Exploring Thermalization and Fluidity in a Hadron Gas Using an Excluded Volume Hadron Resonance Gas Approach

The existence of different phases of matter produced in relativistic heavy-ion collisions requires a hadronic description, creating much interest in the hadronic phase. We explore the possibility of thermalization and applicability of hydrodynamics in a hadron gas medium using the Knudsen number (Kn). \(Kn << 1\) implies a system with a large number of interactions, and hence making the system thermalized. Furthermore, we probe the nature of the system by studying its viscosity and compressibility through Reynolds (Re) and Mach (Ma) numbers. These dimensionless parameters are studied for different system sizes and baryochemical potentials ( \(\mu _B\) ). The results at high temperatures point towards the possibility of inviscid compressible flows in the system ( \(Kn << 1, Re >> 1\) , and \(Ma \sim 1\) ). The comparable values of Kn over different system sizes indicate the applicability of hydrodynamics for different systems, from high multiplicity pp to heavy-ion collisions.