Challenging claims of ?elliptic flow? by comparing azimuth quadrupole and jet-related angular correlations from Au?Au collisions at $\sqrt{{{s}_{NN}}}$ = 62 and 200 GeV

Background: A component of azimuth correlations from high-energy heavy ion collisions varying as and denoted by symbol v2 is conventionally interpreted to represent 'elliptic flow,' a hydrodynamic manifestation of the initial-state A–A overlap geometry. Several numerical methods are used to estimate v2, resulting in various combinations of 'flow' and 'nonflow' that reveal systematic biases in the v2 estimates. QCD jets contribute strongly to azimuth correlations and specifically to the component. Purpose: We question the extent of jet-related ('nonflow') bias in and hydrodynamic 'flow' interpretations of v2 measurements. Method: We introduce two-dimensional model fits to angular correlation data that distinguish accurately between jet-related correlation components and a nonjet (NJ) azimuth quadrupole that might represent 'elliptic flow' if that were relevant. We compare measured jet-related and 'flow'-related data systematics and determine the jet-related contribution to v2 measurements. Results: Jet structure does introduce substantial bias to conventional v2 measurements, making interpretation difficult. The NJ quadrupole exhibits very simple systematics on centrality and collision energy—the two variables factorize. Within a Au–Au centrality interval where jets show no indication of rescattering or medium effects the NJ quadrupole amplitude rises to 60% of its maximum value. Conclusions: Disagreements between NJ quadrupole systematics and hydro theory expectations, the large quadrupole amplitudes observed in more-peripheral Au–Au collisions and a significant nonzero value in N–N ≈ p–p collisions strongly suggest that the NJ quadrupole does not arise from a hydrodynamic flow mechanism.