The weak interaction and unification
- 264 Downloads
Looking through the list of elementary particles given in Table 7.1 it can be seen that lifetimes fall into three categories. First, there are those decays characterized by a ‘width’ (Γ) rather than a lifetime. These widths are measured in MeV and correspond to lifetimes of the order τ(≃ℏ/Γ) ≃ 10-21 s-10-23 s. Decays of this kind are strong interaction processes in which all conservation laws are satisfied, in particular conservation of isospin, hypercharge (strangeness) and parity. Second, there are a few processes (e.g. π0 → 2γ, Σ0 → Λγ) with somewhat longer lifetimes which are electromagnetic in origin; they conserve hypercharge and parity but not isospin. Third, there are many decays with lifetimes greater than ≃ 10-13 s. These decays, of which nuclear β-decay discussed in section 6.5 et seq. is an important example, are attributed to the weak interaction and, in particular, do not conserve parity. It is with these decay processes that we now concern ourselves. They can be divided into three varieties depending on the extent to which leptons are involved. These varieties are referred to as (a) leptonic, (b) semileptonic and (c) non-leptonic decay.
Unable to display preview. Download preview PDF.