Speaker
Description
The QCD cross-over line in the temperature (T) - baryo-chemical
potential ($\mu_{B}$) plane has been computed by several lattice
groups by calculating the chiral order parameter and its susceptibility
at finite values of $\mu_{B}$ . In this work we extract from the
peak position of the static quark entropy ($S_{Q}(T,\mu_{B})$) in
T, which is based on the renormalized Polyakov loop. This observable
was proved to have a peak in the vicinity of the chiral transition
temperature, as was illustrated in arXiv:1603.06637, and has smaller
volume effects, as was shown in arXiv:2405.12320. The small volume
is here useful to mitigate the effects of the sign problem in the
cancellations inside the Taylor coefficients of the Polyakov loop.
We extrapolate $S_{Q}(T,\mu_{B})$ based on high statistics finite
temperature ensembles on a 16$^{3}$ $\times$ 8 lattice to finite
density by means of a Taylor expansion to eighth order in $\mu_{B}$
(NNNLO) along the strangeness neutral line. For the simulations the
4HEX staggered action was used with 2+1 flavors at physical quark
masses. In this setup the phase diagram can be drawn up to unprecedentedly
high chemical potentials. Our results are in rough agreement with
phenomenological estimates of the freeze-out curve in relativistic
heavy ion collisions. In addition, we study the width of the crossover.
We show that up to $\mu_{B}$ ${\approx}$ 400 MeV, the transition
gets broader at higher densities, disfavoring the existence of a critical
endpoint in this range. Finally, we examine the transition line without
the strangeness neutrality condition and observe a hint for the narrowing
of the crossover towards large $\mu_{B}$.
