Collision Geometry and Flow in Uranium+Uranium Collisions
Abstract
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. An enrichment of tip-tip configurations by triggering solely on high-multiplicity in the U+U collisions thus does not work. On the other hand, using the Zero Degree Calorimeters (ZDCs) coupled with event-shape engineering, we identify the selection purity of body-body and tip-tip events in the full-overlap U+U collisions. With additional constraints on the asymmetry of the ZDC signals one can further increases the probability of selecting tip-tip events in U+U collisions.
Cite
@article{arxiv.1502.00603,
title = {Collision Geometry and Flow in Uranium+Uranium Collisions},
author = {Andy Goldschmidt and Zhi Qiu and Chun Shen and Ulrich Heinz},
journal= {arXiv preprint arXiv:1502.00603},
year = {2015}
}
Comments
9 pages, 4 figures, Proceedings of WPCF 2014 in Gy\"ongy\"os, Hungary, Aug.25-29, 2014