626 research outputs found
System size dependence of freeze-out properties at RHIC
The STAR experiment at RHIC has measured identified pi(+/-), K(+/-) and
p(pbar) spectra and ratios from sqrt(s_NN) = 62.4 and 200 GeV Cu+Cu collisions.
The new Cu+Cu results are studied with hydro-motivated blast-wave and
statistical model frameworks in order to characterize the freeze-out properties
of this system. Along with measurements from Au+Au and p+p collisions, the
obtained freeze-out parameters are discussed as a function of collision energy,
system size, centrality and inferred energy density. This multi-dimensional
systematic study reveals the importance of the collision geometry and furthers
our understanding of the QCD phases.Comment: 6 pages, 6 figures, poster proceedings for the Quark Matter 2006
Conference, Shanghai, China, 14th-20th Novermber 2006, submitted to the
International Journal of Modern Physics
Discrepancies between different electron temperature methods: probing the electron energy distribution function
A large panel of diagnostic techniques for the determination of effective electron temperatures Te exists and they rely on different hypothesis/physical phenomena for its measurement. Due to the different underlying assumptions and physical mechanisms used for the calculation of Te, different values of Te may be expected while measuring a plasma in the same conditions, particularly in the case of a non-Maxwellian plasma. To each of these definitions of effective Te, a different effective Te can be defined using the EEDF of the plasma. In this study, we take a low pressure Argon microwave plasma as test case and compare Thomson scattering with line intensity measurements corrected by a collisional radiative model. The results are compared with those obtained from the electron particle balance (ePB)
Idylls of socialism : the Sarajevo Documentary School and the problem of the Bosnian sub-proletariat
This historical overview of the Sarajevo Documentary School considers the films, in the light of their recent re-emergence, as indicative of both the legacy of socialist realism (even in the context of Yugoslav media) and attempted social engineering in the Bosnia of the 1960s and 1970s. The argument is made that the documentaries, despite their questionable aesthetic status (in respect of cinma-vrit and ethnography) and problematic ideological strategies and attempted interventions, document a history and offer insights that counter the prevailing revisionist trends in the presentation of Eastern and Central European history
Strange Particle Production at RHIC
We report STAR measurements of mid-rapidity yields for the ,
, , , , , and
particles in Cu+Cu and Au+Au GeV
collisions. We show that at a given number of participating nucleons, bulk
strangeness production is higher in Cu+Cu collisions compared to Au+Au
collisions at the same center of mass energy, counter to predictions from the
Canonical formalism. We compare both the Cu+Cu and Au+Au yields to AMPT and
EPOS predictions, and find they reproduce key qualitative aspects of the data.
Finally, we investigate other scaling parameters and find bulk strangeness
production for both the measured data and theoretical predictions, scales
better with the number participants that undergo more than one collision.Comment: Conference proceedings for Hot Quarks 2008, 5 pages and 4 figure
The Importance of Correlations and Fluctuations on the Initial Source Eccentricity in High-Energy Nucleus-Nucleus Collisions
In this paper, we investigate various ways of defining the initial source
eccentricity using the Monte Carlo Glauber (MCG) approach. In particular, we
examine the participant eccentricity, which quantifies the eccentricity of the
initial source shape by the major axes of the ellipse formed by the interaction
points of the participating nucleons. We show that reasonable variation of the
density parameters in the Glauber calculation, as well as variations in how
matter production is modeled, do not significantly modify the already
established behavior of the participant eccentricity as a function of collision
centrality. Focusing on event-by-event fluctuations and correlations of the
distributions of participating nucleons we demonstrate that, depending on the
achieved event-plane resolution, fluctuations in the elliptic flow magnitude
lead to most measurements being sensitive to the root-mean-square, rather
than the mean of the distribution. Neglecting correlations among
participants, we derive analytical expressions for the participant eccentricity
cumulants as a function of the number of participating nucleons,
\Npart,keeping non-negligible contributions up to \ordof{1/\Npart^3}. We
find that the derived expressions yield the same results as obtained from
