Transverse Velocity Dependence of the Proton-Antiproton Ratio as a Signature of the QCD Critical Endpoint

Abstract

The presence of a critical point in the QCD phase diagram can deform the trajectories describing the evolution of the expanding fireball in the $μ_B-T$ phase diagram. If the average emission time of hadrons is a function of transverse velocity, as microscopic simulations of the hadronic freeze-out dynamics suggest, the deformation of the hydrodynamic trajectories will change the transverse velocity ($β_{\rm T}$) dependence of the proton-antiproton ratio when the fireball passes in the vicinity of the critical point. An unusual $β_{\rm T}$-dependence of the $\bar{p}/p$ ratio in a narrow beam energy window would thus signal the presence of the critical point.