367 research outputs found
Effect of flow fluctuations and nonflow on elliptic flow methods
We discuss how the different estimates of elliptic flow are influenced by
flow fluctuations and nonflow effects. It is explained why the event-plane
method yields estimates between the two-particle correlation methods and the
multiparticle correlation methods. It is argued that nonflow effects and
fluctuations cannot be disentangled without other assumptions. However, we
provide equations where, with reasonable assumptions about fluctuations and
nonflow, all measured values of elliptic flow converge to a unique mean
v_{2,PP} elliptic flow in the participant plane and, with a Gaussian assumption
on eccentricity fluctuations, can be converted to the mean v_{2,RP} in the
reaction plane. Thus, the 20% spread in observed elliptic flow measurements
from different analysis methods is no longer mysterious.Comment: one typo in Table I correcte
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
Universal parameterization of initial-state fluctuations and its applications to event-by-event anisotropy
We propose Elliptic Power and Power parameterizations for the probability
distribution of initial state anisotropies in heavy-ion collisions. By assuming
a linear eccentricity scaling, the new parameterizations can also be applied to
fluctuations of harmonic flow. In particular, we analyze flow multi-particle
cumulants and event-by-event distributions, both of which are recently measured
at the LHC.Comment: 4 pages and 3 figures, proceedings of the XXIV Quark Matter
conference, May 19-24 2014, Darmstadt (Germany
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]
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.
Are eccentricity fluctuations able to explain the centrality dependence of ?
The fourth harmonic of the azimuthal distribution of particles has been
measured for Au-Au collisions at the Relativistic Heavy Ion Collider (RHIC).
The centrality dependence of does not agree with the prediction from
hydrodynamics. In particular, the ratio , where denotes the
second harmonic of the azimuthal distribution of particles, is significantly
larger than predicted by hydrodynamics. We argue that this discrepancy is
mostly due to elliptic flow () fluctuations. We evaluate these
fluctuations on the basis of a Monte Carlo Glauber calculation. The effect of
deviations from local thermal equilibrium is also studied, but appears to be
only a small correction. Combining these two effects allows us to reproduce
experimental data for peripheral and midcentral collisions. However, we are
unable to explain the large magnitude of observed for the most
central collisions.Comment: talk presented at the Strangeness in Quark Matter Conference, Buzios,
Brazil, Sept. 27 - oct. 2, 200
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