Disoriented Chiral Condensate Formation in Heavy Ion Collisions?

Abstract

One of the main aims of present and upcoming high energy heavy ion collision experiments is to study new phases of matter at extreme temperature and density. It is expected that a nontrivial classical pion field configuration can occasionally form during the out-of-equilibrium chiral phase transition. We have recently shown that, contrarily to what has been assumed so far, this configuration is not identical to the so-called disoriented chiral condensate (DCC), proposed in the early 1990's. A detailed analysis reveals that a more realistic picture is that of an ``unpolarized'' DCC, where the Fourier modes of the field have completely independent orientations in isospin space instead of being aligned with each other as in the original DCC. This has important implications concerning the possible detection of the phenomenon. In particular, the main expected signature of the original DCC, which is used in most experimental searches, is absent in the unpolarized case. We point out that the fact that no evidence of DCC formation has been reported so far in nuclear collisions actually agrees with our present theoretical understanding. New experimental strategies should be designed to look for the unpolarized DCC in existing data from SPS as well as in future searches at RHIC and LHC.