Separate Chemical Freeze-Outs of Strange and Non-Strange Hadrons and Problem of Residual Chemical Non-Equilibrium of Strangeness in Relativistic Heavy Ion Collisions

  • K. A. Bugaev Bogolyubov Institute for Theoretical Physics, Nat. Acad. of Sci. of Ukraine
  • D. R. Oliinychenko Bogolyubov Institute for Theoretical Physics, Nat. Acad. of Sci. of Ukraine, FIAS, Goethe-University
  • V. V. Sagun Bogolyubov Institute for Theoretical Physics, Nat. Acad. of Sci. of Ukraine
  • A. I. Ivanytskyi Bogolyubov Institute for Theoretical Physics, Nat. Acad. of Sci. of Ukraine
  • J. Cleymans Department of Physics, University of Cape Town
  • E. S. Mironchuk Moscow Institute of Physics and Technology
  • E. G. Nikonov Laboratory for Information Technologies, JINR
  • A. V. Taranenko National Research Nuclear University “Moscow Engineering Physics Institute”
  • G. M. Zinovjev Bogolyubov Institute for Theoretical Physics, Nat. Acad. of Sci. of Ukraine
Keywords: chemical freeze-out, strangeness enhancement/suppression factor ys, Strangeness Horn, hadron multiplicities

Abstract

We present an elaborate version of the hadron resonance gas model with the combined treatment of separate chemical freeze-outs for strange and non-strange hadrons and with an additional ys factor which accounts for the remaining strange particle non-equilibration. Within the suggested approach, the parameters of two chemical freeze-outs are connected by the conservation laws of entropy, baryonic charge, third isospin projection, and strangeness. The developed model enables us to perform a high-quality fit of the hadron multiplicity ratios measured at AGS, SPS, and RHIC with X2/dof ≃ 0.93. A special attention is paid to a successful description of the Strangeness Horn. The well-known problem of selective suppression of Λ and Ξ hyperons is also discussed. The main result is that, for all collision energies, the ys factor is about 1 within the error bars, except for the center-of-mass collision energy 7.6 GeV, at which we find about 20% enhancement of strangeness. Also we confirm the existence of strong jumps in the pressure, temperature, and effective number of degrees of freedom at the stage of strange particle chemical freeze-out, when the center-of-mass collision energy changes from 4.3 to 4.9 GeV. We argue that these irregularities may signal about the quark-hadron phase transition.

Published
2019-01-05
How to Cite
Bugaev, K., Oliinychenko, D., Sagun, V., Ivanytskyi, A., Cleymans, J., Mironchuk, E., Nikonov, E., Taranenko, A., & Zinovjev, G. (2019). Separate Chemical Freeze-Outs of Strange and Non-Strange Hadrons and Problem of Residual Chemical Non-Equilibrium of Strangeness in Relativistic Heavy Ion Collisions. Ukrainian Journal of Physics, 61(8), 659. https://doi.org/10.15407/ujpe61.08.0659
Section
Fields and elementary particles