452 research outputs found
Projective and Coarse Projective Integration for Problems with Continuous Symmetries
Temporal integration of equations possessing continuous symmetries (e.g.
systems with translational invariance associated with traveling solutions and
scale invariance associated with self-similar solutions) in a ``co-evolving''
frame (i.e. a frame which is co-traveling, co-collapsing or co-exploding with
the evolving solution) leads to improved accuracy because of the smaller time
derivative in the new spatial frame. The slower time behavior permits the use
of {\it projective} and {\it coarse projective} integration with longer
projective steps in the computation of the time evolution of partial
differential equations and multiscale systems, respectively. These methods are
also demonstrated to be effective for systems which only approximately or
asymptotically possess continuous symmetries. The ideas of projective
integration in a co-evolving frame are illustrated on the one-dimensional,
translationally invariant Nagumo partial differential equation (PDE). A
corresponding kinetic Monte Carlo model, motivated from the Nagumo kinetics, is
used to illustrate the coarse-grained method. A simple, one-dimensional
diffusion problem is used to illustrate the scale invariant case. The
efficiency of projective integration in the co-evolving frame for both the
macroscopic diffusion PDE and for a random-walker particle based model is again
demonstrated
Centrality dependence of charged-particle pseudorapidity distributions from d+Au collisions at sqrt(s_{NN})=200 GeV
Charged-particle pseudorapidity densities are presented for the d+Au reaction
at sqrt{s_{NN}}=200 GeV with -4.2 <= eta <= 4.2$. The results, from the BRAHMS
experiment at RHIC, are shown for minimum-bias events and 0-30%, 30-60%, and
60-80% centrality classes. Models incorporating both soft physics and hard,
perturbative QCD-based scattering physics agree well with the experimental
results. The data do not support predictions based on strong-coupling,
semi-classical QCD. In the deuteron-fragmentation region the central 200 GeV
data show behavior similar to full-overlap d+Au results at sqrt{s_{NN}}=19.4
GeV.Comment: 4 pages, 3figures; expanded discussion of uncertainties; added 60-80%
centrality range; added additional discussion on centrality selection bia
Scanning the phases of QCD with BRAHMS
BRAHMS has the ability to study relativistic heavy ion collisions from the
final freeze-out of hadrons all the way back to the initial wave-function of
the gold nuclei. This is accomplished by studying hadrons with a very wide
range of momenta and angles. In doing so we can scan various phases of QCD,
from a hadron gas, to a quark gluon plasma and perhaps to a color glass
condensate.Comment: 8 pages, 6 figures, proceedings of plenary talk at Quark Matter 2004
conferenc
High Pt Hadron Spectra at High Rapidity
We report the measurement of charged hadron production at different
pseudo-rapidity values in deuteron+gold as well as proton+proton collisions at
= 200GeV at RHIC. The nuclear modification factors and
are used to investigate new behaviors in the deuteron+gold system as
function of rapidity and the centrality of the collisions respectively.Comment: Nine pages 4 figures to be published in the QM2004 Proceedings, typos
corrected and one reference adde
Charged particle densities from Au+Au collisions at sqrt{s_{NN}}=130 GeV
We present charged particle densities as a function of pseudorapidity and
collision centrality for the 197Au+197Au reaction at sqrt{s_{NN}}=130 GeV. An
integral charged particle multiplicity of 3860+/-300 is found for the 5% most
central events within the pseudorapidity range -4.7 <= eta <= 4.7. At
mid-rapidity an enhancement in the particle yields per participant nucleon pair
is observed for central events. Near to the beam rapidity, a scaling of the
particle yields consistent with the ``limiting fragmentation'' picture is
observed. Our results are compared to other recent experimental and theoretical
discussions of charged particle densities in ultra-relativistic heavy-ion
collisions.Comment: 14 pages, 4 figures; to be published in Phys. Lett.
Quark Gluon Plasma an Color Glass Condensate at RHIC? The perspective from the BRAHMS experiment
We review the main results obtained by the BRAHMS collaboration on the
properties of hot and dense hadronic and partonic matter produced in
ultrarelativistic heavy ion collisions at RHIC. A particular focus of this
paper is to discuss to what extent the results collected so far by BRAHMS, and
by the other three experiments at RHIC, can be taken as evidence for the
formation of a state of deconfined partonic matter, the so called
quark-gluon-plasma (QGP). We also discuss evidence for a possible precursor
state to the QGP, i.e. the proposed Color Glass Condensate.Comment: 32 pages, 18 figure
Nuclear Modification Factor for Charged Pions and Protons at Forward Rapidity in Central Au+Au Collisions at 200 GeV
We present spectra of charged pions and protons in 0-10% central Au+Au
collisions at GeV at mid-rapidity () and forward
pseudorapidity () measured with the BRAHMS experiment at RHIC. The
spectra are compared to spectra from p+p collisions at the same energy scaled
by the number of binary collisions. The resulting nuclear modification factors
for central Au+Au collisions at both and exhibit suppression
for charged pions but not for (anti-)protons at intermediate . The
ratios have been measured up to GeV/ at the two
rapidities and the results indicate that a significant fraction of the charged
hadrons produced at intermediate range are (anti-)protons at both
mid-rapidity and
Pseudorapidity distributions of charged particles from Au+Au collisions at the maximum RHIC energy, Sqrt(s_NN) = 200 GeV
We present charged particle densities as a function of pseudorapidity and
collision centrality for the 197Au+197Au reaction at Sqrt{s_NN}=200 GeV. For
the 5% most central events we obtain dN_ch/deta(eta=0) = 625 +/- 55 and
N_ch(-4.7<= eta <= 4.7) = 4630+-370, i.e. 14% and 21% increases, respectively,
relative to Sqrt{s_NN}=130 GeV collisions. Charged-particle production per pair
of participant nucleons is found to increase from peripheral to central
collisions around mid-rapidity. These results constrain current models of
particle production at the highest RHIC energy.Comment: 4 pages, 5 figures; fixed fig. 5 caption; revised text and figures to
show corrected calculation of and ; final version accepted for
publicatio
One and two dimensional analysis of 3pi correlations measured in Pb+Pb interactions
3pi- correlations from Pb+Pb collisions at 158 GeV/c per nucleon are
presented as measured by the focusing spectrometer of the NA44 experiment at
CERN. The three-body effect is found to be stronger for PbPb than for SPb. The
two-dimensional three-particle correlation function is also measured and the
longitudinal extension of the source is larger than the transverse extension
Forward and midrapidity like-particle ratios from p+p collisions at sqrt(s)=200 GeV
We present a measurement of pi-\pi+, K-/K+ and pbar/p from p+p collisions at
sqrt(s) = 20 0GeV over the rapidity range 0<y<3.4. For pT < 2.0 GeV/c we see no
significant transverse momentum dependence of the ratios. All three ratios are
independent of rapidity for y ~< 1.5 and then steadily decline from y ~ 1.5 to
y ~ 3. The pi-\pi+ ratio is below unity for y > 2.0. The pbar/p ratio is very
similar for p+p and 20% central Au+Au collisions at all rapidities. In the
fragmentation region the three ratios seem to be independent of beam energy
when viewed from the rest frame of one of the protons. Theoretical models based
on quark-diquark breaking mechanisms overestimate the pbar/p ratio up to y ~<
3. Including additional mechanisms for baryon number transport such as baryon
junctions leads to a better description of the data.Comment: 15 pages, 4 figures, uses elsart.sty. Changes to references and
discussion based on referee comments, resubmitted to Phys. Lett.
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