Experiments at the Relativistic Heavy Ion Collider have measured the net polarization of Λ and Λ hyperons and attributed it to a coupling between their spin and the vorticity of the fluid created in heavy-ion collisions. Equipartition of energy is generally assumed, but the dynamical mechanism which polarizes them has yet to be determined. We consider two such mechanisms: vorticity fluctuations and helicity flip in scatterings between strange quarks and light quarks and gluons. With reasonable parameters both mechanisms lead to equilibration times orders of magnitude too large to be relevant to heavy-ion collisions. Our conclusion is that strange quark spin or helicity is unchanged from the time they are created to the time they hadronize. A corollary is that vorticity fluctuations do not affect the hyperon spin, either.
Bibliographical noteFunding Information:
The work of J.I.K. was supported by the U.S. Department of Energy Grant No. DE-FG02-87ER40328. The work of E.R. was supported by the U.S. National Science Foundation Grant No. PHY-1630782 and by the Heising-Simons Foundation Grant No. 2017-228.