ENHANCEMENT OF THE Λb DECAY RATE 1

The enhancement ∆Γ(Λb) of the Λb decay rate due to four-fermion processes of weak scattering and Pauli interference is calculated within the quark model. An estimate of the relative bu wave function at zero separation, |Ψ(0)|bu, is obtained in terms of the Σ ∗ b − Σb hyperfine splitting, the B∗ − B hyperfine splitting, and the B meson decay constant fB. For M(Σ∗b)−M(Σb) = 56±16 MeV,M(B ∗)−M(B) = 46 MeV, and fB = 190±40 MeV, we find ∆Γ(Λb) = (0.025± 0.013) ps , to be compared with the observed enhancement Γ(Λb)− Γ(B ) = 0.20± 0.05 ps. Even such a meager enhancement entails a value of |Ψ(0)|bu considerably larger than the corresponding value of |Ψ(0)|cd in the Λc baryon. PACS codes: 14.20.Mr, 14.20.Lq, 13.30.Eg, 12.39.Jh To be submitted to Phys. Lett. B. Permanent address.