193 research outputs found
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
Strangeness production in jets from p+p \sqrt{s} = 200 GeV collisions
Measurements of strangeness production in jets help illuminate the QCD
mechanisms in fragmentation. Furthermore, they provide a crucial baseline for
heavy-ion studies where modifications in jet chemistry have recently been
predicted. We present new results on strange particle production in jets from
p+p \sqrt{s} = 200 GeV collisions measured by the STAR experiment. The momentum
distributions of the \Lambda, \bar{\Lambda} and K0Short particles are obtained
using various jet finding algorithms, and then compared to various models.
Strange particle ratios in jets are obtained and compared to values obtained
from the inclusive spectra. Finally, we show jets tagged with leading strange
baryons and mesons, in order to investigate whether gluon or quark jets can be
isolated in this way.Comment: 5 pages, 4 figures, Winter Workshop on Nuclear Dynamics 2010, Jamaic
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
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
Jet reconstruction and underlying event studies in p+p and d+Au collisions from STAR
Description of parton interaction with the hot and dense nuclear matter
created in heavy-ion collisions at high energies is a complex task, which
requires a detailed knowledge of jet production in p+p and d+Au collisions.
Measurements in these collision systems are therefore essential to disentangle
initial state nuclear effects from cold nuclear matter effects, medium-induced
broadening and jet quenching. To obtain complete description of the p+p
(d+Au) collision it is also important to study particle production in the
underlying event. The measured properties of underlying event can be used to
tune the QCD based Monte-Carlo models.
In this paper some of the recent results on jet and underlying event
properties in p+p and d+Au collisions at = 200 GeV measured by
the STAR experiment are presented. In particular, the preliminary results on
charged and strange particle fragmentation functions in p+p collisions are
discussed and confronted with PYTHIA simulations. Next, the measurement of
inclusive jet spectrum and di-jet correlations in d+Au collisions is presented
and compared with the measurements in p+p collisions to estimate the size of
cold nuclear matter effects. Finally, the study of underlying event properties
in p+p collisions is shown and compared to PYTHIA simulation.Comment: 9 pages, 8 figures, proceedings of the 27th Winter Workshop on
Nuclear Dynamics, Winter Park, Colorado, US
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
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
Energy dependence of kaon production in central Pb+Pb collisions
Recent results from the NA49 experiment on the energy dependence of charged
kaon production in central Pb+Pb collisions are presented. First results from
the new data at 80 AGeV beam energy are compared with those from lower and
higher energies. A difference in the energy dependence of the /
and / ratios is observed. The / ratio shows a
non-monotonic behaviour with a maximum near 40 AGeV.Comment: 8 pages, 7 figures, proceedings of talk at SQM2001, Frankfurt,
Germany, to appear in J. Phys.
Reconstructed Jets at RHIC
To precisely measure jets over a large background such as pile up in high
luminosity p+p collisions at LHC, a new generation of jet reconstruction
algorithms is developed. These algorithms are also applicable to reconstruct
jets in the heavy ion environment where large event multiplicities are
produced. Energy loss in the medium created in heavy ion collisions are already
observed indirectly via inclusive hadron distributions and di-hadron
correlations. Jets can be used to study this energy loss in detail with reduced
biases. We review the latest results on jet-medium interactions as seen in A+A
collisions at RHIC, focusing on the recent progress on jet reconstruction in
heavy ion collisions.Comment: Proceedings for the 26th Winter Workshop on Nuclear Dynamic
Resonances and fluctuations of strange particle in 200 GeV Au-Au collisions
We perform an analysis of preliminary data on strange particles yields and
fluctuations within the Statistical hadronization model. We begin by describing
the theoretical disagreements between different statistical models currently on
the market. We then show how the simultaneous analysis of yields and
fluctuations can be used to differentiate between the different models, and
determine if one of them can be connected to underlying physics. We perform a
study on a RHIC 200 GeV data sample that includes stable particles, resonances,
and the event-by-event fluctuation of the ratio. We show that the
equilibrium statistical model can not describe the fluctuation, unless an
unrealistically small volume is assumed. Such small volume then makes it
impossible to describe the total particle multiplicity. The non-equilibrium
model,on the other hand, describes both the fluctuation and yields
acceptably due to the extra boost to the fluctuation provided by the high
pion chemical potential. and abundance is described
within error bars, but the is under-predicted to 1.5 standard
deviations. We suggest further measurements that have the potential to test the
non-equilibrium model, as well as gauge the effect of re-interactions between
hadronization and freeze-out.Comment: References added, equations corrected. As accepted for publication by
Journal of Physics
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