Consequently, the law of conservation of strangeness holds only approxi mately and not rigorously like the law of conservation of electric charge.
Speaking of the electromagnetic interactions, which occupy an interme diate position between the strong and weak interactions, it must be also remembered that many of the particles possess, in addition to an electric charge, also a magnetic moment. Thus the electron and the positron are "magnetized", and their magnetism is mainly caused by their intrinsic spin, i. e. , they behave as rotating charges. Part of their magnetism is caused by additional complex "vacuum" interactions with the electromagnetic field and the electron-positron field. The extra effects are called vacuum interactions because they refer to virtual fields and particles and not to concretely observable entities. These concepts are highly sophisticated, but there is really nothing extraordinary about them. For instance, an old and familiar concept is that of the electromagnetic field associated with charges. Now if a charged particle is thoroughly "shaken up" —say, it is made to collide with another particle or given a twist in a magnetic field— then part of the field surrounding the particle will detach itself and be emitted as a photon. In a similar way, it has been found that the particles are surrounded not only by an electromagnetic field but also by a field of electron-positron pairs.
As a result, when charged particles collide it is possible that instead of an electromagnetic field quantum being emitted, an electron-positron pair is produced. In a similar manner the baryons are surrounded by a mesic field which is radiated in the form of pions or kaons. It is noteworthy that when highly energetic nucleons and hyperons collide, several short-lived mesons are produced at once. Speaking of magnetism, we may note that the muons, protons, neutrons, and hyperons are also magnetized. The magne tism of the muons is in all respects similar to the magnetism of the electrons. The magnetic moments of the proton and the neutron are conditioned to a large extent by the magnetism of the ir-me son cloud which goes into the structure of these particles.
Apart from the "ordinary" elementary particles, researches in the last few years have uncovered a number of unusual quasi-particles, which might, for brevity, be designated as "resonons" since they appear for the most part as resonances in the scattering of particles (resonance maxima in the effective cross sections). Thus, for instance, nucleons were found to have an excited state N* with the charge +2e, which decays after a very short time, like the other resonons, with an average lifetime of about sec only.
If we adopt the common procedure of expressing the mass or the self energy of a particle in electron-volts, we have for the energy of an ordinary nucleon 938 Mev, while the energy of N* is 1238 Mev. Further nucleon resonons have been found, denoted by N**, N*** and N****, with masses of 1510, 1680, 1900 Mev, respectively (in round, not yet accurate figures).
Hyperon resonons Y' (1385 Mev) have been discovered, which very rapidly decay according to the scheme: and also resonons Yo, and n*, with masses of 1405, 1520, and 1815 Mev, respectively. Resonons have also been discovered in the range of K and n mesons, with the decay schemes: It turned out that the resonons p could be split into two states.
The w resonon was the first of this category of quasi-particles to be discovered, by Alvarez (Berkeley). These formations are so short-lived that there is still no way to record their tracks. By analyzing the annihilation of protons and antiprotons, however, it has been shown that the mesons produced as a result (in batches of 5 as an average) are not all the same. Three of them are produced by the decay of some single intermediate particle, called the w particle. In a similar manner, when protons are irradiated with y photons, i. e. , in a photonuclear reaction, 1 resonons are produced (the 1962 experiments in Frascati): The 1 particles may decay either into three pions, or else emit some y photons. It thus appears that the strong coupling may cause the x and K mesons to "stick" to each other, or to nucleons or hyperons, which leads to the formation of resonons.