An antiproton is an antibaryon
matter particle composed of two upsilon antiquarks
and one delta antiquark.
It has a net charge of -1, and a mass of 1.6727x10-24
grams. Unlike
protons, antiprotons are unstable in isolation and decay,
giving off
gamma radiation in the process. An antiproton is the
antiparticle of a
proton.
Certain
antiproton beams can be used to penetrate Romulan cloaking
devices.
