90 research outputs found
Anisotropic Flow at the SPS and RHIC
The results on directed and elliptic flow for Pb + Pb at the full energy of
the SPS (158 GeV/A) and from the first year of Au + Au at RHIC
(sqrt{s_{_{NN}}=130 GeV) are reviewed. The different experiments agree well and
a consistent picture has emerged indicating early time thermalization at RHIC.Comment: 4 pages. For the proceedings of the International Workshop on the
Physics of the Quark-Gluon Plasma, Palaiseau, France, 4-7 Sept. 0
Collective phenomena in non-central nuclear collisions
Recent developments in the field of anisotropic flow in nuclear collision are
reviewed. The results from the top AGS energy to the top RHIC energy are
discussed with emphasis on techniques, interpretation, and uncertainties in the
measurements.Comment: Review paper, 56 pages, as accepted for publicatio
Centrality dependence of directed and elliptic flow at the SPS
New data with a minimum bias trigger for 158 GeV/nucleon Pb + Pb have been analyzed. Directed and elliptic flow as a function of rapidity of the particles and centrality of the collision are presented. The centrality dependence of the ratio of elliptic flow to the initial space elliptic anisotropy is compared to models
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
Eccentricity distributions in nucleus-nucleus collisions
Physics Letters CInternational audienceWe propose a new parametrization of the distribution of the initial eccentricity in a nucleus-nucleus collision at a fixed centrality, which we name the Elliptic Power distribution. It is a two-parameter distribution, where one of the parameters corresponds to the intrinsic eccentricity, while the other parameter controls the magnitude of eccentricity fluctuations. Unlike the previously used Bessel- Gaussian distribution, which becomes worse for more peripheral collisions, the new Elliptic Power distribution fits several Monte Carlo models of the initial state for all centralities
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Azimuthal anisotropy: The higher harmonics
We report the first observations of the fourth harmonic (v{sub 4}) in the azimuthal distribution of particles at RHIC. The measurement was done taking advantage of the large elliptic flow generated at RHIC. The integrated v{sub 4} is about a factor of 10 smaller than v{sub 2}. For the sixth (v{sub 6}) and eighth (v{sub 8}) harmonics upper limits on the magnitudes are reported
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
Elliptic flow in the Gaussian model of eccentricity fluctuations
We discuss a specific model of elliptic flow fluctuations due to Gaussian
fluctuations in the initial spatial and eccentricity components
\left\{\mean{(\sigma_y^2-\sigma_x^2)/(\sigma_x^2+\sigma_y^2)},
\mean{2\sigma_{xy}/(\sigma_x^2+\sigma_y^2)} \right\}. We find that in this
model \vfour, elliptic flow determined from 4-particle cumulants, exactly
equals the average flow value in the reaction plane coordinate system,
\mean{v_{RP}}, the relation which, in an approximate form, was found earlier
by Bhalerao and Ollitrault in a more general analysis, but under the same
assumption that is proportional to the initial system eccentricity. We
further show that in the Gaussian model all higher order cumulants are equal to
\vfour. Analysis of the distribution in the magnitude of the flow vector, the
distribution, reveals that it is totally defined by two parameters,
\vtwo, the flow from 2-particle cumulants, and \vfour, thus providing
equivalent information compared to the method of cumulants. The flow obtained
from the distribution is again \vfour=\mean{v_{RP}}.Comment: Very minor changes, as submitted to Phys. Lett.
Search for Fragment Emission from Nuclear Shock Waves
Energy spectra and angular distributions have been measured of 3He and 4He fragments emitted from Ag and U targets, bombarded with 2.7-GeV protons, and 1.05-GeV/nucleon alpha particles and 16O ions. All cross sections increase dramatically with projectile mass. No narrow peaks are found in the angular distributions or in the energy spectra
Central collisions of relativistic heavy ions
The energy spectra of protons and light nuclei produced by the interaction of 4He and 20Ne projectiles with Al and U targets have been investigated at incident energies ranging from 0.25 to 2.1 GeV per nucleon. Single fragment inclusive spectra have been obtained at angles between 25° and 150°, in the energy range from 30 to 150 MeV/nucleon. The multiplicity of intermediate and high energy charged particles was determined in coincidence with the measured fragments. In a separate study, fragment spectra were obtained in the evaporation energy range from 12C and 20Ne bombardment of uranium. We observe structureless, exponentially decaying spectra throughout the range of studied fragment masses. There is evidence for two major classes of fragments; one with emission at intermediate temperature from a system moving slowly in the lab frame, and the other with high temperature emission from a system propagating at a velocity intermediate between target and projectile. The high energy proton spectra are fairly well reproduced by a nuclear fireball model based on simple geometrical, kinematical, and statistical assumptions. Light cluster emission is also discussed in the framework of statistical models. NUCLEAR REACTIONS U(20Ne,X), E=250 MeV/nucl.; U(20Ne,X), U(α,X) E=400 MeV/nucl.; U(20Ne,X), Al(20Ne,X), E=2.1 GeV/nucl.; measured σ(E,θ), X=p, d, t, 3He,4He. U(20Ne,X), U(α,X), E=400 MeV/nucl.; U(20Ne,X), E=2.1 GeV/nucl.; measured σ(E, θ), Li to O. U(20Ne,X), U(12C,X), E=2.1 GeV/nucl.; measured σ(E, 90°), 4He to B. Nuclear fireballs, coalescence, thermodynamics of light nuclei production
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