637 research outputs found
The STAR Photon Multiplicity Detector
Details concerning the design, fabrication and performance of STAR Photon
Multiplicity Detector (PMD) are presented. The PMD will cover the forward
region, within the pseudorapidity range 2.3--3.5, behind the forward time
projection chamber. It will measure the spatial distribution of photons in
order to study collective flow, fluctuation and chiral symmetry restoration.Comment: 15 pages, including 11 figures; to appear in a special NIM volume
dedicated to the accelerator and detectors at RHI
A Honeycomb Proportional Counter for Photon Multiplicity Measurement in the ALICE Experiment
A honeycomb detector consisting of a matrix of 96 closely packed hexagonal
cells, each working as a proportional counter with a wire readout, was
fabricated and tested at the CERN PS. The cell depth and the radial dimensions
of the cell were small, in the range of 5-10 mm. The appropriate cell design
was arrived at using GARFIELD simulations. Two geometries are described
illustrating the effect of field shaping. The charged particle detection
efficiency and the preshower characteristics have been studied using pion and
electron beams. Average charged particle detection efficiency was found to be
98%, which is almost uniform within the cell volume and also within the array.
The preshower data show that the transverse size of the shower is in close
agreement with the results of simulations for a range of energies and converter
thicknesses.Comment: To be published in NIM
An Experimental Exploration of the QCD Phase Diagram: The Search for the Critical Point and the Onset of De-confinement
The QCD phase diagram lies at the heart of what the RHIC Physics Program is
all about. While RHIC has been operating very successfully at or close to its
maximum energy for almost a decade, it has become clear that this collider can
also be operated at lower energies down to 5 GeV without extensive upgrades. An
exploration of the full region of beam energies available at the RHIC facility
is imperative. The STAR detector, due to its large uniform acceptance and
excellent particle identification capabilities, is uniquely positioned to carry
out this program in depth and detail. The first exploratory beam energy scan
(BES) run at RHIC took place in 2010 (Run 10), since several STAR upgrades,
most importantly a full barrel Time of Flight detector, are now completed which
add new capabilities important for the interesting physics at BES energies. In
this document we discuss current proposed measurements, with estimations of the
accuracy of the measurements given an assumed event count at each beam energy.Comment: 59 pages, 78 figure
Longitudinal Spin Transfer to and Hyperons in Polarized Proton-Proton Collisions at = 200 GeV
The longitudinal spin transfer, , from high energy polarized protons
to and hyperons has been measured for the first time
in proton-proton collisions at with the STAR
detector at RHIC. The measurements cover pseudorapidity, , in the range
and transverse momenta, , up to . The longitudinal spin transfer is found to be for inclusive
and for
inclusive hyperons with and . The dependence on and is presented.Comment: 5 pages, 4 figure
Spin alignment measurements of the and vector mesons at RHIC
We present the first spin alignment measurements for the and
vector mesons produced at mid-rapidity with transverse momenta up
to 5 GeV/c at = 200 GeV at RHIC. The diagonal spin density
matrix elements with respect to the reaction plane in Au+Au collisions are
= 0.32 0.04 (stat) 0.09 (syst) for the
( GeV/c) and = 0.34 0.02 (stat) 0.03
(syst) for the ( GeV/c), and are constant with transverse
momentum and collision centrality. The data are consistent with the unpolarized
expectation of 1/3 and thus no evidence is found for the transfer of the
orbital angular momentum of the colliding system to the vector meson spins.
Spin alignments for and in Au+Au collisions were also measured
with respect to the particle's production plane. The result,
= 0.41 0.02 (stat) 0.04 (syst), is consistent with that in p+p
collisions, = 0.39 0.03 (stat) 0.06 (syst), also
measured in this work. The measurements thus constrain the possible size of
polarization phenomena in the production dynamics of vector mesons.Comment: 7 pages, 4 figures. fig.1 updated; one more reference added, one typo
corrected, published in PRC.77.06190
System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider
We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)
Measurements of meson production in relativistic heavy-ion collisions at RHIC
We present results for the measurement of meson production via its
charged kaon decay channel in Au+Au collisions at
, 130, and 200 GeV, and in and +Au collisions
at GeV from the STAR experiment at the BNL Relativistic
Heavy Ion Collider (RHIC). The midrapidity () meson transverse
momentum () spectra in central Au+Au collisions are found to be well
described by a single exponential distribution. On the other hand, the
spectra from , +Au and peripheral Au+Au collisions show power-law tails
at intermediate and high and are described better by Levy
distributions. The constant yield ratio vs beam species, collision
centrality and colliding energy is in contradiction with expectations from
models having kaon coalescence as the dominant mechanism for production
at RHIC. The yield ratio as a function of is consistent
with a model based on the recombination of thermal quarks up to GeV/, but disagrees at higher transverse momenta. The measured nuclear
modification factor, , for the meson increases above unity at
intermediate , similar to that for pions and protons, while is
suppressed due to the energy loss effect in central Au+Au collisions. Number of
constituent quark scaling of both and for the meson
with respect to other hadrons in Au+Au collisions at =200 GeV
at intermediate is observed. These observations support quark
coalescence as being the dominant mechanism of hadronization in the
intermediate region at RHIC.Comment: 22 pages, 21 figures, 4 table
Pion interferometry in Au+Au collisions at = 200 GeV
We present a systematic analysis of two-pion interferometry in Au+Au
collisions at = 200 GeV using the STAR detector at RHIC. We
extract the HBT radii and study their multiplicity, transverse momentum, and
azimuthal angle dependence. The Gaussianess of the correlation function is
studied. Estimates of the geometrical and dynamical structure of the freeze-out
source are extracted by fits with blast wave parameterizations. The expansion
of the source and its relation with the initial energy density distribution is
studied.Comment: 21 pages, 30 figures. As published in Physics Review
Inclusive pi^0, eta, and direct photon production at high transverse momentum in p+p and d+Au collisions at sqrt(s_NN) = 200 GeV
We report a measurement of high-p_T inclusive pi^0, eta, and direct photon
production in p+p and d+Au collisions at sqrt(s_NN) = 200 GeV at midrapidity (0
gamma gamma were detected in the
Barrel Electromagnetic Calorimeter of the STAR experiment at the Relativistic
Heavy Ion Collider. The eta -> gamma gamma decay was also observed and
constituted the first eta measurement by STAR. The first direct photon cross
section measurement by STAR is also presented, the signal was extracted
statistically by subtracting the pi^0, eta, and omega(782) decay background
from the inclusive photon distribution observed in the calorimeter. The
analysis is described in detail, and the results are found to be in good
agreement with earlier measurements and with next-to-leading order perturbative
QCD calculations.Comment: 28 pages, 30 figures, 6 tables, the updated version that was accepted
by Phys. Rev.
Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy ion collisions
Parity-odd domains, corresponding to non-trivial topological solutions of the
QCD vacuum, might be created during relativistic heavy-ion collisions. These
domains are predicted to lead to charge separation of quarks along the orbital
momentum of the system created in non-central collisions. To study this effect,
we investigate a three particle mixed harmonics azimuthal correlator which is a
\P-even observable, but directly sensitive to the charge separation effect. We
report measurements of this observable using the STAR detector in Au+Au and
Cu+Cu collisions at =200 and 62~GeV. The results are presented
as a function of collision centrality, particle separation in rapidity, and
particle transverse momentum. A signal consistent with several of the
theoretical expectations is detected in all four data sets. We compare our
results to the predictions of existing event generators, and discuss in detail
possible contributions from other effects that are not related to parity
violation.Comment: 17 pages, 14 figures, as accepted for publication in Physical Review
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