Neutral-Pion Electroproduction on the Proton near Threshold

The double-differential coincidence cross section for the reaction ${}^1\mathrm{H}\left({e,e}^{\prime }p\right){\pi }^0$ has been measured at $Q^2=0.1(\mathrm{GeV}/c{)}^2$ in a range in the invariant mass of 2–14 MeV above threshold. From the angular dependence of the data values of the pion $s$-wave multipoles $E_{0+}$ and $L_{0+}$ have been extracted. The results are compared to predictions from chiral perturbation theory and models based on an effective Lagrangian. None of the models is able to describe both the $E_{0+}$ and the $L_{0+}$ multipoles.