Investigation of the electromagnetic structure of<i>η</i>and η’ mesons by two-photon interactions

The TPC/Two-Gamma facility at the SLAC ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ storage ring PEP was used to study the reactions \ensuremath{\gamma}${\ensuremath{\gamma}}^{\mathrm{*}}$\ensuremath{\rightarrow}\ensuremath{\eta} and \ensuremath{\gamma}${\ensuremath{\gamma}}^{\mathrm{*}}$\ensuremath{\rightarrow}\ensuremath{\eta}'. The \ensuremath{\eta}${\ensuremath{\gamma}}^{\mathrm{*}}$\ensuremath{\gamma} and \ensuremath{\eta}'${\ensuremath{\gamma}}^{\mathrm{*}}$\ensuremath{\gamma} transition form factors were measured as functions of ${Q}^{2}$, the negative of the invariant mass squared of the tagged photon, in the range 0.1${Q}^{2}$7 ${\mathrm{GeV}}^{2}$. These determinations of the electromagnetic structure of the \ensuremath{\eta} and \ensuremath{\eta}' mesons are consistent with both vector-meson dominance and QCD. They also provide new measurements of the pseudoscalar mixing angle and decay constants.