The difference in the decay rates is due to two reasons (i) the Q - values in the decays are different. For Σ− → n + e− + bar νe, Q1 = 257 MeV, while for Σ− → Λ + e− + bar νe, Q2 = 81 MeV, so that by Sargent’s law, the decay rate (ω) will be proportional to Q5. (ii) The first decay involves |ΔS| = 1, so that ω will be proportional to sin2θc, where θc is the Cabibbo angle. The second one involves |ΔS| = 1, so that ω is proportional to cos2θc. In all
where we have used θc = 13◦. The experimental value for R is 17.8
