Advantage of U+U over Au+Au collisions at the Relativistic Heavy Ion Collider*

In a graph of $v_{2}/\epsilon$ vs. $(1/S)(dN_{ch}/dy)$, STAR data [1] reach the reported perfect fluid value of $v_{2}/\epsilon$ for the most central Au+Au collisions at 200 GeV/nucleon. It is interesting to see whether a limit is reached asymptotically by the data when $(1/S)(dN_{ch}/dy)$ is increased further. Collisions of deformed uranium nuclei have been suggested to increase this quantity at fixed beam energy [2-4]. We have studied U+U collisions in a Monte-Carlo Glauber model and attempted to simulate realistic experimental conditions. We have examined $(1/S)(dN_{ch}/dy)$ under different centrality cuts and compared with Au+Au. The most desired U+U configuration (tip-to-tip) increases the $(1/S)(dN_{ch}/dy)$ by about 35\% compared to Au+Au at $b = 0$ fm in the ideal case. In the context of real experiments and with available centrality cuts at the Relativistic Heavy Ion Collider, the predicted increase in $(1/S)(dN_{ch}/dy)$ is about 16\% which we deem still a worthwhile gain. \\ $[ 1 ]$ J.~Adams {\it et al.} [STAR], Nucl.\ Phys.\ A {\bf 757}, 102 (2005) \\ $[ 2 ]$ E.~V.~Shuryak, Phys.\ Rev.\ C {\bf 61}, 034905 (2000) \\ $[ 3 ]$ B.~A.~Li, Phys.\ Rev.\ C {\bf 61}, 021903 (2000) \\ $[ 4 ]$ U.~W.~Heinz and A.~Kuhlman, Phys.\ Rev.\ Lett.\ {\bf 94}, 132301 (2005).