21 research outputs found
BRAHMS Overview
A brief review of BRAHMS measurements of bulk particle production in RHIC
Au+Au collisions at is presented, together with some
discussion of baryon number transport. Intermediate measurements in
different collision systems (Au+Au, d+Au and p+p) are also discussed in the
context of jet quenching and saturation of the gluon density in Au ions at RHIC
energies. This report also includes preliminary results for identified
particles at forward rapidities in d+Au and Au+Au collisions.Comment: 8 pages 6 figures, Invited plenary talk at 5th International
Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPAQGP 2005),
Salt Lake City, Kolkata, India, 8-12 Feb 200
Rapidity and pt dependence of identified-particle elliptic flow at RHIC
Elliptic flow has been measured by the BRAHMS experiment as a function of
transverse momentum and pseudorapidity for the Au+Au reaction at sqrt[s_{NN}] =
200 GeV. Identified-particle v2 (eta, pt) values were obtained with the two
BRAHMS spectrometers at pseudorapidities eta approximately equal to 0, 1, and
3.4. The results show that the differential v2(eta, pt) values for a given
particle type are essentially constant over the covered pseudorapidity range.
It is suggested that the dominant cause of the observed fall-off of the
integral v2 values going away from mid-rapidity is a corresponding softening of
the particle spectra .Comment: 4 pages, 2figure, Quark Matter 2006 parallel session contributio
Identified Particle Production in d+Au and p+p collisions at RHIC
The BRAHMS experiment at RHIC has measured the transverse momentum spectra of
charged pions, kaons and (anti-)protons over a wide range of rapidity in d+Au
and p+p collisions at GeV. The nuclear modification factor
at forward rapidities shows a clear suppression for . The
measured net-proton yields in p+p collisions are compared to PYTHIA and
HIJING/B and seem to be better described by the latter.Comment: 4 pages, 3 figures, presented at the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2006", Shanghai,
China, November 14-20, 2006. to appear in the proceedings of Quark Matter
2006 as a special issue of Journal of Physics G: Nuclear and Particle Physic
The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au sqrt(s_NN) = 200 GeV collisions
Transverse momentum spectra of Lambda and K0Short particles are presented for
Cu+Cu sqrt(s_NN) = 200 GeV collisions observed at STAR, and compared to Au+Au
measurements at the same energy. For both systems, a number of observables are
shown to increase at mid-rapidity (|y| < 0.5) with increasing centrality. These
are the integrated Lambda and K0Short yields, the integrated Lambda and K0Short
yields per participating nucleon, and mid-pT (1 GeV/c -> 4.5 GeV/c)
Lambda/KK0Short ratios. The RCP ratio is found to be higher for the Lambda
yields at mid-pT compared to the K0Short yields for both the Cu+Cu and Au+Au
data. In contrast, when similar numbers of participating nucleons are
considered for the Cu+Cu and Au+Au data, an indication of increased bulk
strangeness production and a higher mid-pT (1 -> 4.5 GeV/c) Lambda/K0Short
ratio are found, for Cu+Cu.Comment: Quark Matter 2006 Proceeding
Is there more than one thermal source?
BRAHMS has the ability to study relativistic heavy ion collisions over a wide
range of pT and rapidity. This allows us to test whether thermal models can be
generalized to describe the rapidity dependence of particle ratios. This
appears to work with the baryo-chemical potential changing more rapidly than
the temperature. Using fits to BRAHMS data for the 5% most central Au+Au
collisions we are able to describe Xi and Omega ratios from other experiments.
This paper is dedicated to Julia Thompson who worked to bring South African
teachers into physics.Comment: 5 pages, 4 figures, proceedings for SQM04 conference, Cape Town South
Afric
Bulk properties and flow
In this report, I summarize the experimental results on {\bf bulk properties
and flow} presented at Quark Matter 2004. It is organized in four sections: 1)
Initial condition and stopping; 2) Particle spectra and freeze-outs; 3)
Anisotropic flow; 4) Outlook for future measurements.Comment: 10 pages, 4 figures, "Rapporteur-Conference Highlights", Quark Matter
2004, Oakland, January 11-1
Centrality dependence of spectra for identified hadrons in Au+Au and Cu+Cu collisions at GeV
The centrality dependence of transverse momentum spectra for identified
hadrons at midrapidity in Au+Au collisions at GeV is
systematically studied in a quark combination model. The
spectra of , , and in
different centrality bins and the nuclear modification factors () for
these hadrons are calculated. The centrality dependence of the average
collective transverse velocity for the hot and dense quark matter
is obtained in Au+Au collisions, and it is applied to a relative smaller Cu+Cu
collision system. The centrality dependence of spectra and
the for , and in Cu+Cu collisions at
GeV are well described. The results show that is only a function of the number of participants and it is
independent of the collision system.Comment: 7 pages, 6 figure
A global reanalysis of nuclear parton distribution functions
We determine the nuclear modifications of parton distribution functions of
bound protons at scales GeV and momentum fractions
in a global analysis which utilizes nuclear hard process
data, sum rules and leading-order DGLAP scale evolution. The main improvements
over our earlier work {\em EKS98} are the automated minimization,
simplified and better controllable fit functions, and most importantly, the
possibility for error estimates. The resulting 16-parameter fit to the N=514
datapoints is good, . Within the error estimates
obtained, the old {\em EKS98} parametrization is found to be fully consistent
with the present analysis, with no essential difference in terms of
either. We also determine separate uncertainty bands for the nuclear gluon and
sea quark modifications in the large- region where they are not stringently
constrained by the available data. Comparison with other global analyses is
shown and uncertainties demonstrated. Finally, we show that RHIC-BRAHMS data
for inclusive hadron production in d+Au collisions lend support for a stronger
gluon shadowing at and also that fairly large changes in the gluon
modifications do not rapidly deteriorate the goodness of the overall fits, as
long as the initial gluon modifications in the region remain
small.Comment: 33 pages, 14 figure
Re-Hardening of Hadron Transverse Mass Spectra in Relativistic Heavy-Ion Collisions
We analyze the spectra of pions and protons in heavy-ion collisions at
relativistic energies from 2 A GeV to 65+65 A GeV by using a jet-implemented
hadron-string cascade model. In this energy region, hadron transverse mass
spectra first show softening until SPS energies, and re-hardening may emerge at
RHIC energies. Since hadronic matter is expected to show only softening at
higher energy densities, this re-hardening of spectra can be interpreted as a
good signature of the quark-gluon plasma formation.Comment: 10 pages, 3 figures, 1 table, Poster presentation at QM2001, Revised
to correct latex error in citation on April 6, 200