4,807 research outputs found
System Size and Energy Dependence of Elliptic Flow
The elliptic flow v2 is presented for the Cu+Cu collisions at sqrt{s_NN} =
62.4 and 200 GeV, as a function of pseudorapidity. Comparison to results for
the Au+Au collisions at the same energies shows a reduction of about 20% in the
flow observed for a centrality selection of 0-40%. The centrality dependent
flow, expressed as a function of the number of participants N_part, is compared
for the Cu+Cu and Au+Au systems using two definitions of eccentricity, the
standard definition epsilon_standard and a participant eccentricity
epsilon_part. The v2 / as a function of N_part, for the Au+Au
and Cu+Cu collisions are consistent within errors, while v2 /
gives unrealistically large values for Cu+Cu, especially for
central collision.Comment: 3 pages, 3 figures, talk given at Particles and Nuclei International
Conference (PANIC05), Santa Fe, New Mexico, 24-28 Oct 2005. Proceeding to be
published by American Institute of Physic
Limitations on Adiabatic Normal Modes in Range Varying Environments
Abstract: Curvilinear coordinates are used to extend adiabatic normal modes to weak range-dependent environments including those with sloping bottoms. Reciprocal vertical wavenumbers of a reference mode provide the coordinate scale factors. This approach is valid for negligible horizontal derivatives of intermodal vertical-wavenumber ratios. Large gradients in the bottom impedance make these ratios large implying significant mode coupling in oceanic regions spanning both soft and hard terrains
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
Event-by-event fluctuations of azimuthal particle anisotropy in Au+Au collisions at sqrt(s_NN) = 200 GeV
This paper presents the first measurement of event-by-event fluctuations of
the elliptic flow parameter v_2 in Au+Au collisions at sqrt(s_NN) = 200GeV as a
function of collision centrality. The relative non-statistical fluctuations of
the v_2 parameter are found to be approximately 40%. The results, including
contributions from event-by-event elliptic flow fluctuations and from azimuthal
correlations that are unrelated to the reaction plane (non-flow correlations),
establish an upper limit on the magnitude of underlying elliptic flow
fluctuations. This limit is consistent with predictions based on spatial
fluctuations of the participating nucleons in the initial nuclear overlap
region. These results provide important constraints on models of the initial
state and hydrodynamic evolution of relativistic heavy ion collisions.Comment: 5 pages, 2 figures, Published in Phys. Rev. Lett
Non-flow correlations and elliptic flow fluctuations in gold-gold collisions at sqrt(s_NN)= 200 GeV
This paper presents results on event-by-event elliptic flow fluctuations in
Au+Au collisions at sqrt(s_NN)=200Gev, where the contribution from non-flow
correlations has been subtracted. An analysis method is introduced to measure
non-flow correlations, relying on the assumption that non-flow correlations are
most prominent at short ranges (Delta eta < 2). Assuming that non-flow
correlations are of the order that is observed in p+p collisions for long range
correlations (Delta eta > 2), relative elliptic flow fluctuations of
approximately 30-40% are observed. These results are consistent with
predictions based on spatial fluctuations of the participating nucleons in the
initial nuclear overlap region. It is found that the long range non-flow
correlations in Au+Au collisions would have to be more than an order of
magnitude stronger compared to the p+p data to lead to the observed azimuthal
anisotropy fluctuations with no intrinsic elliptic flow fluctuations.Comment: 9 pages, 7 figures, Published in Phys. Rev.
Centrality dependence of charged antiparticle to particle ratios near mid-rapidity in d+Au collisions at sqrt(s_NN)=200 GeV
The ratios of the yields of charged antiparticles to particles have been
obtained for pions, kaons, and protons near mid-rapidity for d+Au collisions at
sqrt(s_NN) = 200 GeV as a function of centrality. The reported values represent
the ratio of the yields averaged over the rapidity range of 0.1<y_pi<1.3 and
0<y_(K,p)<0.8, where positive rapidity is in the deuteron direction, and for
transverse momenta 0.1<p_(T)^(pi,K)<1.0 GeV/c and 0.3<p_(T)^(p)<1.0 GeV/c.
Within the uncertainties, a lack of centrality dependence is observed in all
three ratios. The data are compared to results from other systems and model
calculations.Comment: 6 pages, 4 figures, submitted to PR
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
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