Collision Geometry and Flow in Uranium+Uranium Collisions

Understand

Using event-by-event viscous fluid dynamics to evolve fluctuating initial density profiles from the Monte-Carlo Glauber model for U+U collisions, we report a "knee"-like structure in the elliptic flow as a function of collision centrality, located near 0.5% centrality as measured by the final charged multiplicity.

• This knee is due to the preferential selection of tip-on-tip collision geometries by a high-multiplicity trigger.
• Such a knee structure is not seen in the STAR data.
• This rules out the two-component MC-Glauber model for initial energy and entropy production.