(a) \etapai ratio in the two centrality classes measured, 0--10\% (circles) and 20--50\% (squares). (b) Comparison of the \etapai measurement in the 0--10\% centrality class (full circles) to the corresponding ratio in pp collisions  (stars) and to the $K^{\pm}/\pi^{\pm}$ measurement in the same centrality class, system and collision energy  (open circles).