ANTIPARTICLE

subatomic particle having the same mass as one of the particles of ordinary matter but opposite electric charge and magnetic moment. Thus the positron (positive electron) is the antiparticle of the negative electron (negatron). The spinning antineutron with net charge zero, like the ordinary neutron, has its magnetic polarity opposite to that of a similarly spinning neutron. The neutrino, a massless, uncharged particle that travels at the speed of light, spins counterclockwise as viewed from behind, whereas the antineutrino spins clockwise as viewed from behind. A particle and its antiparticle mutually react to produce energy by annihilation.