581 research outputs found
Strangelet search at RHIC
Two position sensitive Shower Maximum Detector (SMDs) for Zero-Degree
Calorimeters (ZDCs) were installed by STAR before run 2004 at both upstream and
downstream from the interaction point along the beam axis where particles with
small rigidity are swept away by strong magnetic field. The ZDC-SMDs provides
information about neutral energy deposition as a function of transverse
position in ZDCs. We report the preliminary results of strangelet search from a
triggered data-set sampling 100 million Au+Au collisions at top RHIC energy.Comment: Strange Quark Matter 2004 conference proceedin
Longitudinal double-spin asymmetry for inclusive jet production in p+p collisions at sqrt(s)=200 GeV
We report a new STAR measurement of the longitudinal double-spin asymmetry
A_LL for inclusive jet production at mid-rapidity in polarized p+p collisions
at a center-of-mass energy of sqrt(s) = 200 GeV. The data, which cover jet
transverse momenta 5 < p_T < 30 GeV/c, are substantially more precise than
previous measurements. They provide significant new constraints on the gluon
spin contribution to the nucleon spin through the comparison to predictions
derived from one global fit of polarized deep-inelastic scattering
measurements.Comment: 7 pages, 4 figures + 1 tabl
Identified baryon and meson distributions at large transverse momenta from Au+Au collisions at GeV
Transverse momentum spectra of , and up to 12 GeV/c
at mid-rapidity in centrality selected Au+Au collisions at GeV are presented. In central Au+Au collisions, both and
show significant suppression with respect to binary scaling at
4 GeV/c. Protons and anti-protons are less suppressed than
, in the range 1.5 6 GeV/c. The and
ratios show at most a weak dependence and no significant
centrality dependence. The ratios in central Au+Au collisions approach
the values in p+p and d+Au collisions at 5 GeV/c. The results at high
indicate that the partonic sources of , and have
similar energy loss when traversing the nuclear medium.Comment: 6 pages, 4 figure
Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive midrapidity jet production in
polarized proton collisions at sqrt(s)=200 GeV. The cross section data cover
transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order
perturbative QCD evaluations. The A_LL data cover 5 < pT < 17 GeV/c and
disfavor at 98% C.L. maximal positive gluon polarization in the polarized
nucleon.Comment: 6 pages, 3 figures. Minor changes from review process in Phys. Rev.
Lett. Plain text tables of data in STAR publications may be found at
http://www.star.bnl.gov/central/publications
Multiplicity and Pseudorapidity Distributions of Charged Particles and Photons at Forward Pseudorapidity in Au + Au Collisions at sqrt{s_NN} = 62.4 GeV
We present the centrality dependent measurement of multiplicity and
pseudorapidity distributions of charged particles and photons in Au + Au
collisions at sqrt{s_NN} = 62.4 GeV. The charged particles and photons are
measured in the pseudorapidity region 2.9 < eta < 3.9 and 2.3 < eta < 3.7,
respectively. We have studied the scaling of particle production with the
number of participating nucleons and the number of binary collisions. The
photon and charged particle production in the measured pseudorapidity range has
been shown to be consistent with energy independent limiting fragmentation
behavior. The photons are observed to follow a centrality independent limiting
fragmentation behavior while for the charged particles it is centrality
dependent. We have carried out a comparative study of the pseudorapidity
distributions of positively charged hadrons, negatively charged hadrons,
photons, pions, net protons in nucleus--nucleus collisions and pseudorapidity
distributions from p+p collisions. From these comparisons we conclude that
baryons in the inclusive charged particle distribution are responsible for the
observed centrality dependence of limiting fragmentation. The mesons are found
to follow an energy independent behavior of limiting fragmentation while the
behavior of baryons seems to be energy dependent.Comment: 17 pages and 20 figure
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
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
Isolation of Flow and Nonflow Correlations by Two- and Four-Particle Cumulant Measurements of Azimuthal Harmonics in 200 GeV Au+Au Collisions
A data-driven method was applied to measurements of Au+Au collisions at
200 GeV made with the STAR detector at RHIC to isolate
pseudorapidity distance -dependent and -independent
correlations by using two- and four-particle azimuthal cumulant measurements.
We identified a component of the correlation that is -independent,
which is likely dominated by anisotropic flow and flow fluctuations. It was
also found to be independent of within the measured range of
pseudorapidity . The relative flow fluctuation was found to be for particles of transverse momentum
less than GeV/. The -dependent part may be attributed to
nonflow correlations, and is found to be relative to the
flow of the measured second harmonic cumulant at
- …