The cross section for the reaction ${}_{}{}^1{}_{}{}^{}\mathrm{H}(\gamma , {\pi }^0)$ has been measured using tagged photons in the threshold region (144.7-169.3 MeV). The total cross section, augmented by angular distribution information, is used to deduce the $S$-wave multipole $E_{0+}$. Extrapolation to threshold yields $E_{0+}=(-1.32\mathrm{}\pm 0.05\pm 0.06)\times {10}^{-3\mathrm{}}/m_{\pi }$, in disagreement with earlier estimates. Suppression of $E_{0+}$ near the ${\pi }^{+}$ threshold is confirmed, in approximate agreement with recent calculations.

• Received 20 November 1995

DOI:https://doi.org/10.1103/PhysRevC.53.R1052