From proton cumulants to baryon number susceptibilities at finite density

Abstract

Lattice QCD based extrapolations and functional QCD methods point to a candidate critical region near T ≈ 100–120 MeV and μ_B ≈ 600–650 MeV, motivating the search for its imprint on fluctuations in heavy-ion collisions. I will first briefly review these predictions, including the latest extensions to the strangeness-neutral conditions of heavy-ion collisions. I will then discuss how to connect equilibrium expectations for baryon number fluctuations to experimental measurements in the RHIC Beam Energy Scan program, which requires controlling several non-critical effects. I will discuss how exact baryon number conservation, kinematic acceptance, and the mapping from baryons to protons affect the measured cumulants and factorial cumulants. Finally, I will present a Bayesian framework that embeds arbitrary baryon number susceptibilities into realistic hydrodynamic freeze-out via maximum-entropy particlization. Applying it to collider-mode BES data, I will extract the susceptibilities of QCD matter at finite baryon density at each collision energy, confront them with lattice-based expectations, and discuss implications for the critical point search.