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Transition from Baryon- to Meson-Dominated Freeze Out -- Early Decoupling around 30 A GeV?

H. Oeschler·J. Cleymans·K. Redlich·S. Wheaton
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Abstract

The recently discovered sharp peak in the excitation function of the K+/pi+ ratio around 30 A GeV in relativistic heavy-ion collisions is discussed in the framework of the Statistical Model. In this model, the freeze-out of an ideal hadron gas changes from a situation where baryons dominate to one with mainly mesons. This transition occurs at a temperature T = 140 MeV and baryon chemical potential mu(B) = 410 MeV corresponding to an energy of sqrt(s) = 8.2 GeV. The calculated maximum in the K+/pi+ ratio is, however, much less pronounced than the one observed by the NA49 Collaboration. The smooth increase of the K-/pi- ratio with incident energy and the shape of the excitation functions of the Lambda/pi+, Xi-/pi+ and Omega/pi ratios all exhibiting maxima at different incident energies, is consistent with the presently available experimental data. The measured K+/pi+ ratio exceeds the calculated one just at the incident energy when the freeze-out condition is changing. We speculate that at this point freeze-out might occur in a modified way. We discuss a scenario of an early freeze-out which indeed increases K+/pi+ ratio while most other particle ratios remain essentially unchanged. Such an early freeze-out is supported by results from HBT studies.

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H. Oeschler, J. Cleymans, K. Redlich, S. Wheaton. 2007-01-26. Transition from Baryon- to Meson-Dominated Freeze Out -- Early Decoupling around 30 A GeV?. https://doi.org/10.1088/0954-3899%2F32%2F12%2Fs28

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