neutron-rich matter.
Implications of these results to current experiments exploring properties of
neutron-rich matter are discussed.Comment: 18 pages & 15 figures, Nuclear Physics A (2001) in pres
Excitation function of nucleon and pion elliptic flow in relativistic heavy-ion collisions
Within a relativistic transport (ART) model for heavy-ion collisions, we show
that the recently observed characteristic change from out-of-plane to in-plane
elliptic flow of protons in mid-central Au+Au collisions as the incident energy
increases is consistent with the calculated results using a stiff nuclear
equation of state (K=380 MeV). We have also studied the elliptic flow of pions
and the transverse momentum dependence of both the nucleon and pion elliptic
flow in order to gain further insight about the collision dynamics.Comment: 8 pages, 2 figure
Differential flow in heavy-ion collisions at balance energies
A strong differential transverse collective flow is predicted for the first
time to occur in heavy-ion collisions at balance energies. We also give a novel
explanation for the disappearance of the total transverse collective flow at
the balance energies. It is further shown that the differential flow especially
at high transverse momenta is a useful microscope capable of resolving the
balance energy's dual sensitivity to both the nuclear equation of state and
in-medium nucleon-nucleon cross sections in the reaction dynamics.Comment: Phys. Rev. Lett. (1999) in pres
Proton Differential Elliptic Flow and the Isospin-Dependence of the Nuclear Equation of State
Within an isospin-dependent transport model for nuclear reactions involving
neutron-rich nuclei, we study the first-order direct transverse flow of protons
and their second-order differential elliptic flow as a function of transverse
momentum. It is found that the differential elliptic flow of mid-rapidity
protons, especially at high transverse momenta, is much more sensitive to the
isospin dependence of the nuclear equation of state than the direct flow.
Origins of these different sensitivities and their implications to the
experimental determination of the isospin dependence of the nuclear equation of
state by using neutron-rich heavy-ion collisions at intermediate energies are
discussed.Comment: 15 pages, 6 figures. Phys. Rev. C (2001) in pres
Kaon differential flow in relativistic heavy-ion collisions
Using a relativistic transport model, we study the azimuthal momentum
asymmetry of kaons with fixed transverse momentum, i.e., the differential flow,
in heavy-ion collisions at beam momentum of 6 GeV/c per nucleon, available from
the Alternating Gradient Synchrotron (AGS) at the Brookhaven National
Laboratory (BNL). We find that in the absence of kaon potential the kaon
differential flow is positive and increases with transverse momentum as that of
nucleons. The repulsive kaon potential as predicted by theoretical models,
however, reduces the kaon differetnial flow, changing it to negative for kaons
with low momenta. Cancellation between the negative differential flow at low
mementa and the positive one at high momenta is then responsible for the
experimentally observed nearly vanishing in-plane transverse flow of kaons in
heavy ion experiments.Comment: Phys. Rev. C in pres