Baryons and Baryonic Matter
Baryons, taken from the Greek word for heavy, is a term that refers to a class of subatomic particles of high mass. With the discovery of the neutron in 1932, the neutron and proton were grouped together as the baryons, in contrast to the considerably lighter electron. With the discovery of subparticles, new categories had to be introduced. A particle called the photon was assigned its own category, while the leptons category includes the electron and the neutrino.
The baryon classification took on new members, including particles more massive than the proton called hyperons. These new baryons included the lambda particle, the sigma particles and the negatively charged omega-minus. The lambda particle is a neutrally charged hyperon that can replace particles in the nucleus of the atom. The sigma particles can be positive, negative, or neutral. The omega-minus particle is another hyperon classified as a baryon. An important characteristic of the baryons is that they contribute to the intensity of the strong nuclear force.
Murray Gell-Mann introduced a new classification system in which baryons became a subclassification of a new category called hadrons. Hadrons were on the same categorical level as photons and leptons, except hadrons are not elementary particles as photons and leptons are. Hadrons are made up of elementary particles called quarks. Gell-Mann distinguished baryons from mesons, the other hadron subclassification, by the number of quarks constituting their make-up. Baryons have three quarks while mesons have two. Gell-Mann found that by classifying known hadrons, he could discover patterns that reveal the probability of the existence of previously unknown particles. Using a method of mathematically grouping known hyperons, he found an empty space in the pattern. He predicted this position in the pattern would be filled through the discovery of another hyperon. He named this empty space omega-minus because it was the place for the last member of the pattern and the particle to fill it was predictably negatively charged. Later the hyperon fulfilling this prediction was discovered and had characteristics Gell-Mann described to the detail.
Baryons are a necessary part of a classification system that represents algebraically the reactions that are known to be possible. With the discovery of subparticles, theoretical speculation held that a proton could break down into a positron and multitudinous photons, although this was never observed. With the many years of research on the proton there was no evidence of the proton breaking down into a positron or any other subparticle. Such speculation was contrary to what was known about the proton's stability and abundance, but there was no clear explanation of the improbability of such an event. The explanation of this phenomenon was developed based on the theoretical assumption that the number of baryons must be conserved.
The law of the conservation of baryon number states that the total number of baryons must be the same before and after any subatomic event. In describing nuclear reactions algebraically all baryons are assigned a value of +1; the antibaryons are assigned a value of -1; and light particles, including electrons, photons, and neutrinos, are given a 0. The baryonic number, which is equivalent to the atomic mass number, has to remain constant for a reaction. Baryons may change within their classification but a baryon will not change into a lepton nor into an antibaryon. This law has been found to hold true with nuclear reactions involving antiparticles by assigning the antiparticles the opposite number of their counterparticle.
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