section_path: Antiproton
section_name: Antiproton
paragraph_text: Antiproton
  
  CPT-symmetry puts strong constraints on the relative properties of particles and antiparticles and, therefore, is open to stringent tests. For example, the charges of a proton and antiproton must sum to exactly zero. This equality has been tested to one part in 10. The equality of their masses has also been tested to better than one part in 10. By holding antiprotons in a Penning trap, the equality of the charge-to-mass ratio of protons and antiprotons has been tested to one part in 6 × 10. The magnetic moment of antiprotons has been measured with an error of 8 × 10 nuclear Bohr magnetons, and is found to be equal and opposite to that of a proton.