Probing New Physics via the B0s → μ+ μ- Effective Lifetime

We have recently seen new upper bounds for B-s(0) -> mu(+) mu(-), a key decay to search for physics beyond the standard model. Furthermore a nonvanishing decay width difference Delta Gamma(s) of the B-s system has been measured. We show that Delta Gamma(s) affects the extraction of the B-s(0) -> mu(+) mu(-) branching ratio and the resulting constraints on the new physics parameter space and give formulas for including this effect. Moreover, we point out that Delta Gamma(s) provides a new observable, the effective B-s(0) -> mu(+) mu(-) lifetime tau(mu+) (mu-), which offers a theoretically clean probe for new physics searches that is complementary to the branching ratio. Should the B-s(0) -> mu(+) mu(-) branching ratio agree with the standard model, the measurement of tau(mu+) (mu-), which appears feasible at upgrades of the Large Hadron Collider experiments, may still reveal large new physics effects.