section_path: Properties/Antineutron
section_name: Antineutron
paragraph_text: Antineutron
  
  The antineutron is the antiparticle of the neutron. It was discovered by Bruce Cork in 1956, a year after the antiproton was discovered. CPT-symmetry puts strong constraints on the relative properties of particles and antiparticles, so studying antineutrons provides stringent tests on CPT-symmetry. The fractional difference in the masses of the neutron and antineutron is (9 ± 6) × 10. Since the difference is only about two standard deviations away from zero, this does not give any convincing evidence of CPT-violation.