561 research outputs found
Performance of prototypes for the ALICE electromagnetic calorimeter
The performance of prototypes for the ALICE electromagnetic sampling
calorimeter has been studied in test beam measurements at FNAL and CERN. A
array of final design modules showed an energy resolution of about
11% / 1.7 % with a uniformity of the response
to electrons of 1% and a good linearity in the energy range from 10 to 100 GeV.
The electromagnetic shower position resolution was found to be described by 1.5
mm 5.3 mm /. For an electron identification
efficiency of 90% a hadron rejection factor of was obtained.Comment: 10 pages, 10 figure
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
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
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
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
System Size and Energy Dependence of Jet-Induced Hadron Pair Correlation Shapes in Cu+Cu and Au+Au Collisions at sqrt(s_NN) = 200 and 62.4 GeV
We present azimuthal angle correlations of intermediate transverse momentum
(1-4 GeV/c) hadrons from {dijets} in Cu+Cu and Au+Au collisions at sqrt(s_NN) =
62.4 and 200 GeV. The away-side dijet induced azimuthal correlation is
broadened, non-Gaussian, and peaked away from \Delta\phi=\pi in central and
semi-central collisions in all the systems. The broadening and peak location
are found to depend upon the number of participants in the collision, but not
on the collision energy or beam nuclei. These results are consistent with sound
or shock wave models, but pose challenges to Cherenkov gluon radiation models.Comment: 464 authors from 60 institutions, 6 pages, 3 figures, 2 tables.
Submitted to Physical Review Letters. Plain text data tables for the points
plotted in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
Measurement of open charm production in +Au collisions at =200 GeV
We present the first comprehensive measurement of and
their charge conjugate states at mid-rapidity in +Au collisions at
=200 GeV using the STAR TPC. The directly measured open charm
multiplicity distribution covers a broad transverse momentum region of
0 GeV/. The measured at mid-rapidity for is
and the measured
and ratios are approximately equal with a magnitude of . The total cross section per
nucleon-nucleon collision extracted from this study is mb. The direct measurement of open charm production is
consistent with STAR single electron data. This cross section is higher than
expectations from PYTHIA and other pQCD calculations. The measured
distribution is harder than the pQCD prediction using the Peterson
fragmentation function.Comment: Quark Matter 2004 Proceeding
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