1,020 research outputs found
Energy Dependence of High Moments for Net-proton Distributions
High moments of multiplicity distributions of conserved quantities are
predicted to be sensitive to critical fluctuations. To understand the effect of
the complicated non-critical physics backgrounds on the proposed observable, we
have studied various moments of net-proton distributions with AMPT, Hijing,
Therminator and UrQMD models, in which no QCD critical point physics is
implemented. It is found that the centrality evolution of various moments of
net-proton distributions can be uniformly described by a superposition of
emission sources. In addition, in the absence of critical phenomena, some
moment products of net-proton distribution, related to the baryon number
susceptibilities ratio in Lattice QCD calculation, are predicted to be constant
as a function of the collision centrality. We argue that a non-monotonic
dependence of the moment products as a function collision centrality and the
beam energy may be used to locate the QCD critical point.Comment: SQM2009 Proceeding, 6 pages, 5 figure
Radial flow afterburner for event generators and the baryon puzzle
A simple afterburner including radial flow to the randomized transverse
momentum obtained from event generators, Pythia and Hijing, has been
implemented to calculate the ratios and compare them with available
data. A coherent trend of qualitative agreement has been obtained in
collisions and in for various centralities. Those results indicate that
the radial flow does play an important role in the so called baryon puzzle
anomaly.Comment: 11 pages, 5 figures. To appear in Journal of Physics
Measurements of Heavy Flavor and Di-electron Production at STAR
Heavy quarks are produced early in the relativistic heavy ion collisions, and
provide an excellent probe into the hot and dense nuclear matter created at
RHIC. In these proceedings, we will discuss recent STAR measurements of heavy
flavor production, to investigate the heavy quark interaction with the medium.
Electromagnetic probes, such as electrons, provide information on the various
stages of the medium evolution without modification by final stage
interactions. Di-electron production measurements by STAR will also be
discussed.Comment: 5 pages, 6 figures, proceedings for CPOD201
Towards a common origin of the elliptic flow, ridge and alignment
It is claimed that elliptic flow, ridge and alignment are effects of
azimuthal asymmetry, which have a common origin evolving with primary energy
and stemming from the general structure of field-theoretical matrix elements.
It interrelates a new ridge-phenomenon, recently found at the LHC and RHIC,
with known coplanarity feature observed in collider jet physics as well as in
cosmic ray studies.Comment: 4 pages, few typos fixed, reference added, version published in JETP
Letter
Polarization of Lambda^0 hyperons in nucleus-nucleus collisions at high energies
The measurement of Lambda^0 hyperons polarization in nucleus-nucleus
collisions is considered as one of possible tools to study the phase
transition. Fixed target and collider experiments are discussed for the case of
Lambda^0's production from Au-Au central collisions at \sqrt{s_{NN}} of several
GeV.Comment: 15 pages, 6 figure
Probe the QCD phase diagram with \phi-mesons in high energy nuclear collisions
High-energy nuclear collision provide a unique tool to study the strongly
interacting medium. Recent results from the Relativistic Heavy Ion Collider
(RHIC) on \phi-meson production has revealed the formation of a dense partonic
medium. The medium constituents are found to exhibit collective behaviour
initiated due to partonic interactions in the medium. We present a brief review
of the recent results on \phi production in heavy-ion collisions at RHIC. One
crucial question is where, in the phase diagram, does the transition happen for
the matter changing from hadronic to partonic degrees of freedom. We discuss
how \phi-meson elliptic flow in heavy-ion collisions can be used for the search
of the QCD phase boundary.Comment: Plenary talk at Strange Quark Matter 2008, Beijing China, 6-10
October 2008. To appear in proceedings of SQM200
RHIC physics overview
The results from data taken during the last several years at the Relativistic
Heavy-Ion Collider (RHIC) will be reviewed in the paper. Several selected
topics that further our understanding of constituent quark scaling, jet
quenching and color screening effect of heavy quarkonia in the hot dense medium
will be presented. Detector upgrades will further probe the properties of Quark
Gluon Plasma. Future measurements with upgraded detectors will be presented.
The discovery perspectives from future measurements will also be discussed.Comment: 9 pages, 4 figures, invited review article, published by Frontier of
Physics in Chin
Anomalous behavior of pion production in high energy particle collisions
A shape of invariant differential cross section for charged hadron production
as function of transverse momentum measured in various collider experiments is
analyzed. Contrary to the behavior of produced charged kaons, protons and
antiprotons, the pion spectra require an anomalously high contribution of an
exponential term to describe the shape.Comment: 4 pages, 6 figure
Parton Energy Loss in Heavy-Ion Collisions Via Direct-Photon and Charged-Particle Azimuthal Correlations
Charged-particle spectra associated with direct photon Ydir) and π0 are measured in p+p and Au+Au collisions at center-of-mass energy √sNN=200 GeV with the STAR detector at the Relativistic Heavy Ion Collider. A shower-shape analysis is used to partially discriminate between Ydirand π0. Assuming no associated charged particles in the γdir direction (near side) and small contribution from fragmentation photons (Yfrag), the associated charged-particle yields opposite to Ydir(away side) are extracted. In central Au+Au collisions, the charged-particle yields at midrapidity (|η|\u3c1) and high transverse momentum (3 \u3c PTassoc \u3c 16 GeV/c) associated with γdir and π0 (|η|\u3c0.9, 8 \u3c PTtrig \u3c16 GeV/c) are suppressed by a factor of 3–5 compared with p+p collisions. The observed suppression of the associated charged particles is similar for Ydir and π0 and independent of the γdirenergy within uncertainties. These measurements indicate that, in the kinematic range covered and within our current experimental uncertainties, the parton energy loss shows no sensitivity to the parton initial energy, path length, or color charge
Extrapolation of Multiplicity distribution in p+p(\bar(p)) collisions to LHC energies
The multiplicity (N_ch) and pseudorapidity distribution (dN_ch/d\eta) of
primary charged particles in p+p collisions at Large Hadron Collider (LHC)
energies of \sqrt(s) = 10 and 14 TeV are obtained from extrapolation of
existing measurements at lower \sqrt(s). These distributions are then compared
to calculations from PYTHIA and PHOJET models. The existing \sqrt(s)
measurements are unable to distinguish between a logarithmic and power law
dependence of the average charged particle multiplicity () on \sqrt(s),
and their extrapolation to energies accessible at LHC give very different
values. Assuming a reasonably good description of inclusive charged particle
multiplicity distributions by Negative Binomial Distributions (NBD) at lower
\sqrt(s) to hold for LHC energies, we observe that the logarithmic \sqrt(s)
dependence of are favored by the models at midrapidity. The dN_ch/d\eta
versus \eta for the existing measurements are found to be reasonably well
described by a function with three parameters which accounts for the basic
features of the distribution, height at midrapidity, central rapidity plateau
and the higher rapidity fall-off. Extrapolation of these parameters as a
function of \sqrt(s) is used to predict the pseudorapidity distributions of
charged particles at LHC energies. dN_ch/d\eta calculations from PYTHIA and
PHOJET models are found to be lower compared to those obtained from the
extrapolated dN_ch/d\eta versus \eta distributions for a broad \eta range.Comment: 11 pages and 13 figures. Substantially revised and accepted for
publication in Journal of Physics
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