Antineutron

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The antineutron is the antiparticle of the neutron. It was discovered by Bruce Cork in the year 1956, a year after the antiproton was discovered. An antineutron has the same mass as a neutron, and no net electric charge. However, it is different from a neutron by being composed of antiquarks, rather than quarks. In particular, the antineutron consists of two anti-down quarks and one anti-up quark.

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.

Since the antineutron is electrically neutral, it cannot easily be observed directly. Instead, the products of its annihilation with ordinary matter are observed.

There are theoretical proposals that there exist neutron-antineutron oscillations, a process which would occur only if there is an undiscovered physical process that violates baryon number conservation.