Examination of directed flow as a signature of the softest point of the equation of state in QCD matter

Understand

We analyze the directed flow of protons and pions in high-energy heavy-ion collisions in the incident energy range from $\sqrt{s_{{\scriptscriptstyle NN}}}=7.7$ to 27 GeV within a microscopic transport model.

• Standard hadronic transport approaches do not describe the collapse of directed flow below $\sqrt{s_{{\scriptscriptstyle NN}}}\simeq 20$ GeV.
• By contrast, a model which simulates effects of a softening of the equation of state, well describes the behavior of directed flow data recently obtained by the STAR Collaboration~\cite{STARv1}.
• We give a detailed analysis of how directed flow is generated.