Search for the decay $K_L\to {\pi }^0\nu \overline{\nu }$ using ${\pi }^0\to e^{+}{e}^{-}\gamma$

We report on a search for the decay $K_L\to {\pi }^0\nu \overline{\nu },$ carried out as a part of E799-II, a rare $K_L$ decay experiment at Fermilab. Within the standard model, the $K_L\to {\pi }^0\nu \overline{\nu }$ decay is dominated by direct $\mathrm{CP}$ violating processes, and thus an observation of the decay implies confirmation of direct $\mathrm{CP}$ violation. No events were observed, and we set an upper limit for the branching ratio of $K_L\to {\pi }^0\nu \overline{\nu }$ to be $<5.9\times {10}^{-7}$ at the 90% confidence level.