261 research outputs found
Anisotropic flow from Lee-Yang zeroes: a practical guide
We present a new method to analyze anisotropic flow from the genuine
correlation among a large number of particles, focusing on the practical
implementation of the method.Comment: 4 pages; contribution to Quark Matter 2004, Oakland, January 11-17,
200
Analysis of directed flow from three-particle correlations
We present a new method for analysing directed flow, based on a
three-particle azimuthal correlation. It is less biased by nonflow correlations
than two-particle methods, and requires less statistics than four-particle
methods. It is illustrated on NA49 data.Comment: Contribution to Quark Matter 2002, Nantes, July 18-24, 200
Determination of the reaction plane in ultrarelativistic nuclear collisions
In the particles produced in a nuclear collision undergo collective flow, the
reaction plane can in principle be determined through a global event analysis.
We show here that collective flow can be identified by evaluating the reaction
plane independently in two separate rapidity intervals, and studying the
correlation between the two results. We give an analytical expression for the
correlation function between the two planes as a function of their relative
angle. We also discuss how this correlation function is related to the
anisotropy of the transverse momentum distribution. Email contact:
[email protected]: Saclay-T93/026 Email: [email protected]
Characterization and analysis of azimuthally sensitive correlations
A unified framework for describing the azimuthal dependence of two-particle
correlations in heavy-ion collisions is introduced, together with the methods
for measuring the corresponding observables. The generalization to azimuthal
correlations between more than two particles is presented.Comment: 7 pages; talk given at Hot Quarks 2004, Taos (NM), July 18-24,200
Does interferometry probe thermalization?
We carry out a systematic study of interferometry radii in ultrarelativistic
heavy-ion collisions within a two-dimensional transport model. We compute the
transverse radii R_o and R_s as a function of p_t for various values of the
Knudsen number, which measures the degree of thermalization in the system. They
converge to the hydrodynamical limit much more slowly (by a factor 3) than
elliptic flow. This solves most of the HBT puzzle for central collisions:
R_o/R_s is in the range 1.1-1.2 for realistic values of the Knudsen number,
much closer to experimental data () than the value 1.5 from
hydrodynamical calculations. The p_t dependence of R_o and R_s, which is
usually said to reflect collective flow, also has a very limited sensitivity to
the degree of thermalization. We then study the azimuthal oscillations of R_o,
R_s, and R_{os} for non central collisions. Their amplitudes depend little on
the Knudsen number, and reflect the eccentricity of the overlap area between
the two nuclei.Comment: 9 page
Directed flow at RHIC from Lee-Yang zeroes
Directed flow in ultrarelativistic nucleus-nucleus collisions is analyzed
using the reaction plane from elliptic flow, which reduces the bias from
nonflow effects. We combine this method with the determination of elliptic flow
from Lee-Yang zeroes. The resulting method is more consistent and somewhat
easier to implement than the previously used method based on three-particle
cumulants, and is also less biased by nonflow correlations. Error terms from
residual nonflow correlations are carefully estimated, as well as statistical
errors. We discuss the application of the method at RHIC and LHC.Comment: 10 pages. Final version, to appear in Nucl. Phys.
New method for measuring azimuthal distributions in nucleus-nucleus collisions
The methods currently used to measure azimuthal distributions of particles in
heavy ion collisions assume that all azimuthal correlations between particles
result from their correlation with the reaction plane. However, other
correlations exist, and it is safe to neglect them only if azimuthal
anisotropies are much larger than 1/sqrt(N), with N the total number of
particles emitted in the collision. This condition is not satisfied at
ultrarelativistic energies. We propose a new method, based on a cumulant
expansion of multiparticle azimuthal correlations, which allows to measure much
smaller values of azimuthal anisotropies, down to 1/N. It is simple to
implement and can be used to measure both integrated and differential flow.
Furthermore, this method automatically eliminates the major systematic errors,
which are due to azimuthal asymmetries in the detector acceptance.Comment: final version (misprints corrected), to be published in Phys.Rev.
Anisotropic flows from initial state of a fast nucleus
We analyze azimuthal anisotropy in heavy ion collisions related to the
reaction plane in terms of standard reggeon approach and find that it is
nonzero even when the final state interaction is switched off. This effect can
be interpreted in terms of partonic structure of colliding nuclei. We use
Feynman diagram analysis to describe details of this mechanism. Main
qualitative features of the appropriate azimuthal correlations are discussed.Comment: 16 pages, 11 figures. This paper is an extended version of a talk
given at Session of Nuclear Physics Division of Russian Academy of Sciences
in November 200
Emission times and opacities from interferometry in non-central Relativistic Nuclear Collisions
The nuclear overlap zone in non-central relativistic heavy ion collisions is
azimuthally very asymmetric. By varying the angle between the axes of
deformation and the transverse direction of the pair momenta, the transverse
HBT radii oscillate in a characteristic way. It is shown that these
oscillations allow determination of source sizes, deformations as well as the
opacity and duration of emission of the source created in any non-central high
energy nuclear collisions. The behavior of the physical quantities with
centrality of the collisions is discussed --- in particular changes caused by a
possible phase transition to a quark-gluon plasma.Comment: Revised version, to appear in Phys. Rev. Letter
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