712 research outputs found
Elliptic flow at large transverse momenta from quark coalescence
We show that hadronization via quark coalescence enhances hadron elliptic
flow at large pT relative to that of partons at the same transverse momentum.
Therefore, compared to earlier results based on covariant parton transport
theory, more moderate initial parton densities dN/d\eta(b=0) ~ 1500-3000 can
explain the differential elliptic flow v_2(pT) data for Au+Au reactions at
s^1/2=130 and 200 AGeV from RHIC. In addition, v2(pT) could saturate at about
50% higher values for baryons than for mesons. If strange quarks have weaker
flow than light quarks, hadron v_2 at high pT decreases with relative
strangeness content.Comment: Minor changes, extended discussion. To appear in PR
Meson and baryon elliptic flow at high pT from parton coalescence
The large and saturating differential elliptic flow v2(pT) observed in Au+Au
reactions at RHIC so far could only be explained assuming an order of magnitude
denser initial parton system than estimated from perturbative QCD.
Hadronization via parton coalescence can resolve this ``opacity puzzle''
because it enhances hadron elliptic flow at large pT relative to that of
partons at the same transverse momentum. An experimentally testable consequence
of the coalescence scenario is that v2(pT) saturates at about 50% higher values
for baryons than for mesons. In addition, if strange quarks have weaker flow
than light quarks, hadron v2 at high pT decreases with relative strangeness
content.Comment: Talk at SQM2003 [7th Int. Conf. on Strangeness in Quark Matter
(Atlantic Beach, NC, USA, Mar 12-17, 2003)] - 6 pages, 5 eps figs, IOP style
file
Particle dependence of elliptic flow in Au+Au collisions at 200 GeV
The elliptic flow parameter () for and
has been measured at mid-rapidity in Au + Au collisions at
GeV by the STAR collaboration. The values for both
and saturate at moderate , deviating
from the hydrodynamic behavior observed in the lower region. The
saturated values and the scales where the deviation begins are
particle dependent. The particle-type dependence of shows features
expected from the hadronization of a partonic ellipsoid by coalescence of
co-moving quarks. These results will be discussed in relation to the nuclear
modification factor () which has also been measured for and
by the STAR collaboration.Comment: 6 pages, 3 figures, Strange Quark Matter 2003 Conference (SQM 2003):
updated with 2 figures from original talk that did not appear in the journa
Parton Collectivity from RHIC to the LHC
Anisotropic flow is recognized as one of the main observables providing
information on the early dynamics in heavy-ion collisions. The large elliptic
flow observed at RHIC is considered to be evidence for almost perfect liquid
behavior of the strongly coupled Quark Gluon Plasma produced in the collisions.
In this report we review our current understanding of this new state of matter
and investigate the predictions for anisotropic flow at the LHC.Comment: 8 pages, proceedings SQM 200
Elliptic Flow from a Transversally Thermalized Fireball
The agreement of elliptic flow data at RHIC at central rapidity with the
hydrodynamic model has led to the conclusion of very rapid thermalization. This
conclusion is based on the intuitive argument that hydrodynamics, which assumes
instantaneous local thermalization, produces the largest possible elliptic flow
values and that the data seem to saturate this limit. We here investigate the
question whether incompletely thermalized viscous systems may actually produce
more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast
primordial longitudinal expansion of the reaction zone, we investigate a toy
model which exhibits thermalization only in the transverse directions but
undergoes collisionless free-streaming expansion in the longitudinal direction.
For collisions at RHIC energies, elliptic flow results from the model are
compared with those from hydrodynamics. With the final particle yield and
\kt-distribution fixed, the transversally thermalized model is shown not to
be able to produce the measured amount of elliptic flow. This investigation
provides further support for very rapid local kinetic equilibration at RHIC. It
also yields interesting novel results for the elliptic flow of massless
particles such as direct photons.Comment: revtex4, 15 pages + 10 embedded EPS figure
Hadronization in heavy ion collisions: recombination or fragmentation?
We show that hadron production in relativistic heavy ion collisions at
transverse momenta larger than 2 GeV/c can be explained by the competition of
two different hadronization mechanisms. Above 5 GeV/c hadron production can be
described by fragmentation of partons that are created perturbatively. Below 5
GeV/c recombination of partons from the dense and hot fireball dominates. This
can explain some of the surprising features of RHIC data like the constant
baryon-to-meson ratio of about one and the small nuclear suppression for
baryons between 2 to 4 GeV/c.Comment: Contribution to the 7th Conference on Strange Quark Matter (SQM
2003), submitted to J.Phys.G; 6 pages LaTeX, 4 eps figures, uses iopart.cl
Partonic effects on the elliptic flow at relativistic heavy ion collisions
The elliptic flow in heavy ion collisions at RHIC is studied in a multiphase
transport model. By converting the strings in the high energy density regions
into partons, we find that the final elliptic flow is sensitive to the parton
scattering cross section. To reproduce the large elliptic flow observed in
Au+Au collisions at GeV requires a parton scattering cross
section of about 6 mb. We also study the dependence of the elliptic flow on the
particle multiplicity, transverse momentum, and particle mass.Comment: 7 pages, 7 figures, revtex, text added to detail the procedure for
conversions between hadrons and parton
Parton coalescence at RHIC
Using a covariant coalescence model, we study hadron production in
relativistic heavy ion collisions from both soft partons in the quark-gluon
plasma and hard partons in minijets. Including transverse flow of soft partons
and independent fragmentation of minijet partons, the model is able to describe
available experimental data on pion, kaon, and antiproton spectra. The
resulting antiproton to pion ratio is seen to increase at low transverse
momenta and reaches a value of about one at intermediate transverse momenta, as
observed in experimental data at RHIC. A similar dependence of the antikaon to
pion ratio on transverse momentum is obtained, but it reaches a smaller value
at intermediate transverse momenta. At high transverse momenta, the model
predicts that both the antiproton to pion and the antikaon to pion ratio
decrease and approach those given by the perturbative QCD. Both collective flow
effect and coalescence of minijet partons with partons in the quark-gluon
plasma affect significantly the spectra of hadrons with intermediate transverse
momenta. Elliptic flows of protons, Lambdas, and Omegas have also been
evaluated from partons with elliptic flows extracted from fitting measured pion
and kaon elliptic flows, and they are found to be consistent with available
experimental data.Comment: 12 pages, 11 figure
The QCD confinement transition: hadron formation
We review the foundations and the applications of the statistical and the
quark recombination model as hadronization models.Comment: 45 pages, 16 figures, accepted for publication in Landolt-Boernstein
Volume 1-23
Charge separation relative to the reaction plane in Pb-Pb collisions at TeV
Measurements of charge dependent azimuthal correlations with the ALICE
detector at the LHC are reported for Pb-Pb collisions at TeV. Two- and three-particle charge-dependent azimuthal correlations in
the pseudo-rapidity range are presented as a function of the
collision centrality, particle separation in pseudo-rapidity, and transverse
momentum. A clear signal compatible with a charge-dependent separation relative
to the reaction plane is observed, which shows little or no collision energy
dependence when compared to measurements at RHIC energies. This provides a new
insight for understanding the nature of the charge dependent azimuthal
correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286
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