Question

Classify the following semileptonic decays of the D⁺(1,869) = c bar d meson as Cabibbo-allowed, Cabibbo-suppressed or forbidden in lowest order weak interactions. 

(a) D⁺ → K⁻ + π⁺ + e⁺ + υ_e 

(b) D⁺ → π⁺ + π⁺ + e⁻ + bar ν_e

Answer 1

For the charmed particles, the selection rule for the Cabibbo allowed decay is ΔC = ΔS = ΔQ = ±1 and for the Cabibbo suppressed decays the selection rule is ΔC = ΔQ = ±1, ΔS = 0. Using these rules we infer that the decays are (a) Cabibbo allowed (b) forbidden