Investigation of the electromagnetic structure ofηand η’ mesons by two-photon interactions

The TPC/Two-Gamma facility at the SLAC $e^{+}$ $e^{\mathrm{-}}$ storage ring PEP was used to study the reactions γ${\gamma }^{\mathrm{*}}$→η and γ${\gamma }^{\mathrm{*}}$→η’. The η${\gamma }^{\mathrm{*}}$γ and η’ ${\gamma }^{\mathrm{*}}$γ 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 η and η’ mesons are consistent with both vector-meson dominance and QCD. They also provide new measurements of the pseudoscalar mixing angle and decay constants.