41 research outputs found
Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX
The intermediate region (2 - 5 GeV/) in central Au+Au collisions at
RHIC has a rich physics content. The (anti)proton to pion ratio at the
intermediate gives us a powerful tool to investigate the bulk properties
of the hot and dense matter created at RHIC and their hadronization processes.
We present the preliminary results of identified charged hadron spectra at the
lower beam energies at RHIC. The excitation function of (anti)proton to pion
ratios from SPS to RHIC are shown. We also discuss the onset of the baryon
enhancement at the high energy heavy ion collisions.Comment: 4 pages, 3 figures, Quark Matter 2006 conference proceeding
Recent Results on Strangeness Production at RHIC
Due to its large acceptance, the STAR experiment has acquired a wealth of
data on strangeness production for a variety of collisions systems and
energies, from p+p to Au+Au. By using the yields and spectra, we address the
evolution of the bulk system, including strangeness enhancement and the flavour
dependence of radial and elliptic flow. Utilising the fact that we can identify
strange baryons and mesons, we investigate different hadronization mechanisms
in the intermediate and high p regions. The ratios of the particle
yields, measured to high p, are used to further investigate the range and
applicability of the previously reported anomalous baryon production. We also
study two-particle azimuthal correlations of identified particles in order to
investigate any flavour dependence of jet fragmentation in the available
p range. Data was presented for a number of different collision systems
and energies.Comment: Proceedings of SQM'06 Conference, LA, 2006 (submitted to J. Phys. G
meson production and partonic collectivity at RHIC
New results on -meson production and elliptic flow measurements
from RHIC 2004 run (Run-IV) have been reviewed. In addition, the di-hadron
correlation function between the trigged and and the associated
soft particles was simulated. Knowledge about these results are discussed.Comment: 8 pages, 7 figures; Invited talk in International Conference on
Strangess in Quark Matter (SQM2006), UCLA, California, USA, March 26-31,
2006; to be publsihed in the Proceeding isuue of J. Phys.
Minijet deformation and charge-independent angular correlations on momentum subspace in Au-Au collisions at = 130 GeV
First measurements of charge-independent correlations on angular difference
variables (pseudorapidity) and (azimuth)
are presented for primary charged hadrons with transverse momentum GeV/ and from Au-Au collisions at
GeV. Strong charge-independent angular correlations are
observed associated with jet-like structures and elliptic flow. The width of
the jet-like peak on increases by a factor 2.3 from
peripheral to central collisions, suggesting strong coupling of semi-hard
scattered partons to a longitudinally-expanding medium. New methods of jet
analysis introduced here provide evidence for nonperturbative QCD medium
effects in heavy ion collisions.Comment: 8 pages, 4 figure
Measurements of meson production in relativistic heavy-ion collisions at RHIC
We present results for the measurement of meson production via its
charged kaon decay channel in Au+Au collisions at
, 130, and 200 GeV, and in and +Au collisions
at GeV from the STAR experiment at the BNL Relativistic
Heavy Ion Collider (RHIC). The midrapidity () meson transverse
momentum () spectra in central Au+Au collisions are found to be well
described by a single exponential distribution. On the other hand, the
spectra from , +Au and peripheral Au+Au collisions show power-law tails
at intermediate and high and are described better by Levy
distributions. The constant yield ratio vs beam species, collision
centrality and colliding energy is in contradiction with expectations from
models having kaon coalescence as the dominant mechanism for production
at RHIC. The yield ratio as a function of is consistent
with a model based on the recombination of thermal quarks up to GeV/, but disagrees at higher transverse momenta. The measured nuclear
modification factor, , for the meson increases above unity at
intermediate , similar to that for pions and protons, while is
suppressed due to the energy loss effect in central Au+Au collisions. Number of
constituent quark scaling of both and for the meson
with respect to other hadrons in Au+Au collisions at =200 GeV
at intermediate is observed. These observations support quark
coalescence as being the dominant mechanism of hadronization in the
intermediate region at RHIC.Comment: 22 pages, 21 figures, 4 table
Azimuthal anisotropy in Au+Au collisions at sqrtsNN = 200 GeV
The results from the STAR Collaboration on directed flow (v_1), elliptic flow
(v_2), and the fourth harmonic (v_4) in the anisotropic azimuthal distribution
of particles from Au+Au collisions at sqrtsNN = 200 GeV are summarized and
compared with results from other experiments and theoretical models. Results
for identified particles are presented and fit with a Blast Wave model.
