Search for the QCD critical point in high energy nuclear collisions

Abstract

QCD critical point is a landmark region in the QCD phase diagram outlined by temperature as a function of baryon chemical potential. To the right of this second-order phase transition point, one expects first order quark–hadron phase transition boundary, towards the left a crossover region, top of it lies the quark–gluon plasma phase and below it the hadronic phase. Hence locating the QCD critical point through relativistic heavy-ion collision experiments is an active area of research. Cumulants of conserved quantities in strong interaction, such as net-baryon, net-charge, and net-strangeness, are suggested to be sensitive to the physics of QCD critical point and are therefore useful observables in the study of the phase transition between quark–gluon plasma and hadronic matter. We review the experimental status of the search for the QCD critical point via the measurements of cumulants of net-particle distributions in heavy-ion collisions. We discuss various experimental challenges and associated corrections in such fluctuation measurements. We also comment on the physics implications of the measurements by comparing them with theoretical calculations. This is followed by a discussion on future experiments and measurements related to high baryonic density QCD matter.