An unstable meson produced in high-energy particle collisions that has charged forms 966.3 times more massive than the electron and a neutral form 974.6 times more massive than the electron.

【理】K 介子(一种在高能粒子相撞时产生的不稳定介子，带电时为电子的 966.3 倍，中性时为电子的 974.6 倍)。