Speaker
Description
We show that results for the thermodynamics of strongly interacting matter obtained by state of the
art Monte-Carlo simulations of lattice QCD can be adequately described within a generalized BethUhlenbeck type approach, where the hadron resonance gas (HRG) phase appears as a mixture of
(multi-) quark clusters. The underlying chiral quark dynamics is coupled to a background gluon
field using the Polyakov gauge. The transition to the quark-gluon plasma (QGP) phase appears as a
Mott dissociation of the quark clusters described by a model for hadron phase shifts that encodes
the dissociation of bound states in the continuum of scattering states triggered by the chiral
symmetry restoration transition. An important ingredient are Polyakov-loop generalized distribution
functions of multi-quark clusters which are derived here for the first time [1].
This new approach gives a quantitative understanding for the observation of ultrarelativistic heavyion collision that the abundances of hadrons produced in these experiments are well described by a
statistical model within a sudden chemical freeze-out at a well-defined hadronization temperature
despite the fact that the melting of the chiral condensate proceeds as a smooth crossover.
We report for the first time the remarkable finding that the ratio of generalized baryon number
susceptibilities $R_{42}^B(T)=\chi_4^B (T)/\chi_2^B (T)$, which interpolates between the value
$R_{42}^B(T\simeq 140 {\rm MeV})=1$ for a pure HRG and
$R_{42}^B(T>250 {\rm MeV}) \sim1/9 $ for the QGP shall not be mistaken for a measure of the
fraction of hadrons in the system. Its deviation from unity can actually quantify the degree of
overlap of quark wave functions which leads to the quark Pauli blocking effect in the HRG which
leads to repulsive residual interactions which we model by a temperature dependent excluded
baryon volume.
[1] D. Blaschke, M. Cierniak, O. Ivanytskyi and G. Röpke, Eur. Phys. J. A 60 (2024)
[2] D. Blaschke, O. Ivanytskyi and G. Röpke, in preparation
