STAR experiment launches the QCD critical point search program at the relativistic heavy ion collider facility

Physical systems undergo phase transitions when external parameters such as temperature (T) or a chemical potential (μ ) are tuned. A phase diagram tells us how matter organizes itself under external conditions at a given degree of freedom. The theory of strong interactions, quantum chromodynamics (QCD), predicts that nuclear matter at high temperature and/or densities makes a transition from a state where quarks and gluons (colour charge carrying basic constituents of matter) are confined in hadrons and chiral symmetry is broken, to a state where they are de-confined and chiral symmetry is restored. QCD has several conserved quantities: the baryon number (B), electric charge (Q) and strangeness (S). Each of these is associated to a chemical potential. As a result, the QCD phase diagram in principle is four dimensional. It has been observed that μQ and μS are relatively small compared to μB (baryonic chemical potential). T and μB are varied in a typical QCD phase diagram