Freeze-out by bulk viscosity driven instabilities

TL;DR

This paper proposes a new freezeout scenario in heavy ion collisions driven by bulk viscosity instabilities, leading to fragmentation into droplets that can explain HBT measurements.

Contribution

It introduces a novel mechanism where bulk viscosity causes fluid instabilities and fragmentation, offering a potential solution to the HBT puzzle in heavy ion collision analysis.

Findings

Bulk viscosity increases near the critical temperature, T_c.

Fluid fragments into droplets that preserve outward flow.

Scenario can reproduce experimental HBT data.

Abstract

We describe a new scenario (first introduced in [G. Torrieri, B. Tom\'a\v{s}ik and I. Mishustin, Phys. Rev. C \textbf{77}, 034903 (2008)]) for freezeout in heavy ion collisions that could solve the lingering problems associated with the so-called HBT puzzle. We argue that bulk viscosity increases as $T$ approaches $T_c$. The fluid {then} becomes unstable against small perturbations, and fragments into clusters of a size much smaller than the total size of the system. These clusters maintain the pre-existing outward-going flow, as a spray of droplets, but develop no flow of their own, and hadronize by evaporation. We show that this scenario can explain HBT data and suggest how it can be experimentally tested.