Strong Interactions

Abstract

In Chaps. 3 and 4 we have studied stable particles as well as unstable particles. The stable particles are neutrinos (ν), photon (γ), electron (e), proton (p) and their antiparticles. The experimental lower limit on the lifetime of electron is ∼10²² years and that of proton ∼10³¹ years-much longer than the lifetime of the universe, 10¹⁰ years. The unstable particles are those which decay by weak or electromagnetic processes. The weak decays like π ⁺→μ ⁺ ν _μ , K ⁺→π ⁺ π ⁰, Λ→pπ ⁻, $\mu^{+} \rightarrow e^{+} \nu_{\mathrm{e}} \overline{\nu}_{\mu}$ etc. have lifetimes <10⁻¹³ sec. The electromagnetic decays like π ⁰→2γ or Σ ⁰→Λγ have lifetimes in the range 10⁻¹⁶–10⁻²⁰ sec.