η′ production in nucleus-nucleus collisions as a probe of chiral dynamics

Abstract

I argue that, because of the peculiar properties of the η ′ meson, it is a promising probe of "chiral" dynamics. In particular, I show that a rotating gluon-dominated plasma might lead to an enhanced production of η ′ 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,I expect a non-trivial dependence on event geometry, such as initial volume and impact parameter.Hence, an observation of η ′ /π ratio depending strongly on impact parameter might be a good indication of chiral effects, either from vorticity or topological phases of QCD. *

Fate of the η′ in the quark gluon plasma

“…Chiral and U(1) A restoration at high temperatures and their implications on the η mesons have been considered by several authors [14,15,16,17,18,19,20,21]. A generalization of the Witten-Veneziano approach at finite temperature [15] indicates a dip in the η mass followed by an increase, leading to a near-degeneracy with the pion mass.…”

“…However, the present understanding of the behaviour of η at high temperatures is incomplete. Studies have been carried out [14,15,16,17,18,19,20,21] within the framework of effective field theory, and we will briefly review them below. The results are inconclusive and call for a first principle analysis.…”