Extraction of the sound velocity from rapidity spectra: Evidence for QGP formation at FAIR/RHIC-BES energies

Abstract

We analyze longitudinal pion spectra from \sqrt{s_{NN}}= 2 GeV to \sqrt {s_{\rm NN}}=20 GeV within Landau's hydrodynamical model and the UrQMD hybrid approach. From the measured data on the widths of the pion rapidity spectra, we extract the sound velocity c_s^2 in the dense stage of the reactions. It is found that the sound velocity has a local minimum (indicating a softest point in the equation of state, EoS) at \sqrt{s_{NN}}= 4-9 GeV, an energy range accessible at the Facility for Antiproton and Ion Research (FAIR) as well as the RHIC-Beam Energy Scan (RHIC-BES). This softening of the EoS is compatible with the formation of a QGP at the onset of deconfinement. The extracted sound velocities are then used to calculate an excitation function for the mean transverse mass of pions from the hybrid model. We find that, above \sqrt{s_{NN}} \approx 10 GeV, even the lowest c_s^{2} gives a considerably larger <m_T> of pions compared to data.

5 pages 3 figures, version accepted by EPJ-A. arXiv admin note: substantial text overlap with arXiv:hep-ph/0509314

References in corpus (5)

• Fully integrated transport approach to heavy ion reactions with an intermediate hydrodynamic stage
• Triangular flow in event-by-event ideal hydrodynamics in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200A$ GeV
• (3+1)-Dimensional Hydrodynamic Expansion with a Critical Point from Realistic Initial Conditions
• Constraining the initial state granularity with bulk observables in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV
• 1+1 Dimensional Hydrodynamics for High-energy Heavy-ion Collisions

Cited by in corpus (4)

• Speed of sound and baryon cumulants in heavy-ion collisions
• Decoding the flow evolution in Au+Au reactions at $1.23A$ GeV using hadron flow correlations and dileptons
• Excitation functions of parameters extracted from three-source (net-)proton rapidity distributions in Au-Au and Pb-Pb collisions over an energy range from AGS to RHIC
• Density Functional Equation of State and Its Application to the Phenomenology of Heavy-Ion Collisions