Off-of-equilibrium effects on Kurtosis Along Strangeness-Neutral Trajectories

TL;DR

This paper investigates how out-of-equilibrium effects influence the kurtosis of proton yield distributions near the QCD critical point using a simplified hydrodynamic model with strangeness-neutral trajectories.

Contribution

It introduces a hydrodynamic model that accounts for out-of-equilibrium effects along strangeness-neutral trajectories near the critical point.

Findings

Out-of-equilibrium effects can significantly alter kurtosis signals.

Trajectory variations impact the kurtosis peak near the critical point.

The model provides insights into the non-equilibrium behavior of QCD matter.

Abstract

The Beam Energy Scan program at the Relativistic Heavy Ion Collider (RHIC) is searching for the QCD critical point. The main signal for the critical point is the kurtosis of the distribution of proton yields obtained on an event-by-event basis where one expects a peak at the critical point. However, its exact behavior is still an open question due to out-of-equilibrium effects and uncertainty in the equation of state. Here we use a simplistic hydrodynamic model that enforces strangeness-neutrality, selecting trajectories that pass close to the critical point. We vary the initial conditions to estimate the effect of out-of-equilibrium hydrodynamics on the kurtosis signal.