Speaker
Description
We propose an observable to probe the content of a bath of quarks and gluons at finite temperature and chemical potential, the net quark number gain $\Delta Q$. QCD is controlled by different degrees of freedom in the various sections of its phase diagram, notably hadrons at low temperatures (and chemical potentials) and quarks and gluons at high temperatures. However, studying the relevant content of a QCD medium across the phase diagram is challenging.
To this end, we correlate the Polyakov or anti-Polyakov loops to the medium’s net quark number $Q$. This gives the net quark number gain $\Delta Q$, which provides information on how the thermal bath reacts to adding a static quark or antiquark probe. While insignificant at high temperatures, it shows the bath's tendency to form hadron-like configurations at low temperatures, which would screen the probe’s color charge. Interestingly, $\Delta Q$ allows one to distinguish meson-like and baryon-like configurations as a function of the chemical potential and for the different probes. This net quark number gain also helps explain how a single quark/antiquark can be added to a supposedly hadronic medium in the first place: the latter provides the missing quarks/antiquarks to form hadron-like states.
We sketch the derivation of this general result for temperatures much smaller than the quark masses and in the limits of large temperature or chemical potential, where perturbative QCD works. We discuss possible further applications to study the various features of the QCD phase diagram, like critical points or color superconductivity.
