199 research outputs found
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
Open Charm Production at STAR
We present the open charm spectra at mid-rapidity from direct reconstruction
of D0, D* and D+/- in d+Au collisions at sqrt(sNN)=200 GeV using the STAR
detector at RHIC. The indirect electron/positron measurements via charm
semileptonic decays in p+p and d+Au collisions are also reported. The total
c\bar(c) cross section per nucleon-nucleon collision is extracted from both
direct and indirect measurements and are consistent with each other. By
combining the D0 and semileptonic measurements together, the cross section of
1.4+/-0.2+/-0.4 mb is higher than expectations from PYTHIA and other pQCD
calculations. The open charm pT distribution from direct measurements covers
the pT range up to ~10 GeV/c and follows a power-law distribution.Comment: 7 pages, 4 figures, proceedings for Hot Quark 04 Conference.
submitted to J. Phys. G: Nucl. Phy
Multi-strange baryon production in Au+Au collisions at top RHIC energy as a probe of bulk properties
We report STAR preliminary results on multi-strange baryon production in
Au+Au collisions at sqrt(s_NN)=200 GeV at RHIC. Its implication for the
formation of a new state of matter is discussed. The system size dependence on
the production of strange baryons is investigated to study the onset of strange
quark equilibration in the medium. The nuclear modification factor of Lambda,
Xi and Omega is also presented. Its suppression at p_T>3 GeV/c supports the
formation of a dense interacting medium at RHIC. The spectra of multi-strange
baryons reveal that within a hydro-inspired model, they may decouple prior than
lighter particles and that their flow may be mostly developed at a partonic
level. This idea is emphasized by the measurement of the v_2 of Xi+AntiXi and
Omega+AntiOmega whose behaviour is close to the Lambda+AntiLambda baryon
elliptic flow in the intermediate p_T region where a constituent quark scaling
of v_2 is observed.Comment: 8 pages, 8 figures, Strange Quark Matter 2004 conference proceeding
Strangeness and the discovery of quark-gluon plasma
Strangeness flavor yield s and the entropy yield S are the observables of the
deconfined quark-gluon state of matter which can be studied in the entire
available experimental energy range at AGS, SPS, RHIC, and, in near future, at
the LHC energy range. We present here a comprehensive analysis of strange, soft
hadron production as function of energy and reaction volume. We discuss the
physical properties of the final state and argue how evidence about the
primordial QGP emerges.Comment: 16 pages: Invited talk at 5th International Conference on Physics and
Astrophysics of Quark Gluon Plasma, February 8 - 12, 2005, Salt Lake City,
Kolkata, India, to appear in: Journal of Physics: Conference Serie
Observation of modified hadronization in relativistic Au+Au collisions: a promising signature for deconfined quark-gluon matter
Measurements of identified particles from Au+Au collisions at
GeV are reviewed. Emphasis is placed on nuclear
modification, baryon-to-meson ratios, and elliptic flow at intermediate
transverse momentum ( GeV/c). Possible connections between (1)
these measurements, (2) the running coupling for static quark anti-quark pairs
at finite temperature, and (3) the creation of a deconfined quark-gluon phase
are presented. Modifications to hadronization in Au+Au collisions are proposed
as a likely signature for the creation of deconfined colored matter.Comment: 8 pages, 5 figures, invited talk at the Strange Quark Matter 2004
conference, Cape Town, South Afric
Hydrodynamic emission of strange and non-strange particles at RHIC and LHC
The hydrodynamic model is used to describe the single-particle spectra and
elliptic flow of hadrons at RHIC and to predict the emission angle dependence
of HBT correlations at RHIC and LHC energies.Comment: 6 pages LaTeX, 3 postscript figures. Proceedings for the conference
"Strange Quark Matter 2003", Atlantic Beach, NC, March 12-17, 2003, to appear
in J. Phys.
Space-time analysis of reaction at RHIC
Space-time information about the Au-Au collisions produced at RHIC are key
tools to understand the evolution of the system and especially assess the
presence of collective behaviors. Using a parameterization of the system's
final state relying on collective expansion, we show that pion source radii can
be tied together with transverse mass spectra and elliptic flow within the same
framework. The consistency between these different measures provide a solid
ground to understand the characteristics of collective flow and especially the
possible peculiar behavior of particles such as Xi, Omega or phi. The validity
of the short time scales that are extracted from fits to the pion source size
is also addressed. The wealth of new data that will soon be available from
Au-Au collisions at sqrt{s_{NN}} = 200 GeV, will provide a stringet test of the
space-time analysis framework developped in these proceedings.Comment: Invited talk given at the SQM2003 conference (March 2003), to be
published in Journal of Physics G. 10 pages, 3 figure
Bulk properties and flow
In this report, I summarize the experimental results on {\bf bulk properties
and flow} presented at Quark Matter 2004. It is organized in four sections: 1)
Initial condition and stopping; 2) Particle spectra and freeze-outs; 3)
Anisotropic flow; 4) Outlook for future measurements.Comment: 10 pages, 4 figures, "Rapporteur-Conference Highlights", Quark Matter
2004, Oakland, January 11-1
A study on the anomaly of over ratios in collisions with jet quenching
The ratios of at large transverse momentum in central
collisions at RHIC are studied in the framework of jet quenching based on a
next-to-leading order pQCD parton model. It is shown that theoretical
calculations with a gluon energy loss larger than the quark energy loss will
naturally lead to a smaller ratios at large transverse momentum in
collisions than those in collisions at the same energy. Scenarios
with equal energy losses for gluons and quarks and a strong jet conversion are
both explored and it is demonstrated in both scenarios ratios at high
in central collisions are enhanced and the calculated ratios of
protons over pions approach to the experimental measurements. However, in the latter scenario is found to fit data better than that in the
former scenario.Comment: 20 pages, 13 figures; revised version; accepted for publication in
Journal of Physics
Is Strangeness still interesting at RHIC ?
With the advent of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven
National Laboratory (BNL), Heavy Ion Physics will enter a new energy regime.
The question is whether the signatures proposed for the discovery of a phase
transition from hadronic matter to a Quark Gluon Plasma (QGP), that were
established on the basis of collisions at the BEVALAC, the AGS, and the SPS,
respectively, are still useful and detectable at these high incident energies.
In the past two decades, measurements related to strangeness formation in the
collision were advocated as potential signatures and were tested in numerous
fixed target experiments at the AGS and the SPS. In this article I will review
the capabilities of the RHIC detectors to measure various aspects of
strangeness, and I will try to answer the question whether the information
content of those measurements is comparable to the one at lower energies.Comment: 12 pages, 7 figures, Invited Talk at the IV International Conference
on Strangeness in Quark Matter, Padova (Italy), July 20-24, 199
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