Collective flow in ultrarelativistic 3He–Au collisions

The triangular flow in ultrarelativistic 3He–Au collisions at RHIC energies is enhanced due to the triangular arrangement of the nucleon configurations in 3He. We study the fireball eccentricities in the Glauber Monte Carlo model and find that since the configurations of the projectile 3He are elongated triangles, the created fireball has not only a significant triangularity but also a large ellipticity. The dependence of the triangularity on centrality is weak, so it cannot be extracted from the centrality dependence of the triangular flow v3v3, as it is dominated by the centrality dependence of the hydrodynamic response. We propose to look at the centrality dependence of the ratio vn{4}/vn{2}vn{4}/vn{2}, where the uncertainties from the hydrodynamic response cancel, and show that the basic signature of the geometry-driven collective flow is the rise of the ratio v3{4}/v3{2}v3{4}/v3{2} with the number of participant nucleons for centralities less than 10%.