The decay of this type of particle is one of the few physical  processes no
The decay of this type of particle is one of the few physical  processes not to exhibit time reversal invariance. Four types  exist; the two electrically charged are antiparticles of each  other, as are the two neutral. Classified as both a boson and a  hadron, their mass is between that of an electron and of a proton.  FTP, name this meson.
The decay of this type of particle is one of the few physical  processes not to exhibit time reversal invariance.
{kaon} or {K}-meson (prompt on "meson")