The "soft ridge" - is it initial-state geometry or modified jets?

Abstract

A same-side (SS, on azimuth $\phi$) 2D peak in measured angular correlations from 200 GeV \pp collisions exhibits properties expected for jet formation. In more-central \auau collisions the SS peak becomes elongated on pseudorapidity $\eta$ and the transverse momentum $p_t$ structure is modified. In the latter case the SS 2D peak has been referred to as a "Soft Ridge", and arguments have been presented that the elongated peak represents flow phenomena ("triangular" and "higher harmonic" flows), possibly related to the initial-state \aa geometry. In this presentation I demonstrate that "higher harmonic flows" are related to SS 2D peak properties and review evidence for a jet interpretation of the SS peak for all \auau centralities.