415 research outputs found
Isospin fractionation in the nucleon emissions and fragment emissions in the intermediate energy heavy ion collisions
The degree of isospin fractionation is measured by /
, where and are the saturated
neutron-proton ratio of nucleon emissions (gas phase) and that of fragment
emissions (liquid phase) in heavy ion collision at intermediate energy . The
calculated results by using the isospin-dependent quantum molecular dynamics
model show that the degree of isospin fractionation is sensitive to the
neutron-proton ratio of colliding system but insensitive to the difference
between the neutron-proton ratio of target and that of projectile. In
particular, the degree of isospin fractionation sensitively depends on the
symmetry potential. However its dependences on the isospin dependent in-medium
nucleon-nucleon cross section and momentum dependent interaction are rather
weak.
The nucleon emission (gas phase) mainly determines the dynamical behavior of
the degree of isospin fractionation in the isospin fractionation process,
compared to the effect of fragment emission. In this case, we propose that
/ or can be directly compared with
the experimental data so that the information about symmetry potential can be
obtaine
Probing the Isospin Dependent In-Medium Nucleon-Nucleon Cross Section by Nucleon Emissions
The effects of the symmetry potential and the isospin dependent in-medium
nucleon-nucleon (NN) cross section on the number of proton(neutron) emissions
N) are studied respectively within an isospin-dependent quantum
molecular dynamics (IQMD) model. The isospin dependent in-medium NN cross
section is found to have a strong influence on N) but N) is not
sensitive to the symmetry potential for the neutron-deficient colliding system
at relatively high energies.We propose to make use of the N) as a probe
to extract information on the isospin dependent in-medium NN cross section.Comment: 7 pages,3 figure
Influence of medium correction of nucleon nucleon cross section on the fragmentation and nucleon emission
The influence of medium correction from an isospin dependent nucleon nucleon
cross section on the fragmentation and nucleon emission in the intermediate
energy heavy ion collisions was studied by using an isospin dependent quantum
molecular dynamical model (IQMD). We found that the medium correction enhances
the dependence of multiplicity of intermediate mass fragment and the
number of nucleon emission on the isospin effect of the nucleon nucleon
cross section,while the momentum dependent interaction (MDI) produces also an
important role for enhancing the influence of the medium correction on the
isospin dependence of two-body collision in the fragmentation and nucleon
emission processes. After considering the medium correction and the role of
momentum dependent interaction the increase for the dependence of and
on the isospin effect of two-body collision is favorable to learn the
information about the isospin dependent nucleon nucleon cross sectionComment: 7 figure
Scaling of anisotropy flows in intermediate energy heavy ion collisions
Anisotropic flows (, and ) of light nuclear clusters are
studied by a nucleonic transport model in intermediate energy heavy ion
collisions. The number-of-nucleon scalings of the directed flow () and
elliptic flow () are demonstrated for light nuclear clusters. Moreover,
the ratios of of nuclear clusters show a constant value of 1/2
regardless of the transverse momentum. The above phenomena can be understood by
the coalescence mechanism in nucleonic level and are worthy to be explored in
experiments.Comment: Invited talk at "IX International Conference on Nucleus-Nucleus
Collisions", Rio de Janeiro, Aug 28- Sept 1, 2006; to appear on the
proceeding issue in Nuclear Physics
Scaling of Anisotropic Flow and Momentum-Space Densities for Light Particles in Intermediate Energy Heavy Ion Collisions
Anisotropic flows ( and ) of light nuclear clusters are studied by
Isospin-Dependent Quantum Molecular Dynamics model for the system of Kr
+ Sn at intermediate energy and large impact parameters.
