π0andηdecays into lepton pairs

A model for the rare decays of the neutral pseudoscalar mesons into lepton pairs is presented. By using a once-subtracted dispersion relation for the amplitude, we are able to obtain form-factor-insensitive results. The calculated branching ratios are $\frac{\Gamma ({\pi }^0\to e^{+}{e}^{-})}{\Gamma ({\pi }^0\to \mathrm{all})}=2.0\mathrm{}\times {10}^{-7\mathrm{}}$ and $\frac{\Gamma (\eta \to {\mu }^{+}{\mu }^{-}}{\Gamma (\eta \to \mathrm{all})}=6.1\mathrm{}\times {10}^{-7\mathrm{}}$, in excellent agreement with experiment. We also predict the branching ratio for $\eta \to e^{+}{e}^{-}$ to be 9.1×${10}^{-9\mathrm{}}$. We suggest that this decay may be accessible to experiment.