Elliptic Flow in Uranium-Uranium Collisions at √ sNN = 193 GeV

The hot, dense nuclear medium created in Gold-Gold collisions at RHIC exhibits strong, anisotropic collective motion, characterized by the elliptic flow coefficient v2. v2 has been extensively studied, and is thought to be related to the initial eccentricity of the colliding system and its resulting density, quantified by 1 S dN dη . Recently, RHIC has begun colliding Uranium ions. Collisions of these heavier, deformed uranium nuclei will introduce greater eccentricities, and were expected to increase the achievable value of 1 S dN dη by 13%. Simulations therefore predict that central Uranium-Uranium collisions will yield a significant increase in v2 over central Gold-Gold collisions. In this paper we present the first v2 measurements from these Uranium-Uranium collisions. We find that Uranium collisions increase v2 and 1 S dN dη , as expected. Contrary to predictions, however, we also find that v2/ vs. 1 S dN dη deviates significantly from the universal curve set by Gold-Gold collisions.