August 23, 2021 to October 7, 2021
Venue: OAC conference center, Kolymbari, Crete, Greece. Participation is possible also via internet.
Europe/Athens timezone

Nonequilibrium cumulants of the chiral order parameter and the net-proton number at lower RHIC energies

Aug 30, 2021, 1:05 PM
Room 3

Room 3


Christoph Herold (Suranaree University of Technology)


STAR’s beam energy scan program at RHIC provides data on net-proton number fluctuations with the goal to detect the QCD critical 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 twofold: First, the presence of an unstable phase causes the well-known bending of the trajectories in the space of temperature and baryochemical potential. For these cases at lower beam energies, the system crosses the freeze-out line more than once, allowing us to calculate a wide range of cumulants for each initial condition. Second, the thermodynamic susceptibilities diverge along the spinodal lines in nonequilibrium. Depending on the freeze-out parameters, these divergences can have a dramatic impact on the calculated cumulants and cumulant ratios.


Christoph Herold, Asst. Prof., Suranaree University of Technology, Thailand,

Is this abstract from experiment? No
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Is the speaker for that presentation defined? Yes
Internet talk Yes

Primary authors

Prof. Ayut Limphirat (Suranaree University of Technology) Mr Poramin Saikham (Suranaree University of Technology) Christoph Herold (Suranaree University of Technology) Marlene Nahrgang (Subatech)

Presentation materials