Speaker
Description
In the study of spin-polarization phenomena in heavy-ion collisions, it is
typically assumed that final-state particles are polarized through thermal vorticity
and shear. In this sense, polarization is a final-state effect. Here, we propose a
different mechanism. We postulate that the collision of spin-carrying nucleons
generates an initial transverse spin density, inducing a net polarization of the QCD
fireball along a random direction. If the net spin is conserved throughout the
evolution of the fireball, the final-state particles should exhibit measurable
polarization. Within a wounded nucleon picture, we estimate that initial-state
fluctuations induce a net polarization of Lambda baryons which is around 1% in
central collisions and 10% in noncentral collisions, exceeding the contributions
from thermal vorticity and shear. We introduce a two-particle angular correlation
observable designed to reveal initial net-spin fluctuations, and emphasize the main
signatures to look for in experiments. We argue that the discovery of these
phenomena would have profound implications for nuclear structure and our
understanding of spin in relativistic hydrodynamics.In the study of spin-polarization phenomena in heavy-ion collisions, it is
typically assumed that final-state particles are polarized through thermal vorticity
and shear. In this sense, polarization is a final-state effect. Here, we propose a
different mechanism. We postulate that the collision of spin-carrying nucleons
generates an initial transverse spin density, inducing a net polarization of the QCD
fireball along a random direction. If the net spin is conserved throughout the
evolution of the fireball, the final-state particles should exhibit measurable
polarization. Within a wounded nucleon picture, we estimate that initial-state
fluctuations induce a net polarization of Lambda baryons which is around 1% in
central collisions and 10% in noncentral collisions, exceeding the contributions
from thermal vorticity and shear. We introduce a two-particle angular correlation
observable designed to reveal initial net-spin fluctuations, and emphasize the main
signatures to look for in experiments. We argue that the discovery of these
phenomena would have profound implications for nuclear structure and our
understanding of spin in relativistic hydrodynamics.