Different anisotropic flow analysis methods are compared and nonflow effects
are extracted from the data. For v_2, scaling with the number of constituent
quarks and parton coalescence is discussed. For v_4, scaling with v_2^2 and
quark coalescence is discussed.Comment: 26 pages. As accepted by Phys. Rev. C. Text rearranged, figures
modified, but data the same. However, in Fig. 35 the hydro calculations are
corrected in this version. The data tables are available at
http://www.star.bnl.gov/central/publications/ by searching for "flow" and
then this pape
Enhanced strange baryon production in Au+Au collisions compared to p+p at sqrts = 200 GeV
We report on the observed differences in production rates of strange and
multi-strange baryons in Au+Au collisions at sqrts = 200 GeV compared to pp
interactions at the same energy. The strange baryon yields in Au+Au collisions,
then scaled down by the number of participating nucleons, are enhanced relative
to those measured in pp reactions. The enhancement observed increases with the
strangeness content of the baryon, and increases for all strange baryons with
collision centrality. The enhancement is qualitatively similar to that observed
at lower collision energy sqrts =17.3 GeV. The previous observations are for
the bulk production, while at intermediate pT, 1 < pT< 4 GeV/c, the strange
baryons even exceed binary scaling from pp yields.Comment: 7 pages, 4 figures. Printed in PR
Strangelet Search in AuAu Collisions at 200 GeV
We have searched for strangelets in a triggered sample of 61 million central
(top 4%) Au+Au collisions at \sNN = 200 GeV near beam rapidities at the STAR
detector. We have sensitivity to metastable strangelets with lifetimes of order
, in contrast to limits over ten times longer in AGS studies and
longer still at the SPS. Upper limits of a few 10^{-6} to 10^{-7} per central
Au+Au collision are set for strangelets with mass GeV/c^{2}.Comment: As publishe
Azimuthal anisotropy and correlations at large transverse momenta in and Au+Au collisions at = 200 GeV
Results on high transverse momentum charged particle emission with respect to
the reaction plane are presented for Au+Au collisions at =
200 GeV. Two- and four-particle correlations results are presented as well as a
comparison of azimuthal correlations in Au+Au collisions to those in at
the same energy. Elliptic anisotropy, , is found to reach its maximum at
GeV/c, then decrease slowly and remain significant up to
-- 10 GeV/c. Stronger suppression is found in the back-to-back
high- particle correlations for particles emitted out-of-plane compared to
those emitted in-plane. The centrality dependence of at intermediate
is compared to simple models based on jet quenching.Comment: 4 figures. Published version as PRL 93, 252301 (2004
Rapidity and Centrality Dependence of Proton and Anti-proton Production from Au+Au Collisions at sqrt(sNN) = 130GeV
We report on the rapidity and centrality dependence of proton and anti-proton
transverse mass distributions from Au+Au collisions at sqrt(sNN) = 130GeV as
measured by the STAR experiment at RHIC. Our results are from the rapidity and
transverse momentum range of |y|<0.5 and 0.35 <p_t<1.00GeV/c. For both protons
and anti-protons, transverse mass distributions become more convex from
peripheral to central collisions demonstrating characteristics of collective
expansion. The measured rapidity distributions and the mean transverse momenta
versus rapidity are flat within |y|<0.5. Comparisons of our data with results
from model calculations indicate that in order to obtain a consistent picture
of the proton(anti-proton) yields and transverse mass distributions the
possibility of pre-hadronic collective expansion may have to be taken into
account.Comment: 4 pages, 3 figures, 1 table, submitted to PR