<i>η</i>-η’ mixing angle

Abstract

The current experimental evidence on the value of the \ensuremath{\eta}-\ensuremath{\eta}' mixing angle is summarized in the light of our present theoretical understanding. A value of ${\ensuremath{\theta}}_{P}$\ensuremath{\simeq}-20\ifmmode^\circ\else\textdegree\fi{} is consistent with all present evidence.