Experimental systematics of particle lifetimes and widths

Abstract

By comparing the lifetimes of the metastable (τ>10−17 s) elementary particles with one another, we find experimentally that these lifetimes occur both as ratios of 2 and as ratios of α=e2/ħc, with supposedly dissimilar particles grouped together, and with no experimental counterexamples. When short-lived (τ ∼ 10−22 s) meson and baryon resonances are studied, it is found that the width is a key identification symbol. Grouping together resonances that have similar (narrow) widths, we obtain very accurate linear mass intervals. This mapping can be extended to include essentially all of the observed narrow-width meson and baryon resonances in a comprehensive pattern. These results suggest a weak-binding-energy approach to elementary-particle structure. This is the same conclusion that emerges from a broad overview of the successes of the quark model. The empirical level spacings point to the existence of two basic mass quanta, a spinless quantum μ ⋍ 70 MeV and a spin-1/2 quantumS ⋍ 330 MeV. Electromagnetic properties of nucleons also indicate the existence of the 330 MeV mass quantum. In reconciling a 330 MeV mass quantumS with a 939 MeV nucleon mass and a 1795 MeV\(\bar pn\) bound-state mass, we are led to the Fermi and Yang formulation of the nucleon rather than to the formulation of Gell-Mann and Zweig. The observed spectrum of narrow-width meson and baryon resonances can be reproduced by forming suitable combinations of the quanta μ andS. Broad-width resonances are interpreted as rotational excitations. Basis states 3 ≡ 3μ and 4 ≡ 4μ, initially selected to account for observed level spacings in hyperon resonances, are shown to have significance with respect to strangeness quantum numbers and with respect to basic characteristics of baryon and meson resonances. These basis states can also be used to account phenomenologically for the observed factors of 2 and α in the lifetimes of the metastable resonances. The predictive power of the present linear systematics is illustrated in a «meson excitation tower» for narrow-width resonances. First published in 1970, this excitation tower is shown with separate groupings for the resonances that were identified in 1970 and for the resonances that have subsequently been identified.