The “horn” in the kaon-to-pion ratio

Abstract

A microscopic approach has been employed to study the kaon productions in heavy-ion collisions. The momentum-integrated Boltzmann equation has been used to study the evolution of strangeness in the system formed in heavy-ion collisions at relativistic energies. The kaon productions have been calculated for different center-of-mass energies ($\sqrt{{s}_{\mathit{NN}}}$) ranging from the Alternating Gradient Synchrotron (AGS) to the Relativistic Heavy Ion Collider (RHIC). The results have been compared with available experimental data. We obtain a nonmonotonic hornlike structure for ${K}^{+}/{\ensuremath{\pi}}^{+}$ when plotted with $\sqrt{{s}_{\mathit{NN}}}$ with the assumption of an initial partonic phase beyond a certain threshold in $\sqrt{{s}_{\mathit{NN}}}$. However, a monotonic rise of ${K}^{+}/{\ensuremath{\pi}}^{+}$ is observed when a hadronic initial state is assumed for all $\sqrt{{s}_{\mathit{NN}}}$. Experimental values of ${K}^{\ensuremath{-}}/{\ensuremath{\pi}}^{\ensuremath{-}}$ are also reproduced within the ambit of the same formalism. Results from scenarios where the strange quarks and hadrons are formed in equilibrium and evolve with and without secondary productions have also been presented.