$\eta'$ Production in Nucleus-Nucleus collisions as a probe of chiral dynamics

We argue that, because of the peculiar properties of the $\eta'$ meson, it is a promising probe of "chiral" dynamics. In particular, we show that a rotating gluon-dominated plasma might lead to an enhanced production of $\eta'$ w.r.t. statistical model expectations. The presence of a strong topological susceptibility might give a similar effect. In both cases, unlike the statistical model,we expect a non-trivial dependence on event geometry, such as initial volume and impact parameter. Hence, an observation of $\eta'/\pi^0$ ratio depending strongly on impact parameter might be a good indication of chiral effects, either from vorticity or topological phases of QCD