The antineutron is the

antiparticle In particle physics, every type of particle of "ordinary" matter (as opposed to antimatter) is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge). For example, the antiparticle of the ...

of the

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

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 Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

as the neutron, and no net

electric charge Electric charge (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...

, but has opposite baryon number (+1 for neutron, −1 for the antineutron). This is because the antineutron is composed of

antiquark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly ...

s, while neutrons are composed of

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...

s. The antineutron consists of one up antiquark and two down antiquarks.

Background

The antineutron was discovered in proton–antiproton collisions at the

Bevatron The Bevatron was a particle accelerator — specifically, a Weak focusing, weak-focusing proton synchrotron — located at Lawrence Berkeley National Laboratory, U.S., which began operations in 1954. The antiproton was discovered there in ...

(

Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory (LBNL, Berkeley Lab) is a Federally funded research and development centers, federally funded research and development center in the Berkeley Hills, hills of Berkeley, California, United States. Established i ...

) by the team of Bruce Cork, Glen Lambertson,

Oreste Piccioni Oreste Piccioni (October 24, 1915 – April 13, 2002) was an Italian-American physicist who made important contributions to elementary particle physics. He is the co-discoverer of the antineutron. Biography He was a graduate student of En ...

, and William Wenzel in 1956, one year after the

antiproton The antiproton, , (pronounced ''p-bar'') is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived, since any collision with a proton will cause both particles to be annihilated in a burst of energy. The exis ...

was discovered. Since the antineutron is electrically neutral, it cannot easily be observed directly. Instead, the products of its

annihilation In particle physics, annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons. The total energy a ...

with ordinary matter are observed. In theory, a free antineutron should decay into an

, a

positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...

, and a

neutrino A neutrino ( ; denoted by the Greek letter ) is an elementary particle that interacts via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small ('' -ino'') that i ...

in a process analogous to the

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

of free neutrons. There are theoretical proposals of neutron–antineutron oscillations, a process that implies the violation of the baryon number conservation. There is a project to search for neutron-antineutron oscillations using ultracold neutrons.

Magnetic moment

The

magnetic moment In electromagnetism, the magnetic moment or magnetic dipole moment is the combination of strength and orientation of a magnet or other object or system that exerts a magnetic field. The magnetic dipole moment of an object determines the magnitude ...

of the antineutron is the opposite of that of the neutron. It is for the antineutron but for the neutron (relative to the direction of the spin). Here ''μ''_N is the

nuclear magneton The nuclear magneton (symbol ) is a physical constant of magnetic moment, defined in SI units by: \mu_\text = and in Gaussian CGS units by: \mu_\text = where: * is the elementary charge, * is the reduced Planck constant, * is the proton ...

References

External links

LBL Particle Data Group: summary tables

suppression of neutron-antineutron oscillation

includes information about antineutron discovery (archived link) *

explains how the antineutron differs from the regular neutron despite having the same, that is zero, charge. {{Particles Antimatter Baryons Neutron Nucleons

Background

Magnetic moment

See also

References

External links