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Quark structure antineutron.svg
The quark structure of the antineutron.
Composition1 up antiquark, 2 down antiquarks
InteractionsStrong, Weak, Gravity, Electromagnetic
DiscoveredBruce Cork (1956)
Mass939.565560(81) MeV/c2
Electric charge0
Magnetic moment+1.91 µN

The antineutron is the antiparticle of the neutron with symbol
. It differs from the neutron only in that some of its properties have equal magnitude but opposite sign. It has the same mass as the neutron, and no net electric charge, but has opposite baryon number (+1 for neutron, −1 for the antineutron). This is because the antineutron is composed of antiquarks, while neutrons are composed of quarks. The antineutron consists of one up antiquark and two down antiquarks.

Since the antineutron is electrically neutral, it cannot easily be observed directly. Instead, the products of its annihilation with ordinary matter are observed. In theory, a free antineutron should decay into an antiproton, a positron and a neutrino in a process analogous to the beta decay of free neutrons. There are theoretical proposals of neutron–antineutron oscillations, a process that implies the violation of the baryon number conservation.[1][2][3]

The antineutron was discovered in proton–antiproton collisions at the Bevatron (Lawrence Berkeley National Laboratory) by the team of Bruce Cork, Glen Lambertson, Oreste Piccioni, and William Wenzel in 1956,[4] one year after the antiproton was discovered.

Magnetic moment[edit]

The magnetic moment of the antineutron is the opposite of that of the neutron.[5] It is +1.91 µN for the antineutron but −1.91 µN for the neutron (relative to the direction of the spin). Here µN is the nuclear magneton.

See also[edit]


  1. ^ R. N. Mohapatra (2009). "Neutron-Anti-Neutron Oscillation: Theory and Phenomenology". Journal of Physics G. 36 (10): 104006. arXiv:0902.0834. Bibcode:2009JPhG...36j4006M. doi:10.1088/0954-3899/36/10/104006. S2CID 15126201.
  2. ^ C. Giunti; M. Laveder (19 August 2010). "Neutron Oscillations". Neutrino Unbound. Istituto Nazionale di Fisica Nucleare. Archived from the original on 27 September 2011. Retrieved 19 August 2010.
  3. ^ Y. A. Kamyshkov (16 January 2002). "Neutron → Antineutron Oscillations" (PDF). NNN 2002 Workshop on "Large Detectors for Proton Decay, Supernovae and Atmospheric Neutrinos and Low Energy Neutrinos from High Intensity Beams" at CERN. Retrieved 19 August 2010.
  4. ^ Cork, Bruce; Lambertson, Glen R.; Piccioni, Oreste; Wenzel, William A. (15 November 1956). "Antineutrons Produced from Antiprotons in Charge-Exchange Collisions". Physical Review. 104 (4): 1193–1197. doi:10.1103/PhysRev.104.1193.
  5. ^ Lorenzon, Wolfgang (6 April 2007). "Physics 390: Homework set #7 Solutions" (PDF). Modern Physics, Physics 390, Winter 2007. Retrieved 22 December 2009.

External links[edit]