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Particle-antiparticle pairs can arise from the interactions of other particles, and can annihilate one another to produce other particles. The annihilation products (and possible means of pair production) depend on the interactions of the particles involved. For example, an electron and positron (or antielectron) will tend to annihilate to photons, the quanta of the electromagnetic field, since their interactions are primarily electromagnetic. Proton- antiprotonThe antiproton is the antiparticle of the proton. Antiprotons are short-lived in nature, since any collision with a proton will cause both particles to be annihilated in a burst of energy. It was discovered in the year 1955 by Emilio Segre and Owen Chambe pairs, interacting through the strong nuclear force, tend to annihilate to collections of mesonIn particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin. In the Standard Model, mesons are composite (non-elementary) particles composed of an even number of quarks and antiquarks. Until the discovery of ths and their own antiparticles, mostly various types of pionIn particle physics, pion (short for 'pi meson') is the collective name for three subatomic particles discovered in 1947: π0, π+ and π−. Pions are the lightest mesons. Basic properties Pions have zero spin and are composed of first generati. In either case, however, increasing the energy of the collision (as in a particle acceleratorA particle accelerator uses electric fields to propel charged particles to great energies. Everyday applications are found in TV sets and X-ray generators. The particles are contained in an evacuated tube so that they do not get dispersed by hitting air m) can lead to the production of more exotic products as the necessary energy becomes available, and this process is an important tool in particle physics.
Antiparticles are produced by certain nuclear reactionIn nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide, to produce products different to the initial products. In principle a reaction can involve more than two particles colliding, but such an event is excepts (most notably positive beta decayIn nuclear physics, beta decay (sometimes called neutron decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. In the case of electron emission, it is referred to as "beta minus" (β−); in the case), and by sufficiently energetic particle collisions, including naturally occurring cosmic rayCosmic rays can loosely be defined as energetic particles originating outside of the Earth. The composition includes electrons, protons, neutrons, and atomic nuclei from a large region of the periodic table. The kinetic energies of these particles span ov collisions. Antimatter is a collection of antiparticles, in particular antiprotons, antineutrons and positrons in a similar composition as matter.
The existence of antiparticles was predicted by Dirac a few years before the first one, the antielectron or positron, was found by Carl D. Anderson in a cloud chamber experiment. Dirac's prediction stemmed from the existence of negative energy states, which in a relativistic universe cannot be discarded a priori. To keep all interacting electrons in his theory from eventually falling into negative energy states, Dirac posited that these extra states must all be filled already. In that case, a negative-energy particle could be promoted to a positive energy state, creating a real particle and leaving a hole that would behave exactly the same, but with opposite charge.