Strangeness Enhancement in Heavy Ion Collisions at the AGS as a Possible Signature of the Quark Gluon Plasma Formation.

Enhanced strangeness production was suggested a decade ago^1 as a possible signature of Quark Gluon Plasma (QGP), which is a state of unconfined quarks and gluons that will exist in superdense and hot nuclear matter as predicted by Quantum Chromodynamics (QCD). Theorists believe that such a state (QGP) existed in the early universe for ~10^{- inni} seconds, and could possibly be created in laboratory with relativistic heavy-ion collisions. We utilized the 14.6 times A GeV/c Si beam provided by the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL) to bombard different targets (Al, Si, W, Au, Pb, etc.) in searching for a QGP. Particles produced in the forward hemisphere (NN center of mass system) from these collisions traveled through up to 3 TPC (Time Projection Chamber) modules which were in a 5 kilogauss magnetic field. Each detected track was recorded individually with regards to position, momentum and charge. A significantly enhanced K_sp{s }{rm O} and Lambda production in relativistic heavy-ion collisions over that of a simple cascade of NN collisions was detected. But the enhancement of single strangeness particles may not be good signature of QGP, because secondary scatterings of resonant states (e.g. Delta and N^*) in a hadron gas may as well increase their production. This makes the multistrange hyperon (e.g. Xi^-) production a better alternative for a QGP signature, because its formation through resonant state rescatterings in hadron gas is more difficult than that of single strangeness particles (e.g. K_sp{x}{rm O}, Lambda). Excessive strangeness content in a QGP may favor Xi^- production (as well as strangelets) during hadronization. Copious production of Xi^ - has been detected with limited statistics. The measured ratio of N(Xi^-)/N (Lambda) = 0.12+/- 0.02 +/- 0.025 is at least 3 times larger than the predictions of generally known hadronic cascade models. Various models and general considerations have been explored trying to understand the physical implications of the experimental results.