717 research outputs found
Measurements of Ks, Lambda and Xi from Au+Au collisions at \sqrt{s_NN} = 7.7, 11.5 and 39 GeV in STAR
We report on the measurements of Ks, Lambda and Xi spectra at mid-rapidity
(|y|<0.5) in the most central (0-5%) Au+Au collisions at \sqrt{s_NN} = 7.7,
11.5 and 39 GeV from the STAR experiment. The extracted yields and the
corresponding data from Pb+Pb collisions measured by the NA49 and CERES
experiments at SPS are consistent. The Lambda, Anti-Lambda, Xi- and Xi+ to pion
ratios agree well with the predictions from a statistical hadronization model
at all three energies.Comment: 6 pages, 4 figures, to appear in the proceedings for Strangeness in
Quark Matter 2011, Cracow, Poland, September 18-24, 201
Elliptic Flow Analysis at RHIC: Fluctuations vs. Non-Flow Effects
The cumulant method is applied to study elliptic flow () in Au+Au
collisions at AGeV, with the UrQMD model. In this approach, the
true event plane is known and both the non-flow effects and event-by-event
spatial () and fluctuations exist. Qualitatively, the hierarchy
of 's from two, four and six-particle cumulants is consistent with the
STAR data, however, the magnitude of in the UrQMD model is only 60% of
the data. We find that the four and six-particle cumulants are good measures of
the real elliptic flow over a wide range of centralities except for the most
central and very peripheral events. There the cumulant method is affected by
the fluctuations. In mid-central collisions, the four and six-particle
cumulants are shown to give a good estimation of the true differential ,
especially at large transverse momentum, where the two-particle cumulant method
is heavily affected by the non-flow effects.Comment: 7 pages, 7 figures, revtex 4; The discussion on the non-flow effects
is extended, a new figure (Fig.3) on v2-eccentricity correlation is added,
accepted for publication in Phys. Rev.
Directed and elliptic flow in heavy ion collisions from MeV/nucleon to GeV/nucleon
Recent data from the NA49 experiment on directed and elliptic flow for Pb+Pb
reactions at CERN-SPS are compared to calculations with a hadron-string
transport model, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD)
model.
The rapidity and transverse momentum dependence of the directed and elliptic
flow, i.e. and , are investigated. The flow results are compared to
data at three different centrality bins. Generally, a reasonable agreement
between the data and the calculations is found. Furthermore, the energy
excitation functions of and from MeV to GeV are explored within the UrQMD framework and discussed in the
context of the available data. It is found that, in the energy regime below
GeV, the inclusion of nuclear potentials is necessary to
describe the data. Above GeV beam energy, the UrQMD model starts to
underestimate the elliptic flow. Around the same energy the slope of the
rapidity spectra of the proton directed flow develops negative values. This
effect is known as the third flow component ("antiflow") and cannot be
reproduced by the transport model. These differences can possibly be explained
by assuming a phase transition from hadron gas to quark gluon plasma at about
GeV.Comment: 19 pages, minor changes and modified title as published in PR
DD correlations as a sensitive probe for thermalization in high-energy nuclear collisions
We propose to measure azimuthal correlations of heavy-flavor hadrons to address the status of thermalization at the partonic stage of light quarks and gluons in high-energy nuclear collisions. In particular, we show that hadronic interactions at the late stage cannot significantly disturb the initial back-to-back azimuthal correlations of DDbar pairs. Thus, a decrease or the complete absence of these initial correlations does indicate frequent interactions of heavy-flavor quarks and also light partons in the partonic stage, which are essential for the early thermalization of light partons
Deformable Generator Network: Unsupervised Disentanglement of Appearance and Geometry
We present a deformable generator model to disentangle the appearance and
geometric information for both image and video data in a purely unsupervised
manner. The appearance generator network models the information related to
appearance, including color, illumination, identity or category, while the
geometric generator performs geometric warping, such as rotation and
stretching, through generating deformation field which is used to warp the
generated appearance to obtain the final image or video sequences. Two
generators take independent latent vectors as input to disentangle the
appearance and geometric information from image or video sequences. For video
data, a nonlinear transition model is introduced to both the appearance and
geometric generators to capture the dynamics over time. The proposed scheme is
general and can be easily integrated into different generative models. An
extensive set of qualitative and quantitative experiments shows that the
appearance and geometric information can be well disentangled, and the learned
geometric generator can be conveniently transferred to other image datasets to
facilitate knowledge transfer tasks.Comment: version
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