Beam energy dependent two-pion interferometry and the freeze-out eccentricity of pions in heavy ion collisions at STAR

Abstract

We present results of analyses of two-pion interferometry in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV measured in the STAR detector as part of the RHIC Beam Energy Scan program. The extracted correlation lengths (HBT radii) are studied as a function of beam energy, azimuthal angle relative to the reaction plane, centrality, and transverse mass ($m_T$) of the particles. The azimuthal analysis allows extraction of the eccentricity of the entire fireball at kinetic freeze-out. The energy dependence of this observable is expected to be sensitive to changes in the equation of state. A new global fit method is studied as an alternate method to directly measure the parameters in the azimuthal analysis. The eccentricity shows a monotonic decrease with beam energy that is qualitatively consistent with the trend from all model predictions and quantitatively consistent with a hadronic transport model.

27 pages; 27 figures

References in corpus (10)

• The order of the quantum chromodynamics transition predicted by the standard model of particle physics
• Beam-energy dependence of charge separation along the magnetic field in Au+Au collisions at RHIC
• Inclusive charged hadron elliptic flow in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 39 GeV
• Systematic parameter study of hadron spectra and elliptic flow from viscous hydrodynamic simulations of Au+Au collisions at sqrt(s_NN) = 200 GeV
• Collision Energy Dependence of Viscous Hydrodynamic Flow in Relativistic Heavy-Ion Collisions
• The effect of "pre-formed" hadron potentials on the dynamics of heavy ion collisions and the HBT puzzle
• Shape analysis of strongly-interacting systems: the heavy ion case
• Azimuthal dependence of pion source radii in Pb+Au collisions at 158 A GeV
• Transport model analysis of particle correlations in relativistic heavy ion collisions at femtometer scales
• Transport model analysis of the transverse momentum and rapidity dependence of pion interferometry at SPS energies