583 research outputs found
Jets and jet-like correlations studies from STAR
I present recent results from jets and jet-like correlation measurements from
STAR. The pp data are compared to those from Au-Au collisions to attempt to
infer information on the medium produced and how hard scattered partons
interact with this matter. Results from d-Au events are utilized to investigate
the magnitude of cold nuclear matter effects on hard scatterings. The evolution
of the underlying event from pp to d-Au collisions is studied. In heavy-ion
collisions, background fluctuations are the major source of systematic
uncertainties in jet measurements. Detailed studies are therefore being made of
these fluctuations and recent progress in our understanding is reported. Jet
and jet-hadron correlations results are presented and give clear indications
that partonic fragmentation at RHIC is highly modified in the presence of a
strongly coupled coloured medium, resulting in a significant broadening and
softening of the jet fragments correlation. Finally di-hadron correlations
utilizing identified particles as triggers indicate that the "ridge" is
stronger for p+K than for pi but that the near-side peak per-trigger yield
remains unaltered from d-Au to Au-Au collisions.Comment: Proceedings for QM201
Centrality and transverse momentum dependence of elliptic flow of multi-strange hadrons and meson in Au+Au collisions at = 200 GeV
We present high precision measurements of elliptic flow near midrapidity
() for multi-strange hadrons and meson as a function of
centrality and transverse momentum in Au+Au collisions at center of mass energy
200 GeV. We observe that the transverse momentum dependence of
and is similar to that of and , respectively,
which may indicate that the heavier strange quark flows as strongly as the
lighter up and down quarks. This observation constitutes a clear piece of
evidence for the development of partonic collectivity in heavy-ion collisions
at the top RHIC energy. Number of constituent quark scaling is found to hold
within statistical uncertainty for both 0-30 and 30-80 collision
centrality. There is an indication of the breakdown of previously observed mass
ordering between and proton at low transverse momentum in the
0-30 centrality range, possibly indicating late hadronic interactions
affecting the proton .Comment: 7 pages and 4 figures, Accepted for publication in Physical Review
Letter
Observation of charge asymmetry dependence of pion elliptic flow and the possible chiral magnetic wave in heavy-ion collisions
We present measurements of and elliptic flow, , at
midrapidity in Au+Au collisions at 200, 62.4, 39, 27,
19.6, 11.5 and 7.7 GeV, as a function of event-by-event charge asymmetry,
, based on data from the STAR experiment at RHIC. We find that
() elliptic flow linearly increases (decreases) with charge asymmetry
for most centrality bins at and higher.
At , the slope of the difference of
between and as a function of exhibits a
centrality dependence, which is qualitatively similar to calculations that
incorporate a chiral magnetic wave effect. Similar centrality dependence is
also observed at lower energies.Comment: 6 pages, 4 figure
Observation of Transverse Spin-Dependent Azimuthal Correlations of Charged Pion Pairs in at GeV
We report the observation of transverse polarization-dependent azimuthal
correlations in charged pion pair production with the STAR experiment in
collisions at RHIC. These correlations directly probe quark
transversity distributions. We measure signals in excess of five standard
deviations at high transverse momenta, at high pseudorapidities eta>0.5, and
for pair masses around the mass of the rho-meson. This is the first direct
transversity measurement in p+p collisions. Comparing the results to data from
lepton-nucleon scattering will test the universality of these spin-dependent
quantities.Comment: 11 pages, 5 figures, 15 tables. Submitted to PR
Azimuthal anisotropy in U+U and Au+Au collisions at RHIC
Collisions between prolate uranium nuclei are used to study how particle
production and azimuthal anisotropies depend on initial geometry in heavy-ion
collisions. We report the two- and four-particle cumulants, and
, for charged hadrons from U+U collisions at =
193 GeV and Au+Au collisions at = 200 GeV. Nearly fully
overlapping collisions are selected based on the amount of energy deposited by
spectators in the STAR Zero Degree Calorimeters (ZDCs). Within this sample, the
observed dependence of on multiplicity demonstrates that ZDC
information combined with multiplicity can preferentially select different
overlap configurations in U+U collisions. An initial-state model with gluon
saturation describes the slope of as a function of multiplicity in
central collisions better than one based on Glauber with a two-component
multiplicity model.Comment: Final paper version accepted for publication in Phys. Rev. Lett. New
version includes comparisons to a constituent quark glauber mode
Energy dependence of acceptance-corrected dielectron excess mass spectrum at mid-rapidity in Au+Au collisions at and 200 GeV
The acceptance-corrected dielectron excess mass spectra, where the known
hadronic sources have been subtracted from the inclusive dielectron mass
spectra, are reported for the first time at mid-rapidity in
minimum-bias Au+Au collisions at = 19.6 and 200 GeV. The excess
mass spectra are consistently described by a model calculation with a broadened
spectral function for GeV/. The integrated
dielectron excess yield at = 19.6 GeV for
GeV/, normalized to the charged particle multiplicity at mid-rapidity, has
a value similar to that in In+In collisions at = 17.3 GeV. For
= 200 GeV, the normalized excess yield in central collisions is
higher than that at = 17.3 GeV and increases from peripheral to
central collisions. These measurements indicate that the lifetime of the hot,
dense medium created in central Au+Au collisions at = 200 GeV
is longer than those in peripheral collisions and at lower energies.Comment: 9 pages, 6 figure
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