Antineutron

Antineutron

The quark structure of the antineutron.
Classification	Antibaryon
Composition	1 up antiquark, 2 down antiquarks
Statistics	Fermionic
Interactions	Strong, Weak, Gravity, Electromagnetic
Status	Discovered
Symbol	n
Particle	Neutron
Discovered	Bruce Cork (1956)
Mass	939.565560(81) MeV/c2
Mean lifetime	1000 s (free)
Electric charge	0
Magnetic moment	+1.91 µN
Spin	​1⁄2
Isospin	​1⁄2

The antineutron is the antiparticle of the neutron with symbol n. 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. In particular, 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 that neutron–antineutron oscillations exist, a process which would occur only if there is an undiscovered physical process that violates baryon number conservation.

The antineutron was discovered in proton–antiproton collisions at the Bevatron (Lawrence Berkeley National Laboratory) by Bruce Cork in 1956, one year after the antiproton was discovered, by passing an antiproton beam through matter. The antineutrons were detected by their annihilation reaction energies with protons and neutrons.

Magnetic moment

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

See also

• Antimatter
• Neutron magnetic moment
• List of particles

External links

• LBL Particle Data Group: summary tables
• suppression of neutron-antineutron oscillation
• Elementary particles: includes information about antineutron discovery (archived link)
• "Is Antineutron the Same as Neutron?" explains how the antineutron differs from the regular neutron despite having the same, that is zero, charge.