295 research outputs found
Stopping and Baryon Transport in Heavy Ion Reactions
In this report I will give an experimental overview on nuclear stopping in
hadron collisions, and relate observations to understanding of baryon
transport. Baryon number transport is not only evidenced via net-proton
distributions but also by the enhancement of strange baryons near mid-rapidity.
Although the focus is on high-energy data obtained from pp and heavy ions from
RHIC, relevant data from SPS and ISR will be considered. A discussion how the
available data at higher energy relates and gives information on baryon
junction, quark-diquark breaking will be made.Comment: 8 pages, 7 figures. Invited plenary talk for the 5'th international
conference on Physics and Astrophysics of Quark Gluon Plasma, February 8-12,
2005, Salt Lake City, Kolkata, Indi
In-beam Tests of a Ring Imaging Cerenkov Detector With a Multianode Photomultiplier Readout
A ring-imaging \v{C}erenkov counter read out by a 100-channel PMT of active
area 1010 cm was operated successfully in a test beam at the BNL
AGS with several radiator gases, including the heavy fluorocarbon
CF. Ring radii were measured for electrons, muons, pions and kaons
over the particle momentum range from 2 to 12 GeV/, and a best resolution of
was obtained.Comment: 11 pages (LaTeX) plus 7 figures in Postscript (gz-compressed and
uuencoded
Rapidity and centrality dependence of particle production for identified hadrons in Cu+Cu collisions at GeV
The BRAHMS collaboration has measured transverse momentum spectra of pions,
kaons, protons and antiprotons at rapidities 0 and 3 for Cu+Cu collisions at
GeV. As the collisions become more central the collective
radial flow increases while the temperature of kinetic freeze-out decreases.
The temperature is lower and the radial flow weaker at forward rapidity. Pion
and kaon yields with transverse momenta between 1.5 and 2.5 GeV/c are
suppressed for central collisions relative to scaled collisions. This
suppression, which increases as the collisions become more central is
consistent with jet quenching models and is also present with comparable
magnitude at forward rapidity. At such rapidities initial state effects may
also be present and persistence of the meson suppression to high rapidity may
reflect a combination of jet quenching and nuclear shadowing. The ratio of
protons to mesons increases as the collisions become more central and is
largest at forward rapidities.Comment: 19 pages, 11 figures and 6 table
Rapidity dependence of deuteron production in Au+Au collisions at = 200 GeV
We have measured the distributions of protons and deuterons produced in high
energy heavy ion Au+Au collisions at RHIC over a very wide range of transverse
and longitudinal momentum. Near mid-rapidity we have also measured the
distribution of anti-protons and anti-deuterons. We present our results in the
context of coalescence models. In particular we extract the "volume of
homogeneity" and the average phase-space density for protons and anti-protons.
Near central rapidity the coalescence parameter and the space
averaged phase-space density are very similar for both protons and
anti-protons. For protons we see little variation of either or the
space averaged phase-space density as the rapidity increases from 0 to 3.
However both these quantities depend strongly on at all rapidities. These
results are in contrast to lower energy data where the proton and anti-proton
phase-space densities are different at =0 and both and depend
strongly on rapidity.Comment: Document updated after proofs received from PR
Nuclear Stopping in Au+Au Collisions at sqrt(sNN) = 200 GeV
Transverse momentum spectra and rapidity densities, dN/dy, of protons,
anti-protons, and net--protons (p-pbar) from central (0-5%) Au+Au collisions at
sqrt(sNN) = 200 GeV were measured with the BRAHMS experiment within the
rapidity range 0 < y < 3. The proton and anti-proton dN/dy decrease from
mid-rapidity to y=3. The net-proton yield is roughly constant for y<1 at
dN/dy~7, and increases to dN/dy~12 at y~3. The data show that collisions at
this energy exhibit a high degree of transparency and that the linear scaling
of rapidity loss with rapidity observed at lower energies is broken. The energy
loss per participant nucleon is estimated to be 73 +- 6 GeV.Comment: 5 pages, 4 figure
Evolution of the nuclear modification factors with rapidity and centrality in d+Au collisions at $\sqrt{s_{NN}} = 200 GeV
We report on a study of the transverse momentum dependence of nuclear
modification factors for charged hadrons produced in deuteron + gold
collisions at GeV, as a function of collision centrality
and of the pseudorapidity () of the produced hadrons. We
find significant and systematic decrease of with increasing rapidity.
The midrapidity enhancement and the forward rapidity suppression are more
pronounced in central collisions relative to peripheral collisions. These
results are relevant to the study of the possible onset of gluon saturation at
RHIC energies.Comment: Four pages, four figures. Published in PRL. Figures 1 and 2 have been
updated, and several changes made to the tex
Recent Results from the BRAHMS Experiment
We present recent results obtained by the BRAHMS experiment at the
Relativistic Heavy Ion Collider (RHIC) for the systems of Au + Au and Cu + Cu
at \rootsnn{200} and at 62.4 GeV, and p + p at \rootsnn{200}. Nuclear
modification factors for Au + Au and Cu + Cu collisions are presented. Analysis
of anti-particle to particle ratios as a function of rapidity and collision
energy reveal that particle populations at the chemical freeze-out stage for
heavy-ion reactions at and above SPS energies are controlled by the baryon
chemical potential. From the particle spectra we deduce significant radial
expansion ( 0.75), as expected for systems created with a large
initial energy density. We also measure the elliptic flow parameter
versus rapidity and \ptn. We present rapidity dependent ratios within
for Au + Au and Cu + Cu at \rootsnn{200}. \Raa is found to increase
with decreasing collision energy, decreasing system size, and when going
towards more peripheral collisions. However, \Raa shows only a very weak
dependence on rapidity (for ), both for pions and protons.Comment: 16 pages and 14 figures, proceedings for plenary talk at Quark Matter
2005, Budapest, Hungar
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
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
Coexistence of 'alpha+ 208Pb' cluster structures and single-particle excitations in 212Po
Excited states in 212Po have been populated by alpha transfer using the
208Pb(18O,14C) reaction at 85MeV beam energy and studied with the EUROBALL IV
gamma multidetector array. The level scheme has been extended up to ~ 3.2 MeV
excitation energy from the triple gamma coincidence data. Spin and parity
values of most of the observed states have been assigned from the gamma angular
distributions and gamma -gamma angular correlations. Several gamma lines with
E(gamma) < 1 MeV have been found to be shifted by the Doppler effect, allowing
for the measurements of the associated lifetimes by the DSAM method. The
values, found in the range [0.1-0.6] ps, lead to very enhanced E1 transitions.
All the emitting states, which have non-natural parity values, are discussed in
terms of alpha-208Pb structure. They are in the same excitation-energy range as
the states issued from shell-model configurations.Comment: 21 pages, 19 figures, corrected typos, revised arguments in Sect.
III
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