Functional form of the high-density chemical freeze-out curve

Determine the functional form of the chemical freeze-out curve in the high-density, low-temperature region of the QCD phase diagram, particularly near the nuclear liquid-gas phase transition, to reduce the uncertainty in baryon-number fluctuation predictions.

Background

The paper studies net-baryon number fluctuations near the nuclear liquid-gas phase transition using the parity-doublet model. Because high-order fluctuations vary strongly near this transition, even small changes in the chemical freeze-out trajectory can produce substantially different predictions for observables compared with heavy-ion collision data.

Existing freeze-out data provide only limited constraints at high baryon chemical potential, especially near the nuclear liquid-gas transition. The authors therefore examine several candidate prescriptions, including a constant chiral-condensate contour, the peak of the second-order fluctuation, and freeze-out points extracted from lower-order experimental cumulants, but no generally established functional form is available in this region.