Models and Methods in the Meson Theory

Abstract

HE starting point of the meson theory was to express the nuclear forces in terms of the Geld theory on the basis of Einstein's principle of relativity. The quanta associated with the nuclear field can be regarded, apart from the mass and the charge, as something similar to Einstein's light quanta associated with the electromagnetic Geld in that both have integer spin and obey Bose-Einstein statistics. The subsequent discovery in cosmic rays of mesons with mass m"about two hundred times the electron mass m, lead us natu- rally to the second assumption that these mesons are identical with the quanta associated with the nuclear field. Moreover, the fact that these mesons are unstable and decay into electrons with the lifetime r"about 2 10 ' sec. has been considered as a confirmation of the third assumption that the nuclear field interacts with the electron-neutrino system in the same way as with the nucleon, the only difference being a much smaller interaction in order to account for the very slow rate of nuclear P-decay. The development of the meson theory based on these three fundamental assumptions seemed to be successful in the qualitative interpretation of almost all phenomena so far known in the Geld of cosmic rays as well as in the field of atomic nuclei. However, it could never arrive at the stag|: of quantitiative agreement with the experiment. This rather puzzling situation of the meson theory changed in 1947 due to the experiment by the Rome group on the decay of negative mesons on the one hand, ' and the discovery by the Bristol group of two kinds of mesons in cosmic rays on the other. ' At first sight these might be looked upon as only adding further confusion and complexity to increasing difficulties in . the meson theory. However, it turned out soon that various phenomena connected with cosmic-ray mesons could be understood with less difhculty than ever by accepting the newly established facts that (i) the mesons mentioned above, which are the main constituent of the hard component of cosmic rays *The main content of this