New irregularities at chemical freeze-out of hadrons

Searchers for irregularities in behaviour of statistical quantities are rather important in a view of experimental studies of signals of quark-gluon plasma formation [1, 2]. In addition to the irregularities discussed in Refs. [1, 2] we found a new set of quantities which demonstrate a significant change in the same narrow range of the center of mass collision energy √SNN = 4.3–4.9 GeV. In particular, using the multicomponent hadron resonance gas model (HRGM), developed in [3], we perform a high-quality fit of 121 hadronic ratios measured for 14 values of the center of mass collision energies between 2.7 GeV and 200 GeV with the overall fit quality χ²/d.o.f.= 63.978/65≈0.98. Based on a new formulation of HRGM [3] a dramatic jump in the center of mass energy dependence of Λ/p, K⁺/p, Ω⁻/p and Ξ⁻/p ratios was found (see Fig. 1). It is interesting that these irregularities are also accompanied by the total to thermal particle yields asymmetry indicating a significant role of the particle decays at chemical freeze-out (see Fig. 2). Since in a hadron phase Λ hyperons and K⁺ mesons are mainly produced in the same reactions, then it is reasonably to expect that a formation of mixed phase will be seen in the behaviour of their ratios at the very same collision energy. Such a similarity, indeed, can be seen in Fig. 2.