67 research outputs found
Longitudinal spin transfer of Lambda and anti-Lambda in polarized pp collisions at \sqrt s=200 GeV at STAR
We report our measurement on longitudinal spin transfer, D_LL, from high
energy polarized protons to and hyperons in
proton-proton collisions at with the STAR detector at
RHIC. The current measurements cover , pseudorapidity
and transverse momenta up to using the data taken
in 2005. The longitudinal spin transfer is found to be D_LL= -0.03\pm 0.13
(stat) \pm 0.04(syst)\LambdaD_{LL} = -0.12 \pm
0.08(stat) \pm 0.03(syst)\bar{\Lambda} =
0.5 = 3.7 GeV/c$. The prospects with 2009 data and the future
measurements are also given.Comment: 6 pages, 3 figures, presentation at the SPIN2010 International
Symposium, Juelich (Germany), Sep. 27-Oct. 2, 201
Test of Chemical freeze-out at RHIC
We present the results of a systematic test applying statistical thermal
model fits in a consistent way for different particle ratios, and different
system sizes using the various particle yields measured in the STAR experiment.
Comparison between central and peripheral Au+Au and Cu+Cu collisions with data
from p+p collisions provides an interesting tool to verify the dependence with
the system size. We also present a study of the rapidity dependence of the
thermal fit parameters using available data from RHIC in the forward rapidity
regions and also using different parameterization for the rapidity distribution
of different particles.Comment: SQM2008 conference proceeding
Open heavy flavor production at RHIC
The study of heavy flavor production in relativistic heavy ion collisions is
an extreme experimental challenge but provides important information on the
properties of the Quark-Gluon Plasma (QGP) created in Au+Au collisions at RHIC.
Heavy-quarks are believed to be produced in the initial stages of the
collision, and are essential on the understanding of parton energy loss in the
dense medium created in such environment. Moreover, heavy-quarks can help to
investigate fundamental properties of QCD in elementary p+p collisions. In this
work we review recent results on heavy flavor production and their interaction
with the hot and dense medium at RHIC.Comment: Quark Matter 2006 proceedings, 8 pages, 5 figure
High pT correlations with strange particles in STAR
We present the highlights of the current identified strange particles
DeltaPhi and DeltaEta correlations analyses, including system-size and
trigger-pT of the jet and ridge, jet, ridge and away-side meson/baryon ratios,
and the current state of the multi-strange baryon analysis. We see clear
azimuthal peaks of comparable strength for all strange baryons and K0-short
mesons. We see no observable species dependence on the same-side jet or ridge
yields as a function of pT. However, while the away side and the ridge have
Lambda to K0-short ratio similar to that of the bulk, the jet-only ratio is
similar to that in . The implications of these findings on current
in-medium jet theoretical explanations are discussed.Comment: Proceedings for the Strangeness in Quark Matter 2007 Conference in
Levoca, Slovaki
Heavy Flavor Production at STAR
e present measurements on meson production via direct reconstruction of
its hadronic decay channel in minimum bias +Au and Au+Au
collisions at =200 GeV with up to 3 GeV/.
Non-photonic electron spectra from the charm semi-leptonic decays are analyzed
from the same data set as well as in + collision at =200 GeV
using the STAR Time-of-Flight (TOF) and Barrel EMC (BEMC) detectors,
respectively. Results of the charm-decayed single muon (prompt muon) spectra
are also presented at low in Au+Au collisions measured by the TOF
detector. The charm production total cross-section per nucleon-nucleon
collision is measured to be 1.260.09(stat.)0.23(sys.) mb in minimum
bias Au+Au collisions, which is consistent with the scaling compared
to 1.40.4 mb in minimum bias +Au collisions, and supports the
idea that charm quarks should be produced mostly via parton fusion at early
stage in relativistic heavy-ion collisions. A Blast-Wave model fit to the low
( GeV/c) non-photonic electrons, prompt muons and spectra shows
that charm hadrons may kinetically freeze-out earlier than light hadrons with a
smaller collective velocity. The nuclear modification factors () of the
non-photonic electrons in central Au+Au collisions are significantly below
unity at 2 GeV/, which indicates a significant amount of energy
loss for heavy quarks in Au+Au collisions. The charm transverse momentum
distribution must have been modified by the hot and dense matter created in
central Au+Au collisions at RHIC.Comment: 7 pages, 4 figures, proceedings for the Strange Quark Matter 2006
conferenc
On saturation of charged hadron production in pp collisions at LHC
First results on charged hadron transverse momentum spectra in pp collisions
obtained by the CMS Collaboration at LHC were analyzed in z-scaling approach.
