Abstract
Differential elliptic flow of v2(pT ) for π − , K 0 , p and Λ is measured at center- of-mass energy of √ sNN=17.3 GeV near the mid-rapidity region in rather central PbAu collisions collected by the CERES/NA45 experiment at CERN. The proton v2(pT )i s ex- tracted from π + sample and particle ratios measured by NA49 experiment adapted to CERES conditions. The proton v2(pT ) data show a downward swing towards low pT with excursions into negative v2 values which was not observed earlier. The results are com- pared with corresponding measurements performed at NA49 and STAR experiments as well as with theoretical predictions from ideal relativistic hydrodynamics. The obtained results for baryons are below hydrodynamic predictions even at the kinetic freeze-out temperature of T f =160 MeV which needs introducing of a viscous hydrodynamics at the late hadronic phase.
Highlights
The elliptic flow v2 is characterized by the second harmonic coefficient of the azimuthal particle distribution measured with respect to the event plane [1, 2]
This was interpreted as creation of a locally equilibrated system of strongly interacting quarks and gluons known as Quark Gluon Plasma (QGP)
The event plane (EP) method is used for the flow analysis itself [2, 9, 1√0]
Summary
The elliptic flow v2 is characterized by the second harmonic coefficient of the azimuthal particle distribution measured with respect to the event plane [1, 2]. The strong interaction between the constituents of the expanding, hot and dense system crated in the collision of two nuclei converts initial spatial anisotropy into the momentum anisotropy. The evolution of the system could be described by relativistic hydrodynamics [3]. This was interpreted as creation of a locally equilibrated system of strongly interacting quarks and gluons known as Quark Gluon Plasma (QGP). The QGP behaves as a nearly perfect liquid with a very small ratio η/s of shear viscosity to entropy density [4, 5]
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