We calculate penguin contributions to the lifetime splitting between the Bs and the Bd meson. In the standard model the penguin effects are found to be opposite in sign, but of similar magnitude as the contributions of the current-current operators, despite the smallness of the penguin coefficients. We predict τ(Bs)/τ(Bd)−1=(−1.2±10.0)×10−3(fBs/190MeV)2, where the error stems from hadronic uncertainties. Since penguin coefficients are sensitive to new physics and poorly tested experimentally,

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... analyze the possibility to extract them from a future precision measurement of τ(Bs)/τ(Bd). Anticipating progress in the determination of the hadronic parameters ɛ1,ɛ2, and fBs/fBd we find that the coefficient C4 can be extracted with an uncertainty of order |ΔC4|≃0.1 from the double ratio [τ(Bs)−τ(Bd)]/[τ(B+)−τ(Bd)], if |ɛ1−ɛ2| is not too small.