The first LHC data confirm z-scaling. The saturation regime of the scaling
function psi(z) observed in pp and antp-pp interactions at lower energy sqrt s
= 19-1960 GeV is verified. The saturation of psi(z) for charged hadrons is
found down to z=0.05 at the highest energy sqrt s = 2360 GeV reached till now
at colliders. A microscopic scenario of hadron production is discussed in
connection with search for new signatures of phase transitions in hadron
matter. Constituent energy loss and its dependencies on the transverse momentum
of charged hadrons and collision energy are estimated. The beam energy scan at
LHC in the saturation region is suggested.Comment: LaTeX, 6 pages, 6 figure
Overview of Strangeness Production at the STAR Experiment
We present an overview of recent STAR results on strangeness production in
p+p and heavy-ion collisions at RHIC. In both Cu+Cu and Au+Au collisions we
show the centrality dependencies of bulk yield and mid- spectrum
measurements with new comparisons to theory. The latest results for
strange particles are presented and prospects for strangeness production in the
low energy scan program will be outlined. Finally, we report new measurements
of strangeness fragmentation functions for jets in p+p collisions.Comment: 8 pages, 7 figures, proceedings for SQM 200
STAR Results on High Transverse Momentum, Heavy Flavor and Electromagnetic Probes
We summarize here recent results from the STAR collaboration focusing on
processes involving large momentum transfers. Measurements of angular
correlations of di-hadrons are explored in both the pseudorapidity (eta) and
azimuthal (phi) projections. In central Au+Au, an elongated structure is found
in the eta projection which persists up to the highest measured pT. After
quantifying the particle yield in this structure and subtracting it from the
near-side yield, we observe that the remainder exhibits a behavior strikingly
similar to that of the near-side yield in d+Au. For heavy flavor production,
using electron-hadron correlations in p+p collisions, we obtain an estimate of
the b-quark contribution to the non-photonic electrons in the pT region 3-6
GeV/c, and find it consistent with FONLL calculations. Together with the
observed suppression of non-photonic electrons in Au+Au, this strongly suggests
suppression of b-quark production in Au+Au collisions. We discuss results on
the mid-rapidity Upsilon cross-section in p+p collisions. Finally, we present a
proof-of-principle measurement of photon-hadron correlations in p+p collisions,
paving the way for the tomographic study of the matter produced in central
Au+Au via gamma-jet measurements.Comment: 8 pages, 4 figures. Proceedings of "Quark Matter 2006", 19th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collision
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
Exploring Early Parton Momentum Distribution with the Ridge from the Near-Side Jet
In a central nucleus-nucleus collision at high-energies, medium partons
kicked by a near-side jet acquire a momentum along the jet direction and
subsequently materialize as the observed ridge particles. They carry direct
information on the early parton momentum distribution which can be extracted by
using the ridge data for central AuAu collisions at \sqrt{s_{NN}}=200 GeV. The
extracted parton momentum distribution has a thermal-like transverse momentum
distribution but a non-Gaussian, relatively flat rapidity distribution at
mid-rapidity with sharp kinematic boundaries at large rapidities that depend on
the transverse momentum.Comment: In Proceedings of 20th International Conference on Ultra-Relativistic
Nucleus Nucleus Collisions, Jaipur, India, Feb. 4-10, 200
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