The KTeV E799 experiment has conducted a search for the rare decay
KL​→π0π0γ via the topology
KL​→π0πD0​γ (where πD0​→γe+e−). Due to Bose
statistics of the π0 pair and the real nature of the photon, the
KL​→π0π0γ decay is restricted to proceed at lowest order
by the CP conserving direct emission (DE) of an E2 electric quadrupole photon.
The rate of this decay is interesting theoretically since chiral perturbation
theory predicts that this process vanishes at level O(p4). Therefore, this
mode probes chiral perturbation theory at O(p6). In this paper we report a
determination of an upper limit of 2.43×10−7 (90% CL) for
KL​→π0π0γ. This is approximately a factor of 20 lower than
previous results.Comment: six pages and six figures in the submission. Reformatted for Physics
Review