Number-of-nucleon scaling of the elliptic flow () are demonstrated for the
light fragments up to = 4, and the ratio of shows a constant
value of 1/2. In addition, the momentum-space densities of different clusters
are also surveyed as functions of transverse momentum, in-plane transverse
momentum and azimuth angle relative to the reaction plane. The results can be
essentially described by momentum-space power law. All the above phenomena
indicate that there exists a number-of-nucleon scaling for both anisotropic
flow and momentum-space densities for light clusters, which can be understood
by the coalescence mechanism in nucleonic degree of freedom for the cluster
formation.Comment: 8 pages, 3 figures; to be published in Physics Letters
Hadron production in heavy ion collisions: Fragmentation and recombination from a dense parton phase
We discuss hadron production in heavy ion collisions at RHIC. We argue that
hadrons at transverse momenta P_T < 5 GeV are formed by recombination of
partons from the dense parton phase created in central collisions at RHIC. We
provide a theoretical description of the recombination process for P_T > 2 GeV.
Below P_T = 2 GeV our results smoothly match a purely statistical description.
At high transverse momentum hadron production is well described in the language
of perturbative QCD by the fragmentation of partons. We give numerical results
for a variety of hadron spectra, ratios and nuclear suppression factors. We
also discuss the anisotropic flow v_2 and give results based on a flow in the
parton phase. Our results are consistent with the existence of a parton phase
at RHIC hadronizing at a temperature of 175 MeV and a radial flow velocity of
0.55c.Comment: 25 pages LaTeX, 18 figures; v2: some references updated; v3: some
typos fixe
Probing the isospin dependent mean field and nucleon nucleon cross section in the medium by the nucleon emissions
We study the isospin effects of the mean field and two-body collision on the
nucleon emissions at the intermediate energy heavy ion collisions by using an
isospin dependent transport theory. The calculated results show that the
nucleon emission number depends sensitively the isospin effect of
nucleon nucleon cross section and weakly on the isospin dependent mean field
for neutron-poor system in higher beam energy region . In particular, the
correlation between the medium correction of two-body collision and the
momentum dependent interaction enhances the dependence of nucleon emission
number on the isospin effect of nucleon nucleon cross section.
On the contrary, the ratio of the neutron proton ratio of the gas phase to
the neutron proton ratio of the liquid phase, i.e., the degree of isospin
fractionation depends sensitively on the
isospin dependent mean field and weakly on the isospin effect of two-body
collision for neutron-rich system in the lower beam energy region. In this
case, and are the probes for
extracting the information about the isospin dependent nucleon nucleon cross
section in the medium and the isospin dependent mean field,respectively.Comment: 4 pages,4 figure
J/psi suppression at forward rapidity in Au+Au collisions at sqrt(s_NN)=39 and 62.4 GeV
We present measurements of the J/psi invariant yields in sqrt(s_NN)=39 and
62.4 GeV Au+Au collisions at forward rapidity (1.2<|y|<2.2). Invariant yields
are presented as a function of both collision centrality and transverse
momentum. Nuclear modifications are obtained for central relative to peripheral
Au+Au collisions (R_CP) and for various centrality selections in Au+Au relative
to scaled p+p cross sections obtained from other measurements (R_AA). The
observed suppression patterns at 39 and 62.4 GeV are quite similar to those
previously measured at 200 GeV. This similar suppression presents a challenge
to theoretical models that contain various competing mechanisms with different
energy dependencies, some of which cause suppression and others enhancement.Comment: 365 authors, 10 pages, 11 figures, 4 tables. Submitted to Phys. Rev.
C. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Double Spin Asymmetry of Electrons from Heavy Flavor Decays in p+p Collisions at sqrt(s)=200 GeV
We report on the first measurement of double-spin asymmetry, A_LL, of
electrons from the decays of hadrons containing heavy flavor in longitudinally
polarized p+p collisions at sqrt(s)=200 GeV for p_T= 0.5 to 3.0 GeV/c. The
asymmetry was measured at mid-rapidity (|eta|<0.35) with the PHENIX detector at
the Relativistic Heavy Ion Collider. The measured asymmetries are consistent
with zero within the statistical errors. We obtained a constraint for the
polarized gluon distribution in the proton of |Delta g/g(log{_10}x=
-1.6^+0.5_-0.4, {mu}=m_T^c)|^2 < 0.033 (1 sigma), based on a leading-order
perturbative-quantum-chromodynamics model, using the measured asymmetry.Comment: 385 authors, 17 pages, 15 figures, 5 tables. Submitted to Phys. Rev.
D. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
- âŠ