859 research outputs found
Anomalous centrality variation of minijet angular correlations in Au-Au collisions at 62 and 200 GeV from STAR
We have measured 2D autocorrelations for all charged hadrons in STAR with
0.15 GeV/c and 1 from Au+Au collisions at 62 and 200
GeV. The correlation structure is dominated by a peak centered at zero relative
opening angles on and which we hypothesize is caused by
minimum-bias jets (minijets). We observe a large excess of minijet correlations
in more-central Au-Au collisions relative to binary-collision scaling (more
correlated pairs than expected from surface emission or even volume emission).
We also observe a sudden increase of the minijet peak amplitude and
width relative to binary-collision scaling of scattered partons which occurs at
an energy-dependent centrality point. There is a possible scaling of the
transition point with transverse particle density.Comment: Quark Matter 2008 proceedings, submitted to Journal of Physics G. v2:
added STAR Collaboration to author lis
K* production in Cu+Cu and Au+Au collisions at sqrt(s_{NN}) = 62.4 GeV and 200 GeV in STAR
We report the measurements of spectra of up to intermediate
region in mid-rapidity through its hadronic decay channel using the STAR
detector in Au+Au and Cu+Cu collisions at = 62.4 GeV
and 200 GeV. Particle ratios such as and is used to
understand the rescattering and regeneration effect on production in
the hadronic medium. The measurement using a high statistics
Au+Au 200 GeV dataset and nuclear modification factor measurement supports the
quark coalescence model of particle production in the intermediate range.Comment: 5 page
STAR's measurement of Long-range forward-backward multiplicity correlations as the signature of "dense partonic matter" in the Heavy Ion collisions at 200 GeV.}
Forward-backward multiplicity correlations have been measured with the STAR
detector for Au+Au, Cu+Cu and {\it p+p} collisions at = 200
GeV. A strong, long-range correlation is observed for central heavy ion
collisions that vanishes in semi-peripheral events and {\it pp} collisions.
There is no apparent scaling of correlation strength with the number of
participants involved in the collision. Both the Dual Parton Model and the
Color Glass condensate indicate that the long range correlations are due to
multiple parton interactions. This suggests that the dense partonic matter
might have been created in mid-central and central Au+Au collisions at
= 200 GeV.Comment: 4 pages, 3 figures,presented at the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 200
production in p+p and Au+Au collisions in STAR
The study of quarkonium production in relativistic heavy ion collisions
provides insight into the properties of the produced medium. The lattice
studies show a sequential suppression of quarkonia states when compared to
normal nuclear matter; which further affirms that a full spectroscopy including
bottomonium can provide us a better thermometer for the matter produced under
extreme conditions in relativistic heavy ion collisions. With the completion of
the STAR Electromagnetic Calorimeter and with the increased luminosity provided
by RHIC in Run 6 and 7, the study of production via the di-electron
channel becomes possible. We present the results on measurements in
p+p collisions (from Run 6) along with the first results from Au+Au collisions
(in Run 7) at GeV from the STAR experiment.Comment: 4 pages and 2 figures, Oral Presentation at QM2008 February 4-10,
2008: Jaipur India. submitted to Journal Of Physics-G:Nuclear and Particle
Physic
Direct photon-charged hadron azimuthal correlations
Azimuthal correlations of direct photons at high transverse energy (8
E 16 GeV) with away-side hadrons of transverse momentum (3 p
6 GeV/c) have been measured over a broad range of centrality for
collisions and collisions at = 200 GeV. The presented
results are the first measurements at RHIC for -hadron azimuthal
correlations in collisions.Comment: 4 pages, 3 figure
Baryon to Meson Ratios on the Near and Away-Side of Jets and their Centrality Dependence at STAR
We measure relative abundances of , and
in near-side and away-side cones correlated with triggered high-
particles in Au + Au collisions at = 200 GeV.
