Probing vorticity through femtoscopic correlations

Abstract

In heavy-ion collisions, as the two nuclei pass through one another and create hot and dense matter, part of their initial angular momentum is transferred to the fireball, generating a nonzero average vorticity. Understanding heavy-ion collision dynamics and its influence on key observables, including those used to probe the initial state or assess thermodynamics of nuclear matter, requires understanding the magnitude of effects tied to vorticity. In this work, we use simulations of non-central Au+Au collisions at $E_{\rm{kin}}=1.23~A\rm{GeV}$ to show that the rotation of the system impacts the space-time picture of particle emission and, in particular, leaves imprints on proton-pion femtoscopic correlations. Next, we use coarse-graining of the simulation outputs to extract the collective velocity as a function of position and time, shedding light on the dynamical origin of this effect. Moreover, we demonstrate that the displacement between the proton and pion emission centers quantifies the strength of the rotation and propose it as a new signal of vorticity in heavy-ion collisions.