# Searching for Minimum in Dependence of Squared Speed-of-Sound on Collision Energy

Liu, Fu-Hu  (Institute of Theoretical Physics, Shanxi University, Taiyuan, Shanxi 030006, China) ; Gao, Li-Na (Institute of Theoretical Physics, Shanxi University, Taiyuan, Shanxi 030006, China) ; Lacey, Roy A. (Departments of Chemistry & Physics, Stony Brook University, Stony Brook, NY 11794, USA)

13 May 2016

Abstract: Experimental results of the rapidity distributions of negatively charged pions produced in proton-proton ( $p$ - $p$ ) and beryllium-beryllium (Be-Be) collisions at different beam momentums, measured by the NA61/SHINE Collaboration at the super proton synchrotron (SPS), are described by a revised (three-source) Landau hydrodynamic model. The squared speed-of-sound parameter ${c}_{s}^{\mathrm{2}}$ is then extracted from the width of rapidity distribution. There is a local minimum (knee point) which indicates a softest point in the equation of state (EoS) appearing at about $40A$  GeV/ $c$ (or 8.8 GeV) in ${c}_{s}^{\mathrm{2}}$ excitation function (the dependence of ${c}_{s}^{\mathrm{2}}$ on incident beam momentum (or center-of-mass energy)). This knee point should be related to the searching for the onset of quark deconfinement and the critical point of quark-gluon plasma (QGP) phase transition.

Published in: Advances in High Energy Physics 2016 (2016) 9467194