Annihilation in the context of Weakly interacting massive particles

The positron or antielectron is the particle with an electric charge of +1e, a spin of 1/2 (the same as the electron), and approximately 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.

Positrons can be created by positron emission radioactive decay (through weak interactions), or by pair production from a sufficiently energetic photon which is interacting with an atom in a material.

In particle physics, a pion (/ˈpaɪ.ɒn/, PIE-on) or pi meson, denoted with the Greek letter pi (π), is any of three subatomic particles: π
, π
, and π
. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the charged pions π
and π
decaying after a mean lifetime of 26.033 nanoseconds (2.6033×10 seconds), and the neutral pion π
decaying after a much shorter lifetime of 85 attoseconds (8.5×10 seconds). Charged pions most often decay into muons and muon neutrinos, while neutral pions generally decay into gamma rays.

The exchange of virtual pions, along with vector, rho and omega mesons, provides an explanation for the residual strong force between nucleons. Pions are not produced in radioactive decay, but commonly are in high-energy collisions between hadrons. Pions also result from some matter–antimatter annihilation events. All types of pions are also produced in natural processes when high-energy cosmic-ray protons and other hadronic cosmic-ray components interact with matter in Earth's atmosphere. In 2013, the detection of characteristic gamma rays originating from the decay of neutral pions in two supernova remnants has shown that pions are produced copiously after supernovas, most probably in conjunction with production of high-energy protons that are detected on Earth as cosmic rays.

The antiproton, p, (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 existence of the antiproton with electric charge of −1 e, opposite to the electric charge of +1 e of the proton, was predicted by Paul Dirac in his 1933 Nobel Prize lecture. Dirac received the Nobel Prize for his 1928 publication of his Dirac equation that predicted the existence of positive and negative solutions to Einstein's energy equation (${\displaystyle E=mc^{2}}$) and the existence of the positron, the antimatter analog of the electron, with opposite charge and spin.

Weakly interacting massive particles (WIMPs) are hypothetical particles that are one of the proposed candidates for dark matter.

There exists no formal definition of a WIMP, but broadly, it is an elementary particle which interacts via gravity and any other force (or forces) which is as weak as or weaker than the weak nuclear force, but also non-vanishing in strength. Many WIMP candidates are expected to have been produced thermally in the early Universe, similarly to the particles of the Standard Model according to Big Bang cosmology, and usually will constitute cold dark matter. Obtaining the correct abundance of dark matter today via thermal production requires a self-annihilation cross section of ${\displaystyle \langle \sigma v\rangle }$ ≃ 3×10 cm⋅s, which is roughly what is expected for a new particle in the 100 GeV/c mass range that interacts via the electroweak force.

Electron–positron annihilation occurs when an electron (e
) and a positron (e
, the electron's antiparticle) collide. At low energies, the result of the collision is the annihilation of the electron and positron, and the creation of energetic photons:

At high energies, other particles, such as B mesons or the W and Z bosons, can be created. All processes must satisfy a number of conservation laws, including:

In theoretical physics, a Feynman diagram is a pictorial representation of the mathematical expressions describing the behavior and interaction of subatomic particles. The scheme is named after American physicist Richard Feynman, who introduced the diagrams in 1948.

The calculation of probability amplitudes in theoretical particle physics requires the use of large, complicated integrals over a large number of variables. Feynman diagrams instead represent these integrals graphically.