1,627 research outputs found
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
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
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
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
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
Review of HBT or Bose-Einstein correlations in high energy heavy ion collisions
A brief review is given on the discovery and the first five decades of the
Hanbury Brown - Twiss effect and its generalized applications in high energy
nuclear and particle physics, that includes a meta-review. Interesting and
inspiring new directions are also highlighted, including for example source
imaging, lepton and photon interferometry, non-Gaussian shape analysis as well
as many other new directions. Existing models are compared to two-particle
correlation measurements and the so-called RHIC HBT puzzle is resolved.
Evidence for a (directional) Hubble flow is presented and the conclusion is
confirmed by a successful description of the pseudorapidity dependence of the
elliptic flow as measured in Au+Au collisions by the PHOBOS Collaboration.Comment: 14 pages, 1 figure, 8 sub-figures, invited plenary talk at the
ICPA-QGP 2005 conference in Kolkata, Indi
Angular hadron correlations probing the early medium evolution
Hard processes are a well calibrated probe to study heavy-ion collisions.
However, the information to be gained from the nuclear suppression factor R_AA
is limited, hene one has to study more differential observables to do medium
tomography. The angular correlations of hadrons associated with a hard trigger
appear suitable as they show a rich pattern when going from low p_T to high
p_T. Of prime interest is the fate of away side partons with an in-medium
pathlength O(several fm). At high p_T the correlations become dominated by the
punchtrough of the away side parton with subsequent fragmentation. We discuss
what information about the medium density can be gained from the data.Comment: Talk given at the 19th International Conference on Ultrarelativistic
Nucleus-Nucleus Collisions: Quark Matter 2006 (QM 2006), Shanghai, China,
14-20 Nov 200
Quarkonium Results in PbPb Collisions at CMS
We summarize the results from the study of charmonium and bottomonium via the
dimuon decay channel in PbPb collisions with the CMS experiment. We discuss the
observation of sequential suppression of the Upsilon states. We present
preliminary results of prompt J/psi and psi' production, as well as of
non-prompt J/psis coming from the weak decay of b-quarks. This latter
measurement is sensitive to b-quark energy loss. We discuss the results and
compare to model predictions.Comment: 8 pages, 4 figures. Proceedings of 29th Winter Workshop on Nuclear
Dynamic
Research Project as Boundary Object: negotiating the conceptual design of a tool for International Development
This paper reflects on the relationship between who one designs for and what one designs in the unstructured space of designing for political change; in particular, for supporting âInternational Developmentâ with ICT. We look at an interdisciplinary research project with goals and funding, but no clearly defined beneficiary group at start, and how amorphousness contributed to impact. The reported project researched a bridging tool to connect producers with consumers across global contexts and show players in the
supply chain and their circumstances. We explore how both the nature of the research and the toolâs function became contested as work progressed. To tell this tale, we invoke
the idea of boundary objects and the value of tacking back and forth between elastic meanings of the projectâs artefacts and processes. We examine the projectâs role in India, Chile and other arenas to draw out ways that it functioned as a catalyst and how absence of committed design choices acted as an unexpected strength in reaching its goals
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.
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