167 research outputs found
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
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
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity 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 Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
Correlations and Fluctuations in STAR
We report measurements for the balance function, transverse momentum
fluctuations, and net charge fluctuations from Au+Au collisions at 20, 130, and
200 GeV as well as p+p and d+Au collisions at 200 GeV using STAR at RHIC. For
Au+Au collisions at 200 GeV, we observe a narrowing of the balance function in
central collisions. We observe dynamic transverse momentum fluctuations at all
incident energies. Observables related to transverse momentum fluctuations and
net charge fluctuations are similar for peripheral Au+Au collisions and
inclusive p+p collisions while central Au+Au collisions deviate significantly
from HIJING predictions.Comment: 4 pages, 3 figures, Contribution to Quark Matter 2004 Proceeding
Strange Resonance Production in p+p and Au+Au Collisions at RHIC Energies
Resonance yields and spectra from elementary p+p and Au+Au collisions at
200 GeV from the STAR experiment at RHIC are presented
and discussed in terms of chemical and thermal freeze-out conditions. Thermal
models do not adequately describe the yields of the resonance production in
central Au+Au collisions. The approach to include elastic hadronic interactions
between chemical freeze-out and thermal freeze-out suggests a time of 5 fm/c.Comment: 4 pages, 7 figures, proceedings of the Quark Matter 2004, in Oakland,
California, to be published in Journal of Physics G: Nuclear and Particle
Physic
Identified particles at large transverse momenta in STAR in Au+Au collisions @ sqrt(s_NN) = 200 GeV
We report measurements of the ratios of identified hadrons (pi,K,p,Lambda) in
Au+Au collisions at sqrt(s_NN) = 200 GeV as a function of both collision
centrality and transverse momentum (p_T). Ratios of anti-baryon to baryon
yields are independent of p_T within 2<p_T <6 GeV/c indicating that, for such a
range, our measurements are inconsistent with theoretical pQCD calculations
predicting a decrease due to a stronger contribution from valence quark
scattering. For both strange and non-strange species, a strong baryon
enhancement relative to meson yields is observed as a function of collision
centrality in this intermediate p_T region, leading to p/pi and Lambda/K ratios
greater than unity. The nuclear modification factor, R_cp (central relative to
peripheral collisions), is used to illustrate the interplay between jet
quenching and hadron production. The physics implications of these measurements
are discussed with reference to different theoretical models.Comment: 5 pages, 4 figures. Proceedings of Quark Matter 2004 Conference, Jan
2004, Oakland, USA. Submitted to Journal of Physics
High- electron distributions in d+Au and p+p collisions at RHIC
We present preliminary measurements of electron and positron spectra in d+Au
and p+p collisions at GeV for GeV/c.
These measurements were carried out using the STAR Time Projection Chamber
(TPC) and the Barrel Electromagnetic calorimeter (EMC). Overall hadron
rejection factors in the range of have been achieved. In this work we
describe the measurement technique used to discriminate electrons from hadrons
and compare the results for single electron spectra with Pythia based pQCD
calculations for electrons from heavy-quark semi-leptonic decays.Comment: Quark Matter 2004 conference proceeding
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
Azimuthal anisotropy: the higher harmonics
We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 4 pages, 6 figures, contribution to the Quark Matter 2004 proceeding
Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV
We report the STAR measurement of Phi meson production in Au+Au and p+p
collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi
spectra and yields are obtained at mid-rapidity for five centrality bins in
Au+Au collisions and for non-singly-diffractive p+p collisions. It is found
that the Phi transverse momentum distributions from Au+Au collisions are better
fitted with a single-exponential while the p+p spectrum is better described by
a double-exponential distribution. The measured nuclear modification factors
indicate that Phi production in central Au+Au collisions is suppressed relative
to peripheral collisions when scaled by the number of binary collisions. The
systematics of versus centrality and the constant Phi/K- ratio versus beam
species, centrality, and collision energy rule out kaon coalescence as the
dominant mechanism for Phi production.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let
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