Extracting the QCD Diffusivity and Charge Susceptibilities from Heavy Ion Collisions
Charge Susceptibilities, or charge fluctuations, represent critical observables for characterizing the chemistry and equation of state of QCD matter. Unfortunately, a heavy-ion collision traverses a wide swath of the density-temperature plane, and due to the short time scale charge conservation restricts the degree to which fluctuations represent equilibrium quantities. I will show how one can use charge correlations, binned by relative rapidity, relative azimuthal angle, and indexed by species, to not just constrain the susceptibilities, but to extract their evolution in time throughout the collision. Additionally, the ability of such correlations to simultaneously constrain the charge diffusivity of QCD matter will be presented. A detailed microscopic model of such correlations is then compared to data from the STAR Collaboration at RHIC and from the ALICE Collaboration at the LHC. The prospects to quantitatively constrain fundamental properties of QCD matter are found to be very encouraging.