antineutron

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2008)

Antineutron
The quark structure of the antineutron.
Classification:	Antibaryon
Composition:	1 up antiquark, 2 down antiquarks
Statistical behavior:	Fermion
Group:	Hadron
Interaction:	Strong, Weak, Gravity
Status:	Discovered
Symbol(s):	n
Particle:	Neutron
Discovered:	Bruce Cork (1956)
Mass:	939.565560(81) MeV/c2
Electric charge:	0
Magnetic moment:	1.91 µN
Spin:	1⁄2
Isospin:	1⁄2

The antineutron is the antiparticle of the neutron. 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–proton collisions at the Bevatron (Lawrence Berkeley National Laboratory) by Bruce Cork in 1956, one year after the antiproton was discovered.

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

• list of particles
• antimatter
• neutron magnetic moment

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

This particle physics-related article is a stub. You can help Wikipedia by expanding it. v • d • e