Net-proton number cumulant ratios as function of beam energy from an expanding nonequilibrium chiral fluid

Abstract

The beam energy scan program at RHIC provides data on net-proton number fluctuations with the goal to detect the QCD critical end point and first-order phase transition. Interpreting these experimental signals requires a vital understanding of the interplay of critical phenomena and the nonequilibrium dynamics of the rapidly expanding fireball. We study these aspects with a fluid dynamic expansion coupled to the explicit propagation of the chiral order parameter sigma via a Langevin equation. Assuming a sigma-proton coupling through an effective proton mass, we relate cumulants of the order parameter and the net-proton number at freeze-out and obtain observable cumulant ratios as a function of beam energy. We emphasize the role of the nonequilibrium first-order phase transition where a mixed phase with gradual freeze-out can significantly alter the cumulants. We find that the presence of a critical end point is clearly visible in the cumulant ratios for a relatively wide range of center-of-mass energies.

7 pages, 3 figures

References in corpus (12)

• The order of the quantum chromodynamics transition predicted by the standard model of particle physics
• The equation of state in (2+1)-flavor QCD
• Phase structure of three and four flavor QCD
• The renormalization group and quark number fluctuations in the Polyakov loop extended quark-meson model at finite baryon density
• Phase transition dynamics for baryon-dense matter
• (3+1)-Dimensional Hydrodynamic Expansion with a Critical Point from Realistic Initial Conditions
• Chiral phase transition in the presence of spinodal decomposition
• Energy Dependence of Moments of Net-Proton and Net-Charge Multiplicity Distributions at STAR
• Net-baryon number variance and kurtosis within nonequilibrium chiral fluid dynamics
• Lattice QCD results on cumulant ratios at freeze-out
• Higher order conserved charge fluctuations inside the mixed phase
• Cumulants of the chiral order parameter at lower RHIC energies

Cited by in corpus (1)

• The time evolution of light nuclei cumulants and ratios with a first-order phase transition in the UrQMD transport model