New high-statistics measurement of the ${\pi }^0\to e^{+}{e}^{-}\gamma$ Dalitz decay at the Mainz Microtron

The Dalitz decay ${\pi }^0\to e^{+}{e}^{-}\gamma$ has been measured with the highest statistical accuracy obtained so far in the $\gamma p\to {\pi }^{0}p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value of the slope parameter for the ${\pi }^0$ electromagnetic transition form factor, $a_{\pi }=0.0315\pm {0.0026}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}}\pm {0.0010}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}}$, is obtained from the analysis of $2.4\times {10}^6$ ${\pi }^0\to e^{+}{e}^{-}\gamma$ observed decays. Within experimental uncertainties, it is in agreement with existing measurements and theoretical calculations, with its own uncertainty being smaller than previous results based on the analysis of ${\pi }^0\to e^{+}{e}^{-}\gamma$ decays.