Excluding MeV-scale QCD axions by $K_L\to {\pi }^0{\pi }^{0}a$ at KTeV

Takaya Iwai, Ryosuke Sato, Kohsaku Tobioka +1

An interesting proposal suggests that a QCD axion $(a)$ coupling to the up quark, down quark, and electron remains viable for an axion mass near 10~MeV. In this paper, this possibi…