The centrality dependence of identified particles in the triggered particle
cones is also presented. Particle yields and ratios are extracted on the
near-side and away-side of the trigger particle. The associate-particle ratios
are studied as a function of the angle relative to the trigger particle azimuth
. Such studies should help elucidate the origin of the
modifications in the jet like correlations observed in Au+Au collisions
relative to p+p collisions. And these studies also will help understand the
variation of local parton densities at the away side. We discuss how these
measurements might be related to several scenarios for interactions of fast
partons with the medium created in Au+Au collision.Comment: 6 pages, 4 figures, Proceedings for SQM 2007 Talk, Levoca, Slovakia,
June 24-29, 200
First results from Au+Au collisions at = 9.2 GeV in STAR
One of the primary aims of heavy-ion collisions is to map the QCD phase
diagram and search for different phases and phase boundaries. RHIC Energy Scan
Program was launched to address this goal by studying heavy-ion collisions at
different center of mass energies. The first test run with Au+Au collisions at
= 9.2 GeV took place in early 2008. The large acceptance STAR
detector has collected few thousands minimum bias collisions at this beam
energy. We present the first results for identified particle yields and
particle ratios. The results for the azimuthal anisotropy parameters and
and those from pion interferometry measurements are also discussed in
this paper. These results are compared to data from the SPS at similar beam
energies.Comment: six pages, eight figures, proceedings for the talk given at Strange
Quark Matter 2008, Beijing, China, October 6 - 10, 200
Strangeness and bulk freeze-out properties at RHIC
Identified charged kaon, pion, and proton spectra and ratios from sqrt(s_NN)
= 200 and 62.4 GeV Cu+Cu collisions are studied with a hydro-motivated
blast-wave and a statistical model framework in order to explore the
strangeness production at RHIC and characterize the bulk freeze-out properties
of the created system. The spectra are measured at mid-rapidity |y|<0.1 over
the transverse momentum range of 0.25 < p_T < 1.2 GeV/c with particle
identification derived from the ionization energy loss in the STAR Time
Projection Chamber.
The multi-dimensional systematic study of pi(+/-), K(+/-), p and pbar
production in Cu+Cu, Au+Au, d+Au and p+p collisions is used to discuss the
energy, system size and inferred energy density dependence of freeze-out
parameters and strangeness production. The new data from Cu+Cu collisions
bridge the gap between the smaller d+Au and larger Au+Au systems, allowing a
detailed study of the onset of strangeness equilibration at RHIC.Comment: 6 pages, 5 figures, proceedings to Strangeness in Quark Matter 200
Heavy-flavor correlation measurements via electron azimuthal correlations with open charm mesons
We report first STAR measurement on two heavy-flavor particle correlations in
p+p collisions at RHIC. Heavy-flavor (charm and bottom) events are identified
and separated on a statistical basis by the azimuthal correlation of their
decay electrons and open charm mesons, which yield important information about
the underlying production mechanism. The azimuthal correlation distribution
exhibits a two-peak structure which can be attributed to B decays on the
near-side and predominantly charm pair production on the away-side. These
assumptions are supported by dedicated simulations using PYTHIA and MC@NLO
event generators. This novel correlation technique will allow comprehensive
energy-loss measurements of heavy quarks in heavy-ion collisions.Comment: 6 pages, 3 figures. Invited talk at the International Conference on
Strangeness in Quark Matter, Levoca, Slovakia, June 24-29, 200
K* production in Heavy Ion Collisions at RHIC
Study of resonances with their short life-times provides useful tools to
probe the properties of hot and dense matter produced in relativistic heavy ion
collisions. The high density and/or high temperature of the medium can modify
resonance properties such as mass and width. Therefore, measurement of these
properties can reveal important information about the evolution dynamics in
heavy ion collisions. We report the measurements of transverse
momentum() spectra at mid-rapidity via its hadronic decay channel up to
intermediate of 2.9 GeV/c using the STAR detector in Au+Au and Cu+Cu
collisions at = 62.4 GeV and 200 GeV. These results are
compared to previously reported results from Au+Au collisions at RHIC.
Integrated yield ratios of and are used to understand
the rescattering and regeneration effects on production.Comment: 6 pages, SQM-07 proceeding
- …