Source anisotropy in non-central heavy ion collisions in the RHIC energy scan - model expectations

The beam energy scan program at RHIC aims to identify nontrivial structure (phase boundaries, critical points) in the phase diagram of strongly-interacting matter. There may be corresponding features in the QCD Equation of State (e.g. ``soft spots'') which affect the dynamic evolution of the system, generating observables that vary non-trivially with the collision energy. We focus on the freezeout spatial anisotropy of the source created in non-central heavy ion collisions; this anisotropy is estimated from the azimuthal dependence of HBT radii from two-pion correlations [1]. While measurements of this anisotropy have been made at only a few energies, an intriguing and unexplained non-monotonic behaviour has been noted [2]. Using several transport model calculations, we will discuss the effect of the Equation of State and timescales on the freezeout anisotropy. Important technical aspects of model-to-data comparisons will be discussed. This will provide important context on the data available thus far, as well as newly emerging results from the beam energy scan by STAR Collaboration. \\[4pt] [1] Retiere and Lisa, Phys. Rev. {\bf C70} 044907 (2004); nucl-th/0312024\\[0pt] [2] Lisa and Pratt, arXiv:0811.1352