Department of Physics and Astronomy

Nuclear and Particle Physics Seminar

Monday, September 20

12:30pm-1:30pm

Stevenson Center, Room 6333

Julia Velkovska

Vanderbilt University

The Baryon Anomaly at RHIC

At the Relativisic Heavy Ion Collisder (RHIC), Au-Au collisions at sqrt(s) = 200 GeV produced nuclear matter at the highest temperatures and energy densities yet achieved in laboratory conditions. The goal is to search for signatures of deconfinement and chiral symmetry restoration and to study the transition from normal to deconfined nuclear matter by utilizing a wide variety of probes. One of the most convincing pieces of evidence for Quark Gluon Plasma comes form hard scattering processes which probe the earliest stages of the collisions. The PHENIX experiment has discovered supression of high-pT pion production which is consistent with jet-queching form the dense plasma, as predicted by theory. Surprisingly, the production of baryons appears unsupressed in the measured range. Recent theoretical development explains the baryon/meson behavior by invoking quark-recombination from the deconfined phase making this feature a direct signature for partonic degrees of freedom. There are, however, experimental results that pose problems to this theory. As of today, the large (anti)baryon to pion excess relative to expectations from parton fragmentation functions remains the most striking unpredicted experimental observation at RHIC.