mixed-event MCG calculations which remove the correlations stemming from the
nuclear collision process. Most importantly, we conclude from the comparison
with MCG calculations that the fourth order participant eccentricity cumulant
does not approach the spatial anisotropy obtained assuming a smooth nuclear
matter distribution. In particular, for the Cu+Cu system, these quantities
deviate from each other by almost a factor of two over a wide range in
centrality.Comment: 18 pages, 10 figures, submitted to PR
System Size, Energy and Centrality Dependence of Pseudorapidity Distributions of Charged Particles in Relativistic Heavy Ion Collisions
We present the first measurements of the pseudorapidity distribution of
primary charged particles in Cu+Cu collisions as a function of collision
centrality and energy, \sqrtsnn = 22.4, 62.4 and 200 GeV, over a wide range of
pseudorapidity, using the PHOBOS detector. Making a global comparison of Cu+Cu
and Au+Au results, we find that the total number of produced charged particles
and the rough shape (height and width) of the pseudorapidity distributions are
determined by the number of nucleon participants. More detailed studies reveal
that a more precise matching of the shape of the Cu+Cu and Au+Au pseudorapidity
distributions over the full range of pseudorapidity occurs for the same
Npart/2A value rather than the same Npart value. In other words, it is the
collision geometry rather than just the number of nucleon participants that
drives the detailed shape of the pseudorapidity distribution and its centrality
dependence at RHIC energies.Comment: Submitted to Physical Review Letter
System size and centrality dependence of charged hadron transverse momentum spectra in Au+Au and Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV
We present transverse momentum distributions of charged hadrons produced in
Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV. The spectra are measured for
transverse momenta of 0.25 < p_T < 5.0 GeV/c at sqrt(s) = 62.4 GeV and 0.25 <
p_T < 7.0 GeV/c at sqrt(s) = 200 GeV, in a pseudo-rapidity range of 0.2 < eta <
1.4. The nuclear modification factor R_AA is calculated relative to p+p data at
both collision energies as a function of collision centrality. At a given
collision energy and fractional cross-section, R_AA is observed to be
systematically larger in Cu+Cu collisions compared to Au+Au. However, for the
same number of participating nucleons, R_AA is essentially the same in both
systems over the measured range of p_T, in spite of the significantly different
geometries of the Cu+Cu and Au+Au systems.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Identified charged antiparticle to particle ratios near midrapidity in Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV
Antiparticle to particle ratios for identified protons, kaons and pions at
sqrt(s) = 62.4 and 200 GeV in Cu+Cu collisions are presented as a function of
centrality for the midrapidity region of 0.2 < eta < 1.4. No strong dependence
on centrality is observed. For the / ratio at ~ 0.51 GeV/c, we
observe an average value of 0.50 +/- 0.003_(stat) +/- 0.04_(syst) and 0.77 +/-
0.008_(stat) +/- 0.05_(syst) for the 10% most central collisions of 62.4 and
200 GeV Cu+Cu, respectively. The values for all three particle species measured
at sqrt(s) = 200 GeV are in agreement within systematic uncertainties with that
seen in both heavier and lighter systems measured at the same RHIC energy. This
indicates that system size does not appear to play a strong role in determining
the midrapidity chemical freeze-out properties affecting the antiparticle to
particle ratios of the three most abundant particle species produced in these
collisions.Comment: 5 Pages, 4 figures Made changes to the figures to include the panel
numbers. Slight changes to the text. Updated data points from other
experiment
Cluster properties from two-particle angular correlations in p+p collisions at = 200 and 410 GeV
We present results on two-particle angular correlations in proton-proton
collisions at center of mass energies of 200 and 410 GeV. The PHOBOS experiment
at the Relativistic Heavy Ion Collider has a uniquely large coverage for
charged particles, giving the opportunity to explore the correlations at both
short- and long-range scales. At both energies, a complex two-dimensional
correlation structure in and is observed. In the
context of an independent cluster model of short-range correlations, the
cluster size and its decay width are extracted from the two-particle
pseudorapidity correlation function and compared with previous measurements in
proton-proton and proton-antiproton collisions, as well as PYTHIA and HIJING
predictions.Comment: 10 pages, 10 figures, submitted to Phys. Rev.
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