PHENIX results on collective behavior in small systems from geometry-controlled experiments at sNN=200Â GeV

Recent measurements in small collisions systems at LHC and RHIC indicate that the particles produced in high-multiplicity collisions exhibit collective behavior very similar to that observed in large systems where QGP is formed. In large systems, it is well established that the final-state particle correlations arise from anisotropic pressure gradients in the initial state of the collisions that drive a near-perfect fluid evolution. Whether QGP is also formed in small collision systems is presently under intense investigation. To study the origin of the collective behavior in small systems, the PHENIX experiment performed a series of geometry-controlled experiments using p+Al, p+Au, d+Au, and 3He+Au collisions at sNN=200 GeV. The elliptic (v2) flow coefficients are measured as a function of pT for inclusive and identified charged hadrons. Mass dependence is observed in v2(pT) indicative of hydrodynamic evolution. The distinct initial geometries provide discriminating power against the models.