xi baryon

/ zī,sī,ksē /

1. Either of two subatomic particles in the baryon family, one neutral and one negatively charged, with masses of 2,572 and 2,585 times that of the electron and average lifetimes of 2.9 × 10 ^-10 and 1.6 × 10 ^-10 seconds.
2. See Table at subatomic particle