Either of two subatomic particles in the meson family, one neutral and one positively charged, both of which have masses 10,331 times that of an electron and average lifetimes of 1.6 × 10-12 seconds. B粒子：介子系列两种次原子粒中任一种，一种为中性，另一种带正电，这两种的质量都是电子的10,331倍，平均寿命为1.6×10-12秒