Search for K_{L}→π^{0}π^{0}γγ and K_{L}→π^{0}π^{0}X where X→γγ at the KOTO Experiment

We performed searches for K_{L}→π^{0}π^{0}X where X may be an axionlike particle that promptly decays to two photons, and the first search for K_{L}→π^{0}π^{0}γγ at the KOTO experiment using data taken in 2021. The search is performed for X mass in the range of 160-220  MeV/c^{2}. Three events were observed in the signal region, with two events near an X mass of 177  MeV/c^{2}. This result led to a range of upper limits on the branching ratio, BR(K_{L}→π^{0}π^{0}X) <(1-20)×10^{-7} at the 95% confidence level (CL). No events were observed for the analysis of K_{L}→π^{0}π^{0}γγ, setting an upper limit on the branching ratio, BR(K_{L}→π^{0}π^{0}γγ) <1.69×10^{-6} at the 95% CL.