Antimatter

The positron or antielectron is the particle with an electric charge of +1e, a spin of 1/2 ħ (the same as the electron), and the same mass as an electron. It is the antiparticle (antimatter counterpart) of the electron. When a positron collides with an electron, annihilation occurs. If this collision occurs at low energies, it results in the production of two or more photons.

thumb|A cloud chamber photograph of the first observed [[positron, 2 August 1932]]

thumb|alt=Diagram illustrating the particles and antiparticles of electron, neutron and proton, as well as their "size" (not to scale). It is easier to identify them by looking at the total mass of both the antiparticle and particle. On the left, from top to bottom, is shown an electron (small red dot), a proton (big blue dot), and a neutron (big dot, black in the middle, gradually fading to white near the edges). On the right, from top to bottom, are shown the anti electron (small blue dot), anti proton (big red dot) and anti neutron (big dot, white in the middle, fading to black near the edg

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.

thumb|A Feynman diagram showing the mutual annihilation of a bound state [[electron positron pair into two photons. This bound state is more commonly known as positronium.]]

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.

interaction of photon with matter resulting into ejection of electron-positron pair

thumb|right|upright=1.2|Antihydrogen consists of an antiproton and a [[positron]] thumb|right|upright=1.2|Simplified model of an antihydrogen atom in ground state

thumb|200px|right|An electron and [[positron orbiting around their common centre of mass. An s state has zero angular momentum, so orbiting around each other would mean going straight at each other until the pair of particles is either scattered or annihilated, whichever occurs first. This is a bound quantum state known as positronium.]]

In physical cosmology, baryogenesis (also known as baryosynthesis) is the physical process that is hypothesized to have taken place during the early universe to produce baryonic asymmetry, the observation that only matter (baryons) and not antimatter (antibaryons) is detected in the universe (other than in cosmic ray collisions). Since it is assumed in cosmology that the particles we see were created using the same physics we measure today, and in particle physics experiments today matter and antimatter are always symmetric, the dominance of matter over antimatter is unexplained.

radioactive decay in which a proton is converted into a neutron while releasing a positron and a neutrino

In physics, charge conjugation is a transformation that switches all particles with their corresponding antiparticles, thus changing the sign of all charges: not only electric charge but also the charges relevant to other forces. The term C-symmetry is an abbreviation of the phrase "charge conjugation symmetry", and is used in discussions of the symmetry of physical laws under charge-conjugation. Other important discrete symmetries are P-symmetry (parity) and T-symmetry (time reversal).

abundance of matter (baryons) and lack of antimatter (antibaryons) in our Observable Universe

collision causing gamma ray emission

theoretical weapon

Di-positronium, or dipositronium, is an exotic molecule consisting of two atoms of positronium. It was predicted to exist in 1946 by John Archibald Wheeler, and subsequently studied theoretically, but was not observed until 2007 in an experiment performed by David Cassidy and Allen Mills at the University of California, Riverside. The researchers made the positronium molecules by firing intense bursts of positrons into a thin film of porous silicon dioxide. Upon slowing down in the silica, the positrons captured ordinary electrons to form positronium atoms. Within the silica, these were long l

chemical compound

CERN infrastructure

theory of gravity on antimatter

exotic matter with an antiproton in place of an electron

Rockets using antimatter as their power source

proposed nuclear pulse propulsion through antimatter-catalyzed nuclear chain reactions

hypothetical object

radiation resulting from particle-antiparticle collisions