653 research outputs found
Constraining the initial temperature and shear viscosity in a hybrid hydrodynamic model of =200 GeV Au+Au collisions using pion spectra, elliptic flow, and femtoscopic radii
A new framework for evaluating hydrodynamic models of relativistic heavy ion
collisions has been developed. This framework, a Comprehesive Heavy Ion Model
Evaluation and Reporting Algorithm (CHIMERA) has been implemented by augmenting
UVH 2+1D viscous hydrodynamic model with eccentricity fluctuations,
pre-equilibrium flow, and the Ultra-relativistic Quantum Molecular Dynamic
(UrQMD) hadronic cascade. A range of initial temperatures and shear viscosity
to entropy ratios were evaluated for four initial profiles, and
scaling with and without pre-equilibrium flow. The model results
were compared to pion spectra, elliptic flow, and femtoscopic radii from 200
GeV Au+Au collisions for the 0--20% centrality range.Two sets of initial
density profiles, scaling with pre-equilibrium flow and
scaling without were shown to provide a consistent description of all three
measurements.Comment: 21 pages, 32 figures, version 3 includes additional text for
clarification, division of figures into more manageable units, and placement
of chi-squared values in tables for ease of viewin
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J/psi suppression at forward rapidity in Au+Au collisions at sqrt(s_NN)=200 GeV
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Production of π0 and η mesons in Cu+Au collisions at sNN =200 GeV
Production of π0 and η mesons has been measured at midrapidity in Cu+Au collisions at sNN=200GeV. Measurements were performed in π0(η)→γγ decay channel in the 1(2)-20GeV/c transverse momentum range. A strong suppression is observed for π0 and η meson production at high transverse momentum in central Cu+Au collisions relative to the p+p results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to Au+Au with comparable nuclear overlap. The η/π0 ratio measured as a function of transverse momentum is consistent with mT-scaling parametrization down to pT=2GeV/c, its asymptotic value is constant and consistent with Au+Au and p+p and does not show any significant dependence on collision centrality. Similar results were obtained in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions as well as in e+e- collisions in a range of collision energies sNN=3-1800 GeV. This suggests that the quark-gluon-plasma medium produced in Cu+Cu collisions either does not affect the jet fragmentation into light mesons or it affects the π0 and η the same way
First Observation of -odd Asymmetry in Polarized Neutron Capture on Hydrogen
We report the first observation of the parity-violating 2.2 MeV gamma-ray
asymmetry in neutron-proton capture using polarized cold
neutrons incident on a liquid parahydrogen target at the Spallation Neutron
Source at Oak Ridge National Laboratory. isolates the , \mbox{} component of the weak
nucleon-nucleon interaction, which is dominated by pion exchange and can be
directly related to a single coupling constant in either the DDH meson exchange
model or pionless EFT. We measured , which implies a DDH weak coupling of
and a pionless
EFT constant of MeV. We describe the experiment, data
analysis, systematic uncertainties, and the implications of the result.Comment: 6 pages, 5 figure
Polarizing a stored proton beam by spin flip?
We discuss polarizing a proton beam in a storage ring, either by selective
removal or by spin flip of the stored ions. Prompted by recent, conflicting
calculations, we have carried out a measurement of the spin flip cross section
in low-energy electron-proton scattering. The experiment uses the cooling
electron beam at COSY as an electron target. The measured cross sections are
too small for making spin flip a viable tool in polarizing a stored beam. This
invalidates a recent proposal to use co-moving polarized positrons to polarize
a stored antiproton beam.Comment: 18 pages, 6 figure
Measurement of the Spin-Dependence of the pbar-p Interaction at the AD-Ring
We propose to use an internal polarized hydrogen storage cell gas target in
the AD ring to determine for the first time the two total spin-dependent pbar-p
cross sections sigma_1 and sigma_2 at antiproton beam energies in the range
from 50 to 450 MeV. The data obtained are of interest by themselves for the
general theory of pbar-p interactions since they will provide a first
experimental constraint of the spin-spin dependence of the nucleon-antinucleon
potential in the energy range of interest. In addition, measurements of the
polarization buildup of stored antiprotons are required to define the optimum
parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to
feed a double-polarized asymmetric pbar-p collider with polarized antiprotons.
Such a machine has recently been proposed by the PAX collaboration for the new
Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany.
The availability of an intense stored beam of polarized antiprotons will
provide access to a wealth of single- and double-spin observables, thereby
opening a new window on QCD spin physics.Comment: 51 pages, 23 figures, proposal submitted to the SPS committee of CER
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
J/psi suppression at forward rapidity in Au+Au collisions at sqrt(s_NN)=39 and 62.4 GeV
We present measurements of the J/psi invariant yields in sqrt(s_NN)=39 and
62.4 GeV Au+Au collisions at forward rapidity (1.2<|y|<2.2). Invariant yields
are presented as a function of both collision centrality and transverse
momentum. Nuclear modifications are obtained for central relative to peripheral
Au+Au collisions (R_CP) and for various centrality selections in Au+Au relative
to scaled p+p cross sections obtained from other measurements (R_AA). The
observed suppression patterns at 39 and 62.4 GeV are quite similar to those
previously measured at 200 GeV. This similar suppression presents a challenge
to theoretical models that contain various competing mechanisms with different
energy dependencies, some of which cause suppression and others enhancement.Comment: 365 authors, 10 pages, 11 figures, 4 tables. Submitted to Phys. Rev.
C. 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
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