PHENIX results on collectivity tests in high-multiplicity p + p and p + Au collisions at [formula omitted

Abstract

The observation of possible collective effects in high-multiplicity p+p and p+Pb collisions at the LHC and in d+Au and 3He+Au collisions at RHIC challenge our understanding of the ingredients necessary for quark-gluon plasma formation. For further investigation of these effects, the PHENIX collaboration has taken high statistics data in p+p and p+Au and p+Al collisions in 2015. For these data sets, high-multiplicity triggers were implemented using the forward silicon detector (FVTX) and the beam-beam counter (BBC) covering pseudo-rapidity 1.0<|η|<3.0 and 3.1<|η|<3.9, respectively. The multi-hundred million high-multiplicity event samples recorded enable highly differential analysis to look for collective effects. We report results on large pseudo-rapidity separation correlations to elucidate if the so-called ridge phenomena exists in certain p+p event classes at RHIC. The flow coefficients from azimuthal anisotropies in p+Au are extracted and compared with theoretical expectations in various models, including viscous hydrodynamics where the elliptic flow strength is expected to be substantially smaller than in d+Au and 3He+Au at the same energy due to the smaller initial spatial eccentricity.