An antiproton is the antiparticle of the proton, which is one of the fundamental constituents of atomic nuclei. In particle physics, every particle has a corresponding antiparticle that has the same mass but opposite charge and other quantum numbers. Specifically, an antiproton has: - A mass equal to that of a proton (approximately 938.3 MeV/c²). - A negative electric charge (-1e), as opposed to the positive charge (+1e) of a proton.
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The antiproton is the antiparticle of the proton: it has the same rest mass and spin , with opposite electric charge and baryon number. A negative electric charge alone cannot identify an antiproton, because a negative pion also bends in that direction in a magnetic field. Combining magnetic rigidity with velocity determines a rest mass; agreement with the proton rest mass then makes the identification much more discriminating.
The mode expansion of a Dirac field explains how independent particle and antiparticle excitations enter a relativistic field description. It supplies a theoretical language for the antiproton, while the Chamberlain-Segrè antiproton identification supplies an experimental test. The proton is a composite baryon, so a free Dirac field is not a complete account of its internal dynamics or of antiproton production in a target.