Sonic Boom in the Little Bang at RHIC ?

The Big Bang Model is a widely accepted theory for the origin and evolution of our universe. It postulates that ∼ 12−14 billion years ago, a hot and dense plasma of quarks and gluons (QGP) was produced a few micro seconds after the “big bang”. A pervading uniform glow of cold cosmic microwave background provides an unequivocal signature for the subsequent expansion from this hot and dense state to the vast and significantly cooler cosmos we currently inhabit [ 1]. Recent experiments at Brookhaven’s Relativistic Heavy Ion Collider (RHIC), give evidence for the creation of locally equilibrated hot and dense QCD matter in a “little bang” initiated in relativistic Au+Au collisions [ 2]. A short time after this bang (∼ 1fm/c), the energy density is estimated to be ≃ 5.4 GeV/fm [ 2] – a value significantly larger than the ∼ 1 GeV/fm required for the transition from low-temperature hadronic matter to the high-temperature QGP phase of QCD [ 3]. The subsequent expansion and ultimate hadronization of this high energy density matter, results in the emission of particles which signal its thermodynamic and dynamical properties. An important challenge is to develop robust experimental constraints for these properties. This contribution discusses the role of both elliptic flow and hot QCD “sonic boom” measurements as constraints.