204 research outputs found
Recent high pT measurements in STAR
After five years of data taking, the STAR experiment at the Relativistic
Heavy Ion Collider (RHIC) at Brookhaven National Laboratory provides precise
measurements of particle production at high transverse momentum in p-p, d-Au,
and Au-Au collisions at sqrt(s) = 200 GeV. We review recent results on the
flavor dependence of high pT particle suppression and hadron particle spectra
at sqrt(s) = 62.4 GeV. New results on two-particle angular correlations for
identified trigger particles and for low momentum associated charged hadrons in
p-p and Au-Au as well as near-side correlations will be presented
and discussed.Comment: 5th International Conference on Physics and Astrophysics of Quark
Gluon Plasma, Calcutta. 8 pages, 10 figures, submitted to J. Phys. G: Nucl.
Part. Phy
Overview on jet results from STAR
Full jet reconstruction allows access to the parton kinematics over a large
energy domain and can be used to constrain the mechanisms of energy loss in
heavy-ion collisions. Such measurements are challenging at RHIC, due to the
high-multiplicity environments created in heavy-ion collisions. In these
proceedings, we report an overview of the results on full jet reconstruction
obtained by the STAR experiment. Jet measurements in 200 GeV p+p show that jets
are calibrated pQCD probes and provide a baseline for jet measurements in Au+Au
collisions. Inclusive differential jet production cross sections and ratios are
reported for central 200 GeV Au+Au collisions and compared to p+p. We also
present measurements of fully reconstructed di-jets at mid-rapidity, and
compare spectra and fragmentation functions in p+p and central Au+Au
collisions.Comment: Proceedings for the 26th WWND conferenc
Traces of Thermalization at RHIC
I argue that measurements of Au+Au collisions at 20, 130 and 200 GeV of the
centrality dependence of the mean p_t together with p_t and net-charge
fluctuations reflect the approach to local thermal equilibrium.Comment: 4 pages, 4 eps figures, for proc. Quark Matter 2004, to be published
in J. Phys.
Heavy ion collisions: Correlations and Fluctuations in particle production
Correlations and fluctuations (the latter are directly related to the
2-particle correlations) is one of the important directions in analysis of
heavy ion collisions. At the current stage of RHIC exploration, when the
details matter, basically any physics question is addressed with help of
correlation techniques. In this talk I start with a general introduction to the
correlation and fluctuation formalism and discuss weak and strong sides of
different type of observables. In more detail, I discuss the two-particle
correlations/\mpt fluctuations. In spite of not observing any dramatic
changes in the event-by-event fluctuations with energy, which would indicate a
possible phase transition, such correlations measurements remain an interesting
and important subject, bringing valuable information. Lastly, I show how radial
flow can generate characteristic azimuthal, transverse momentum and rapidity
correlations, which could qualitatively explain many of recently observed
phenomena in nuclear collisions.Comment: 8 pages, 8 figures. Invited talk at 5th International Conference on
Physics and Astrophysics of Quark Gluon Plasma, February 8-12, 2005, Salt
Lake City, Kolkata, Indi
Event-by-Event Fluctuations at 40, 80, and 158 AGeV/c in Pb+Au Collisions
Event-by-event fluctuations of mean pt and net charge in 40, 80, and 158
AGeV/c Pb+Au collisions are presented. The observed dynamical mean pt
fluctuations in central events of about 1 % are very similar to results from
RHIC. The centrality dependence of mean pt fluctuations at 158 AGeV/c shows a
peculiar non-monotonic pattern with respect to the extrapolation from the
fluctuations measured in p+p collisions. Dynamical net charge fluctuations
smaller than the charge conservation limit are observed. After correction for
charge conservation, the measured fluctuation signal in central events is
comparable to RHIC results.Comment: 4 pages, 6 figures, proceedings of the Quark Matter 2004, in Oakland,
USA, to be published in Journal of Physics G: Nuclear and Particle Physic
Global polarization measurement in Au+Au collisions
The system created in non central relativistic nucleus-nucleus collisions
carries large angular orbital momentum. Due to spin-orbital coupling, produced
particles could be globally polarized along the direction of the system angular
momentum. We present results of a measurement of Lambda hyperon global
polarization in Au+Au collisions at the center of mass energies 62 and 200 GeV
with the STAR detector at RHIC. The observed global polarization of Lambda
hyperons in the STAR acceptance is consistent with zero within the precision of
the measurement. The obtained upper limit, |P_Lambda| < 0.01, is significantly
below the theoretical values discussed recently in the literature.Comment: Talk given at SQM 2006, International Conference on Strangeness in
Quark Matter, March 26-31, 2006, Los Angeles CA; 4 pages, 2 figure
An Overview of Fluctuation and Correlation Results in Relativistic Heavy Ion Collisions
A great deal of recent data on event-by-event fluctuation and correlation
measurements has been released by several experiments at the SPS and RHIC.
Recent results on charge fluctuations, balance functions in pseudorapidity, and
average transverse momentum fluctuations will be reviewed. The results will be
compared to various model predictions after examining contributions to each
observable from known physics processes.Comment: 8 pages, 3 figures. Contribution to the Proceedings of the 17th
International Conference on Ultra Relativistic Nucleus-Nucleus Collisions
(Quark Matter 2004), Oakland, California, 11-17 Jan 2004. Submitted to
J.Phys.
K0s and \Lambda\ production in Pb--Pb collisions with the ALICE experiment
We present the study of K0s and Lambda production performed with the ALICE
experiment at the LHC in Pb--Pb collisions at \sqrt{s_NN}=2.76 TeV and pp
collisions at \sqrt{s}=0.9 and 7 TeV. The K0s and Lambda particles are
reconstructed via their V0 decay topology allowing their identification up to
high transverse momenta. The corresponding baryon/meson ratios as a function of
transverse momentum are extracted for Pb--Pb collisions in centrality bins and
in the transverse momentum range from 1 to 6 GeV/c. They are also compared with
those measured in pp events at the LHC energies of 0.9 and 7 TeV as well as in
Au--Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV from RHIC.Comment: 4 pages, 4 figures, proceedings of Quark Matter 2011 (May 23rd-28th
2011, Annecy, France
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
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