Symbols for Fundamental Particles

Abstract

IN recent years we have witnessed startling developments in the field of fundamental particles. One of the consequences has been the appearance in the scientific literature of a new jargon and of a large number of new symbols. Some symbols (such as π, µ, τ) designate specific kinds of particles. Others (such as ρ, σ) have been used to describe merely a phenomenological behaviour. Various authors have called the same particle by different names or have attached different meanings to the same symbol. Sometimes the meaning of a symbol has changed through the years. To give an example, the Greek letter χ was used initially to describe a heavy meson which stops in the emulsion and afterwards decays, giving rise to a single ionizing particle. Later, the Latin letter K replaced the Greek letter χ as a code for the above phenomenological description, while the letter χ acquired a more definite physical meaning: that of a heavy meson which decays into one charged and two neutral particles. Sometimes, however, the letter K is also used to designate any charged particle, heavier than a π-meson and lighter than a proton, the mode of decay of which is unknown. As another example, the neutral particle of mass about 1,000 m _e, which decays into two π-mesons, has been variously named v ⁰, V ₂ ⁰, V ₄ ⁰, whereas some authors have used the letter V ₂ ⁰ to designate any V ⁰-particle different from the so-called V ₁ ⁰.